Tc-99m PYP Heart-to-Lung Ratio for Cardiac Amyloidosis
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Question
On this Tc-99m PYP scan, two ROI circles are drawn over the heart and lung, and the calculated heart-to-lung ratio is displayed as 1.6. What does this ratio indicate about the study result?
- AA heart-to-lung ratio ≥ 1.5 is considered positive for cardiac ATTR amyloidosis, and this value of 1.6 supports a positive result consistent with transthyretin amyloid cardiomyopathy
- BA heart-to-lung ratio of 1.6 is within the normal range for Tc-99m PYP studies, as ratios must exceed 2.0 before the scan is considered positive for cardiac amyloid deposition
- CThe heart-to-lung ratio is calculated only to confirm adequate tracer injection and does not contribute to the interpretation of cardiac amyloidosis on planar images
- DA heart-to-lung ratio ≥ 1.5 is a nonspecific finding seen in all bone-seeking radiopharmaceutical studies and cannot differentiate cardiac amyloid from other causes of cardiac uptake
Show the answer and explanation
A. A heart-to-lung ratio ≥ 1.5 is considered positive for cardiac ATTR amyloidosis, and this value of 1.6 supports a positive result consistent with transthyretin amyloid cardiomyopathy
On Tc-99m pyrophosphate (PYP) cardiac amyloid imaging, a heart-to-contralateral lung (H/CL) ratio ≥ 1.5 measured at 1 hour post-injection is considered a positive result for ATTR (transthyretin) cardiac amyloidosis. A ratio of 1.6 exceeds this threshold and, when combined with visual grading, supports a positive study. This scan is used specifically to detect ATTR amyloid cardiomyopathy (both wild-type and hereditary forms) and is typically negative in AL (light-chain) amyloidosis.
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