Threshold method for volume and activity determinations using single-photon emission computed tomography phantom for possible use in clinical liver therapies

A threshold method for volume and activity determinations was developed through the use of a series of single-photon emission computed tomography (SPECT) phantom studies. The estimated threshold values were used to calculate the liver volume (LV) and radioactivity measurements on ^99mTc-S colloid SPECT/CT images in patients with cirrhosis. Series of phantom measurements were performed using volumes of 6-3200 ml and varying concentrations between 0.4 and 10.27 µCi/mL acquired on dual-headed gamma camera (Symbia T16, SIEMENS, Germany); 120 projections (20 s/projections); 128 × 128 matrix; zoom 1. Images were reconstructed by filtered backprojection using Butterworth filter (cutoff 0.5 cycles/cm). ^99mTc-S colloid SPECT/CT scan with standardized parameters was performed on cirrhotic patients (n = 11). LV, spleen volume (SV), quantitative liver uptake (QLU), quantitative spleen uptake (QSU), % injected dose/mL (%ID/mL) liver, and % injected dose/mL (%ID/mL) spleen were calculated. Threshold was calculated using three-dimensional volumetric analysis 8.5.10.1 software. The best threshold value for both attenuation and nonattenuation corrected images for 6-3800 mL is 38 and 37 (r = 0.978; 0.989). For concentration from 0.4 to 10.27 µCi/mL, the regression line equation obtained for concentration on attenuation corrected and nonattenuation corrected images is counts/cc = 3829 × µCi/cc + 3790 (r = 0.97) and counts/cc = 2533 × µCi/cc + 268 (r = 0.99), respectively. For patients of Child Pugh score Class A (n = 6) and Class C (n = 5), LV (1469 ± 247; 630 ± 62), SV (545 ± 34; 479 ± 19), QLU (41.72 ± 14.48; 10.34 ± 1.25), QSU (51.53 ± 17.62; 58.23 ± 2.64), %ID/mL liver (0.0287 ± 0.008; 0.017 ± 0.0006) %ID/mL spleen (0.05 ± 0.02; 0.107 ± 0.012) were obtained. The best threshold value for both attenuation and nonattenuation corrected data was found to be 38%. SPECT quantitation may be a useful tool for assessment of severity of liver disease and its quantification after liver therapies. (author)