Partial-volume correction in PET: validation of an iterative postreconstruction method with phantom and patient data.
Partial-volume errors (PVEs) in PET can cause incorrect estimation of radiopharmaceutical uptake in small tumors. An iterative postreconstruction method was evaluated that corrects for PVEs without a priori knowledge of tumor size or background.


METHODS
Volumes of interest (VOIs) were drawn on uncorrected PET images. PVE-corrected images were produced using an iterative 3-dimensional deconvolution algorithm and a local point spread function. The VOIs were projected on the corrected image to estimate the PVE-corrected mean activity concentration. These corrected mean values were compared with uncorrected maximum and mean values. Simulated data were generated as a first test of the correction algorithm. Phantom measurements were made using (18)F-FDG-filled spheres in a scattering medium. Clinical validation used 154 surrogate tumors from 9 patients. The surrogate tumors were blood-pool images of the descending aorta as well as mesenteric and iliac arteries and veins. Surrogate tumors ranged in diameter from 5 to 25 mm. Analysis used (18)F-FDG and (11)C-CO datasets (both dynamic and static). Values representing "truth" were derived from imaging the blood pool in large structures (e.g., the left ventricle, left atrium, or sections of the aorta) where PVEs were negligible. Surrogate tumor sizes were measured from contrast CT.


RESULTS
The PVE-correction technique, when applied to the mean value in spheric phantoms, yielded recovery coefficients of 87% for an 8-mm-diameter sphere and between 100% and 103% for spheres between 13 and 29 mm. For the human studies, PVE-corrected data recovered a large fraction of the true activity concentration (86% +/- 7% for an 8-mm-diameter tumor and 98% +/- 8% for tumors between 10 and 24 mm). For tumors smaller than 18 mm, the PVE-corrected mean values were less biased (P<0.05) than the uncorrected maximum or mean values.


CONCLUSIONS
Iterative postreconstruction PVE correction generated more accurate uptake measurements in subcentimeter tumors for both phantoms and patients than the uncorrected values. The method eliminates the requirement for segmenting anatomic data and estimating tumor metabolic size or tumor background level. This technique applies a PVE correction to the mean voxel value within a VOI, yielding a more accurate estimate of uptake than the maximum voxel value.
Teo
Boon-Keng
BK
Department of Radiology, University of California, San Francisco, San Francisco, CA 94107, USA. kteo@radiology.ucsf.edu
Seo
Youngho
Y
Bacharach
Stephen L
SL
Carrasquillo
Jorge A
JA
Libutti
Steven K
SK
Shukla
Himanshu
H
Hasegawa
Bruce H
BH
Hawkins
Randall A
RA
Franc
Benjamin L
BL
D000465:Algorithms; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary*; D008297:Male; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity