Is a low-dose Tc-99m-MIBI protocol suitable for first-pass RNV?

Tc-99m-labelled radiopharmaceuticals, such as Tc-99m-sestamibi (Tc-99m-MIBI), offer the opportunity to measure myocardial perfusion and function with one injection only. The aim of this study was to evaluate whether first-pass (FP) radionuclide ventriculography (RNV) consecutively followed by myocardial perfusion single photon emission computed tomography (SPECT) may be performed according to a low-dose MIBI 1-day protocol using a multi-crystal gamma camera. Two hundred and seventy consecutive, predominantly obese [61% with a body mass index (BMI) of >25 kg x m(-2)] patients (169 male, 101 female), referred for myocardial perfusion SPECT with Tc-99m-MIBI [4 MBq x kg(-1) (>300 MBq) at stress; 9 MBq x kg(-1) (> 650 MBq) at rest], were studied with FP RNV prior to SPECT. Bicycle ergometry (29%), dobutamine (6%) or dipyridamole stress (65%) was performed. Adequate count (ct) statistics for FP RNV were defined as follows: (1) > 2000 cts within the background-corrected, end-diastolic (ED), left ventricular (LV) region of interest (ROI) of the representative cycle; and (2) >4 heart beats with > 1000 cts within the ED LV ROI (> 50% of maximal cts). A net mean dose of 318+/-64 MBq (4.3+/-1.1 MBq x kg(-1)) was injected during stress and 674+/-55 MBq (9.1+/-1.7 MBq x kg(-1)) during rest. There was no statistical difference among the three stress modalities concerning the net dose. Two hundred and fifty-six out of 270 (95%) stress and a basis for reliable all 270 (100%) rest FP RNV studies showed adequate count statistics as functional analysis. The 14 patients with insufficient count statistics were all obese and had received less than the planned dose. For the vast majority of patients, even a low-dose 1-day protocol with Tc-99m-MIBI is suitable for the assessment of FP RNV prior to SPECT. A minimum of 300 MBq and 4 MBq x (kg body weight)(-1) should be administered in order to obtain technically adequate results even in obese patients.