Sources of attenuation-correction artefacts in cardiac PET/CT and SPECT/CT

272

149

In view of the commercial success of integrated PET/CT scanners, there is an increasing interest in comparable SPECT/CT systems. SPECT in combination with CT enables a direct correlation of anatomic information and functional information, resulting in better localization and definition of scintigraphic findings. Besides anatomic referencing, the added value of CT coregistration is based on the attenuation correction capabilities of CT. The number of clinical studies is limited, but pilot studies have indicated a higher specificity and a significant reduction in indeterminate findings. The superiority of SPECT/CT over planar imaging or SPECT has been demonstrated in bone scintigraphy, somatostatin receptor scintigraphy, parathyroid scintigraphy, and adrenal gland scintigraphy. Also, rates of detection of sentinel nodes by biopsy can be increased with SPECT/CT. This review highlights recent technical developments in integrated SPECT/CT systems and summarizes the current literature on potential clinical uses and future directions for SPECT/CT in cardiac, neurologic, and oncologic applications.

Section: Use Of Ct For Attenuation Correctionmentioning

confidence: 99%

“…The superiority of cardiac PET over cardiac SPECT was demonstrated in several publications (3,58,71,76,77). However, in almost all of these reports, non-attenuation-corrected SPECT was used.…”

Section: Cardiac Spect Versus Pet and Absolute Quantificationmentioning

confidence: 99%

Spect/Ct

Buck¹,

Nekolla²,

Ziegler³

et al. 2008

272

149

“…For the current analysis, the radiotracer activity in different organs was not misregistered relative to each other. The axial mismatches between the attenuation and the emission maps caused by breathing have been shown to cause artifacts, especially in the anterior wall, in both PET and SPECT MPI (19,20). Reregistration of such misalignment in SPECT/CT leads to superior image quality if based on internal rather than external landmarks, whether performed with a free-breathing CT protocol or during breath holding after a normal exhalation (20).…”

Section: Discussionmentioning

confidence: 99%

Directions and Magnitudes of Misregistration of CT Attenuation-Corrected Myocardial Perfusion Studies: Incidence, Impact on Image Quality, and Guidance for Reregistration

Kennedy¹,

Israel²,

Frenkel³

2009

CT-based attenuation-corrected (AC) myocardial perfusion imaging (MPI) studies may show significant artifacts caused by misregistration between SPECT and CT data. The present study aimed at identifying the directions and magnitudes of misregistration with greatest impact on AC myocardial perfusion image quality. Methods: The incidence, magnitude, and direction of misregistration were assessed in 248 consecutive stress-rest MPI studies in 124 patients. In addition, cardiac SPECT/CT registration was artificially modified in 40 studies, shifting CT data by 61, 62, and 63 pixels along the cephalad/caudal, dorsal/ventral, and left/right axes. Percentage of change in 5-wall AC-MPI polar map scoring was calculated for each region, and the direction of the shift along each axis was analyzed statistically (Student t test, P , 0.05) and compared to determine the region most significantly affected by each shift (Newman-Keuls test, P , 0.05). Changes in the normal and abnormal summed stress score (SSS) due to artificial misregistration were assessed (k-statistics, McNemar differences). Results: SPECT/CT misregistration of more than 1 pixel was found in 73% (181/248) of studies and more than 2 pixels in 23% of studies (57/248). A 3-pixel ventral shift most significantly affected polar map scoring (215.4% 6 6.1% change in lateral wall; 27.5% 6 5.5% change in inferior wall). A 3-pixel dorsal shift resulted in a 29.5% 6 5.3% apical and 28.8% 6 5.8% septal change. Polar map scoring was least affected by the cephalad/caudal shift (,5% average change in all regions except for the anterior wall; 29.9% 6 7.4% change for 3-pixel caudal shift). The most significant changes occurred in the lateral and anterior walls when the myocardium on SPECT overlapped lung tissue on CT, encountered in 16% of studies (40/248). Clinically significant changes (in SSS) occurred for the 3-pixel caudal, dorsal, and right shifts. Conclusion: A misregistration of significant magnitude occurred in 23% of studies and in the direction of the most severe artifacts in 16% of studies. Severe misregistration along the dorsal/ventral axis most significantly affected AC-MPI. Quality control of SPECT and CT registration and manual realignment should be performed routinely, with the highest priority in AC studies showing an overlay of the myocardium on SPECT with lung tissue on the CT component of AC-MPI. Cl inically significant artifacts on CT-based attenuationcorrected (AC) myocardial perfusion imaging (MPI) studies may be caused by misregistration of 1 pixel or more between the SPECT and CT data (1). The present study was performed to identify the directions and magnitudes of misregistration that have the greatest effect on AC myocardial perfusion image quality.Hybrid SPECT/CT scanners provide an efficient method of obtaining CT-based AC-MPI (2,3). Frequent artifacts seen on MPI studies include an apparent reduction in radiotracer uptake due to breast attenuation in women or to diaphragmatic attenuation, more often found in men (4). These findings are reduced or r...

“…The CZT solid-state detector technology allows MPI with increased resolution and a minimized scan time (10,17) and may therefore have the potential to emerge as an alternative to conventional SPECT cameras. Tissue attenuation plays a major role in SPECT MPI because it can affect the diagnostic accuracy, mainly by decreasing specificity, and as a consequence reduce costeffectiveness (18,19) or even lead to nondiagnostic studies (20). Therefore, several strategies for AC have been evaluated, among which CT AC has proven most successful (1).…”

Section: Discussionmentioning

confidence: 99%

Validation of CT Attenuation Correction for High-Speed Myocardial Perfusion Imaging Using a Novel Cadmium-Zinc-Telluride Detector Technique

Herzog¹,

Buechel²,

Husmann³

et al. 2010

The aim of this study was to validate attenuation correction (AC) using low-dose standard CT for myocardial perfusion imaging (MPI) on a novel ultra fast g-camera with cadmium-zinc-telluride (CZT) detector technology. Methods: Sixty-six patients (body mass index 6 SD, 27.2 6 3.5 kg/m 2 ; range, 19.1-36.0 kg/m 2 ) underwent a 1-d 99m Tc-tetrofosmin adenosine stress-rest imaging protocol with 15-min acquisitions on a standard dualhead SPECT camera. All scans were repeated within minutes on the CZT camera, with 3-min acquisitions for stress (low dose) and 2-min acquisitions for rest (high dose) as recently established. We compared maximum myocardial uptake (20-segment model) from CZT versus standard SPECT MPI by intraclass correlation without and with CT AC. In addition, clinical agreement for each coronary territory for all scans from both devices was assessed, and Bland-Altmann (BA) limits of agreement for percentage uptake were calculated. Results: The clinical agreement between CZT and standard SPECT cameras was 96% for noncorrected low-and high-dose images (r 5 0.90 and BA 5 218 to 15, and r 5 0.91 and BA 5 215 to 16, respectively), and agreement after AC was 96% for low-and 99% for high-dose images (r 5 0.87 and BA 5 216 to 14, and r 5 0.88 and BA 5 216 to 14, respectively). Conclusion: Our results support that AC of MPI on the novel CZT camera, compared with AC MPI on a conventional SPECT camera, is feasible because it provides a high correlation of segmental tracer uptake and an excellent clinical agreement.