QUANTITATION OF MYOCARDIAL I-123 MIBG UPTAKE IN SPET STUDIES - A NEW APPROACH USING THE LEFT-VENTRICULAR CAVITY AND A BLOOD-SAMPLE AS A REFERENCE

In patients with chronic heart failure increased sympathetic activity is related to unfavourable prognosis. Since myocardial iodine-123 meta iodobenzylguanidine ([-I-123]MLBG) uptake is related to myocardial nor adrenaline content, i.e. cardiac sympathetic activity, measurement of myocardial [I-123]MIBG uptake may be of clinical use in determining pr ognosis or the effect of pharmacological intervention in these patient s. The aim of the present study was to evaluate a new method to quanti tate myocardial [I-123]MlBG uptake with respect to reproducibility and accuracy. Eighteen [I-123]MIBG pla nar and single-photon emission tom ographic (SPET) studies of patients with chronic heart failure were ev aluated. Myocardial uptake was calculated from the myocardial (MYO) to left ventricular cavity (C) count density ratio and the I-123 activit y in a blood sample. This was performed employing planar LAO images, a single-slice SPET method using the midventricular myocardial short-ax is slice, and finally a multi-slice SPET method analysing semi-automat ically drawn volumes of interest (VOIs). The accuracy of the multi-sli ce SPET method was verified using a cardiac phantom. The planar method was found to be reproducible [intra- and interobserver coefficients o f variation (IACV and IRCV) were 0.025 and 0.012 respectively] but the mean MYO/C count density ratio was only 1.31+/-0.16 as a consequence of overprojection. For the single-slice SPET method IACV was 0.2 and I RCV was 0.13, representing poor reproducibility. For the multi-slice S PET method IACV was 0.051, IRCV was 0.047 and the mean MYO/C count den sity ratio was 5.4+/-2.42. Accuracy was 81% at a true MYO/C count dens ity ratio of 6 in the phantom. It is concluded that the multi-slice SP ET method using the left ventricular cavity VOI and a blood sample as a reference is a reproducible and accurate method for assessing myocar dial [I-123]MIBG uptake.