Vascular CT and MRI: a practical guide to imaging protocols
Insights into Imaging
Vascular CT and MRI: a practical guide to imaging protocols
D. J. Murphy 0
A. Aghayev 0
M. L. Steigner 0
0 Cardiovascular Imaging Program, Department of Radiology, Brigham and Women's Hospital , Boston, MA , USA
1 D. J. Murphy
Non-invasive cross-sectional imaging techniques play a crucial role in the assessment of the varied manifestations of vascular disease. Vascular imaging encompasses a wide variety of pathology. Designing vascular imaging protocols can be challenging owing to the non-uniform velocity of blood in the aorta, differences in cardiac output between patients, and the effect of different disease states on blood flow. In this review, we provide the rationale behind-and a practical guide to-designing and implementing straightforward vascular computed tomography (CT) and magnetic resonance imaging (MRI) protocols. Teaching Points There is a wide range of vascular pathologies requiring bespoke imaging protocols. Variations in cardiac output and non-uniform blood velocity complicate vascular imaging. Contrast media dose, injection rate and duration affect arterial enhancement in CTA. Iterative CT reconstruction can improve image quality and reduce radiation dose. MRA is of particular value when imaging small arteries and venous studies.
Computed tomography angiography; Magnetic resonance imaging; Angiography; Magnetic resonance angiography; Atherosclerosis
Non-invasive cross-sectional imaging plays a crucial role in
the assessment of the varied manifestations of vascular
disease, and in both the planning and follow-up of minimally
invasive interventional techniques. Designing vascular
imaging protocols can be challenging owing to the non-uniform
velocity of blood in the aorta, differences in cardiac output
between patients and the effect of different disease states on
blood flow that cannot be predicted pre-scan. The complexity
of the disease under investigation also influences vascular
imaging protocols; for example, the need for a delayed phase
to detect endoleaks in patients post endovascular aortic
aneurysm repair (EVAR). In this review, we endeavour to provide
the rationale behind and a practical guide to designing and
implementing straightforward vascular computed tomography
(CT) and magnetic resonance imaging (MRI) protocols
(Tables 1 and 2).
Computed tomography angiography (CTA)
CT is a quick, non-invasive imaging modality with
excellent spatial and temporal resolution. Modern CT
scanners can provide sub-millimetre isotropic
threedimensional (3D) datasets within a single breath-hold
during the first past of intravenous (IV) iodinated
contrast medium (CM). One of the minimum requirements
for more advanced CTA applications, such as coronary
CTA, is a 64-channel CT; for many of the other less
challenging vascular CT protocols, such as abdominal
aorta or visceral aneurysm assessment, a 16-channel
CT is adequate. The continued evolution of CT
technology is based in no small part on the demands that
cardiovascular imaging places in terms of speed,
temporal resolution and scan volume. To help cope with the
I rate (ml/s) Bolus tracking
Delay (immediate unless specified)
Coeliac artery –
Coeliac artery –
Coeliac artery –
Main PA –
Descending TA +
Descending TA –
Descending TA +
Renal artery –
Renal artery –
Descending TA +
Coeliac artery –
Coeliac artery –
Coeliac artery –
Coeliac artery –
Aorta bifurcation –
Aorta bifurcation –
Peak kilovoltage (kVp) is chosen at 140/120/100/80 kVp dependent on BMI
Tube current (mA) is determined by automatic exposure control
Tube rotation time is maximum
All phases are reconstructed with a slice thickness of 1 mm at an interval of 0.8 mm and sent to a 3D post-processing workstation
AA abdominal aorta, TA thoracic aorta, C chest, A abdomen, P pelvis, I iodinated contrast, Arch aortic arch, MPA main pulmonary artery, CTA CT
angiogram, CTV CT venogram, DIEP deep inferior epigastic perforators, SGAP superior gluteal artery perforators, ROI region of interest
All protocols receive 100 ml of iodinated contrast, except for venogram protocolsa , which receive 125 ml
demands of cardiovascular imaging, manufacturers have
made significant improvements in z-axis volume
coverage, detector and tube technology, with different
emphasis depending on the vendor [
]. State of the art
widearea detector CT scanners, with up to 320-detector rows,
can provide up to 16-cm z-axis detector coverage in a
single gantry rotation; this allows for large volume
coverage in both helical and axial (step and shoot) acquisition
]. Dual-source CT scanners provide the
maximum temporal resolution available, as the temporal
resolution is equal to a quarter of the gantry rotation time; this
is as low as 66 milliseconds (ms) in the third-generation
scanners. Maximising temporal resolution is
advantageous when imaging structures prone to cardiac motion
artefact, such as the aortic root [
], or when imaging
patients prone to motion, such as trauma patients or poor
Obtaining satisfactory arterial enhancement is crucial
in the assessment of intravascular pathology. One of the
important scan parameters that can influence arterial
enhancement is scan acquisition time. A short acquisition
time is preferable once the scan begins (in most
situations) to ensure uniform arterial opacification on the
acquired images. For helical scans, the acquisition time is
equal to the gantry rotation time multiplied by the number
of gantry rotations required to cover the anatomical area.
The number of gantry rotations is determined by the scan
range divided by the product of the detector bank width
and the pitch. Axial scanning acquires multiple volumes,
and is used in particular when performing ECG-gated
studies such as coronary and aortic CTA, to help reduce
radiation dose [
]. For axial acquisitions of volumes
smaller than the width of detectors, the scan time is equal
to the gantry rotation time. When axial scanning is used
Sample MRI vascular protocols
Arm/chest Axe + Cor
Knee Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor AV
Axe + Cor –
Axe + Cor AV
Axe + Cor –
Axe + –
Cor + Sag –
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Cor (3 Stn) –
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
Axe + Cor
T2 SSFSE T2-weighted single shot fast spin echo, GRE gradient echo, DIR double inversion recovery, TR-MRA time-resolved MRA, CE-MRA T1
spoiled gradient echo contrast-enhanced MRA, T1FS GRE T1-weighted 3D spoiled gradient echo sequence with a fat selective prepulse, HRT1FS
GRE ± C high resolution T1-weighted 3D spoiled gradient echo sequence with a fat selective prepulse pre- and post-contrast, PC phase contrast
C Gadolinium-based contrast agent, Abdo abdomen, Axe axial, Cor coronal, Sag sagittal, Sag Obl sagittal oblique, AV aortic valve, Stn station
a Contrast dose is expressed in mmol/kg unless otherwise specified and is injected at a rate of 1.5 ml/s followed by a saline chaser
b Protocol is performed with the feet in the neutral, dorsiflexed and plantarflexed positions
for volumes larger than the detector width, the total scan
time is equal to the total number of volumes required to
cover the desired anatomical area multiplied by the gantry
rotation time, added to the sum of the interscan time
intervals required for table repositioning.
Optimising IV contrast medium (CM) administration
is important in obtaining strong arterial enhancement
during CTA. The degree of enhancement of a system
is proportionally related to the concentration of iodine
within it. There is variation in the relationship between
enhancement and iodine concentration in different CT
scanners, but it is the range of approximately 25-30
Hounsfield units (HU) per milligram (mg) of iodine
per millilitre (ml) at 120 peak kilovoltage (kV) [
The easily adjustable factors that determine arterial
enhancement in CTA are the concentration of iodine in the
CM used, the injection rate and the injection duration.
There is an almost linear relationship between
enhancement and iodine concentration, which makes CM
preparations with a high iodine concentration ideal
(preferably 350-400 mg/ml) for CTA when the injection
rate is fixed, resulting in a higher iodine delivery rate.
The concept of iodine delivery rate (IDR, mg/s) is a
method of standardising the rate of iodine delivery
across CM with different iodine concentrations, and is
calculated from the following formula: IDR = [CM
iodine concentration (mg/ml)/1,000] × flow rate (ml/s)
]. High iodine delivery rates are important in
providing diagnostic image quality in CTA [
]. If CM
preparations with lower concentrations of iodine are used, for
example 300 mg/ml, the injection parameters can be
adjusted to ensure a similar iodine delivery rate to that
of a higher iodine concentration CM preparation[
example, in a porcine model undergoing CT pulmonary
angiography, CM with an iodine concentration of
300 mg/ml injected at a rate of 5 ml/s provided an
identical IDR of 1.5 g/s to 370 mg/ml CM injected at
a rate of 4.1 ml/s [
]. CM with lower iodine
concentrations have lower viscosity, with reduced injection
pressures, which may potentially reduce extravasation risk
]; however, for a fixed scan duration, the higher
injection rate required to keep the same iodine delivery
rate would result in an increase in total CM volume
required . Experimental models suggest that an IDR
of 1.5-2 g/s provides adequate arterial opacification
(>200 HU) in CTA protocols, regardless of the
concentration of CM used [
The strength of arterial enhancement (peak HU) is
proportional to the injection rate, and the duration of
enhancement to the injection length [
the injection rate leads to a faster accumulation of
contrast in the aorta, increasing peak aortic enhancement.
For a fixed contrast volume, however, this reduces
injection duration, and in turn reduces the available time
window to acquire the CT within. With modern
scanners, an injection rate of 4-5 ml/s is usually sufficient in
providing excellent arterial opacification for most
vascular studies; venous imaging does not require as high
injection rates. The traditional approach to determine
injection duration was to match it to scan duration time;
however, with modern multi-detector, fast CT scanners,
this may result in inadequate opacification due to a
lower volume of CM being delivered. One approach
for estimating injection duration is to set a minimum
duration of 10 s, and to add on the estimated scan
duration time, which is available from all vendors after
the scan range has been chosen. CTA requires use of a
power-injector to allow uniform high injection rate CM
bolus delivery. Use of a saline flush should be routine
to help push the tail of the CM bolus into the central
blood volume, as without it, the bolus tail would remain
unused in the peripheral veins [
]. The saline chaser
also helps reduce intravascular CM dispersion and
reduces streak artefact from dense contrast in the
brachiocephalic veins and superior vena cava, which is
especially important in thoracic CTAs [
Obtaining high-quality arterial enhancement depends
on various CT scanner, CM and patient-related factors.
Even when CM and scanner use remain constant, patient
factors such as body size, cardiac output and disease state
can influence inter-individual variation in arterial
enhancement. For example, large calibre and diseased
vessels may take longer to opacify than normal. Reduction in
cardiac output means that the CM bolus is slower to arrive
and clear, resulting in delayed, but stronger peak arterial
enhancement. These differences mean that the same scan
timing delay cannot be used for everyone, and it needs to
be tailored to the individual. Two methods commonly
used to provide accurate CTA scan timing are the test
bolus and bolus tracking methods. The test bolus method
is based on injecting a small quantity (10-20 ml) of CM,
then obtaining multiple low radiation dose images at a
fixed time interval. By placing a region of interest (ROI)
over the target vessel, a time-enhancement curve can be
plotted to determine the time to peak enhancement. This
can then be used to estimate the scan delay for the CTA.
The bolus tracking technique involves acquiring a
precontrast image at a reference level with placement of an
ROI over a target vessel. After the CM injection is started,
a l o w - d o s e m o n i t o r i n g s c a n i s p e r f o r m e d a t a
predetermined level after a fixed time delay, usually 5 s,
and thereafter every 1-3 s until the enhancement in the
ROI reaches a specified level (typically 150 HU). The
CTA then begins after a pre-specified adjustable delay to
allow peak arterial enhancement (approximately 8 s); this
delay must also take into account time for table
repositioning. The two methods are comparable in terms of
satisfactory CTA timing, with bolus-tracking frequently used
due to its reduced examination time and ease of use [
The test bolus method is useful in patients with
challenging anatomy, such as congenital heart disease patients post
complex surgical repair [
The role of CM as a causative agent in acute kidney
injury (AKI) is currently a topic of debate, with recent
studies suggesting the risk of contrast-induced
nephropathy (CIN) may not be as high as previously thought
]. The use of CM in patients with normal renal
function is safe, with no evidence of a significant drop
in glomerular filtration rate (GFR) post CM
]. To mitigate against the possible risk of CIN,
CM should only be given to patients with severe renal
dysfunction (GFR <30 ml/min) or AKI on a case-by-case
basis after a risk-benefit analysis [
]. There is no
evidence available that reducing CM volume in patients
with mild-to-moderate renal impairment (GFR 60-30 ml/
min) has an effect on development of CIN.
Many modern scanners automate peak kilovoltage (kV)
selection based on the topogram. Reducing the kV, for
example from 120 to 100 in patients with a body mass index (BMI)
of <25, can help improve image quality, and may potentially
reduce radiation dose [
]. Much of the radiation dose
reduction achieved by reducing kV is offset in the presence of
automatic exposure control (AEC), which increases the tube
current to maintain a user-specified noise level [
example, to maintain diagnostic image quality, the tube current
approximately doubles for a reduction from 120 to 100 kV
]. Small radiation dose reductions are still achievable with
the use of model-based iterative reconstruction techniques
], but most of the benefit from reduced kV scanning in
the presence of AEC in CTA comes from improved vessel
contrast. Lower kV CTA has higher vessel HU values due to
relatively increased attenuation of iodine as the kV nears its
kedge of 33 kV, improving image signal to noise and contrast to
noise ratios [
]. Lower injection rates should be used in
reduced kV CTA (for example, 4 ml/s at 100 kV, 3 ml/s at
80 kV) to prevent the vessels appearing too high density, like
bone; this has the added benefit of reducing the overall
volume of CM required [
10, 29, 30
]. There is, however, a cost to
low kV CTA: the higher tube current required to reduce noise
requires a larger focal spot, reducing spatial resolution [
Blooming artefact from calcified atherosclerotic plaque or
metal stents is also exaggerated at lower kV, which can be
problematic in CTA interpretation [
Dual-energy CT (DECT) is a state-of-the art
technology that can improve image contrast in CTA by
providing monoenergetic lower-energy reconstructions closer
to the k-edge of iodine, with improved image contrast
by a relatively increased contribution of the
photoelectric effect [
]. This can be accomplished using
dual-source dual-energy (DSDE) CT systems that employ
two separate X-ray tubes situated 90° apart that can
operate at two different voltages, single-source
dual-energy (SSDE) CT systems with fast kV switching or with
single-source CT systems with a dual-layer of detectors
. Low-energy monoenergetic reconstructions in
CTAs with suboptimal vessel opacification can improve
iodine attenuation to levels similar to conventional
polyenergetic images obtained with higher volumes of
contrast, allowing ‘rescuing’ of a suboptimal CTA
]; this also has the potential to reduce the iodine
load required to obtain a diagnostic CTA, allowing the
use of reduced concentration CM preparations and/or a
lower volume [
]. Virtual monoenergetic datasets
reconstructed at a high kV can help reduce blooming
artefact, allowing improved assessment of vascular stent
], and of heavily calcified vessels [
DECT allows reconstruction of virtual non-contrast
images from post-contrast CT acquisitions by excluding
iodine-containing pixels, thus enhancing water
]; this has the potential to reduce radiation dose
in multiphase vascular CT protocols, by obviating the
need to acquire a separate non-contrast CT [
DECT can provide an assessment of organ perfusion
using iodine map imaging. This is often presented using
a colour look-up table, and can improve the detection of
embolic disease by detecting areas of parenchymal
hypoperfusion; this technique has been shown to improve
the diagnostic accuracy of CTA in the detection of
pulmonary emboli [
Cardiac motion artefact can be problematic when assessing
the aortic root, and the use of ECG-gating in thoracic aorta
CTA can help to address this. Motion artefact at the aortic root
is dependent on several factors; chief among them, the gantry
rotation time of the CT scanner and the patient’s heart rate [
ECG-gating can help to reduce the ill-effects of cardiac
motion on the aortic root, but it does not eliminate it. Pre-scan
beta-blockade is another step that can help to reduce motion
artefact, and is commonly used in coronary CTA; in practice,
the administration of beta-blockers to patients undergoing
routine thoracic aorta CTA is not often necessary to obtain
satisfactory image quality, particularly with the improved temporal
resolution of modern CTs [
]. The available ECG-gating
techniques include prospective, retrospective or high pitch
gating, with the optimum choice largely scanner dependent
]. Scanners with large banks of detectors can cover the
thorax quickly, making prospective gating ideal. Smaller
detector-width scanners are more suited to retrospective
gating with tube current modulation. High pitch gated
acquisitions are suited to dual-source scanners. The use of
ECGgating does increase radiation dose, primarily determined by
the number of cardiac phases, rather than the type of
ECGgating used. The optimum phase (percent of the R-R interval)
for image acquisition is heart-rate dependent [
]. When the
heart rate is less than 75 beats per minute (bpm), a diastolic
acquisition window of approximately 70-80% is preferred,
with a systolic phase acquisition (30-40%) used in patients
with higher heart rates.
There is no single best ‘one size fits all’ CTA protocol.
Depending on the specific indication, it may be useful to obtain
a non-contrast phase first; this can be of particular use when
assessing calcified plaque, in postoperative patients, and in
cases of suspected active haemorrhage. One approach
described for a 64-channel CTA is to: (1) fix the scan duration
to 10s for all CTAs; (2) adjust the pitch depending on the
volume of coverage required; (3) fix the injection duration to
18 s; (4) operate a constant scan delay time of 8 s after CM
arrival; (5) adjust the injection rate according to patient weight
(5.0 ml/s for a 75-kg patient, ±0.5 ml/s for every 10 kg of body
]. With this protocol, the long injection duration,
combined with the extra 8 s delay post CM arrival, allows
adequate time for arterial filling in nearly every patient. A
delayed phase may also be helpful depending on the indication,
with the timing measured from the end of the CM injection.
Magnetic resonance angiography (MRA)
MRA is a multiparametric imaging modality, with
excellent contrast resolution. Contrast-enhanced MRA
(CEMRA) involves the administration of a gadolinium based
contrast agent (GBCA), which shortens blood longitudinal
relaxation (T1). A rapid 3D T1-weighted spoiled gradient
echo (GRE) pulse sequence with a short repetition time
(TR) and echo time (TE) is ideal for CE-MRA. This
provides images with high signal-to-noise ratio (SNR), good
spatial resolution and is free from flow-related artefacts
]. Subtraction techniques improve contrast resolution
in CE-MRA. This reduces signal from background tissues
by acquiring a mask image prior to GBCA injection, and
subtracting it from the post-contrast imaging.
In general, an injection rate of 1.5 ml/s provides arterial
imaging with high vessel to background contrast; this can be
improved by increasing the injection rate, but similar to CTA,
this reduces the available time window to acquire the scan for
a fixed volume of contrast. Two methods are commonly used
to appropriately time CE-MRA imaging. Similar to the
method described for CTA, a test bolus method can be performed,
administering 1-2 ml of GBCA and acquiring a series of rapid
two-dimensional (2D) images of the vessel in question to
determine the optimum time to start imaging post injection. In
fluoroscopic triggering, the full bolus of contrast is
administered and fluoroscopic-like images of the area of interest are
obtained, and when the bolus is detected within the vessel, the
technologist can trigger scan acquisition.
Two different acquisition modes are common in CE-MRA,
single phase and time-resolved MRA. Single phase MRA
captures vascular images at a single point in time.
Timeresolved MRA consists of multiple acquisitions of an imaged
volume over successive time points post GBCA
administration. It is often known under vendor-specific acronyms such
as TWIST (Siemens, Erlangen, Germany), TRICKS (General
Electric, Chicago, IL, USA), 4D-TRAK (Philips, Best,
Netherlands), TRAQ (Hitachi, Tokyo, Japan) and Freeze
Frame (Toshiba, Otawara, Japan). This technique is
particularly useful in displaying the passage of the contrast bolus
through smaller vessels, such as the hands and feet. The core
of time-resolved MRA is a 3D–spoiled GRE sequence
employing k-space filling tricks to quicken image acquisition,
such as non-Cartesian k-space filling, oversampling the centre
of k-space (responsible for image contrast) and under
sampling of the periphery (responsible for spatial resolution)
]. These techniques, aligned with the use of parallel
imaging, delivers ultra-fast imaging [
Paramagnetic contrast agents shorten the T1 and T2
relaxation times of water protons in their immediate surroundings,
creating a locally increased magnetic field strength. This
change in the local magnetic field strength results in increased
local field inhomogeneity, driving the shortening of T1 and T2
relaxation. The resultant increased signal intensity (SI) on
T1weighted images provides the basis behind the use of contrast
agents in MR. GBCAs are the most commonly used in MRA,
and there are currently nine available GBCAs licensed by the
European Medicines Agency (EMA) and the Food and Drug
Administration (FDA) in the USA for clinical use. GBCAs
can be divided into two different groups, linear and
macrocyclic, based on how the ligand chelates the gadolinium ion [
In the linear agents, the ligand wraps around the gadolinium
(Gd3+) ion, but does not completely enclose it. The
macrocyclic agents consist of a chelator, which completely surrounds
the Gd3+ ion in a cage-like structure. The latter agents
demonstrate greater stability in vivo than the linear agents, with little
(if any) free Gd3+ ion dissociation, reducing the risk of
nephrogenic systemic fibrosis (NSF) [
]. The recent
discovery of cerebral gadolinium deposition in patients with
normal renal function is also of concern, although the clinical
significance of this phenomenon is yet to be determined .
Linear GBCAs are thought to confer a higher risk of cerebral
deposition, and their use is now discouraged by the EMA [
although this guidance has not been reciprocated by the FDA
]. Cerebral gadolinium deposition is not only associated
with linear GBCA use, however, and has been demonstrated
in macrocyclic GBCAs in both animals [
] and humans, in
particular the macrocyclic agent gadobutrol [
The majority of GBCAs in routine clinical use are
extracellular fluid (ECF) agents. After injection, they initially
distribute in the intravascular space, before rapidly diffusing
across the vascular membranes into the interstitial space,
eventually establishing an equilibrium between the
intravascular and interstitial compartments after approximately
10 min. ECF GBCA agents that demonstrate weak plasma
protein binding, such as gadobenate dimeglumine
(GdBOPTA), help increase relaxivity compared to the other
ECF GBCAs [
]. Gadofosveset trisodium
(Gd-DTPADO3A/MS-325) is currently the only intravascular GBCA
licensed by the FDA. It was licensed by the European
Medicines Agency for distribution in the European Union
(EU) in 2005, but was voluntarily withdrawn from
commercial use in the EU by the manufacturer in 2011. It is a linear
ionic agent, which binds strongly to albumin, limiting its
diffusion into the extravascular space [
GBCAs with high relaxivity that remain within the
bloodpool are the most attractive from an image quality point of
view, however, safety considerations should be taken into
account when choosing an agent. Gadobenate dimeglumine has
the highest relaxivity of the ECF GBCAs, and gadofosveset
trisodium is the only intravascular GBCA. These are both
linear ionic agents, placing them in the intermediate risk
category for NSF in susceptible patients, and at potentially higher
risk for cerebral deposition. The current commercially
available GBCA with the most favourable risk profile in terms of
NSF and cerebral deposition is the macrocyclic ionic agent
gadoterate meglumine. This agent has inferior protein binding
and relaxivity compared with some of the other GBCAs, but
this is offset by its safety profile. There have to-date been no
reported cases of NSF with this agent, even in patients with
severe renal dysfunction [
], and it is also the only
GBCA in which cerebral deposition has not been
For routine MRAs, a straightforward protocol is to begin
with localisers of the anatomical area in question, followed by
coronal and axial T2-weighted single-shot fast spin echo
sequences, which allow a global anatomic assessment. This is
then followed with 3D CE-MRA with two successive arterial
phase acquisitions, providing anisotropic images, which
allows reconstruction of the dataset on a 3D workstation.
Finally, an axial T1-weighted 3D spoiled GRE sequence with
a fat selective prepulse of the anatomical area can be acquired,
allowing for an assessment for significant incidental findings.
This basic MRA protocol can then be modified/added to
according to the clinical question, as outlined in the
anatomical site-specific sections below. It is our practice to administer
weight-based GBCA dosing to all patients with GFR >30 ml/
min, followed by a saline chaser (Table 2). There is no
evidence available to support GBCA dose reduction in patients
with mild to moderate renal impairment (GFR 60-30 ml/min).
The risk of NSF remains in patients with severe renal
dysfunction (GFR <30 ml/min); in these patients the decision to
administer GBCA should be made on a case-by-case basis [
For patients who cannot have gadolinium, such as those
with severe renal impairment (GFR <30 ml/min),
noncontrast imaging of the aorta and larger vessels can be
performed. In these circumstances, a bright blood imaging, such
as a balanced steady state free precession (SSFP) sequence
can be used; this is a coherent gradient echo sequence that
provides bright blood imaging without gadolinium. In the
setting of acute aortic syndromes, this can detect the presence of
an aortic dissection with high accuracy when compared with
CE-MRA [61, 62]. The major disadvantage of this sequence,
however, is the presence of off-resonance artefact; this artefact
is more pronounced at higher magnetic field strengths . To
overcome this, where possible we perform non-contrast
MRAs on 1.5 T rather than at 3.0 T.
CTA and MRA post-processing
In order to obtain the spatial resolution required, vascular
imaging techniques tend to produce large datasets, which can be
intimidating and difficult to negotiate. A minimum
requirement of any post-processing software package is the ability
to perform multiplanar reformats (MPR) of 3D CT or MRI
datasets to create 2D images in coronal, sagittal, oblique or
curved planes . As the course of vessels tends to not
follow along anatomical axial, coronal or sagittal planes; this
hinders accurate measurement. Routine use of MPRs to
perform measurements in a plane short axis to the centerline of a
vessel is the most reliable and reproducible method of
performing measurements (Figs. 1 and 2, ESM 1) . The
use of semi-automated tools to determine the vessel centerline
improves measurement time .
Maximum intensity projection (MIP) reconstruction is an
algorithm that selects and displays only the voxels with the
highest HU (CT) or SI (MRI) of a selected slab in the imaged
plane . MIPs allow a global assessment of the imaged
vasculature, and are useful in the rapid detection of vascular
stenosis and occlusion. Readers must, however, be aware of
limitations with this technique such as the overestimation of
stenosis due to calcified plaque on CT, and findings should be
confirmed with the thin-slice raw data .
Segmented volume-rendered (VR) images can be created
using most modern post-processing software packages.
Volume rendering operates by assigning opacity values to
image data on a scale from 0 to 100% along an artificial line of
sight projection [67–69]. VR images are visually attractive,
can be useful in pre-procedure planning and are an excellent
means of displaying complex anatomy, especially to clinicians
with varying knowledge of cross-sectional anatomy (Figs. 3,
ESM 2 and 4, ESM 3) .
Notes on specific protocols
In the emergency setting, imaging of the aorta is primarily
focused on the assessment of the acute aortic syndrome
(dissection, intramural haematoma or penetrating atherosclerotic
ulcer) or for active haemorrhage, and CT is generally the
preferred modality (Figs. 3, 4 and 5). Common elective
indications for thoracic or abdominal aorta imaging includes the
assessment and follow-up of aortic aneurysms, pre- and
post-procedure assessment of endovascular aneurysm repair
(EVAR) and in the setting of suspected aortitis. Aorta MRA
can be used to assess thoracic aortic aneurysms, is the
preferred modality in cases of suspected aortitis and aortic
coarctation, and can be used to image acute aortic syndromes in
selected cases, for example those with a severe iodinated
contrast allergy (Figs. 6 and 7).
Acquiring a non-contrast CT prior to aorta CTA is useful to
look for high-density intramural haematoma, which can be
difficult to visualise after contrast administration. In the
post-operative setting, it helps distinguish high-density
surgical material such as felt pledgets routinely from a
pseudoaneurysm [71–73]. Using ECG-gating in thoracic aorta
CTA helps to overcome the effect of cardiac motion on the
aortic root, which can hide or mimic significant pathology,
such as aortic dissection.
For patients undergoing consideration for EVAR, an
additional non-contrast CT of the abdomen and pelvis can help
delineate calcified plaque (CT AA pre-EVAR, Table 1).
Following aneurysm endovascular stent graft repair (EVAR),
Fig. 1 A 45-year-old man with
Marfan’s syndrome post aortic
valve replacement with a fusiform
ascending aortic aneurysm.
Measurement of ascending
thoracic aorta dimension (double
arrows) in an axial plane (a) will
yield erroneous values due to
oblique orientation relative to the
centerline of the aorta, as
demonstrated on sagittal (red line, b) and
coronal (red line, c) multiplanar
Threedimensional segmented volume
rendered (VR) image of the
thoracic aorta (d) demonstrates the
site of measurement (line)
Fig. 3 a Three-dimensional
segmented volume rendered (VR)
image of the thoracic aorta with b
standard sites of measurement. a
Sinuses of Valsalva, b sinotubular
junction, c ascending thoracic
aorta, d aortic arch, between
origin of left common carotid and
left subclavian arteries, e
descending thoracic aorta, f aortic
a CTA with additional 70 s delayed phase imaging (Table 1)
embolisation (Fig. 9) [76, 77]. When performing multiphasic
can assess both the size of the excluded aneurysm and for the
presence of an endoleak (Fig. 8) [74, 75]. This identical
proaortic CTA using a DECT system, reconstruction of a virtual
non-contrast image may obviate the need to acquire a separate
tocol can also be used to assess for the presence of active
non-contrast CT [
]. For patients undergoing post-EVAR
bleeding, with the arterial and delayed phases demonstrating
active extravasation, and can help triage patients for IR
CTA follow-up to detect endoleak, use of a split-bolus
injection technique has the potential to reduce radiation dose, by
Fig. 4 a Three-dimensional
segmented VR image of the
abdominal aorta with b standard sites of
measurement. a Proximal
abdominal aorta, b juxtarenal
abdominal aorta, c infrarenal
abdominal aorta, d right common
iliac artery, e left common iliac
Fig. 6 A MR angiogram in a
45year-old woman who presented
with acute onset of tearing chest
pain. Sagittal oblique image from
a ECG gated T1-weighted
postgadolinium 3D acquisition (a)
demonstrates a dissection flap
(arrow) arising in the aortic arch
distal to the origin of left
subclavian artery consistent with a type
B aortic dissection, with the
dissection flap extending into the
abdominal aorta. Corresponding
3D segmented volume rendered
image of the thoracic aorta (b)
from the thoracic MRA
demonstrates the dissection flap (arrow).
Coronal abdominal T1-weighted
post gadolinium MRA image (c)
demonstrates the distal extent of
the dissection flap (arrow) into
the common iliac arteries
bilaterally, with a 3D segmented volume
rendered image of the abdominal
aorta (d) demonstrating the
dissection flap in the abdominal
Fig. 7 Selected axial images from
T1-weighted 3D spoiled gradient
echo sequence with a fat selective
prepulse sequence pre- (a) and
post- (b) gadolinium in a
55-yearold woman with giant cell arteritis
circumferential mural aortic soft
thickening (arrow) of the juxtarenal
aorta (Ao) consistent with a large
allowing acquisition of a simultaneous arterial and
delayed phase. The split-bolus technique involves injecting
two sequential CM boluses separated by a time delay
(approximately 35 s), and acquiring a simultaneous
arterial and venous phase CTA after the second CM bolus
. This can be further combined with DECT’s
capability to reconstruct virtual non-contrast images,
reducing the protocol down to a single CT acquisition, with
significant radiation dose saving .
Performing a CTA prior to re-do cardiac surgery, with
extra-cranial coverage to include the origin of the
internal mammary arteries, allows identification of the
location and can help surgeons alter surgical strategy,
reducing the risk of intra-operative injury and improve
outcomes [80, 81].
In thoracic aorta MRA (MR TA, Table 2), in addition to the
routine MRA protocol, six to eight cine GRE short-axis slices
can be acquired through the aortic valve, allowing
characterisation of the aortic valve morphology (tricuspid/bicuspid/
unicuspid), valve leaflet opening and coaptation. Using
ECG-gating for the sagittal oblique ‘candy-cane’ CE-MRA
helps combat aortic root motion (Fig. 6) . ECG gating is
not required for imaging the abdominal aorta. For combined
MRA of the thoracic and abdominal aorta, for example in
suspected aortitis, we perform separate gadolinium injections
Fig. 8 Selected images from a CT
angiogram in a 55-year-old man
undergoing imaging surveillance
post abdominal aortic aneurysm
endovascular stent graft repair
(EVAR). Axial non-contrast (a),
arterial phase (b) and 70 s delayed
phase (c) images demonstrate
iodinated contrast material within
the excluded aneurysm sac
(arrow) consistent with an
endoleak. Sagittal oblique MPR
of the right common iliac artery
(d) demonstrates the endoleak
arising from the distal insertion
point of the right iliac limb of the
EVAR consistent with a type 1b
Fig. 9 Selected axial images
(ad) from an arterial phase CT
angiogram of the abdominal aorta
in a 55-year-old man with
hypotension and abdominal pain
demonstrates a large retroperitoneal
haematoma (curved arrow) and
active extravasation from the
infrarenal abdominal aorta
(arrow) consistent with aortic
rupture. A ruptured mycotic
aneurysm was found in the
In patients in whom there is a clinical suspicion of
large vessel vasculitis, or in cases of suspected aortic
infection, acquisition of additional pre- and
postcontrast high-resolution T1-weighted 3D spoiled GRE
sequences with a fat selective prepulse allows an
assessment for arterial mural enhancement (Aortitis, Table 2)
(Fig. 7) [83, 84]. T1 double inversion recovery (DIR)
ECG-gated, breath-held images provide excellent images
of the aortic wall. DIR involves two successive 180°
radiofrequency (RF) inversion pulses to null signal from
moving blood in the aortic lumen, preserving the
magnetisation of stationary tissues, and is excellent in
delineating the structural anatomy of the aorta,
particularly the aortic wall. Turbulence or slow flow within the
lumen will result in incomplete nulling of the lumen,
which can be difficult to distinguish from thrombus.
Each slice requires a single breath-hold, which adds a
considerable time penalty to the study when imaging of
the entire aorta is required; therefore we recommend
reserving DIRs for equivocal cases.
In cases of suspected aortic coarctation, additional phase
contrast (PC) imaging is helpful (Coarctation, Table 2). This
technique allows for a functional assessment of coarctation
including quantification of peak gradient and collateral flow.
PC is based on the principle that the spin phase of moving
protons will change in proportion to their velocity. A bipolar
magnetic gradient is applied to a volume of tissue; stationary
spins will experience no net phase shift, but moving spins will
experience a phase shift proportional to their velocity . By
applying a flow-sensitive PC sequence orthogonal to the
direction of blood flow, flow can be quantified as either velocity or
volume per unit time. PC imaging is performed at the site of the
coarctation, immediately distal to the coarctation, and in the
distal descending thoracic aorta immediately above the
diaphragm. The severity of coarctation can be assessed by
measuring the volume of collateral flow present, or by estimating
the pressure gradient across the stenosis. The flow volume of
the collateral circulation is calculated by subtracting the total
flow volume in the proximal descending thoracic aorta
immediately distal to the site of the coarctation from the volume in
the distal descending thoracic aorta . The percentage
increase in flow volume from the collateral circulation increases
linearly with the severity of stenosis at the coarctation site, and
is the most useful measurement in the assessment of coarctation
severity . The PC acquisition through the site of maximal
stenosis can be used to measure the peak velocity (v) across the
site of coarctation and the maximal pressure gradient across the
coarctation (ΔP) can then be measured by use of the modified
Bernoulli equation (ΔP = 4v2) . In patients with previous
coarctation repair, the percentage increase in flow from the
proximal to distal descending thoracic aorta is the most reliable
indicator of haemodynamically significant restenosis .
In the setting of suspected gastro-intestinal (GI) haemorrhage,
endoscopy remains the initial test of choice, with CTA the
imaging test of choice, reserved for those in whom endoscopy
fails, or in the unstable patient with lower GI bleeding .
The same protocol used in post-EVAR assessment is suitable
(CT post-EVAR, Table 1), and oral contrast should not be
administered, as this reduces the ability to detect intraluminal
haemorrhage . CTA has a high diagnostic accuracy in
detecting and localising the source of acute GI bleeding, both
upper and lower, with a sensitivity of approximately 85%
, and it can detect bleeding rates of as little as 0.3 ml/
min (Fig. 10) . Performing CTA prior to catheter
angiography can increase the ability to successfully localise the
bleeding source at catheter angiography . DECT has the
potential to improve the detection of active GI haemorrhage,
with iodine map reconstructions providing additional
diagnostic information regarding the presence and source of active
In patients with suspected acute mesenteric ischaemia,
CTA is the first-line imaging test (CT mesenteric angiogram,
Table 1) . Whilst occlusive arterial disease is causative in
85% of cases, 15% are secondary to mesenteric venous
thrombosis, which makes the acquisition of delayed venous phases
helpful . CT can also detect the ancillary findings of
mesenteric ischaemia, such as bowel wall hypoenhancement,
bowel wall thickening, fat stranding, pneumatosis intestinalis,
portal venous gas, intra-peritoneal free gas and ascites
(Fig. 11) [95, 96].
MRI is useful in the evaluation of chronic mesenteric
ischaemia, and when CT is contraindicated (MRA mesenteric,
Table 2). Mesenteric MRA has a high sensitivity and
specificity in evaluating the proximal coeliac and superior mesenteric
arteries , but is limited in its ability to detect distal
mesenteric stenosis and occlusions compared to CTA .
Dedicated renal vessel imaging is primarily performed in
patients with suspected renovascular hypertension, and in the
workup of potential donors and recipients in the live renal
A standard renal CTA protocol (Table 1) consists of a
single post-contrast bolus tracked arterial phase acquisition, with
CTA performing well in the assessment of haemodynamically
significant renal artery stenosis and fibromuscular dysplasia
with high sensitivity and specificity [
coverage should include the adrenals superiorly and extend
inferiorly to the aortic bifurcation to exclude the presence of a
pheochromocytoma arising from the adrenal medulla or an
extra-adrenal paraganglioma, the most common site for which
Fig. 10 A 50-year-old man with
oesophageal cancer was referred
to CT following discovery of a
mesenteric haematoma during
exploratory laparoscopy. Axial
non-contrast (a), arterial phase (b)
and 70-s post contrast (c) images
demonstrate an ill-defined
mesenteric haematoma (arrow), a
pseudoaneurysm (curved arrow),
with no active extravasation. The
patient was taken to the
interventional radiology suite and the
pseudoaneurysm was occluded
with coils; selected spot
fluoroscopic image (d) demonstrates the
arcade filled with coils (curved
Fig. 11 An 85-year-old woman
developed severe abdominal pain
two days post percutaneous aortic
valve replacement and was
referred for a CT mesenteric
angiogram. Axial (a) and coronal (b)
images from an arterial phase CT
demonstrate hypoenhancement of distal
ileal loops (straight arrow)
compared with adjacent proximal ileal
and jejunal loops with normal
mural enhancement (curved
arrow). Axial (c) and coronal
oblique images from the same
study demonstrate focal occlusion
of the mid-superior mesenteric
artery with calcified plaque
(arrow). Coronal oblique
maximum intensity projection (MIP)
reformat (d) is useful in
demonstrating the point of SMA
obstruction (arrow). Exploratory
laparoscopy revealed extensive
small bowel ischaemia, and the
patient unfortunately expired
is the organ of Zuckerkandl, extra-adrenal chromaffin tissue
near the origin of the inferior mesenteric artery [
Laparoscopic living donor nephrectomy requires accurate
pre-procedural vascular mapping (CT renal donor, Table 1).
There is a large number of potential normal variants in renal
arterial vascular anatomy. CT provides a better depiction of
small renal arteries than MRI, and is the generally preferred
]. CTA has a very high accuracy in identifying
accessory renal arteries and pre-hilar arterial branching, which
are important variants that the surgeon needs to be aware of
(Fig. 12, ESM 4) [
]. The non-contrast CT phase
identifies renal calculi, with the arterial and nephrographic phases
providing an accurate assessment of renal size, vascular
anatomy and for any renal parenchymal lesions such as incidental
renal tumours, an exclusion criterion for donors [
urographic phase is used to evaluate for any anomalies of
the renal collecting systems or ureters.
Although it does not offer the spatial resolution of CT, the
lack of radiation makes renal artery CE-MRA (Table 2) an
attractive modality, especially in younger patients. In a
prospective comparison of 58 patients with suspected
renovascular hypertension, Rountas et al.  found that CE-MRA has a
slightly lower sensitivity than CTA for the detection of renal
artery stenosis or fibromuscular dysplasia, 90% versus 94%
respectively; this is likely due to the lower spatial resolution of
MRI compared with CT.
For patients who cannot have gadolinium, a non-contrast
renal MRA be performed with a respiratory-gated inflow
Fig. 12 Three dimensional segmented volume rendered image of the
kidneys and their arterial supply in a renal donor volunteer, segmented
from an arterial phase renal artery angiogram CT, demonstrates bilateral
accessory renal arteries supplying the lower renal poles
Fig. 13 A 45-year-old man with
bilateral leg swelling underwent
an MR venogram of the abdomen
and pelvis. Coronal image from a
T2-weighted sequence (a)
demonstrated an expanded suprarenal
IVC with heterogeneous T2 high
signal material, likely thrombus
(arrow). Coronal (b) and axial (c)
images from a venous phase
enhancement of the intraluminal IVC
material, concerning for tumour
thrombus. A coronal image from
a T1-weighted fat-saturated
postgadolinium sequence of the
abdomen (d) demonstrates a
horseshoe kidney with an exophytic
mass arising from the right lower
moiety (curved arrow), which
was subsequently confirmed as a
papillary renal cell carcinoma on
Fig. 14 A 35-year-old woman
underwent an abdominal MR
venogram 5 days post dilatation
and curettage for an intrauterine
fetal death at 25 weeks. Coronal
images from a post-contrast
venous phase fat saturated T1
sequence of the abdomen
demonstrates the post-partum uterus (a,
curved arrow), with marked
dilatation of the right (b, arrow) and
left (c, arrow) gonadal veins with
central filling defects consistent
with bilateral gonadal vein
thrombosis. The thrombus
extends up to the juxtarenal IVC (c,
curved arrow). Axial image from
a T1 post-contrast venous phase
fat saturated T1 sequence of the
abdomen (d) demonstrates the
expanded gonadal veins
bilaterally with central filling defects
balanced-SSFP sequence with inversion recovery saturation
(examples: Inhance Inflow IR, General Electric; NATIVE
TrueFISP, Siemens; B-TRANCE, Philips). These sequences
accentuate the high signal of arterial blood by exploiting
inflow-enhancement, similar to that used in time-of-flight (TOF)
]. Firstly, the volume of interest is saturated with a
180° radiofrequency pulse, inverting signal from background
tissue and venous blood. Fresh, unsaturated arterial blood then
flows into the slab, and a rapid 3D SSFP sequence is acquired
after an appropriate inversion time to null signal from
background tissue [
]. This is a useful technique in patients
suspected of having renovascular hypertension, with good
agreement with CE-MRA and CTA for the presence of renal
artery stenosis or fibromuscular dysplasia [
Thoracic venous imaging
The most common reason for dedicated imaging of the
thoracic venous circulation is in the evaluation of suspected
superior vena cava (SVC) obstruction or thrombosis.
Contrastenhanced MR venography (CE-MRV) allows better
differentiation of intraluminal thrombus from contrast mixing than CT
venography (CTV), is equivalent to conventional venography
in the assessment of central venous obstruction and is the
noninvasive imaging modality of choice (CT SVC, Table 1; MR
SVC, Table 2) [
]. In patients who have difficulty with
breath-holding, the post-contrast imaging can be performed
free-breathing with respiratory gated navigator MRA .
Abdominal and pelvic venous imaging
CT/MR venography of the abdomen and pelvis is commonly
performed to assess for extension of lower limb deep vein
thromboses (DVTs) or for a compressive venous syndrome,
such as May-Thurner syndrome (obstruction of the left
common iliac vein by the crossing right common iliac artery)
]. MRV is preferable to CTV due to the presence of
contrast mixing artefact with the latter, and imaging of the thighs
can be included (Figs. 13 and 14). CTV is preferred when
assessing potential inferior vena cava (IVC) filter
complications, such as malposition, migration, tilting, caval thrombosis
or perforation [
CTA and MRA both provide a highly accurate vascular map, and
have largely replaced catheter angiography in the diagnosis of
lower limb ischaemia, acute and chronic [
]. A meta-analysis
of the diagnostic performance of CTA and CE-MRA to detect
haemodynamically significant arterial stenosis or occlusion
demonstrated equal diagnostic accuracy of both techniques [
Acquiring a non-contrast CT phase allows for the
assessment of calcified plaque, whilst the bolus-tracked CTA is
Fig. 16 A 45-year-old man with a
previous history of left radial
artery thrombosis post coeliac
artery stenting with persistent arm
claudication. Time resolved MRA
(a-d) of the left forearm
demonstrates opacification of the left
brachial artery, and left ulnar
artery (arrows) with occlusion of
the proximal left radial artery
(curved arrows) (b, c), followed
by venous filling (d)
highly accurate in depicting arterial occlusions and
haemodynamically significant stenosis (CTA lower limbs, Table 1)
]. This may be omitted in DECT systems with the
capability to perform virtual non-contrast reconstructions
]. The smaller below-the-knee runoff vessels are more
challenging to interrogate due to their small size and difficulty
opacifying adequately. Due to the speed of modern CT
scanners, the CT often outruns the contrast bolus, affecting
opacification of the below-the-knee arteries; acquiring an
additional CTA phase with coverage from the knees through to
the toes immediately after the bolus-tracked CTA can help
assess these hard to image vessels. Providing separate
reconstructions of each leg with a small field of view is also useful
in improve spatial resolution.
CE-MRA provides an accurate luminal map of the arterial
tree, with equal performance to CTA in the detection of
arterial stenosis and occlusion (MRA lower limbs, Table 2) [
CE-MRA is often preferable to CTA, especially in patients
with distal disease, and in those with heavily calcified vessels,
which can hinder stenosis assessment on CTA [
]. MRA is
limited in the assessment of stent patency due to local
susceptibility artefact, where CTA is the preferred technique.
Time-resolved CE-MRA is an excellent method of
assessing small vessel patency, and is particularly useful when
imaging the below-the-knee vessels, where it is superior to
standard CE-MRA [
]. Both calves can be imaged
simultaneously in the coronal plane following gadolinium
injection, and when used, should be performed first in a lower
limb CE-MRA. After this, a standard three-station (abdomen
and pelvis, thighs, calves) bolus CE-MRA can be performed
with a separate gadolinium injection. If foot arterial imaging is
required, a separate time-resolved foot MRA is performed at
the start of the examination before the calf MRA, using a boot
coil with a sagittal acquisition separate gadolinium injection
for the calves and for each foot (Fig. 15, ESM 5).
For patients with suspected popliteal artery entrapment
syndrome, MRA is the preferred technique (MRA popliteal
entrapment, Table 2). Typically, these are young patients, and
definitive diagnosis requires imaging in multiple degrees of
plantar and dorsiflexion. MRA allows precise analysis of local
muscle anatomy, making it an ideal modality for diagnosis
]. Time-resolved CE-MRA with the toes in the
neutral position, in plantar flexion and then in dorsiflexion, with
separate gadolinium injections for each.
Upper limb angiography
Upper limb CTA and MRA is usually limited to one upper
limb, and IV cannulation should be performed in the
contralateral arm to avoid injection-related artefact. CTA is preferred
in cases of suspected acute upper limb ischaemia due to its
relatively quick time of acquisition, with MRA preferred in
the chronic setting [
]. Where possible, upper limb CTAs
should be acquired with the arm of interest raised above the
head, with imaging extending from the aortic arch through the
fingers (Upper extremity CTA, Table 1). A delayed CTA
phase can help in assessment of the small arteries of the
forearm, which may not be adequately opacified on the
bolustracked CTA due to the scanner out-running the CM bolus.
In upper extremity MRA (Table 2), time-resolved MRA is
preferred for the forearm and hand vessels, with a standard
CE-MRA for the proximal vessels (Fig. 16, ESM 6).
In cases of suspected thoracic outlet syndrome (TOS),
MRA (Table 2) with positional manoeuvres is the preferred
imaging modality for diagnosis, pre-operative planning and
post-surgical follow-up [
]. CE-MRA with coverage
including the bilateral subclavian and axillary vessels is
performed with the arms abducted approximately 150-160°, and
repeated with the arms adducted, with separate contrast
injections at each position.
Acute pulmonary embolism (PE) is the third most common
acute cardiovascular disorder after myocardial infarction and
]. CT pulmonary angiography (CTPA) is the
noninvasive reference standard for PE diagnosis and risk
stratification, identifying adverse prognostic indicators such as right
ventricular dilatation, interventricular septal bowing and a high
embolus burden [
]. DECT, in particular iodine map
reconstructions, have been shown to improve the accuracy of pulmonary
emboli detection on CT, by demonstrating areas hypoperfused
]. MR pulmonary angiography (MRPA, Table 2) is
a suitable alternative modality to diagnose PE in patients who
cannot undergo CT, and is useful in the follow-up of pulmonary
artery aneurysms (Fig. 17, ESM 7). In our experience, a
timeresolved CE-MRA of the chest performed in the coronal plane
with approximately nine phases yields diagnostic pulmonary
arterial imaging in the majority of cases.
angiogram image (b) demonstrate fusiform aneurysmal dilatation of the
main pulmonary artery (PA)
Breast reconstruction flap planning
The deep inferior epigastric perforator (DIEP) flap is the most
common flap used in breast reconstruction. Raising a DIEP
Fig. 18 A 45-year-old woman with breast cancer undergoes a CT deep
inferior epigastric artery perforator (DIEP) protocol prior to breast
reconstruction. Coronal oblique 3D segmented VR image from the CT displays
the abdominal wall musculature and superficial arterial supply. The
location of the largest DIEP relative to the umbilicus is annotated with
craniocaudal and mediolateral distance measurements to help the surgeon
locate the vessel during surgery
flap requires meticulous dissection of the DIEP vessels;
however, there is significant heterogeneity in their branching
pattern and location [
]. CTA is the current ‘gold standard’ for
pre-operative vascular mapping, reducing operative time and
postoperative complications [
]. A standard CT DIEP
protocol is a single bolus-tracked CTA of the abdomen and
pelvis, acquired in the caudo-cranial direction to mirror the
direction of blood flow in the DIEP arteries (CT DIEP,
Table 1). A segmented batch of 3D VR images displaying
the number and site of DIEPs relative to the rectus sheath
and overlying skin, providing the distance of the largest
perforator from the umbilicus, is of particular use in surgical
planning (Fig. 18, ESM 8). CTA is also used in patients
undergoing pre-operative assessment for a superior gluteal artery
perforator (SGAP) flap (Table 1); in this protocol, the patient
is scanned prone, with anatomical coverage from the
umbilicus to the mid-thighs.
A basic understanding of the technical, physiological and
pathological challenges posed by vascular imaging allows
the creation of bespoke, safe imaging protocols that can help
improve diagnosis and impact outcomes. The challenges
posed by cardiovascular imaging will continue to drive
technological improvements in scanner technology, and it is
important that radiologists continue to improve and streamline
vascular imaging practices.
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