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Effects of Noise, Image Resolution, and ROI Definition on the Accuracy of Standard Uptake Values: A Simulation Study

PET Center, VU University Medical Center, Amsterdam, The Netherlands

View larger version (30K): [in a new window]   FIGURE 1. Recovery coefficients as function of sphere size for phantom data (A) and simulation data (B) and ROI values as function of maximum pixel value for phantom data (C) and simulated data (D). (A and B only) = maximum pixel value; = ROI70; = ROI0.5(BG+MAX); = ROI50; • = ROI15x15.

View larger version (21K): [in a new window]   FIGURE 2. Recovery coefficients as function of sphere size for various noise levels. = low NEC; = medium NEC; = high NEC. (A and B) No smoothing of images. (C and D) Smoothing of images. A and C represent maximum pixel value; B and D represent ROI50. Error bars equal 1 SD.

View larger version (23K): [in a new window]   FIGURE 3. Recovery coefficients for various ROIs. = maximum pixel value; = ROI70; • = ROI0.5(BG+MAX); = ROI50. A and C represent data for TBR = 2; B and D represent data for TBR = 8. (A and B) Nonsmoothed data. (C and D) Smoothed data. SEs varied from 9% to 4% and from 5% to 2% for 10- to 30-mm spheres for all ROI methods for nonsmoothed (A and B) and smoothed data (C and D), respectively.

View larger version (33K): [in a new window]   FIGURE 4. Measured residual uptake using various ROIs for simulated tumors showing a decrease in uptake only. (A and B) Nonsmoothed data. (C) Smoothed data. A and C give response of tumors with constant tumor size of 10-mm diameter; B and D show response of tumors with constant tumor size of 30 mm. Residual uptake was measured using maximum pixel value, ROI50, ROI70, ROI0.5(BG+MAX), and ROI15x15 as shown from left to right in each set of 5 bars. Error bars represent 1 SD. Missing bars in this figure correspond to missing data due to impossible ROI definition—that is, ROI enclosed entire patient.

View larger version (40K): [in a new window]   FIGURE 5. Measured residual uptake using various ROIs keeping tumor uptake constant. Max = maximum pixel value; 50% = ROI50; 70% = ROI70; 0.5BGM = ROI0.5(BG+MAX); 15x15 = ROI15x15. (A and B) No smoothing of image. (C and D) Smoothing of image. A and C represent tumor data with TBR = 2; B and D represent tumor data with TBR = 8. Reduction of diameter to 10, 15, and 20 mm and not at all (it stays 30 mm) is shown from left to right in each set of 4 bars. Missing bars in this figure correspond to missing data due to impossible ROI definition—that is, ROI enclosed entire patient.

View larger version (26K): [in a new window]   FIGURE 6. Effects of sinogram statistics on measured residual uptake for nonsmoothed data (A and B) and smoothed data (C and D), assuming constant tumor size of 10 mm (A and C) and 30 mm (B and D). Low, medium, and high NEC data are shown from left to right in each set of 3 bars.

View larger version (13K): [in a new window]   FIGURE 7. (A) Recovery coefficients determined using maximum pixel value within ROI as function of ROI size for various noise levels. = COV of 10%; = COV of 20%; • = COV of 35%; = COV of 50%. (B) Recovery coefficients based on maximum pixel value as function of ROI size for noise level = 35%. Error bars now illustrate variation of reproducibility (1 SD) as function of ROI size.