## 2 Materials and Methods
### Semiquantitative NM Indexes Calculation with the CM  
On a random subset of 30 patients, a semiquantitative analysis of Hr, WBr, and H/WBr was calculated by the drawing region of interest (ROI) on target organs, following the CM described by [PERSON] et al. [9]. In brief, the heart, kidneys, and bladder were manually contoured by an NM physician on the anterior images of the early acquisition on a referring workstation (Xeleris Functional Imaging Workstation 4.0; GE Healthcare, Milwaukee, Brookfield, WI, USA). These ROIs were copied, mirrored, and manually positioned to match the organs on the posterior images. The same procedure was applied to late-acquisition images. The background correction (evaluated by placing a rectangular background ROI near the tibia) was applied on all ROIs to subtract the noise component spread over the entire image. Total counts of the images were taken as WB counts. For each ROI, the GM of the counts of the two projections was obtained. Early and late images were corrected for background signal, scan duration, and the physical decay between early and late acquisitions. Data were extracted in.csv format for the computation of Hr, WBr, and H/WBr.  
In particular, the scan duration correction was applied considering the actual frame duration of the early (AFD\({}_{\text{E}}\)) and late (AFD\({}_{\text{L}}\)) images, as reported in the DICOM header. The decay correction accounted for the \({}^{99\text{m}}\)Tc physical decay between the early and late image scan acquisition times (\(\Delta t\)). This correction was applied by considering the radioactive exponential decay law, using the decay constant \(\lambda\) of \({}^{99\text{m}}\)Tc (\(\lambda=3.209\times 10^{-5}\) s\({}^{-1}\)), with half-life T\({}_{1/2}\) = 6.01 h.  
The WBr was evaluated considering the total counts in WB and subtracting the total counts in the bladder and kidneys, by comparing the decay and scan speed-corrected counts in the late images with early WB counts as follows:  
\[WB_{r}=\frac{[WB_{L}-(Bladder_{L}+L\_Kidney_{L}+R\_Kidney_{L})]\cdot\text{e}^{ \lambda\cdot\Delta t}}{WB_{E}}\cdot\frac{AFD_{E}}{AFD_{L}} \tag{1}\]  
where WB\({}_{\text{L}}\), Bladder\({}_{\text{L}}\), L\(\_\)Kidney\({}_{\text{L}}\), and R\(\_\)Kidney\({}_{\text{L}}\) represent the background-corrected total counts in the WB, bladder, left kidney, and right kidney ROIs, respectively, determined using the late image scans, while WB\({}_{\text{E}}\) indicates the total counts in the whole body ROI in the early image scan.  
The Hr was evaluated by comparing decay and scan speed-corrected counts of the heart in late images with counts in early WB images. The Hr was computed as follows:  
\[H_{r}=\frac{Heart_{L}\cdot\text{e}^{\lambda\cdot\Delta t}}{WB_{E}}\cdot\frac{ AFD_{E}}{AFD_{L}} \tag{2}\]  
where Heart\({}_{\text{L}}\) represents the total counts in the heart ROI in the late image scan, and WB\({}_{\text{E}}\) indicates the total counts in the WB ROI in the early image scan.  
The H/WBr was therefore obtained by dividing the counts in the heart by the counts in late WB images, as follows:  
\[H/WB_{r}=\frac{Heart_{L}}{[WB_{L}-(Bladder_{L}+L\_Kidney_{L}+R\_Kidney_{L})]} \tag{3}\]  
where Heart\({}_{\text{L}}\), WB\({}_{\text{L}}\), Bladder\({}_{\text{L}}\), L\(\_\)Kidney\({}_{\text{L}}\), and R\(\_\)Kidney\({}_{\text{L}}\) represent the total CNTS in the heart, WB, bladder, left kidney, and right kidney in the late image scan, respectively.