Diagnostic implications of CZT SPECT and impact of CT attenuation correction
Received Jun
Diagnostic implications of CZT SPECT and impact of CT attenuation correction
Andrew Peters 0 1
Jeevan Kumar 0 1
Pravin V. Patil 0
0 agency in the public, commercial, or not-for-profit sectors. Reprint requests: Pravin V. Patil MD, Section of Cardiology, Department of Medicine, Lewis Katz School of Medicine at Temple University , 9th Floor Parkinson Pavilion, 3401 N. Broad Street, Philadelphia, PA 19140 , USA
1 Section of Cardiology, Department of Medicine, Lewis Katz School of Medicine at Temple University , Philadelphia, PA , USA
In the current issue, Kennedy et al.1 further validate cadmium-zinc-telluride (CZT) SPECT, including the use of customized databases for automated perfusion scoring. They also demonstrate the utility of CT attenuation correction to reduce false positives and improve diagnostic accuracy. They examined three groups of patients, performing a comparison of CZT and conventional SPECT, establishing a customized database for automated perfusion scoring with CZT, and demonstrating the impact of CT attenuation correction (CTAC) in CZT SPECT. While there have been many studies comparing conventional SPECT to invasive angiography and CZT SPECT to invasive angiography, not many have directly compared them in the same population.
CZT VERSUS CONVENTIONAL SPECT
Single-photon emission computed tomography
(SPECT) myocardial perfusion imaging (MPI) is an
important non-invasive tool for the evaluation of
coronary artery disease (CAD). The relationship of
functional ischemia on non-invasive testing and
angiographic disease on invasive angiography has been
debated heavily, but strong evidence supports the use
of stress MPI for diagnosis and prognosis of CAD in
certain patients. SPECT MPI has its limitations, such as
attenuation artifact and image resolution, which can
affect the predictive value and impact the clinical utility.
Conventional SPECT consists of a scintillation
detector of sodium iodide (NaI) crystals. These cameras
have been validated with good sensitivity and specificity
leading to widespread clinical use. Conventional SPECT
MPI has a sensitivity ranging between 0.82 and 0.91,
and specificity ranging between 0.70 and 0.90.2 During
the first decade of the twenty first century, CZT SPECT
systems emerged promising ultrafast acquisition, dose
reduction, and similar diagnostic accuracy. The direct
conversion of gamma radiation into signal by the
semiconductor ensured improved image fidelity.
CZT SPECT has been discussed extensively in the
literature since cameras have a higher sensitivity
compared to conventional cameras and reduced imaging
time.2 Many of these studies have assessed the
diagnostic performance of MPI with CZT cameras
(Table 1).1,3–8 Further, in a meta-analysis by Nudi
et al., the sensitivity of CZT SPECT was found to be
range between 0.78 and 0.89 and the specificity ranged
from 0.62 to 0.76.9 While the sensitivity is comparable
to prior studies, the specificity is lower. Neill et al.
further emphasized this with a direct comparison of CZT
to conventional SPECT MPI in patients with correlative
invasive angiography. CZT SPECT again had superior
sensitivity but decreased specificity when compared to
conventional SPECT.8 It is speculated that the lower
specificity of CZT imaging is due to the practice of
performing upright imaging, which may enhance patient
comfort but results in more abdominal attenuation
artifact, as well as the clinical tendency for use in an
obese patient subgroup.
Kennedy et al.1 demonstrate a reasonable
correlation between CZT and conventional NaI scanners. Their
data are in agreement with prior studies that indicate
CZT could be associated with lower specificity and a
higher number of false positives. Further, they provide
low-intermediate risk patient data that support the use of
Author
Sensitivity (%)
Specificity (%)
N/A
a separate custom database for CZT automated perfusion
scoring, which potentially could improve specificity. It
will be important for further research to be performed
with a higher risk cohort. The authors also incorporated
CTAC into their analysis, validating its use.
ROLE FOR CT ATTENUATION CORRECTION
SPECT MPI is susceptible to attenuation artifacts
from tissues such as breast, diaphragm, abdomen, and
lateral chest wall that reduce specificity.10,11 Numerous
techniques have been shown to reduce attenuation
artifact including breast binding, prone imaging, and
attenuation maps created by external sources. External
fixed line source attenuation correction (AC) using
most frequently gadolinium-153 but also cobalt-57,
barium-133, americium-241, and technetium-99m has
been used.12 Nishiyama et al. demonstrated a technique
involving combined supine and prone SPECT
acquisition could reduce the false-positive rate associated with
supine image acquisition.6 Supine and upright imaging
with CZT in obese patients has also demonstrated
diagnostic accuracy for CAD.13,14 Although these
techniques have been used, more rece (...truncated)