Value of automatic patient motion detection and correction in myocardial perfusion imaging using a CZT-based SPECT camera
Value of automatic patient motion detection and correction in myocardial perfusion imaging using a CZT-based SPECT camera
Joris D. van Dijk 0
Jorn A. van Dalen 0 2
Mohamed Mouden 0 3
Jan Paul Ottervanger 0 3
Siert Knollema 0
Cornelis H. Slump 0 1
Pieter L. Jager 0
0 Reprint requests: Joris D. van Dijk, MSc, Department of Nuclear Medicine, Isala Hospital , PO Box 10400, 8000, Zwolle, GK , The Netherlands
1 MIRA: Institute for Biomedical Technology and Technical Medicine, University of Twente , Enschede , The Netherlands
2 Department of Medical Physics, Isala Hospital , Zwolle , The Netherlands
3 Department of Cardiology, Isala Hospital , Zwolle , The Netherlands
4 Department of Nuclear Medicine, Isala Hospital , Zwolle, GK , The Netherlands
Background. Correction of motion has become feasible on cadmium-zinc-telluride (CZT)based SPECT cameras during myocardial perfusion imaging (MPI). Our aim was to quantify the motion and to determine the value of automatic correction using commercially available software. Methods and Results. We retrospectively included 83 consecutive patients who underwent stress-rest MPI CZT-SPECT and invasive fractional flow reserve (FFR) measurement. Eightminute stress acquisitions were reformatted into 1.0- and 20-second bins to detect respiratory motion (RM) and patient motion (PM), respectively. RM and PM were quantified and scans were automatically corrected. Total perfusion deficit (TPD) and SPECT interpretation-normal, equivocal, or abnormal-were compared between the noncorrected and corrected scans. Scans with a changed SPECT interpretation were compared with FFR, the reference standard. Average RM was 2.5 ± 0.4 mm and maximal PM was 4.5 ± 1.3 mm. RM correction influenced the diagnostic outcomes in two patients based on TPD changes ‡7% and in nine patients based on changed visual interpretation. In only four of these patients, the changed SPECT interpretation corresponded with FFR measurements. Correction for PM did not influence the diagnostic outcomes. Conclusion. Respiratory motion and patient motion were small. Motion correction did not appear to improve the diagnostic outcome and, hence, the added value seems limited in MPI using CZT-based SPECT cameras. (J Nucl Cardiol 2016)
Fractional flow reserve
Myocardial perfusion imaging
Single photon emission computed tomography Total perfusion deficit
Myocardial perfusion imaging (MPI) is known as
one of the best validated noninvasive methods to test for
ischemia,1 although artefacts negatively influence the
clinical accuracy. Introduction of patient-specific
activities and CT-based attenuation correction have limited
this influence.2–4 However, artefacts still occur and may
mainly be the result of motion.5,6 Artefacts resulting
from patient movement, respiration, and myocardial
contraction are difficult to distinguish from real
perfusion defects and can lead to false positive studies.6–10
Several types of motion tracking and techniques to
correct for overall patient motion (PM) on conventional
SPECT cameras have been introduced and validated.9,11,12
However, these techniques cannot be applied in SPECT
cameras equipped with stationary cadmium zinc telluride
(CZT) detectors with pinhole collimators. Two recent
studies showed that motion detection and correction seems
feasible on a CZT-based SPECT camera.8,13 However,
they did not compare their motion correction to a reference
standard. It is therefore unknown whether the corrections
improved the diagnostic outcomes.
A commercially available automatic motion
detection and correction software has become available which
can detect and correct for both respiratory motion (RM)
and PM in all directions using a CZT-based SPECT
camera. This program (MCD for Alcyone, GE
Healthcare) has—to the best of our knowledge—not been
described or validated in clinical practice before. Hence,
the aim of our study was to quantify the motion and to
determine the value of automatic correction using
commercially available software.
We retrospectively included 83 consecutive patients in
this study who underwent clinically indicated elective FFR
measurement of intermediate anatomical coronary lesions
demonstrated by recent invasive angiography between January
2011 and July 2014.14 One day after the FFR measurement,
patients underwent CZT-SPECT/CT 1-day stress-rest MPI
(Discovery NM/CT 570c, GE Healthcare). All patients
provided written informed consent for the use of their data for
research purposes. Inclusion criteria were referral for elective
FFR measurement of target lesions with a reduction in
diameter of 40% to 80% as determined during previous
coronary angiography, conform a previous study using the
same population.14 Patients with concomitant severe coronary
stenosis ([80%), serial coronary stenosis, and prior myocardial
infarction in the territory of the target lesion or for whom list
mode data were missing were excluded.
CZT-SPECT Data Acquisition
Patients were instructed not to use any nicotine or
caffeine containing beverages for 24 hours and to discontinue
persantin for 48 hours prior to scanning. Pharmacological
stress was induced by intravenous adenosine (140
lg kg-1 minute-1 for 6 minutes) or dobutamine (starting from
10 lg kg-1 minute-1, increased along three minute intervals
to a maximum of 50 lg kg-1 minute-1 until 85% of the
predicted maximum heart rate was reached). Only
pharmacologic stress was used due to logistic reasons, in particular the
high patient throughput in our center.15 At peak stress, patients
were injected intravenously with 370 MBq (10 mCi) Tc-99m
tetrofosmin (500 MBq (13.5 mCi) for patients with a body
weight of more than 100 kg). Rest imaging was performed on
the same day using 740 MBq (20mCi) Tc-99m tetrofosmin.
Patients were scanned in supine position, with arms
placed above their head using a fixed scan time of 8 minutes
for the stress acquisition. The patient’s chest was positioned
close to the SPECT detectors, with the heart in the center of the
field of view, assisted by using real-time persistence imaging.
Both stress and rest acquisitions were performed 45-60
minutes post injection using a 20% symmetrical energy window
centered at 140 keV. Data were acquired in list mode.
Attenuation correction was not used in this study to prevent
reproducibility errors.16 A full description of the CZT detector
system used in this study is described in several studies.15,17–19
In short, the scans were acquired using 19 stationary pinhole
detectors, each containing 32 9 32 pixelated (2.46 9
2.46 mm) CZT elements, all focused on the myocardium.
Motion Detection and Correction
All emission data were reformatted into 1.0- and
20second time bins for RM and PM detection and correction,
respectively. Next, a volume of interest was drawn manually
around the myocardium to exclude extra cardiac activity.
Motion was tracked by commercially available software
(MDC for Alcyone, Xeleris 3.1, GE Healthcare). In short, the
algorithm determines the center of mass in the detected
counts for five pinhole projections in the user-defined volume
of interest. Next, five virtual lines originating from these
center of mass’ are drawn through these pinholes, and the
point (x,y,z) with the smallest distance from these lines is
calculated. This process is repeated for each time bin, and
afterwards all points are compared to identify motion. The
magnitude of RM was only assessed in the z-direction,
caudal-cranial, as this is the main contributor to respiratory
motion.8 PM was assessed in all three directions: lateral
motion, ventral-dorsal motion, and cranial-caudal motion.
Overall PM was estimated by calculating the square root of
the summed squared motions in all three directions for each
time bin. All motions were automatically corrected using the
same software by generating a system matrix that
incorporated the identified motion which was then used to reconstruct
the images from the original projections.
The noncorrected and motion-corrected images were
reconstructed by applying an iterative dedicated reconstruction
algorithm with maximum-likelihood expectation maximization
(Myovation, Xeleris 3.1, GE Healthcare). The use of dedicated
software (Make SA and Fil3DBatch, Xeleris 3.1, GE
healthcare) allowed to reconstruct both the noncorrected and
motioncorrected images using the exact same alignment and masking,
excluding possible reproducibility errors.16
Each image was automatically normalized to the
maximum peak activity and the 17-segmental uptake values were
presented as the percentage of the maximum myocardial
regional uptake. Total perfusion deficit (TPD) was
automatically calculated for all scans (Quantitative Perfusion SPECT
(QPS) 2009, Sedar Senai). TPD is defined as the percentage of
segments below the predefined uniform average deviation
threshold, as explained in detail by Berman et al.20 Scans were
displayed in the traditional short, vertical long, and horizontal
long axes and reviewed using a color scale.
FFR measurements were derived in the same way as
previously described.14 In short, we introduced a pressure
monitoring wire (PressureWire ; RADI Medical Systems)
into the coronary artery and positioned the pressure wire distal
to the stenosis. Adenosine (140 lg kg-1 minute-1) was
infused continuously to obtain a maximal coronary blood
flow. The FFR was calculated by dividing the mean distal
intracoronary pressure by the mean arterial pressure proximal
of the possible stenosis. FFR ratios \0.80 were considered
positive for ischemia and FFR ratios C0.80 were considered
negative for ischemia.21
Added Value of Motion Correction
The mean and maximum RM and PM were derived from
all time bins. The mean RM and PM across all patients during
the scan were assessed to determine a possible increase in
motion with longer scan times. Next, the noncorrected scans
were compared with the RM-corrected scans and also with the
PM-corrected scans to determine the possible change in
In the qualitative evaluation, two experienced readers
interpreted in consensus whether there was a change in
diagnostic outcome (categorized as normal, equivocal, or
abnormal) between the noncorrected and motion-corrected
scans. Readers were aware which series were noncorrected or
motion-corrected but they had no knowledge of patients’
history or other clinical findings. In the quantitative evaluation,
the differences in TPD and segmental uptake values were
determined between the noncorrected and corrected scans. A
difference in TPD of C7% was considered to result in a change
in diagnostic outcome, as previously described by Berman et al
and Iskandrian et al.20,22 A difference of C5% in at least one
segment was also considered to affect the diagnostic outcomes
as it is associated with mild to severe ischemia.23,24
Next, we compared the conclusion of the scans in which
the diagnostic outcome was changed after motion correction
with the FFR measurements to determine whether motion
correction resulted in a better correspondence with FFR.
Concordance with SPECT interpretation was determined on a
per-vessel basis by comparing the changed perfusion in the
area supplied by the vessel with the FFR measurement
performed in that vessel.
Patient-specific parameters and characteristics were
determined as mean ± SD using Stata (StataSE, version 12.0). The
correlation between the amount of movement and scan time
was assessed using the Pearson correlation coefficient.
Correlations between the detected motion and change in visual
SPECT interpretation and number of segments differing C5%
were tested using the Spearman rank correlation coefficient.
The correlation between the amount of motion and change in
TPD was assessed using the Pearson correlation coefficient.
The level of statistical significance was set to .05 for all
The baseline characteristics of all included patients
are summarized in Table 1.
RM and PM were observed in all 83 patients. The
mean RM, in cranial-caudal direction only, was
2.5 ± 0.4 mm, as shown in Table 2. The maximum
PM across all patients in all three directions were 2.4 ±
0.8 mm, 2.8 ± 0.9, and 3.4 ± 1.5 mm in the lateral,
ventral-dorsal, and cranial-caudal direction,
The mean RM across all patients decreased
significantly during the scan (P = .01). Especially in the first
2 minutes the RM decreased and seemed to stabilize or
slightly increase again after 4 minutes, as shown in
Figure 1. A similar trend was observed for the mean
PM, although this was not significant (P = .06).
Diagnostic Value of Respiratory Motion
The visual SPECT interpretation remained
unchanged after RM correction in 74 (89%) patients
but changed in nine patients (11%) after applying RM
correction, as shown in Figure 2A. These changes were
in correspondence with FFR in only four of these nine
patients: the SPECT interpretation changed from normal
to equivocal in six patients (7%) corresponding with
FFR in two. So, in these two patients, the SPECT result
was closer to the reference standard and the motion
correction could therefore be considered a slight
improvement. However, in four out of these six patients,
the change could be considered a deterioration. The
SPECT interpretation changed from abnormal to
equivocal in two of the nine patients. In these two patients, a
positive FFR was measured in one (0.65)—considered a
deterioration—and a negative FFR was measured in the
other patient (0.85), considered an improvement. In the
remaining patients, the SPECT interpretation changed
from equivocal to normal, which was an improvement as
it corresponded with the negative FFR measurement
(0.88). In summary, motion correction produced a total
of four improvements and five deteriorations in the
overall diagnostic outcome of the SPECT study based on
By analyzing the impact of RM correction using
TPD as a semiquantitative parameter, we found a C7%
change in TPD after RM correction in only two patients
(3% of the whole group), as shown in Figure 3A. In one
patient, the TPD increased from 1% to 9% which was
considered an improvement as the FFR was positive
(0.77). In the other patient, the TPD decreased from 21%
to 12% which was considered a deterioration as the FFR
was positive (0.65). So, RM correction resulted in one
improvement and one deterioration in the overall
diagnostic outcome based on TPD.
By analyzing the impact of RM correction using the
segmental uptake values as semiquantitative parameter,
we observed a change of C5% in uptake value in one or
more segments in 57 patients (69%). The mean
difference in segmental uptake values varied between -2.0%
and 2.1% points and seemed unrelated to territorial
areas. The difference between the segmental uptake
values of both noncorrected and RM-corrected scans
seems to increase for lower average segmental uptake
values, as shown in Figure 3B. Corrections in
segments that already show perfusion defects can be
considered as less important than segments which are
corrected from or to normal which occurred less
frequently. The C5% segmental uptake changes
corresponded with FFR in 30 patients but were in
discordance with 15 patients and remained unknown
in 12 patients, in whom segmental defects both
appeared and disappeared after RM correction. One
or more segments were positively corrected with an
uptake value of C5% in 23 patients, indicating a
correction of a possible defect. In 17 of these 23
patients a negative FFR was found, which can be
considered as an improvement but in the other six
patients the correction was considered a deterioration.
In 22 patients, the changed segments were corrected
negatively, indicating the existence of a possible
defect. In these 22 patients, a positive FFR was found
in 13 patients. However, in the other nine of these 22
patients, a negative FFR was found, possibly
indicating a deterioration after RM correction. In the twelve
(14%) remaining patients, both positive and negative
segmental uptake corrections of C5% were observed.
So the correction resulted in the disappearance of one
or more defects but in the originating of other defects.
In eight of these 12 patients, a negative FFR was
found and in four a positive FFR but it is unknown
whether this was an improvement or deterioration. So
RM correction resulted in 30 improvements but also in
15 deteriorations in the overall diagnostic outcomes
based on segmental uptake values.
Diagnostic Value of Patient Motion
Applying PM correction resulted in less differences
between the noncorrected and corrected scans. The
diagnostic outcomes did not change in any of the
patients based on SPECT interpretation or TPD after PM
correction, as shown in Figures 2D and 3C. However,
the diagnostic outcome was influenced in seven patients
(8%) based on a C5% change in segmental uptake
values, as shown in Figure 3D. The segmental uptake
values were corrected positively for all seven patients,
indicating possible corrections of defects. However, in
only four patients a negative FFR was found, considered
an improvement. In the other three patients, a positive
FFR was found, indicating a deterioration of the
Relation Between Motion Detection and
The amount of motion correction and the mean RM
or PM did not to correlate, as shown in Figure 2. The
correlation between the mean RM and differences in
SPECT interpretation, TPD or segmental uptake were
not significant (P = .26, P = .65, and P = .27,
respectively). This was also the case for mean PM and number
of deviating segments (P = .13). As PM correction did
not influence the diagnostic outcomes for SPECT
interpretation or TPD, the correlation between PM and
these variables was not derived.
In this study, we have shown that patients
undergoing an 8-minute CZT-SPECT scan barely move, as
both respiratory motion and patient motion were limited.
Nevertheless, applying automatic motion correction
changed the SPECT interpretation in 11% of the stress
scans. However, these changes were both deteriorations
and improvements which led us to conclude that motion
correction did not seem to improve the overall
diagnostic outcomes of CZT-SPECT. Moreover, motion
correction also changed semiquantitative outcome
parameters, such as TPD and segmental uptake values,
but neither these changes could be considered an overall
improvement, as compared to the FFR measurements.
Both the RM and PM measured in this study were
smaller than reported in previous studies using the same
CZT-based SPECT camera.8,13 Ko et al reported a mean
RM of 10.5 mm in the cranial-caudal direction using a
pharmaceutical stress agent, which is much larger than
the mean RM of 2.5 mm as we encountered in the
present study.8 The smaller motion in our study might be
due to the following reasons: the use of longer timing
bins in our study (1.0 second instead of 0.5 second);
higher myocardial count rates due to the use of
99mTechnicium instead of Thallium-201, which decreases
noise and increases the count statistics and resolution;
and the exclusion of reproducibility errors in the
masking and manual alignment prior to reconstruction.
Although they performed a phantom study
demonstrating the correctness of their motion tracking program,
they filled their cardiac phantom with a fifth of the
activity administered to their patients. Hence, they had
far more count statistics during their phantom study than
encountered in their patient studies. This might indicate
that they detected more noise during their patient
studies, possibly explaining the larger detected RM.
They reported, based on their phantom study, that a RM
larger than 15 mm could cause visual and quantitative
image deterioration. However, this RM threshold was
never reached in our study. Nevertheless, we applied
RM correction in all patients, resulting in a changed
SPECT interpretation in 11% of our scans. As we did
not find a correlation between RM correction and
changes in SPECT interpretation, TPD or segmental
values, the changes we observed were possibly due to
overcorrections by the automatic software because of
inadequate count statistics. This is in agreement with a
phantom study we performed in which we validated the
motion detection software (this phantom study is
described in more detail in the supplementary materials).
A manually induced motion was detected within an
uncertainty of typically 2 mm using 1-second time bins
(corresponding to RM) and 1 mm using 20-second time
bins (corresponding to PM). The maximum detection
error was in the order of 8 mm for RM. Correction of the
limited motion, within the margin of error, is therefore
not expected to result in an improvement in the scan in
relation to the diagnostic outcome. It may even lead to a
deterioration of image quality. Hence, due to the limited
detected motion, it is likely that RM correction is not
useful in our patient population and application only
resulted in overcorrections.
In contrast to the limited effect of correcting for
respiratory motion in our study, a recent study by Clerc
et al suggested that deleting respiratory motion by deep
inspiration breath holding during MPI CZT-SPECT
acquisition was beneficial.25 Breath holding resulted in
12.5% more normal scans in their 40 patients when also
using attenuation correction. Acquisition during breath
holding causes a caudal shift of the abdominal structures
which may prevent inferior wall artefacts and improve
co-registration with the inspiration breath-hold CT used
for attenuation correction. However, the reported results
have not been compared with a reference standard. In
addition, starting and stopping the acquisition after each
breath hold should be perfectly timed by the operators
and be available on the SPECT system. Repeated long
breath holding can also be quite difficult for patients and
it may even require the administration of higher tracer
activities in order to limit the length of total acquisition,
which in turn raises radiation dose again.26,27
The detected PM in the present study was also
lower than the PM reported by Redgate et al, who even
used a shorter acquisition time of 6 minutes.13 Using
data of 40 patients, they recently reported a mean PM of
0-4, 4-8, and C8 mm in 62%, 35%, and 3%,
respectively. However, none of the 83 patients in our study had
a mean PM larger than 4 mm. We only encountered a
maximum PM of C8 mm in 2% (
) of the patients, in
contrast to the 10% they reported. The lower PM in our
study could be due to exclusion of reproducibility errors
in the present study and the comfortable patient
environment in combination with extensive patient
preparation to calm the patients. Redgate et al concluded
from their phantom study that PM should be corrected
when it exceeds 10 mm for more than 60 seconds. The
maximum PM encountered in this study was 8.9 mm in
one time bin of 20 seconds and PM correction did not
result in changed SPECT interpretation. Hence, these
figures seem to confirm our finding that, similar to RM,
PM correction is not necessary in our patient population.
Several assumptions underpinned this study. First,
we used a retrospective cohort of patients; all referred
for elective FFR measurements after invasive coronary
angiography. The incidence of ischemia and irreversible
defects was 4% and 11% higher in the present study,
respectively, in comparison to what we commonly
encounter in our population eligible for MPI
CZTSPECT.28 Although the incidence of perfusion defects
was not expected to influence RM or PM, it induces
lower count statistics, possibly resulting in a higher
tracking—and therefore also correction—error.
Second, we used FFR as a reference standard to
assess the added value of motion correction on the
diagnostic outcome. Although the accuracy of FFR is
limited in patients with collateral circulation or serial
stenosis,29 it is nowadays considered as one of the most
accurate tests to detect ischemia. We only compared the
motion-corrected stress acquisitions with FFR,
eliminating the possibility to distinguish reversible (ischemic)
from irreversible defects as would have been possible
when using both stress and rest acquisitions. Although
occluded vessels were also interpreted as positive FFR,
this might have led to a slight underestimation of the
correspondence with FFR for negative motion
corrections (normal scans corrected to equivocal or
abnormal, or an increasing TPD or decreasing segmental
values) and overestimation of positive motion
corrections. Moreover, co-registration of MPI with coronary
CT angiography was not performed. Therefore some of
the changes in perfusion after RM correction may have
occurred in a different coronary territory than the
territory supplied by the vessel in which FFR
measurement was done.30 Nevertheless, the discrepancies
between FFR and MPI were considered to be too
limited to influence the outcomes of this study.
Third, we only compared the motion-corrected
scans with nonattenuation corrected scans. It was not
possible to apply motion correction to attenuation
corrected scans and as attenuation correction is not
expected to compensate for motion, it would not have
contributed to our aim.
Fourth, the percentage of patients in which motion
correction changed the diagnostic outcomes differed
between the three endpoints: SPECT interpretation,
TPD, and segmental uptake values. Although the
influence of motion correction seemed limited for all three
endpoints, one should be cautious in future studies when
using only one of these semiquantitative endpoints. It
appears that a segmental uptake difference of 5% is a
very sensitive parameter for a change in defects but not a
very specific one in comparison to the SPECT
interpretation, which is still the reference standard in most
institutions. Moreover, using a TPD difference of 7%
appears not sensitive enough in detecting change in
perfusion deficits in comparison to the visual SPECT
Finally, there is a current trend towards lower
activities and patient-specific dose protocols.31,32
Lowering the activity can easily be achieved by enlarging the
scan time, as both are interchangeable within a certain
range. In this study, we showed that a scan time up to
8 minutes does not introduce significant motion. The
motion even decreased in the first minutes. Using longer
scan times in combination with lower activities might
therefore even decrease the influence of the higher
motion in the first minutes of the acquisition. However,
one should be aware that correction of observed motion
will be harder with lower count statistics and that
acquisitions should be repeated instead of corrected. The
amount of motion depends on the calmness and
relaxedness of the patients. We think it is of great
importance to create a comfortable patient environment,
provide clear instructions and to provide extensive
patient information prior to MPI to reduce motion.
Both respiratory motion and patient motion were
small in patients undergoing an 8-minute MPI acquisition
on a CZT-based SPECT camera. Correction of this small
motion did not appear to improve the diagnostic
outcomes. Hence, the value of applying motion correction
seems limited in MPI using a CZT-based SPECT camera.
NEW KNOWLEDGE GAINED
The respiratory motion and patient motion detected
in this study by commercial software are lower than
reported by previous studies using self-developed
tracking algorithms. Correction of small motion did not
appear to improve the diagnostic outcomes and, hence,
the added value seems limited in 8-minute MPI
acquisitions using a CZT-based SPECT camera.
The authors received a research grant by GE Healthcare
to validate the MCD software in clinical practice.
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unrestricted use, distribution, and reproduction in any
medium, provided you give appropriate credit to the original
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