I-123 MIBG cardiac uptake measurements: limitations of collimator choice and scatter correction in the clinical context.
OBJECTIVE
Low uptake of metaiodobenzylguanidine (MIBG) in patients with heart failure generally indicates poor prognosis. Our objective was to determine the best method for calculating I-123 MIBG uptake. MIBG uptake as a percentage of the injected dose is presented as an alternative method for serial assessment.


METHODS
Patients with chronic heart failure were imaged with I-123 MIBG with both a medium-energy (ME) collimator and a low-energy high-sensitivity (LEHS) collimator. Scatter correction was used to correct the LEHS images. Heart-to-mediastinal (H/M) ratio and the percentage of myocardial uptake of MIBG were obtained.


RESULTS
Mean H/M ratios for the ME images, LEHS images and scatter-corrected LEHS images were 2.45+/-0.61, 2.22+/-0.47 and 2.51+/-0.62, respectively. Mean H/M ratio was significantly different among all the three sets (P<0.001) of images. The average difference in H/M ratios between the ME images and LEHS images was lower when scatter correction was applied (4.95% vs. 9.79%). The error in calculating the myocardial uptake as a percentage of the injected dose was significantly lower than the error in calculating H/M ratio (0.2 vs.10.2% LEHS; 0.3 vs.16.0% ME; 0.2 vs.11.8% LEHS scatter corrected).


CONCLUSIONS
For quantitative assessment of H/M ratio in I-123 MIBG imaging a LEHS collimator can be used in place of a ME collimator to achieve better counting statistics, but scatter correction must be used. The calculation of the myocardial uptake as a percentage of the injected dose has potential as an alternative method of measurement, particularly for serial assessment.
Department of Nuclear Cardiology, Royal Infirmary, Glasgow, UK. alison.fletcher2@nhs.net
Alison M
AM
Fletcher
Duncan W
DW
Motherwell
Alexander D
AD
Small
Graham M
GM
McCurrach
Nicholas E R
NE
Goodfield
Mark C
MC
Petrie
William
W
Martin
Stuart M
SM
Cobbe
D019797:3-Iodobenzylguanidine / Q000008:administration & dosage / Q000493:pharmacokinetics*; D016477:Artifacts; D001692:Biological Transport; D005260:Female; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000378:metabolism; D006801:Humans; D007267:Injections; D008297:Male; D008482:Mediastinum; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D011829:Radiation Dosage; D011877:Radionuclide Imaging; D012542:Scattering, Radiation
D019797:3-Iodobenzylguanidine