ATTR Cardiac Amyloidosis: A direct comparison between conventional gamma camera heart/lung ratio quantification and D-SPECT methodology in 50 consecutive patients

Objectives: D-SPECT (Spectrum Dynamics) is a novel, cardiac-dedicated SPECT system based on solid-state detectors currently being utilized for non-invasive cardiac perfusion imaging. We evaluated whether D-SPECT can be reliably used for the diagnosis of transthyretin-associated cardiac amyloidosis (ATTR), using a beta-version software for image acquisition and processing. This is especially salient given the recent emergence of disease modifying therapies for ATTR which calls for a rapid and highly sensitive diagnostic tool.

Methods: 50 subjects (56% male, age 72 + 14 years, BMI 29.6 + 8) referred for suspected ATTR were scanned sequentially, first using conventional gamma camera SPECT/planar system followed immediately by D-SPECT system for comparison. Imaging acquisition time was 8 minutes for planar system compared to 10 minutes for D-SPECT. TC-PYP dose administered was 18 + 3.5 mCi (range 10-26 mCi). We utilized a ß-version image acquisition and processing software to display myocardial uptake of Tc-99m-pyrophosphate and quantify it by calculating a Heart to Contralateral lung ratio (H/CL) from two separate yet similar sized regions. A previously validated H/CL ratio cutoff of greater than or equal to 1.5 was used for ATTR diagnosis. We used linear regression analysis to correlate the ratios obtained from the two imaging systems.

Results: The group mean H/CL ratios obtained from conventional planar/SPECT system and the D-SPECT system were similar (1.19 + 0.20, range: 0.83-1.83 from conventional gamma camera compared to 1.22 + 0.20 , range 0.83-1.9 from D-SPECT). Correlation analysis by linear regression had an r² of 0.80, and a root mean square error of 0.08. Importantly, there were six positives or abnormal studies indicating ATTR cardiac amyloidosis utilizing standard gamma camera (12%). All six were also positive for ATTR cardiac amyloidosis on D-SPECT.

Conclusions: Our single center analysis shows that the D-SPECT system is quantitively comparable to conventional gamma cameras for non-invasive diagnosis of ATTR. D-SPECT estimates of the H/CL ratio correctly identified all the positive ATTR studies performed by the standard gamma camera methodology. However, its advantages include compactness, region-centric scanning, higher sensitivity and higher resolution. In addition, due to its upright acquisition design, D-SPECT is a promising modality for patients who are unable to lie flat for conventional gamma camera systems either due to congestive heart failure or obesity.

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