Comparison of weight- and BMI-adjusted dosing for dynamic ⁸²Rb PET myocardial perfusion imaging

Objectives: PET scanner saturation can lead to inaccurate myocardial blood flow (MBF) quantification. Previous studies have shown that saturation can be reduced by adjusting radiotracer dose based on the patient weight to account for variable photon attenuation. However, saturation can still be present under this protocol depending on patient habitus. We investigated whether BMI-adjusted dosing reduces PET saturation beyond weight-adjusted dosing.

Methods: We studied two groups of consecutive patients, weight-adjusted protocol (WT) and BMI-adjusted protocol (BMI), who underwent PET/CT imaging (WT: N=132, 85 males, age 65±11 yrs; BMI: N=305, 168 males, age 61±11 yrs). A CT scan was acquired for attenuation correction (AC). PET data were acquired for 7 min at rest and at regadenoson-induced stress for a subset of patients (Cardiogen-82, Bracco Diagnostics, Monroe Township, NJ). Patients who underwent WT were administered 12 MBq/kg of ⁸²Rb, and those who underwent BMI were administered 33.3 MBq/kg/m² of ⁸²Rb. Dynamic ⁸²Rb PET images were binned into 30 frames (16 x 5 sec, 6 x 10 sec, 3 x 20 sec, 4 x 30 sec, 1 x 90 sec). PET detector saturation was defined as the presence of a total peak singles rate (PSR) > 64 Mcps, or one or more detector blocks with > 450 kcps. For scans that met these criteria, a saturation severity index (SSI) was calculated using the following formula: SSI = 10⁵/(T × N_det)Σt_iB_i where T is 2 x radionuclide half-life, N_det is the total number of detector blocks in the scanner, t_i is the duration of the i^th frame, and B_i is the number of saturated detector blocks in the i^th frame, where the sum is over all frames in the time period T. MBF was estimated by kinetic modeling of dynamic ⁸²Rb PET. The extent and severity of perfusion defects was quantified using the total perfusion deficit (TPD). Myocardium-to-blood ratio (MBR) was determined in remote normal myocardium. Welch's unequal variances t-test was used to compare continuous parameters between dosing protocols with a significance level of 0.05. Results are reported as mean±standard deviation (SD).

Results: Patient height and weight were not significantly different between the subgroups (Table). Quantitative imaging parameters (TPD, MBR, MBF) were not significantly different between subgroups. Compared to weight-adjusted dosing, the use of BMI-adjusted dosing reduced the incidence of PET saturation (26 vs 36%, p<0.05). In cases where saturation was present, the SSI was also reduced for BMI-adjusted scans (5.9±8.9 vs 9.2±12.8, p<0.001). Additionally, using the BMI-adjusted protocol reduced both mean ⁸²Rb dose and effective radiation exposure by 4.8% (p=0.006).

Conclusions: The use of a BMI-dosing protocol significantly reduced both the frequency and severity of PET saturation, as well as significantly reducing the overall mean ⁸²Rb dose and effective radiation exposure that patients received.

• Download figure
• Open in new tab
• Download powerpoint