^99mTc-labelled bone tracer myocardial quantification: About correlation with heart function

Excerpt

Amyloid Transthyretin Cardiac Amyloidosis (ATTR-CA) is one of the main causes of heart failure, especially in elderly population. Because of promising medical treatment like tafamidis, ^99mTc-labelled bone tracer myocardial investigation provides the challenge of diagnosing and monitoring ATTR-CA patients.1 However, isotopic explorations reflect relative uptakes in tissues, here namely bone and myocardium. Furthermore, tissue tracer uptake mainly depends on kidney, liver and heart functions. As such, brain natriuretic peptide (BNP) is a widely used biomarker allowing follow-up of heart function. About ^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) uptake in patients with Perugini 2 or 3 bone scan, we analyzed retrospectively 13 patients and quantified 2D myocardial uptake (planar H/WB ratio: myocardial uptake related to whole body; planar H/B ratio: myocardial uptake related to femoral diaphysis). There was a negative correlation (Spearman coefficient) between each ratio and BNP blood level: r_s =  − 0.57, p = 0.045 (Figure 1: H/WB ratio) and r_s =  − 0.61, p = 0.03 (Figure 2: H/B ratio). Such a statement should be expected but it questions isotopic quantification methods. Castano et al. showed that myocardial retention due to ATTR-CA might be of interesting prognostic importance.2 Hence, ATTR-CA monitoring treatment should need molecular imaging parameters, which provide data not only related to myocardial failure but more interestingly to disease progression, like probably summarized in ^99mTc-labelled bone tracer myocardial quantification. This index might be corrected by the state of cardiac neuro-humoral adaptation, usually assessed by BNP, for specifically emphasizing information due to pathophysiological stage of ATTR-CA. Of course, this biological caution should not make forget to go on improving uptake quantification accuracy. Indeed, Manrique et al. recently demonstrated that 3D semi-quantitative analysis of CZT SPECT optimizes heart to background uptake ratio.3 As usual in nuclear medicine, both physical and biological considerations should improve imaging performance.

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