How variable are the volumetric measurements from gated perfusion SPECT when a one-day stress-rest protocol is used?
How variable are the volumetric measurements from gated perfusion SPECT when a one-day stress-rest protocol is used?
C. Fielder Camm 0
Alexander Emery 0
(Hons.) 0 2
Elizabeth Rose-Innes 0
(Hons.) 0 2
Sergei Pavlitchouk 0
Nikant Sabharwal 0
Andrew D. Kelion 0
DM FRCP 0 1
0 Reprint requests: C. Fielder Camm MA(Cantab.), BM BCh, MRCP, Department of Cardiology, Oxford University Hospitals NHS Foundation Trust , Oxford , UK
1 Department of Cardiology, Oxford University Hospitals NHS Foundation Trust , Oxford , UK
2 Keble College, University of Oxford , Oxford , UK
3 Radcliffe Department of Medicine, University of Oxford , Oxford , UK
Background. Using myocardial perfusion scintigraphy (MPS), an increase in left ventricular (LV) volumes or a decrease in ejection fraction (EF) from rest to stress may be clinically important. The variation in these measures between the low-dose stress acquisition and highdose rest acquisition in a one-day stress-rest protocol has not been established. We assessed the reproducibility of gated volumetric indices between stress and rest and the normal variation in ungated TID ratio for a one-day stress-rest 99mTc-tetrofosmin protocol. Methods. Two thousand and one hundred and fifty eight (2158) 99mTc-tetrofosmin MPS patient studies were analyzed retrospectively. Studies were excluded for incomplete data, significant technical difficulties, or (for gated analysis but not for analysis of TID ratio) if the LV EF was > 75%. An analysis of gated data was undertaken to establish the reproducibility of ventricular volumes and EF between stress and rest scans. Ungated volume data were analyzed to determine the confidence limits of TID ratio according to ventricular volume. Results. Gated data were analyzed for 621 patients without inducible hypoperfusion. Mean EF at rest was slightly higher than after stress (62.4% ± 10.3% vs 61.2% ± 10.4%, P < 0.001), and the standard deviation of the difference was 5.2% (95% CI 4.9% to 5.5%). Ungated volumes were available for 992 non-ischaemic patients. The upper 95% CI for TID ratio was 1.23. This increased from 1.20 to 1.37 between the highest and lowest deciles of rest ungated volume. Conclusion. Using a one-day stress-rest 99mTc-tetrofosmin protocol, a fall in LV EF between rest and stress of > 11.6% or a TID ratio of > 1.23 is likely to be clinically reliable. The upper limit of normal for TID ratio needs to be increased for patients with small LV chamber volumes. (J Nucl Cardiol 2018)
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Funding CFC is funded by a National Institute for Health Research
Academic Clinical Fellowship.
Coronary artery disease
Myocardial perfusion scintigraphy
Standard deviation of the difference
Single photon emission computed
Transient ischaemic dilatation
Transient ischaemic dilatation ratio
Coronary artery disease (CAD) represents the
leading cause of mortality and morbidity in the developed
world.1 MPS has been recommended by the European
Society of Cardiology as a first-line investigation for
investigating ischemia in patients with chest pain.2 The
extent and severity of perfusion defects on myocardial
perfusion scintigraphy (MPS) provide important
prognostic information.3 Measurements of left ventricular
volume and function derived from both ungated and
gated single photon emission computed tomography
(SPECT) are also important predictors of risk. Thus the
annual rate of cardiac death increases sharply as resting
or post-stress left ventricular (LV) ejection fraction (EF)
falls below 45%,4,5 or end-systolic volume increases
above 70 mls.5
It has been demonstrated that differences in LV
indices between the post-stress acquisition and the rest
acquisition are clinically important. A larger LV cavity
volume on the ungated SPECT images post stress
compared with rest has been termed ‘‘transient
ischaemic dilatation’’ (TID).6,7 It is uncertain whether this
phenomenon represents true cavity dilatation due to
post-ischaemic stunning,8 or generalized subendocardial
hypoperfusion during stress which gives the appearance
of dilatation.9,10 On occasion, TID occurs with relatively
minor or even no perfusion abnormality, and can
sometimes be a clue to extensive, but to some degree
balanced, multi-vessel ischemia.6,11–13 However TID is
a relatively non-specific marker of ischemia, and
correlates poorly with findings on computed tomographic
coronary angiography.14 Additionally, in those with
otherwise normal MPS studies, TID does not predict
CAD at coronary angiography performed within
6 months.15 It now appears that TID occurs almost
exclusively in patients with diabetes or LV
hypertrophy,16,17 and hence it may be a more important indicator
of microvascular dysfunction as opposed to epicardial
CAD. Regardless of its physiology, TID has repeatedly
been shown to be an independent predictor of adverse
Post-stress end-systolic volume, as measured by
echocardiography, has been shown to be an independent
predictor of mortality;19 and increased post-stress
endsystolic volume has been suggested as a marker for
ischemia. A fall in LV EF post stress compared with rest
may also indicate extensive inducible ischemia and an
impaired prognosis.19,20 However, the value of such
measures is limited without sufficient knowledge of
normal intraindividual variation between stress and rest
TID can be identified qualitatively by visual
inspection of the raw data of the SPECT acquisitions and
processed tomograms.21 Modern quantitative software
can provide added confidence by fitting myocardial
contours to the ungated stress and rest tomograms and
calculating chamber volumes, which can be expressed as
a TID ratio (stress volume/rest volume).11 The clinical
value of this index depends on its upper limit of normal,
which has been quoted as 1.23 in publications from the
Cedars-Sinai team.7 However, this upper limit of normal
is likely to be dependent on LV size, as the spatial
resolution of a gamma camera is poor, and hence a
relatively small error in calculated volume in a small
heart will have a greater impact on TID ratio than in a
larger heart. The gated stress and rest tomograms can be
inspected qualitatively for stress-induced wall motion
abnormalities, but recognition of a change in global LV
function requires quantification. It is therefore essential
to establish the normal limits of variation in LV volumes
and ejection fraction derived from gated SPECT, so that
the maximal allowable fall in ejection fraction post
stress can be determined.
In the United Kingdom, 99mTc MPS studies are
frequently performed using a one-day protocol, most
commonly with a stress-rest order.22 Typically, doses of
250/750 MBq are given.22 It cannot be assumed that
quoted normal ranges and reproducibilities for TID ratio
and gated indices obtained using higher doses apply
when a low-dose acquisition has been performed.
Using a one-day stress-rest
technetium-99m-tetrofosmin protocol, we investigated: (
) The variation in
the upper limit of normal for TID ratio with LV size, (
The variation in LV ejection fraction and volumes
between stress and rest gated SPECT acquisitions.
Patients undergoing myocardial perfusion scintigraphy
between 01/01/2015 and 31/12/2015 at the John Radcliffe
Hospital (Oxford, UK) were retrospectively included in the
analysis. Patients [ 18 year old were included if they
underwent a one-day stress-rest protocol. Patients were
excluded if: (
) complete data were not available preventing
comparison between stress and rest volumes, and (
) if the
study report indicated significant technical difficulties
preventing reliable volumetric measurement. For gated analysis
only, patients were excluded if the ejection fraction on either
the rest or stress scan was [ 75% (i.e., likely to be inaccurate
and due to the poor spatial resolution of SPECT).
MPS Protocol and Analysis
MPS was performed using a one-day stress-rest
99mTctetrofosmin protocol. Prior to attendance, patients were asked
to omit beta-blockers for 48 hours, and avoid caffeine for
12 hours. Patients were stressed using symptom-limited
treadmill exercise, or where necessary regadenoson 400 mcg IV.
99mTc-tetrofosmin was administered intravenously at a
weightadjusted dose of 250 to 400 MBq during stress and 750 to
1200 MBq at rest. Patients with a significant perfusion defect
on the stress acquisition received sublingual glyceryl trinitrate
prior to the rest injection to optimize assessment of viability/
SPECT acquisition was performed 20 to 60 minutes after
stress injections and 1 to 2 hours after rest injections using a
two-headed ‘‘Pulse CDC’’ gamma camera (IS2) equipped with
low energy general purpose tungsten foil collimators. Although
termed ‘‘general purpose,’’ we have shown that these
collimators yield a full-width at half-maximum of 8 mm at 10 cm,
similar to ‘‘high resolution’’ collimators on most cameras. A
180 contoured orbit with 32 steps of 40 seconds each for the
stress acquisition and 30 seconds for the resting acquisition
was used (energy window 140 keV ± 10%, matrix 64 9 64,
pixel size 6.5 mm). Acquisitions were gated whenever possible
with 16 frames and an RR acceptance window of ± 40%.
Each MPS study was processed and analyzed using a
Hermes workstation. Iterative (HOSEM) reconstruction was
performed on the summed projections. Filtered back projection
was used to reconstruct the gated projections. Tomograms
were reoriented to the standard orthogonal planes of the heart.
The studies were analyzed and displayed using Cedars-Sinai
quantitative software (QPS and QGS), and the relevant
quantitative parameters were recorded. The final clinical report
was used to establish the normality of a study, or the presence
of fixed or inducible perfusion defects. Data were extracted by
two authors AE and ERI.
Continuous variables are expressed as either mean
(standard deviation) or median (interquartile range [IQR]) and
compared between stress and rest acquisitions using the paired
Student’s t-test or Mann-Whitney U-test, respectively.
Categorical and original variables are reported as frequency
(percentage). To determine TIDr upper limits, participants
were grouped into deciles of ungated rest volume. TIDr upper
limits were calculated within each group as the mean plus 1.96
times the standard deviation. Homogeneity of variance of TIDr
within each decile was assessed using Bartlett’s test. A
regression model for the association between TIDr upper limits
and rest ungated volume was determined using the
GaussNewton method. Statistical analysis for this paper was
performed using SAS software, Version 9.3 of the SAS system for
Windows. Copyright 2002-2010 by SAS Institute Inc., Cary,
A total of 2158 patient studies were undertaken by
the nuclear cardiology department of the John Radcliffe
Hospital (Oxford, UK) during 2015. Of these, 1486 had
complete volumetric data available and were suitable for
inclusion in the ungated analysis. Following removal of
those individuals with EF [ 75%, 1014 (68.2% of
studies with complete data) were suitable for inclusion
in the gated analysis (Figure 1). The mean age of
patients included in the analysis was 63.4 ± 12.0 and
833 (82.2%) were male, mean weight was
87.8 ± 18.1 kg (n = 987). Fifty-four (5.3%) had had
previous CAD revascularisation, and 22 (2.2%) had
passed away prior to this study (Table 1).
Gated Analysis of Normal Limits
Between Stress and Rest
Six hundred and twenty-one studies (61.2%)
showed no inducible hypoperfusion (no defect 539,
fixed defect only 82). In these patients, mean EF at rest
was higher than after stress (62.4% ± 10.3% vs
61.2% ± 10.4%, P \ 0.001). The mean difference was
1.2% [95% confidence interval (CI) (0.8% to 1.6%)],
with a standard deviation of the difference (SDD) of 5.2
[95% CI (4.9 to 5.5)]. This change in EF was the result
of a lower systolic volume (40.4 ± 26.9 mL vs
41.4 ± 28.3 mL, P = 0.001) and a higher diastolic
volume (100.8 ± 35.7 mL vs 99.6 ± 36.3 mL,
P = 0.002) at rest (Table 2).
Ungated Analysis of Normal Limits of TIDr
Of those with complete data (n = 1486), 992
participants had no inducible hypoperfusion. In this
group, the mean TID ratio (TIDr) derived from ungated
volumes was 1.00 ± 0.12. These participants were
divided into deciles grouped by rest ungated volumes.
TIDr was associated with resting chamber volume
(ANOVA P \ 0.001). The overall upper 95%
confidence limit for TIDr was 1.23. However, the upper 95%
CI rose from 1.20 to 1.37 between the highest and lowest
deciles of rest ungated volume (Table 2, Figure 2).
An assessment of TIDr variance between decile
groups suggested heterogeneity (P \ 0.001). Visual
examination of Figure 2 suggested that the association
between TIDr and resting chamber volume and TIDr
heterogeneity of variance may have resulted from a
significant difference in the lowest two deciles. When
these two groups were removed from the analysis,
significant heterogeneity of variance remained
(P = 0.018), though TIDr was no longer associated with
resting chamber volume (P = 0.843). The equation most
closely modeling the relationship between 95% upper
confidence limit of TIDr and median rest ungated
volume within each decile is detailed in Table 3. Similar
results for overall TID ratio and predictive equations
were obtained when the cohort was split by gender
The results presented in this paper indicate that
ejection fraction values obtained between stress and rest
acquisitions demonstrate significant variability. The
mean DEF was 1.2%, in line with previous studies.23
However, the standard deviation of the difference
between stress and rest values was 5.2% (4.9 to 5.5).
This suggests that a fall from rest to stress of at least
11.6% is required for the change to be statistically
significant. The mean TIDr is 1.00, and is independent
of chamber volume. However, the upper 95%
confidence limit varies with chamber volume, and at smaller
volumes TIDr may need to be as high as 1.37 to be
This large cohort confirms the results of previous
small studies (n \ 150) which have demonstrated a 95%
CL for the DEF of between 5.2% and 10.5%.23–25 The
large number of participants in the present study allowed
for selection of only those without reversible ischemia,
in whom there is no physiological reason for the EF to
change between the post-stress and rest acquisitions. In
previous analyses the ischaemic burden was not clearly
detailed,23,24 or only selected patients with defects on
their stress scan were included.25 Ferro et al.
demonstrated that a DEF of - 5% or more was associated with
stress-induced ischemia within a cohort of patients with
Demographic features for the gated and ungated analysis are those participants without inducible ischemia
Those included in the gated analysis are a subset of those in the ungated analysis. Values are provided as n(%) or mean ±
Standard deviation of the difference Probability
Values are mean ± standard deviation or mean (95% confidence interval). Probability refers to difference between stress and rest
type-2 diabetes mellitus.20 However, within a
nonselected population in a large cohort, our findings would
suggest that such a change could be expected due to
intraindividual variability and would not necessarily be
TID is a widely used marker that suggests the
possibility of significant underlying ischemia.26 The
upper limit for normal TIDr is dependent on the protocol
and isotope used. Previous results from Xu et al. have
suggested that a TIDr [ 1.19 should be considered
abnormal in ungated images using a one-day rest /
exercise stress single isotope (99mTc-sestamibi)
protocol;7 this has been supported by a number of other
groups.27–30 TIDr upper limits have been broadly similar
between different software packages including QPS
(TIDr 95% upper limit 1.19),7 Emory Cardiac Toolbox
(TIDr 95% upper limit 1.19 to 1.25),29,30 and 4DM
(TIDr 95% upper limit 1.24).28 Data from Rivero et al.
support a similar overall value for TIDr but also
demonstrates that this may vary by gender.30 Our results
are in line with the findings from these groups regarding
the overall TIDr (upper 95% confidence limit = 1.23) in
a cohort of 992 patients with no inducible ischemia,
significantly larger than other cohorts that have assessed
the normal limits of TID. However when split by gender
the overall TIDr remained similar, in contrast to
previous studies. The large cohort size of this study
allowed for stratification by chamber volume. This
demonstrated that the upper 95% confidence limit for
TIDr increased as chamber size decreased, suggesting
that a single cut-off to define TID should be used with
This study has a number of limitations which are
acknowledged by the authors. First, it has been conducted
as a retrospective analysis of ‘real world’ clinical data.
The LV indices were not remeasured by the trial team.
Although key findings have been established in patients
without inducible ischemia on SPECT, the underlying
population is heterogeneous and represents all-comers
referred for investigation in the nuclear cardiology
department of a tertiary center. The above limitations
may contribute to an increase in the variability seen
between patients; however, the intraindividual variability
should be minimally impacted.
This study was undertaken using Cedars-Sinai QPS
and QGS software. Reports of TIDr 95% upper limits
using different software packages have been generally
comparable. However, the findings of this study should
be considered in the knowledge that they represent
results from a single center using a single 99mTc MPS
protocol and analyzed by a single software package.
Additional analyses by other groups is required to
determine more generalizable applicability.
This study removed those with an LVEF [ 75%
from inclusion in the gated analysis. This was to remove
those with non-physiological ejection fractions which
are likely to be numerically inaccurate, and a reflection
of the poor spatial resolution of a gamma camera system
in small hearts. This led to the removal of 31.8% of
scans with complete data from the gated analysis, and
disproportionately affected women (Table 1). Such
patients are generally regarded as having ‘‘normal’’ LV
systolic function, but we do not quote the LVEF values
in clinical practice. Previous studies in this area have
either included patients with LVEF [ 75%
uncritically,23,24 or have appeared not to include patients with
such values (perhaps because they were excluded from
the outset).25 We would argue that inclusion of such data
would distort the results of the gated analysis.
In a single center analysis, this study represents the
largest cohort to assess variability in volumetric
measures and TIDr using a one-day stress-rest 99mTc MPS
protocol. An analysis of gated volumetric data shows a
small but significant variation in EDV, ESV, and LVEF
between stress and rest acquisitions. Although a
decrease in LV EF between rest and post-stress
acquisitions may be suggestive of ischemia, this needs to
exceed 11.6% before it can be considered outside of
normal variation. TIDr values assessed using non-gated
volumes show an upper confidence limit of 1.23 overall.
However, there is significant variation with rest ungated
volume which should be taken into consideration when
determining clinical significance.
NEW KNOWLEDGE GAINED
) Using a one-day stress rest 99mTc MPS protocol, a
fall in LV EF from rest to post stress of [ 11.6% is
required for the change to be statistically significant
(and hence clinically reliable).
) Overall, a TIDr of [ 1.23 is likely to be statistically
reliable, but for small chamber volumes (\ 50mLs)
higher cut-offs are appropriate.
CFC: Conception and design, analysis and interpretation
of data, drafting of the manuscript, critical manuscript revision
for important intellectual content, final approval of
manuscript, final approval of the manuscript submitted. AE, ERI,
SP, NS: Active involvement in collecting data, critical
manuscript revision for important intellectual content, final
approval of the manuscript submitted. ADK: Conception and
design, analysis and interpretation of data, critical manuscript
revision for important intellectual content, final approval of
the manuscript submitted.
All authors report no conflicts of interest
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and the source, provide a link to the Creative Commons
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