How to use cardiac IQ•SPECT routinely? An overview of tips and tricks from practical experience to the literature
Eur J Nucl Med Mol Imaging
How to use cardiac IQ SPECT routinely? An overview of tips and tricks from practical experience to the literature
Eric Gremillet 0 1 2
Denis Agostini 0 1 2
0 Department of Nuclear Medicine, University Hospital of Caen and Normandie Université , EA4650 Caen , France
1 Centre d'Imagerie Nucléaire, Hôpital Privé de la Loire , Saint-Etienne , France
2 Eric Gremillet
The main part of the IQ SPECT tomographic system
developed by Siemens dedicated to cardiac imaging is a
multifocal collimator called SMARTZOOM. The system
can be installed on Symbia cameras from the same
manufacturer. Besides a pair of SMARTZOOM collimators, it
includes cardiocentric acquisition software and
reconstruction software that takes into account this particular
geometry of detection in an OSEM algorithm and can
correct for scatter diffusion. Although presented as
optional by the manufacturer, attenuation correction (AC)
using a CT scan (with 2 to 16 detectors, depending on
the exact model of Symbia camera) is an additional and
e s s e n t i a l f e a t u r e . T h e m u l t i f o c a l g e o m e t r y o f
SMARTZOOM enables magnification of the centre of
the field of view where the heart lies by a factor of up
to four while avoiding truncation of lateral parts of the
Concerning the multifocal acquisition geometry, the
manufacturer calls the region of the field of view where the
magnification is fourfold the Bsweet spot^. The
technologist has to centre the heart as precisely as possible within
the sweet spot and the myocardial contrast may often be
less than optimal, and thus the effects of mispositioning
on the reconstructed image is a concern. This question
was addressed by Rajaram et al. [
] in a phantom study.
They found that final images were significantly affected
by different positioning (centring on the base vs. the apex)
when they were reconstructed without AC (NAC), while
no difference was observed with AC. A recent phantom
study by Caobelli et al. [
] confirmed these results. The
effects of mispositioning by up to 2.5 cm were considered
unlikely to affect clinical results when AC was applied.
The reason for this AC dependency can be understood
from careful consideration of the ray paths through the
patient’s body. For rays originating from the heart base,
the path length is longer with a SMARTZOOM collimator
than with a parallel collimator, while there is no
difference for rays originating from the apex. This
phenomenon, which is purely geometrical, can vary with the heart
positioning around the sweet spot region. Thus
attenuation artefacts are not only more marked than with parallel
collimation (as discussed below) but also unpredictable
and position-dependent, making AC mandatory. Users of
a Symbia camera not equipped with a CT scanner who are
considering installing an IQ SPECT system should be
aware of this limitation.
Regarding detection characteristics, IQ SPECT has been
compared with parallel collimation and with two dedicated
CZT cameras in phantom and human imaging [
parameters were analysed with the systems under study:
sensitivity, resolution, contrast/noise ratio, and image
sharpness. To summarize, CZT cameras are better than Anger
cameras for all parameters, and IQ SPECT is not different from
parallel collimation except for its sensitivity which is four
times better, as expected.
NAC images obtained with IQ SPECT often exhibit a hot
apex and poor contrast in basal segments due to attenuation,
while AC images usually show a more homogeneous pixel
intensity throughout the left ventricle wall. We have
previously discussed a likely explanation for this phenomenon: the
basal parts of the ventricle are more prone to attenuation
artefacts than with conventional parallel collimation. But apex
thinning is often observed in AC images. In some cases the
apex even looks quite normal in NAC images but unusually
thin in AC images. In addition to correcting for the particular
attenuation artefacts of IQ SPECT, AC allows correction of
common attenuation artefacts such as low pixel counts in the
inferior wall. AC also makes it possible to obtain satisfying
images in very obese patients or in patients with the left arm
along the body.
The additional radiation dose from CT may be a concern.
On the one hand, our physicists have found that the CT
voltage can be reduced to 110 kV (in patients up to 130 kg)
without loss of AC accuracy (unpublished data from Hopital prive
de la Loire), and on the other hand, we have demonstrated that
the same CT acquisition can be used for both stress and rest
AC if the CT and rest SPECT images are carefully manually
registered. However, it is reasonable to obtain a separate CT
scan at rest in patients in whom similar repositioning is very
uncertain (for example, very large breast, left arm kept along
the body, marked kyphosis).
Volumes and LVEF assessment
Using the Amsterdam gated (AGATE) dynamic cardiac
phantom (Vanderwilt techniques, Boxtel, The Netherlands),
Bailliez et al. [
] used CZT cameras and IQ SPECT to
determine volumes and left ventricular ejection fraction (LVEF).
Eighteen acquisitions were processed on each CZT and Anger
(IQ SPECT) camera. New CZT cameras yielded different
results for global left ventricular function compared to Anger
camera with cardiofocal collimators. Left ventricular volumes
were higher with the DNM 530c than with D-SPECT and
IQ SPECT, leading to decreased LVEF in normal subjects.
These differences should be taken into account in clinical
practice and indicate the need for the collection of a specific
As an expected consequence of the fourfold increase in
sensitivity, the first published clinical work comparing IQ SPECT
and conventional parallel collimation showed that the
acquisition duration could be divided by approximately four with
similar image quality and diagnostic accuracy. Other workers
have confirmed this finding in both phantom studies [
clinical studies [
]. The phantom study also confirmed that
either the activity or the acquisition duration can be reduced.
While all the previously mentioned studies used 99mTc tracers,
the technique has also been used and validated with 201Tl [
]. In both studies with 201Tl, concordance between
IQ SPECT CT and conventional parallel collimation was
better when AC was used. The second study also showed that
inferior wall attenuation artefacts often observed with 201Tl
and conventional parallel collimation are improved by AC.
Thus overall, it appears that AC IQ SPECT gives clinical
results similar to those with conventional parallel collimation
whatever the tracer, while allowing the Binjected dose × image
duration^ product to be divided by 4.
Despite the fact that contrast/noise ratio and image
sharpness are not improved with IQ SPECT, image quality may be
improved over conventional parallel collimation. Indeed,
since acquisition duration is greatly reduced, the likelihood
of motion (whether of the heart within the patient, e.g. upward
creep, or of the patient) is also reduced. Thus motion artefact is
less likely to occur. It has been known for a long time that such
artefacts can be very subtle, are unpredictable and can mimic
IQ SPECT with ECG gating often produces unexpected
results for LVEF. Rigorous results on this particular point have
been found in only one study in 80 patients [
] in which
functional parameters obtained with IQ SPECT were
compared with those from parallel collimation. LVEF was
significantly lower with IQ SPECT: −8 % on stress images, −9 %
on rest images. Since this was related to slightly higher left
ventricular volumes overall, the authors hypothesized that
scatter correction which is included in IQ SPECT
reconstruction software could indirectly have been responsible by
improving resolution, which can result in slightly higher cavity
volumes both at end diastole and end systole. However, we
have previously stated that resolution is actually identical with
IQ SPECT and parallel collimation, which is not in favour of
this hypothesis. The findings of the previous study [
not dependent upon the contouring software used (4 DM
SPECT) because similar results have been observed by many
others, including our group, using concurrent software (QGS),
although no data have been published on this topic.
It is possible to make the most of the increased sensitivity of
IQ SPECT by shortening stress–rest protocols. The basic
ideas behind such protocols are:
1. Stress injected activity can be greatly reduced while
maintaining good image quality.
2. It is thus possible to greatly increase the rest injected
activity in a given patient while keeping the total daily
activity within recommended limits [
3. The ratio between rest and stress injected activities is thus
4. Finally, the delay between injections can be reduced while
keeping contamination of the rest image by residual stress
counts at an acceptable level.
By combining the results of several substudies it is possible to
design a short 1-day protocol (stress then, if necessary, rest).
For example, for a 70-kg patient, the delay between stress and
rest injections is reduced to 1 h and the acquisition duration is
9 min under stress (to which must be added around 5 min for
the CT acquisition) and 3 min at rest (without CT acquisition).
The reconstruction OSEM parameters routinely used are 10
iterations and 3 subsets for summed nongated images and 12
iterations and 1 subset for gated images, with a 10-mm
Gaussian filter and scatter correction for both.
Takamura et al. [
] investigated whether prone
myocardial perfusion SPECT with 201Tl acquired with IQ-SPECT could
correct for soft-tissue attenuation in 39 patients. They
concluded that attenuation was better and defect decisions were
similar with prone IQ-SPECT images than with supine
IQSPECT images in the anterior, anteroseptal, lateral and inferior
Tips and tricks
Although the interpretation of IQ SPECT images is already
well understood by experienced IQ SPECT users and experts
in nuclear cardiology, the following tips on interpretaion may
be helpful to future users.
Prefer prone positioning for acquisition whenever
Inferior wall attenuation artefacts are less marked on
NAC images and NAC images must be considered in
There is less motion in the prone position than in the
supine position (heart within torso and/or patient on
Quality control: check the acquisition data for quality of
ECG gating, centring and motion. Since the acquisition
duration is short, do not hesitate to repeat if necessary
(the CT part does not need to be repeated).
CT and SPECT image registration:
Check the CT images for artefacts, in particular for
the presence of a notch on the left margin of the heart,
a finding that is not uncommon with single-slice or
two-slice CT scans. This can produce marked
artefacts in AC images, mimicking true hypoperfusion.
When the CT scan is acquired at the same time,
generally no user action is required, or there is a shift of a
few millimetres. When using a separately acquired
CT scan, manual registration may involve a shift of
a few centimetres in all three directions. Adjust the
colour scale such that the left myocardium is well
seen, look only at the coronal and transverse plane
displays (the sagittal image can be misleading due
to variable overlap of the right and left ventricles),
use the arrow keys (more precise than the mouse),
and make wide and frequent use of the blend slider
to check registration.
If an abnormality is seen only on the AC images
while the NAC images look normal, then an AC
artefact is very likely (e.g. due to misregistration of CT
and SPECT images since alignment cannot always be
perfect, or due to a notch artefact).
If a nonreversible apical thinning pattern is seen (a
frequent finding), look carefully at the beating slices
since evidence of akinesis, or at least hypokinesis, of
the apex can lead to the (rare) conclusion that a small
nontransmural or transmural apical scar is present.
Similarly, if the apical thinning pattern is partially
reversible, an artefact is likely.
More generally, as a rule of thumb, if abnormalities
are seen on AC images, always cross-check the AC
images with the NAC images. If the abnormalities are
real at least a faint similar trend should be observed.
The aim of AC is to correct for artefactual patterns
due to attenuation problems, whether general such as
diaphragmatic or SMARTZOOM-specific as
Since gated images are not corrected for attenuation,
they sometimes, and perhaps often, exhibit a hot apex
and a faint base. Moreover, this pattern may be more
or less marked depending on the time bin. Thus it is
Perfusion nongated images:
Functional gated images:
more reliable and easier to visually assess wall motion
rather than wall thickening. We use the three-plane
display called Slice in QGS, setting the colour to grey
and the gamma to a high value in the range 1.5 to 1.7.
To limit the problem of an erroneously small LVEF,
avoid masking out the heart on gated slices or, if
masking is necessary, avoid masking too close to
the left ventricle.
Compared with conventional parallel collimation, IQ SPECT
shows similar global image quality, including resolution, but a
fourfold higher sensitivity which allows the use of short 1-day
protocols. Since attenuation artefacts are more problematic
than with conventional parallel collimation, we strongly
advise the use of CT attenuation correction. Taking into account
these precautions and the interpretation tips, IQ SPECT may
be a good cardiac imaging modality that would increase the
throughput of patients with coronary artery disease.
1. Rajaram R , Bhattacharya M , Ding X , Malmin R , Rempel TD , Vija AH , et al. Tomographic performance characteristics of the IQ·SPECT system . IEEE Nuclear Science Symposium Conference Record; 2011 . p. 2451 - 6 . doi: 10 .1109/NSSMIC. 2011 . 6152666
2. Caobelli F , Ren Kaiser S , Thackeray JT , Bengel FM , Chieregato M , Soffientini A , et al. The importance of a correct positioning of the heart using IQ-SPECT system with multifocal collimators in myocardial perfusion imaging: a phantom study . J Nucl Cardiol . 2015 ; 22 ( 1 ): 57 - 65 .
3. Imbert L , Poussier S , Franken PR , Songy B , Verger A , Morel O , et al. Compared performance of high-sensitivity cameras dedicated to myocardial perfusion SPECT: a comprehensive analysis of phantom and human images . J Nucl Med . 2012 ; 53 : 1897 - 903 .
4. Bailliez A , Lairez O , Merlin C , Piriou N , Legallois D , Blaire T et al. Global and regional left ventricular function assessment using two different semiconductor cadmium zinc telluride (CZT) cameras compared to conventional gamma camera with cardiofocal collimators: dynamic cardiac phantom study and clinical validation . J Nucl Med 2015 (abstract SNM) .
5. Caobelli F , Ren Kaiser S , Thackeray JT , Bengel FM , Chieregato M , Soffientini A , et al. IQ SPECT allows a significant reduction in administered dose and acquisition time for myocardial perfusion imaging: evidence from a phantom study . J Nucl Med . 2014 ; 55 : 2064 - 70 .
6. Caobelli F , Pizzocaro C , Paghera B , Guerra UP . Evaluation of patients with coronary artery disease: IQ-SPECT protocol in myocardial perfusion imaging - preliminary results . Nuklearmedizin . 2013 ; 582 : 178 - 85 .
7. Horiguchi Y , Ueda T , Shiomori T , Kanna M , Matsuhita H , Kawaminami T , et al. Validation of a short-scan-time imaging protocol for thallium-201 myocardial SPECT with a multifocal collimator . Ann Nucl Med . 2014 ; 28 : 707 - 15 .
8. Matsuo S , Nakajima K , Onoguchi M , Wakabayash H , Okuda K , Kinuya S . Nuclear myocardial perfusion imaging using thallium201 with a novel multifocal collimator SPECT/CT: IQ-SPECT versus conventional protocols in normal subjects . Ann Nucl Med . 2015 ; 29 : 452 - 9 .
9. Pirich C , Keinrath P , Barth G , Rendl G , Rettenbacher L , Rodrigues M. Diagnostic accuracy and functional parameters of myocardial perfusion scintigraphy using accelerated cardiac acquisition with IQ SPECT technique in comparison to conventional imaging . Q J Nucl Med Mol Imaging . 2014 (Epub ahead of print).
10. Verberne HJ , Acampa W , Anagnostopoulos C , Ballinger J , Bengel F , De Bondt P , et al. EANM procedural guidelines for radionuclide myocardial perfusion imaging with SPECT and SPECT/CT: 2015 revision . Eur J Nucl Med Mol Imaging . 2015 ; 42 ( 12 ): 1929 - 40 .
11. Takamura T , Horiguchi Y , Kanna M , Matsushita H , Sudo Y , Kikuchi S , et al. Validation of prone myocardial perfusion SPECT with a variable-focus collimator versus supine myocardial perfusion SPECT with or without computed tomographyderived attenuation correction . Ann Nucl Med . 2015 ; 29 ( 10 ): 890 - 6 .