Abstract
2008
Objectives: Cardiac amyloidosis is the most common etiology of restrictive cardiomyopathy. Myocardial Tc-99m pyrophosphate (PYP) scintigraphy has been successfully used for diagnosis of transthyretin (TTR) positive cardiac amyloidosis. Both quantitative myocardial to contralateral lung ratio and semi-quantitative visual grading of PYP uptake by comparison to bone have been adopted as the standard Tc-99m PYP interpretation reporting system. However, neither approach can provide an accurate tracer distribution pattern in the myocardium. The left ventricular segmentation model is a standard reporting model for Nuclear Cardiology and Echocardiography. Given the fact that Echocardiogram is the first line modality to diagnose restrictive cardiomyopathy, it is important to find a common interpretive and quantitative tool that can be used to correlate the findings of both exams. In this study, we aim to set up a left ventricle 17-segment model in displaying the Tc-99m PYP distribution in TTR positive cardiac amyloidosis.
Methods: There are 22 patients with positive Tc-99m PYP exams included in the current study. All patients had undergone both Tc-99m PYP planar and SPECT/CT imaging. Utilizing the Volumetrix MI and Myovation applications from the Xeleris Workstation, the SPECT/CT imaging data was processed in the following steps: Step 1) Using an iterative reconstruction algorithm, attenuation-corrected images were generated with the Volumetrix MI application. Step 2) Myocardial images were reformatted into three planes: short-axis (SA), vertical long-axis (VLA), and horizontal long-axis (HLA) by identification of the long axis of the left ventricle utilizing the Myovation application. Step 3) Processed myocardial images were displayed in array of formats, including a bull's eye display, in which the left ventricle 17-segmnet model was applied utilizing the QGS/QPS tool within the Myovation application.
Results: All 22 patients’ SPECT/CT imaging data generated a full-set array of display formats, including the three axes image, bull’s eye display, and left ventricle 17-segment model. On pseudo-color scale, the intensity of color represents the PYP accumulation density at the specific segment of left ventricle (Figure 1 - 2). The apex is usually spared.
Conclusions: With the left ventricle 17-segment model, positive Tc-99m PYP exams can provide detailed amyloidosis distribution information, and may correlate with strain information derived on echocardiogram. These improved results can then also be used to evaluate therapeutic candidacy and effects of newly developed medications for cardiac amyloidosis. With a standardized tool across the imaging modalities, a more accurate and non-invasive diagnosis can be made to provide the best care for the patient.