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

Abstract

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...

Cause of apical thinning on attenuation-corrected myocardial perfusion SPECT

“…Matsunari et al showed slight misregistration of a 7-mm shift (1 pixel) produced up to 15 % change in relatively regional uptake in the phantom study [15]. Misregistrations of more than 1 pixel were found 73 % of 248 consecutive MPS studies in the clinical study [18]. In addition, a 3-pixels misregistered shift significantly affected summed stress score for the detection of CAD． Nevertheless, misregistration induced artificial perfusions were simultaneously showed not only at the apex but also at the other regions.…”

A variational model for SPECT reconstruction with a nonlinearly transformed attenuation prototype

“…[20, p. 174]. Unfortunately, repositioning and movement of the patient during the measurements can cause misalignments, which then result in severe reconstruction artefacts [8,15,17,18]. A mathematical approach is to solve Problem I simultaneously for attenuation and density.…”

“…However, due to repositioning of the patient while being transferred from one imaging device (CT) to another (SPECT) or due to internal organ motion such as respiratory or cardiac motion, the attenuation prototype is in general inconsistent with the measured data. This can result in serious reconstruction artefacts in particular in cardiac SPECT [8,15,17,18]. To overcome these difficulties, deformable attenuation prototype is considered.…”

Cardiac SPECT/CT Imaging: CT Attenuation Correction and SPECT/CT Hybrid Imaging

“…Thus, quality control can be used to avoid reconstruction artifacts. PET/CT [28,29] and SPECT/CT [30,31] studies have shown that the frequency of misalignment can be high. Recently, it has been shown that the effects of misalignment are less severe for SPECT/CT than for PET/CT, mainly because of the low spatial resolution of SPECT [32].…”