Indicator measurement in tissues: CT with iohexol versus storage-phosphor autoradiography with carbon-14-labeled inulin.
OBJECTIVE
Computed tomography (CT) provides accurate measurement of blood iodine concentration in vivo, as well as in phantoms simulating tissue; however, its ability to measure radiopaque agents in biologic tissues in comparison with a standard technique does not seem to have been demonstrated. To validate the performance of CT imaging for quantification of contrast media in a variety of biologic tissues in vivo, a comparison between CT imaging with an iodinated contrast agent (iohexol) and the reference tracer quantification technique (storage-phosphor autoradiography with carbon-14-labeled inulin) was performed.


METHODS
Six New Zealand White rabbits were injected intravenously with a cocktail of iohexol and C-14-labeled inulin at different dose ratios and sacrificed shortly after injection to arrest blood flow at different stages of tissue tracer distribution. One rabbit received no iohexol-inulin mixture and provided baseline data. Liver, spleen, kidneys, testis, and heart were excised and rapidly frozen. Each organ was scanned with CT (1-mm contiguous sections) to determine tissue iodine distribution. Twenty-micrometer tissue slices were made in the same planes in which the CT images had been acquired, and storage-phosphor screen autoradiography was performed to quantify C-14-labeled inulin distribution.


RESULTS
Digital image analysis of CT images and autoradiograms was performed on spatially matched regions, and resultant tracer concentrations were compared. Tracer concentrations were highly correlated, with resultant R2 values exceeding 0.9 in all tissues.


CONCLUSIONS
The highly correlated results for iodinated tracer quantification in tissues for CT versus those obtained with the reference technique validate the performance of CT as an accurate means of measuring concentration of radiopaque agent in tissue, independent of tracer dose.
Whiteman
K R
KR
Department of Radiology, Massachusetts General Hospital, Charlestown 02129, USA.
Wolf
G L
GL
D000818:Animals; D001345:Autoradiography; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics*; D003287:Contrast Media / Q000493:pharmacokinetics*; D007444:Inulin / Q000493:pharmacokinetics*; D007472:Iohexol / Q000493:pharmacokinetics*; D007677:Kidney Function Tests; D008297:Male; D011817:Rabbits; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014057:Tomography, X-Ray Computed
D002250:Carbon Radioisotopes; D003287:Contrast Media; D007472:Iohexol; D007444:Inulin