Error analysis of measured cerebral vascular response to acetazolamide stress by I-123-IMP autoradiographic method with single photon emission computed tomography: errors due to distribution volume of I-123-IMP.
OBJECTIVE
Iodine-123 (123I)-labeled N-isopropyl-p-iodoamphetamine (IMP) has been used as a cerebral blood flow (CBF) tracer for single-photon emission computed tomography (SPECT), and measurements of the CBF response to acetazolamide stress by SPECT with IMP are widely used to assess cerebral vascular reserve. To quantitate CBF by means of SPECT with IMP, an autoradiographic (ARG) method has been developed and is widely used. In the ARG method, CBF is calculated from the brain counts of the SPECT scan with an assumed distribution volume value of IMP (Vd). However, differences between true Vd and assumed Vd results in errors in calculated CBF. In the present study, errors in the CBF response to acetazolamide stress as calculated by the ARG method were investigated.


METHODS
SPECT studies were performed on 12 patients with steno-occlusive lesions of the major cerebral artery. Two studies were performed on separate days. The first study was performed at rest (baseline), and the second during acetazolamide stress. SPECT scans were performed at 40 min (early scan) and 180 min (delayed scan) after intravenous injection of IMP.


RESULTS
Although a simulation study showed that errors in calculated changes in CBF in response to acetazolamide stress, which result from differences between the true Vd and the assumed Vd, were larger when the baseline CBF and change in CBF were larger, values calculated by the ARG method with an assumed Vd were in good agreement with those calculated with true Vd obtained from early and delayed scan data.


CONCLUSIONS
These data indicate that errors in the calculated CBF response to acetazolamide stress as calculated by the ARG method are negligible even at high CBF responses. The ARG method is therefore reliable for measurement of CBF response to acetazolamide stress.
Ito
Hiroshi
H
Department of Nuclear Medicine and Radiology, Division of Brain Sciences, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan. hito@idac.tohoku.ac.jp
Inoue
Kentaro
K
Goto
Ryoi
R
Kinomura
Shigeo
S
Sato
Tachio
T
Kaneta
Tomohiro
T
Sato
Kazunori
K
Fukuda
Hiroshi
H
D000086:Acetazolamide; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001345:Autoradiography / Q000379:methods; D001921:Brain / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000378:metabolism; D002539:Cerebral Arterial Diseases / Q000000981:diagnostic imaging* / Q000378:metabolism; D002560:Cerebrovascular Circulation; D003627:Data Interpretation, Statistical; D003951:Diagnostic Errors; D005080:Exercise Test; D005260:Female; D015637:Gated Blood-Pool Imaging / Q000379:methods; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D020367:Iofetamine / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
D019275:Radiopharmaceuticals; D020367:Iofetamine; D000086:Acetazolamide