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© Schattauer 2013 Nuklearmedizin 5/2013
178Original article
Evaluation of patients with
coronary artery disease
IQ-SPECT protocol in myocardial perfusion imaging:
Preliminary results
F. Caobelli1; C. Pizzocaro1; B. Paghera2; U. P. Guerra1
1Department of Nuclear Medicine, Fondazione Poliambulanza, Brescia, Italy; 2Department of Nuclear Medicine,
Spedali Civili di Brescia, Italy
Keywords
Coronary artery disease, 99mTc tetrofosmin
SPECT/CT, IQ-SPECT, low counts acquisition,
myocardial perfusion imaging
Summary
Quantification of myocardial perfusion scinti-
graphy is often performed to assist phys-
icians in detecting coronary artery disease
(CAD). Modern software and hardware pack-
ages provide improvements able to shorten
scan time and/or reduce administered activ-
ity, without compromising image quality in
radionuclide myocardial perfusion imaging
(MPI). Recently, multifocal collimators were
introduced with dedicated reconstruction
software, named IQ-SPECT, able to shorten
considerably scan time. The aim of our study
was to compare this new protocol to the al-
ready validated standard ones. Patients,
methods: We enrolled 43 patients with sus-
pected or diagnosed CAD. All patients under-
went a two-days protocol radionuclide myo-
cardial perfusion scan at rest and after a
standard stress test (exercise or dipyrida-
mole) after administering 99mTc-tetrofosmin.
Images were acquired on a 2-head gamma
camera and reconstructed with attenuation
correction. All the images were scored using
a 17-segments model by three experienced
physicians, blind to clinical data and to ac-
quisition and processing modality. Results,
conclusion: No significant differences were
recorded in perfusion scores on paired t-test
and Wilcoxon among the full-time images re-
constructed with standard protocol or IQ-
SPECT, both overall on a 17-segments evalu-
ation and when considering different territori-
es of distribution. MPI with IQ-SPECT protocol
can be acquired at about a quarter scan time
without disagreement compared to full time
scan acquisition performed with standard
protocols.
Schlüsselwörter
Koronare Herzkrankheit, 99mTc-Tetrofosmin
SPECT/CT, IQ-SPECT, Erfassung niedriger
Counts, Myokard-Perfusions-aufnahmen
Zusammenfassung
Häufig werden myokardiale Perfusionsszinti-
graphien quantifiziert, um den Arzt bei der
Diagnose der koronaren Herzkrankheit (KHK)
zu unterstützen. Moderne Hard- und Software
bietet Verbesserungen, die verkürzte Aufnah-
mezeiten und/oder geringere Strahlenbelas-
tungen ermöglichen ohne die Bildqualität der
myokardialen Perfusionsszintigraphie (MPS)
zu beeinträchtigen. Kürzlich wurden multifo-
kale Kollimatoren mit Rekonstruktionssoft-
ware, genannt IQ-SPECT, eingeführt, womit
die Scanzeit erheblich verkürzt werden kann.
In unserer Studie sollte dieses neue Protokoll
mit dem bereits validierten Standardvorge-
hen verglichen werden. Patienten, Metho-
den: Eingeschlossen wurden 43 Patienten mit
vermuteter oder diagnostizierter KHK. Sie
wurden einem zweitägigen Protokoll mit Ra-
dionuklid-Myokard-Perfusionsscan in Ruhe
und nach standardisiertem Belastungstest
(Ergometrie oder Dipyridamol) nach Gabe
von 99mTc-Tetrofosmin unterzogen. Die Auf-
nahmen mit einer Doppelkopf-Gammakame-
ra wurden mittels Abschwächungskorrektur
rekonstruiert. Alle Aufnahmen wurden von
drei erfahrenen Ärzten, die bezüglich der kli-
nischen Angaben sowie der Aufnahme- und
Verarbeitungsmodalitäten verblindet waren,
anhand eines 17-Segment-Modells ausge-
wertet. Ergebnisse, Schlussfolgerung: Im
t-Test für verbundene Stichproben und
Wilcoxon- Test wurden keine wesentlichen
Unterschiede bei den Perfusionswerten zwi-
schen den Vollzeit-Aufnahmen mit Standard-
protokoll und IQ-SPECT festgestellt, sowohl
insgesamt in der 17-Segment-Auswertung
als auch unter Berücksichtigung verschiede-
ner Verteilungsgebiete. Die MPS mit einem
IQ-SPECT-Protokoll kann ohne Abweichun-
gen in etwa einem Viertel der Scanzeit akqui-
riert werden, die für die Aufnahmen in Voll-
zeit mit dem Standardprotokoll benötigt
wird.
Correspondence to:
Dr. Federico Caobelli,
Department of Nuclear Medicine, Fondazione
Poliambulanza, Via Bissolati 57
25100 Brescia,Italy
Tel./Fax +39/030/351 81 04
E-mail: fedefournier@libero.it
Beurteilung von Patienten mit koronarer
Herzkrankheit
IQ-SPECT Protokoll zur Darstellung der Myokard-
Perfusion: vorläufige Ergebnisse
Nuklearmedizin 2013; 52: 178–185
DOI:10.3413/Nukmed-0570-13-03
received: March 14, 2013
accepted in revised form: May 14, 2013
prepublished online: May 24, 2013
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Nuklearmedizin 5/2013 © Schattauer 2013
179 F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
Coronary artery disease (CAD) is a major
cause of mortality and morbidity in Europe
and its management consumes a large pro-
portion of national healthcare budgets (19).
Quantification of myocardial perfusion
scintigraphy is often performed to assist
physicians in detecting CAD. Single-
photon emission computed tomography
(SPECT) myocardial perfusion imaging
(MPI) has been widely validated for the di-
agnosis and prognosis of cardiac disease
and the technique is heavily embedded in
national and international guidelines (2).
All perfusion tracers have comparable
accuracy for CAD detection (12) and are
taken up by intact cardiac myocytes but not
myocardial scar, thus reflecting both myo-
cardial perfusion and viability.
Numerous studies have confirmed the
excellent prognostic power of MPI and its
important role in risk stratification and pa-
tient management (3, 11). Although the
anatomical extent of the disease is best
demonstrated by coronary angiography,
which is considered as the standard tech-
nique for assessing coronary anatomy, MPI
provides a complementary assessment of
its physiological significance. In fact, al-
though coronary angiography is the “gold
standard” for imaging coronary arteries,
this might under-represent the physiologi-
cal significance of stenosis or hypoperfu-
sion, which are shown by MPI studies (22).
The need to shorten scan time, because
of department workloads and in order to
improve patients’ discomfort against long
time examinations, led to the development
of new hardware and modern software
packages, which provide an iterative recon-
struction algorithm able to shorten scan
time and/or to reduce administered activ-
ity, without compromising image quality in
radionuclide MPI (4).
Several new dedicated hardware camera
systems with optimized acquisition ge-
ometry, collimator design, and associated
reconstruction software have been recently
introduced by various vendors (17). These
systems combine an improvement in
spatial resolution and sensitivity. By faster
imaging times due to increased sensitivity,
patient comfort is dramatically improved
in comparison to standard filter-back-pro-
jection (FBP). As a consequence, these sys-
tems have the additional benefit of reduc-
ing patient motion during a scan.
Recently, multifocal collimators with
dedicated reconstruction software have
been introduced named IQ-SPECT, able to
considerably shorten scan time. The aim of
our study was to compare this new proto-
col to already validated standard ones.
Patients, material, methods
Patient population
We prospectively enrolled 43 patients (30
men and 13 women, aged between 34 and
76, mean BMI 27.31 ± 4.52) with suspected
or diagnosed CAD. All studies have been
performed on the basis of clinical indi-
cations. We excluded patients with cardiac
conditions such as cardiomyopathies, val-
vular diseases, existence of cardiac pace-
maker and presence of left bundle branch
block. Patients’ demographic character-
istics are reported (
▶
Tab. 1). A written
consensus was obtained by all patients be-
fore each study.
Gated SPECT
All patients were kept in the fasting state
for at least eight hours before the examin-
ation and underwent a two-days protocol
radionuclide myocardial perfusion scan at
rest and after a standard stress test (symp-
tom-limited exercise or dipyridamole)
using 99mTc-tetrofosmin. Dipyridamole
(0.56 mg/kg) was administered in four
minutes. Two minutes after drug injection,
the radiopharmaceutical has been intra-
venously injected. Three minutes after
radiopharmaceutical administration,
amino phyllin (10 mg) was injected in 90 s.
Symptom-limited exercise test was per-
formed on a bicycle: the radiopharmaceuti-
cal was administered after reaching the
85% of predicted max heart rate, corrected
for patient’s age. 99mTc-tetrofosmin was
used for both stress and rest studies and the
dose was calculated according to the for-
mula: 400 + 20 × (BMI–25) MBq, min. dose
400 MBq.
Both, IQ-SPECT and standard acquisi-
tion were sequentially performed, using the
same CT acquisition for attenuation cor-
rection in both studies. Time interval be-
tween the two examinations was about five
minutes.
Standard acquisition and
OSEM reconstruction
Scan acquisitions were performed using a
dual-headed hybrid SPECT/CT system
(Symbia T- Siemens Medical Solutions)
with the following camera settings: scan arc
90° (180° orbit), body contour, 64 views, 25
sec/view, 64 × 64 matrix size, zoom factor
of 1.3. At each projection, 8 electrocardio-
graphic gated frames per cardiac cycle were
acquired. Raw data were visually inspected
in cine mode and, if needed, motion cor-
rected (15).
patients’ characteristic
patients
major risk factors, n (%)
stress test, n (%)
n (men/women)
age, years: range
body mass index (mean ± SD)
hypertension
hypercolesterolaemia
smoking
family history for CAD
diabetes mellitus
prior known CAD
prior myocardial infarction
prior PCI
exercise
43 (30/13)
34–76
27,31 ± 4,52
25 (60)
15 (35)
6 (14)
35 (81)
10 (23)
31 (73)
6 (14)
9 (20)
24 (56)
Tab. 1
Demographic charac-
teristics of the patients
of our study
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180F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
Both, attenuation corrected and uncor-
rected SPECT images were then recon-
structed after scatter correction by OSEM
(ordered subset expectation maximum) it-
erative reconstruction. The co-registration
of transmission and emission scans was
verified for all patients. In presence of mis-
alignment between SPECT and CT moda-
lities, a manual realignment in the three or-
thogonal planes was performed by experi-
enced technologists. Gated SPECT was
analyzed using the QPS-QGS protocol.
IQ-SPECT protocol
A description of the components of the IQ-
SPECT system (Siemens Medical Solution
AG) has been described by Vija et al. (21).
The main components of the IQ-SPECT
system are (16)
•
a multifocal collimator (named Smart-
zoom), especially designed so that the
centre of the field of view magnifies the
heart, while the edges can sample the
entire body, thus avoiding truncation
artefacts.
•
a cardio-centric orbit where the detec-
tors keep the heart in the most sensitive
area of the collimator, the so-called
“sweet spot”.
•
an advanced reconstruction engine
based on the conjugate-gradient algo-
rithm including in the system matrix
the view-angle dependent gantry deflec-
tions, a vector map of the collimator
hole angles and the system’s point re-
sponse function.
•
a software for resolution recovery, CT
based attenuation correction with a
dedicated parametric map and a scatter
correction.
IQ-SPECT protocol was performed before
the standard acquisition, using the same
CT scan for attenuation correction. The
protocol had some modification with re-
spect to the standard one:
1. different multifocal collimators were
used,
2. 34 views were obtained at 12 seconds
per view;
3. both attenuation corrected and uncor-
rected SPECT images were then recon-
structed after motion, attenuation and
scatter correction by IQ-SPECT iter-
ative reconstruction;
4. gated SPECT was analyzed using a dedi-
cated protocol.
Scan acquisitions were performed using
the same dual-headed hybrid SPECT/CT
system with 128 × 128 matrix size and
zoom factor of 1. Likewise standard proto-
col, in presence of misalignment between
SPECT and CT modalities, a manual real-
ignment in the three orthogonal planes was
performed by experienced technologists.
Gated SPECT was analyzed using the QPS-
QGS protocol provided in the IQ-SPECT
package.
Visual analysis
For a semiquantitative analysis of segmen-
tal perfusion and function we adopted a
17-segments model. The QPS-QGS and
the dedicated IQ-SPECT protocol derived
polar maps of perfusion and regional wall
motion and left ventriculum was therefore
divided into 17 segments. For each seg-
ment, the different parameters were scored
by three experienced physicians using a
five points score according to ASNM
guidelines (10):
•
normal perfusion = 0,
•
mild reduction in counts not defini-
tively abnormal = 1,
•
moderate reduction in counts-defini-
tively abnormal = 2,
•
severe reduction in uptake = 3,
•
absent uptake = 4.
Interobserver discrepancies were resolved
by consensus. When assessing ischemic al-
terations, we used a cut-off score of ≥ 3. In
addition to individual scores, summed
scores were calculated. The
•
summed stress score (SSS) equals the
sum of stress scores of all segments,
•
summed rest score (SRS) equals the sum
of rest scores,
•
summed difference score (SDS) equals
the difference between SSS and SRS and
is a measure of reversibility.
In particular, SSS has been shown to have a
significant prognostic value (29). To avoid
any subjective interferences by the oper-
ators, the three physicians were blind to
clinical data and acquisition and process-
ing modality. Automated analysis on gated
SPECT was used to determine
•
end-diastolic volume (EDV),
•
end-systolic volume (ESV),
•
left ventricular ejection fraction (LVEF),
•
transient ischaemic dilation (TID).
Finally, a clinical diagnosis was determined
from perfusion, TID and wall motion as
normal, probably normal, equivocal, prob-
ably abnormal or abnormal.
Statistical analysis
Statistical analysis was performed using
SPSS software (version 16.00 for Windows,
SPSS Inc., Chicago, Illinois). All numerical
values are given as mean ± SD. A single-
subject study was performed using paired
t-test and Wilcoxon test. Analysis was per-
formed both for all segments overall and
for each left ventricular region. All p-values
< 0.05 were considered to be statistically
significant.
Results
Subjectively, IQ-SPECT images were
scored as of better quality because of im-
proved uptake-to-background ratio. Two
case studies evaluated with the two proto-
cols are shown (
▶
Fig. 1) for a normal sub-
ject (
▶
Fig. 1a, 1b) and a patient with scar
(
▶
Fig. 1c, 1d). Mean SSS was 5.37 ± 7.01
for IQ-SPECT and 5.65 ± 7.46 for standard
acquisition, respectively (p = 0.65); mean
SRS was 3.42 ± 4.61 for IQ-SPECT and
4.23 ± 6.92 for standard acquisition re-
spectively (p = 0.13); mean SDS was 2.40 ±
4.94 for IQ-SPECT and 1.74 ± 4.52 for
standard acquisition, respectively (p =
0.23). No significant differences were
recorded.
Summed scores were also calculated in
each ventricular regions and again, no sig-
nificant differences were evidenced.
Quantitative analysis of left ventricular
end-diastolic volume (LVEDV), left ven-
tricular end-systolic volume (LVESV) and
left ventricular ejection fraction (LVEF)
showed no significant differences between
OSEM and IQ-SPECT protocols.
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181 F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
•
LVEDV mean value was 105.65 ± 44.29
ml for IQ-SPECT and 103.13 ± 47.25 for
standard acquisition (p = 0.065);
•
LVESV mean value was 49.03 ± 34.01
for IQ-SPECT and 47.83 ± 34.63 for
standard acquisition (p = 0.068);
•
LVEF mean value was 57.31% ± 12.03
for IQ-SPECT and 57.58% ± 12.64 for
standard acquisition (p = 0.63).
All results are shown (
▶
Tab. 2,
▶
Tab. 3).
Differences between IQ-SPECT and OSEM
protocols were limited. Nevertheless, we re-
ported significant differences in 8 out of 43
patients. In just 3 of these patients differ-
ences led to different interpretation in
hypo perfusion reversibility, while in the re-
maining 5 patients differences concerned
only the degree of perfusion defect, which
seemed to be to a lesser extent on IQ-
SPECT images.
Left anterior coronary (LAD)
In the territory of distribution of LAD
(
▶
Fig. 2a), mean
•
SSS was 3.23 ± 4.06 for IQ-SPECT and
3.46 ± 4.67 for standard acquisition, re-
spectively (p = 0.60);
•
SRS was 2.46 ± 3,05,61 for IQ-SPECT
and 3.03 ± 4.90 for standard acquisition,
respectively (p = 0.24);
•
SDS was 1.16 ± 2.32 for IQ-SPECT and
0.74 ± 2.19 for standard acquisition, re-
spectively (p = 0.27).
Left circumflex artery (LCX)
In the territory of distribution of LCX
(
▶
Fig. 2b), mean
•
SSS was 2.13 ± 4.32 for IQ-SPECT and
2.18 ± 3.78 for standard acquisition, re-
spectively (p = 0.87);
•
SRS was 0.95 ± 2.49 for IQ-SPECT and
1.20 ± 2.80 for standard acquisition, re-
spectively (p = 0.17);
•
SDS was 1.23 ± 3.28 for IQ-SPECT and
1 ± 2.70 for standard acquisition, re-
spectively (p = 0.34).
Right coronary artery (RCA)
In the territory of distribution of RCA
(
▶
Fig. 2c), mean
Fig. 1 IQ-SPECT algorithm (a, c) versus standard acquisition (b, d): examin-
ation of patient 1 (a, b) and patient 2 (c, d)
a) IQ-SPECT algorithm with CT-based attenuation correction: normal;
b) with standard acquisition: result unremarkable
c) IQ-SPECT algorithm: a non-reversible hypoperfusion can be evidenced in
medial-distal antero-septal segments (LAD territory of distribution);
d) with standard acquisition: the same alterations
a c
b d
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182F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
pa-
tient
no.
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43
IQ
SSS
1
9
3
1
0
6
3
16
4
0
1
6
7
0
0
0
4
0
1
18
7
2
1
6
1
2
18
18
6
4
0
4
16
3
0
33
0
2
3
1
12
0
12
SRS
1
9
3
1
0
13
3
10
4
0
0
6
0
0
0
0
4
0
1
18
2
2
1
2
1
2
12
0
2
0
0
2
12
3
0
12
0
2
3
1
3
0
12
SDS
0
0
0
0
0
2
0
6
0
0
1
0
6
0
0
0
0
0
1
0
5
0
0
4
0
0
6
18
4
4
0
2
4
0
0
21
0
0
0
0
9
0
0
OSEM
SSS
1
9
3
0
0
24
2
18
3
0
1
2
6
0
0
0
1
0
1
19
8
2
8
1
1
6
18
27
6
4
0
4
16
3
0
23
0
1
6
1
6
0
12
SRS
1
9
3
0
0
24
3
12
3
0
0
2
0
0
0
0
1
0
1
19
6
2
0
1
1
6
12
0
2
0
0
2
16
3
0
30
0
1
6
1
3
0
12
SDS
0
0
0
0
0
0
0
6
0
0
1
0
6
0
0
0
0
0
0
0
2
0
8
0
0
0
6
27
4
4
0
2
0
0
0
6
0
0
0
0
3
0
0
IQ
SSS
LAD
1
9
3
1
0
2
3
7
4
0
1
6
0
0
0
0
4
0
1
6
7
2
1
6
1
2
18
3
2
4
0
0
10
1
0
15
0
2
3
1
9
0
4
SRS
LAD
1
9
3
1
0
11
3
7
4
0
0
6
0
0
0
0
4
0
1
6
2
2
1
2
1
2
12
0
2
0
0
0
6
1
0
6
0
2
3
1
3
0
4
SDS
LAD
0
0
0
0
0
0
0
7
0
0
1
0
0
0
0
0
0
0
1
0
5
0
0
4
0
0
6
3
0
4
0
0
4
0
0
9
0
0
0
0
6
0
0
OSEM
SSS
LAD
1
9
3
0
0
15
2
9
3
0
1
2
0
0
0
0
1
0
1
7
8
2
4
1
1
2
18
12
2
4
0
0
10
1
0
15
0
1
6
1
3
0
4
SRS
LAD
1
9
3
0
0
15
3
9
3
0
0
2
0
0
0
0
1
0
1
7
6
2
0
1
1
2
12
0
2
0
0
0
10
1
0
24
0
1
6
1
3
0
4
SDS
LAD
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
2
0
4
0
0
0
6
12
0
4
0
0
0
0
0
3
0
0
0
0
0
0
0
IQ
SSS
LCX
0
0
0
0
0
4
0
9
0
0
0
0
7
0
0
0
0
0
0
12
0
0
0
0
0
0
0
15
4
0
0
4
6
2
0
18
0
0
0
0
3
0
8
SRS
LCX
0
0
0
0
0
2
0
3
0
0
0
0
0
0
0
0
0
0
0
12
0
0
0
0
0
0
0
0
0
0
0
2
6
2
0
6
0
0
0
0
0
0
8
SDS
LCX
0
0
0
0
0
2
0
9
0
0
0
0
6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
4
0
0
2
0
0
0
12
0
0
0
0
3
0
0
OSEM
SSS
LCX
0
0
0
0
0
9
0
9
0
0
0
0
6
0
0
0
0
0
0
12
0
0
4
0
0
4
0
15
4
0
0
4
6
2
0
8
0
0
0
0
3
0
8
SRS
LCX
0
0
0
0
0
9
0
3
0
0
0
0
0
0
0
0
0
0
0
12
0
0
0
0
0
4
0
0
0
0
0
2
6
2
0
6
0
0
0
0
0
0
8
SDS
LCX
0
0
0
0
0
0
0
6
0
0
0
0
6
0
0
0
0
0
0
0
0
0
4
0
0
0
0
15
4
0
0
2
0
0
0
3
0
0
0
0
3
0
0
IQ
SSS
RCA
1
3
3
1
0
1
3
13
3
0
1
3
7
0
0
0
4
0
1
16
7
2
1
4
1
2
9
15
4
2
0
4
4
2
0
21
0
2
1
1
12
0
8
SRS
RCA
1
3
3
1
0
3
3
7
3
0
0
3
0
0
0
0
4
0
1
16
2
2
1
2
1
2
5
0
2
0
0
2
3
2
0
12
0
2
1
1
3
0
8
SDS
RCA
0
0
0
0
0
1
0
13
0
0
1
0
6
0
0
0
0
0
1
0
5
0
0
2
0
0
4
15
2
2
0
2
4
0
0
9
0
0
0
0
9
0
0
OSEM
SSS
RCA
1
3
3
0
0
12
2
15
3
0
1
2
6
0
0
0
1
0
1
17
8
2
6
1
1
4
9
21
4
2
0
4
4
2
0
16
0
1
2
1
6
0
8
SRS
RCA
1
3
3
0
0
12
3
9
3
0
0
2
0
0
0
0
1
0
1
17
6
2
0
1
1
4
5
0
2
0
0
2
4
2
0
12
0
1
2
1
3
0
8
SDS
RCA
0
0
0
0
0
0
0
6
0
0
1
0
6
0
0
0
0
0
0
0
2
0
6
0
0
0
4
21
2
2
0
2
0
0
0
6
0
0
0
0
3
0
0
Tab. 2 Values of SSS, SRS and SDS of each patient for the 17 segments and for each territory of distribution; see also Figure 2
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183 F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
•
SSS was 3.76 ± 4.93 for IQ-SPECT and
3.93 ± 5.18 for standard acquisition, re-
spectively (p = 0.68);
•
SRS was 2.30 ± 3.22 for IQ-SPECT and
2.58 ± 3.79 for standard acquisition, re-
spectively (p = 0.28);
•
SDS was 1.76 ± 3.56 for IQ-SPECT and
1.41 ± 3.58 for standard acquisition, re-
spectively (p = 0.29).
Discussion
Long acquisition time and radiation expo-
sure are the main limits of MPI. Recent re-
construction algorithms allow us to reduce
acquisition time without affecting image
quality.
Testing quarter-time acquisition scans
we used the new hardware and software
package (IQ-SPECT) to compensate for the
low counts due to shortened scan time,
reporting a high overall correlation and not
significant differences in evidenced areas of
hypoperfusion, ventricular volumes and
function.
Recently, other packages have been de-
veloped to allow shortened acquisition
time, using general purposes cameras and
collimators, like Evolution for Cardiac (GE
Healthcare) (1), Wide-beam reconstruc-
tion (WBR) (UltraSPECT) (18), Astonish
(Philips Medical System) (18), 3D Flash
(Siemens Medical Solutions) (13).
All 3D reconstruction packages have the
same physics principle, that is to model the
3D depth-dependent detector spatial re-
sponse and to suppress the noise to achieve
the best compromise of resolution/contrast
improvement and noise reduction (14).
Fast computing time by modern processors
allows to adopt iterative reconstruction
(IR) with resolution recovery (RR) in a
clinical setting as a practical alternative to
FBP. IR algorithms are of great importance
in this context, especially for improved
noise properties over FBP, such as reduced
noise correlation length at low numbers of
iterations (6). Many studies determined the
equivalent accuracy of half-time protocols
to full-time FBP: De Puey et al. compared
two new reconstruction algorithms with
FBP using metrics of image quality, LV vol-
umes, LVEF and wall motion, demonstrat-
ing that half-time protocols (OSEM-RR)
and WBR offered stress and rest image
quality and diagnostic accuracy equivalent
to full-time FBP (8). As somehow ex-
pected, AC provided improved specificity,
suggesting the ideal use of depth-depend-
ent resolution recovery algorithms in con-
junction with a validated form of attenu-
ation correction (20). De Puey et al. also
evaluated the diagnostic potential of a
quarter-time WBR package in comparison
to full-time FBF acquisition (7).
IQ-SPECT package represents a com-
pletely different approach to the need of
shortening either scan time or adminis-
tered dose. In fact, unlike previous proto-
cols, a new kind of collimator is proposed,
designed to magnify the region around the
myocardium including the entire torso in
the field of view, the camera heads run on a
cardio-centric orbit where the detectors
keep the heart in the region of four-fold
magnification for the entire scan and a
dedicated reconstruction engine is pro-
vided.
The possibility of using AC both for
standard acquisition and for IQ-SPECT
protocol with comparable efficacy is of
great importance, since AC has been dem-
onstrated to grant improved specificity in
MPI in recent studies (1, 5).
Only a few reports can be found in lit-
erature about the use of IQ-SPECT proto-
col (16, 21), but (with) evaluating ex-
tremely small patient samples and without
score
SSS
SRS
SDS
LAD
LCX
RCA
LV (ml)
LV EF (%)
SSS
SRS
SDS
SSS
SRS
SDS
SSS
SRS
SDS
EDV
ESV
IQ-SPECT
5.37 ± 7.01
3.42 ± 4.61
2.40 ± 4.94
3.23 ± 4.06
2.46 ± 3.05
1.16 ± 2.32
2.13 ± 4.32
0.95 ± 2.49
1.23 ± 3.28
3.76 ± 4.93
2.30 ± 3.22
1.76 ± 3.56
105.65 ± 44.29
49.03 ± 34.01
57.31 ± 12.03
standard protocol
5.65 ± 7.46
4.23 ± 6.92
1.74 ± 4.52
3.46 ± 4.67
3.03 ± 4.90
0.74 ± 2.19
2.18 ± 3.78
1.20 ± 2.80
1 ± 2.70
3.93 ± 5.18
2.58 ± 3.79
1.41 ± 3.58
103,13 ± 47.25
47.83 ± 34.63
57.58 ± 12.64
p
0.65
0.13
0.23
0.60
0.24
0.27
0.87
0.17
0.34
0.68
0.28
0.29
0.07
0.07
0.63
Tab. 3
Mean values of SSS,
SRS, SDS for all
segments as well as
for each left ventricu-
lar regions and values
of LV EDV, LV ESV and
LV EF
Fig. 2 Segments of the territories of distribution of the three coronary arteries, evidenced by a V.
territory of distribution of
A) LAD; B) LCX; C) RCA
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184F. Caobelli et al.: IQ SPECT in myocardial perfusion imaging
comparing results to those obtained with
standard protocols.
We compared the diagnostic perform-
ances for CAD detection in a study group
with balanced prevalence of patients af-
fected and not affected by CAD and our
findings did not show a significant differ-
ence regarding perfusion defects extent
and severity between the two protocols.
Like previous studies, we performed a
visual evaluation of myocardial perfusion
and scored each segment by consensus
among three experienced physicians. Auto-
matic software packages such as QGS/QPS
provide an automatic scoring of myo-
cardial perfusion, but, in our opinion, these
software still suffer from large discrep-
ancies between visual and semiquantitative
evaluation. The huge variability in heart di-
mension and shape and the difficulties in
obtaining an age- and gender-matched
normal database can limit the clinical use
of automatic scoring, thus suggesting that,
at least up to now, visual interpretation,
made by consensus among more nuclear
medicine physicians may be the best way to
evaluate diagnostic accuracy.
Although not reaching a statistical sig-
nificance, IQ-SPECT seems to be a little
more specific although less sensitive. A
possible explanation is that the geometry of
IQ-SPECT collimators and IQ-SPECT pro-
cessing engine provides a slightly lower res-
olution of tomographic images, thus loos-
ing small defects, as evidenced by lower
perfusion scores.
The importance of adopting quarter-
time protocols is also prospectively the
possibility of administering a quarter dose
and perform a full-time scan, thus minim-
izing the required radionuclide activity
while obtaining a good image quality with-
out sacrificing diagnostic accuracy, accord-
ing to strategies recommended to mini-
mize radiation exposure to patients under-
going SPECT imaging (9).
Due to the design of the study, the dose
was the same in standard protocol and IQ-
SPECT. Nevertheless, first experiences in
our Department with other Patients
acquired after being injected a mean of 250
MBq 99m
Tc-tetrofosmin are encouraging in
order to foresee the possibility of a signifi-
cant dose reduction. Moreover, the high
image quality achieved by IQ-SPECT im-
ages suggests the possibility of a further
dose reduction, below one half, able to pro-
vide diagnostic accuracy similar to current
levels. Not less important, 99mTc shortage
often causes limitations which can have a
dramatic impact on waiting lists and de-
partments workloads. This new technology
might have a positive impact on myo-
cardial perfusion SPECT, since studies may
be performed with the IQ-SPECT protocol
limiting to one quarter the scan time or
with a significant dose reduction, without
compromising qualitative or quantitative
imaging results.
Limitations
Our study has some limitations.
1. Angiographic evaluation was not avail-
able, therefore conclusions regarding
diagnostic accuracy, sensitivity and spe-
cificity, characterization of perfusion
defects and associated wall motion ab-
normalities using IQ-SPECT protocols
are somehow limited. Anyway, since we
compared this new technique to an al-
ready validated one, which has been ex-
tensively demonstrated to have a high
diagnostic accuracy, this limit can be at
least partly considered as overcome.
2. We did not evaluate patients affected by
complex pathologies such as cardio-
myopathies, left-bundle branch block or
with pacemaker. Although such patients
represent important cohorts needing to
be tested with a new imaging protocol
to assess its diagnostic performance.
Nevertheless, these conditions could
represent a drawback for possible arte-
facts. Therefore, we were firstly inter-
ested in comparing Patients in the most
standard conditions in order to assess
an equivalence between the two proto-
cols. Once demonstrated, other studies
should test also patients with other pa-
thologies for a comparison.
3. Another possible limit is the fact that
the standard acquisition was performed
after IQ-SPECT, with consequent lower
radiopharmaceutical activity due to
radioisotope decay.
4. Finally, the patients sample is relatively
small (n = 43); however, we performed a
single-subject study whose numbers
were sufficient for an adequate statisti-
cal analysis.
Conclusion
With the new IQ-SPECT protocol, MPI
can be acquired at quarter scan time or
prospectively administering a quarter
radiopharmaceutical dose, with minimal
disagreement in comparison to full time
scan acquisition. Allowing using a quarter
tracer dose, IQ-SPECT could also be an
optimal method to reduce patients’ radi-
ation exposure and might be helpful to
overcome limitations due to 99m
Tc shortage.
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