Phantom studies for estimation of defect size on cardiac (18)F SPECT and PET: implications for myocardial viability assessment.
SPECT with (18)F-FDG has emerged as an alternative to dedicated PET for the assessment of myocardial viability. However, whether FDG SPECT can reliably quantify the extent of viable and scarred myocardium is uncertain. The aim of this study was to investigate whether SPECT with an (18)F-labeled agent would provide information on defect size similar to that provided by dedicated PET.


METHODS
Imaging was performed using an elliptic cylinder chest phantom with simulated bone, lung, mediastinum, liver, and heart. (18)F was administered into the myocardium, mediastinum, right and left ventricular cavities, and liver. Plastic inserts (n = 11) ranging in size from 2% to 60% of the myocardium were used to simulate transmural myocardial infarctions. The chest phantom was imaged with a dedicated PET camera and with a double-head SPECT camera equipped with ultra-high-energy collimators. Both SPECT and PET data were analyzed using a semiquantitative polar map approach. Defects were quantified using various cutoff thresholds ranging from 30% to 80% of peak activity and were expressed as a percentage of the left ventricular myocardium. Defect size as measured by SPECT or PET was compared with true defect size.


RESULTS
The measured SPECT defect size was highly variable depending on the cutoff used, whereas PET defect size was relatively constant over the range of cutoffs tested. The mean absolute difference between measured and true defect sizes was minimal at a cutoff of 50% of peak activity for both SPECT (3.3% +/- 3.3%) and PET (2.7% +/- 2.5%). For this threshold, both SPECT and PET measurements showed an excellent correlation with true defect size (r = 0.98 for SPECT and 0.99 for PET). The correlation between SPECT and PET measurements was also excellent (r = 0.99; P < 0.01).


CONCLUSIONS
If an appropriate threshold is used to define a defect, SPECT with an (18)F-labeled agent can accurately measure defect size similarly to the manner of PET.
Matsunari
I
I
The Medical and Pharmacological Research Center Foundation, Wo 32, Inoyama-town, Hakui-city, Ishikawa, 925-0613, Japan.
Yoneyama
T
T
Kanayama
S
S
Matsudaira
M
M
Nakajima
K
K
Taki
J
J
Nekolla
S G
SG
Tonami
N
N
Hisada
K
K
D019788:Fluorodeoxyglucose F18; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D009206:Myocardium / Q000473:pathology; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D012044:Regression Analysis; D014055:Tomography, Emission-Computed; D015899:Tomography, Emission-Computed, Single-Photon
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18