Standardization of the heart-to-mediastinum ratio of 123I-labelled-metaiodobenzylguanidine uptake using the dual energy window method: feasibility of correction with different camera-collimator combinations.
BACKGROUND
Although the heart-to-mediastinum (H/M) ratio in a planar image has been used for practical quantification in (123)I-metaiodobenzylguanidine (MIBG) imaging, standardization of the parameter is not yet established. We hypothesized that the value of the H/M ratio could be standardized to the various camera-collimator combinations.


RESULTS
Standard phantoms consisting of the heart and mediastinum were made. A low-energy high-resolution (LEHR) collimator and a medium-energy (ME) collimator were used. We examined multi-window correction methods with (123)I- dual-window (IDW) acquisition, and planar images were obtained with IDW correction and the LEHR collimator. The images were obtained using the following gamma camera systems: GCA 9300A (Toshiba, Tokyo), E.CAM Signature (Toshiba/Siemens, Tokyo) and Varicam (GE, Tokyo). Cardiac phantom studies demonstrated that contamination of the H/M count ratio was greater with the LEHR collimator and least with the ME collimator. The corrected H/M ratio with the LEHR collimator was similar to that with ME collimators. The uncorrected H/M ratio with the ME collimator was linearly related to the H/M ratio with IDW correction with the LEHR collimator. The relationship between the uncorrected H/M ratios determined with the LEHR (E.CAM) and the ME collimators was y = 0.56x + 0.49, where y = H/M ratio with the E.CAM and x = H/M ratio with the ME collimator. The average normal values for the low-energy collimator (n=18) were 2.2+/-0.2 (initial H/M ratio) and 2.42+/-0.2 (delayed H/M ratio), and for the low/medium-energy (LME) collimator (n=14) were 2.63+/-0.25 (initial H/M ratio) and 2.87+/-0.19 (delayed H/M ratio). H/M ratios in previous clinical studies using LEHR collimators are comparable to those with ME collimators.


CONCLUSIONS
The IDW-corrected H/M ratios determined with the LEHR collimator were similar to those determined with the ME collimator. This finding could make it possible to standardize the H/M ratio in planar imaging among various collimators in the clinical setting.
Matsuo
Shinro
S
Department of Nuclear Medicine, Kanazawa University Hospital, Kanazawa 920-8641, Japan. smatsuo@nmd.m.kanazawa-u.ac.jp
Nakajima
Kenichi
K
Okuda
Koichi
K
Kawano
Masaya
M
Ishikawa
Takehiro
T
Hosoya
Tetsuo
T
Taki
Junichi
J
Kinuya
Seigo
S
D019797:3-Iodobenzylguanidine / Q000737:chemistry*; D001331:Automation; D002309:Cardiology / Q000379:methods; D003952:Diagnostic Imaging / Q000295:instrumentation* / Q000592:standards*; D004867:Equipment Design; D006321:Heart / Q000000981:diagnostic imaging*; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008482:Mediastinum / Q000000981:diagnostic imaging*; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000494:pharmacology; D012542:Scattering, Radiation
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine