Article Figures & Data
Figures
- Fig 1.
Representative reference scan at 190 mAs (A) and simulated 44-mAs scan (B) in a single section of a CTP examination. Dose reduction, achieved through tube current reduction, primarily results in increased image noise, demonstrated as increased “graininess” in the simulated 44-mAs scan.
- Fig 2.
A representative blood volume map obtained in a single participant. The map shows placement of 26 uniform regions of interest: 12 in the right lobe, 12 in the left lobe, and 1 each over the right and left basal ganglia. Similar ROIs were placed over each section of a CTP dataset. The positions of ROIs from all sections in a given reference dataset were saved as a template and then were pasted onto the 5 generated noise datasets, ensuring perfect uniformity of position.
- Fig 3.
Frequency of quality scores assigned by the 6 observers to noise datasets at each noise level for (A) CBF (Spearman rank coefficient = −0.34; P < .0001), (B) CBV (Spearman rank coefficient = −0.35; P < .0001), and (C) MTT (Spearman rank coefficient = −0.44; P < .0001).
Tables
Noise Level Added Noise Distribution, σ(add) Simulated Exposure, E2 (Range) (mAs) 1 0.8 188 (187–188) 2 2.0 177 (174–180) 3 2.8 167 (161–171) 4 5.3 127 (116–135) 5 13.7 44 (36–51) Note:—The range is determined using noise values of the reference scans at 1 SD above and below the mean, σ(E1) = 7.5 ± 0.8.
E2 indicates second exposure level.
- Table 2:
Difference of least square means in perfusion parameters between reference dataset and noise datasets across all ROIs in all participants and across ROIs in participants with perfusion abnormalities (subanalysis)
Perfusion Parameter Simulated Exposure (mAs) All ROIs Only in ROIs with Perfusion Abnormalities Difference from Reference Dataset Standard Error P Adj P Difference from Reference Dataset Standard Error P Adj P CBF (mL/100 g/min) 188 −0.12 0.68 .87 >.99 −0.35 0.86 .69 >.99 177 −0.20 0.68 .77 >.99 −0.22 0.86 .80 >.99 167 −0.72 0.68 .29 .73 −0.67 0.86 .44 .90 127 −0.60 0.68 .38 .85 −0.01 0.86 .99 >.99 44 −1.81 0.68 .01 .04 0.47 0.86 .58 .97 CBV (mL/100 g/min) 188 0.00 0.02 .89 >.99 −0.01 0.02 .74 >.99 177 0.00 0.02 .91 >.99 0.00 0.02 .99 >.99 167 0.00 0.02 .92 >.99 0.00 0.02 .93 >.99 127 0.02 0.02 .26 .68 0.01 0.02 .62 .98 44 0.07 0.02 <.0001 <.001 0.10 0.02 <.0001 <.0001 MTT (sec) 188 0.00 0.06 .94 >.99 0.03 0.10 .79 >.99 177 0.02 0.06 .74 >.99 0.05 0.10 .66 >.99 167 0.06 0.06 .32 .78 0.07 0.10 .47 .92 127 0.11 0.06 .08 .28 0.07 0.10 .51 .95 44 0.46 0.06 <.0001 <.001 0.33 0.10 .00 .01 Note:—ROIs with perfusion abnormalities were identified by a trained neuroradiologist (P.S.) with 12 years of experience.
Adj P indicates adjusted P value.
- Table 3:
Coefficient of variance of perfusion parameters in noise datasets generated in 6 trials at each noise level
Simulated Exposure (mAs) Coefficient of Variance (%) CBF CBV MTT 188 1.3 0.3 1.2 177 2.1 0.7 1.9 167 3.2 0.9 2.9 127 4.1 1.9 4.6 44 7.1 4.5 6.7 Note:—Coefficient of variance is defined as SD/mean × 100.
Simulated Exposure (mAs) Mean PABAK Score of CBF Maps (range) Mean PABAK Score of CBV Maps (range) Mean PABAK Score of MTT Maps (range) 188 0.95 (0.88-1) 1.00 (1-1) 0.83 (0.70-0.98) 177 0.98 (0.93-1) 1.00 (1-1) 0.86 (0.70-0.98) 167 0.98 (0.93-1) 1.00 (1-1) 0.88 (0.73-1) 127 0.95 (0.88-1) 1.00 (1-1) 0.74 (0.43-1) 44 0.51 (0.18-0.93) 0.83 (0.58-1) 0.05 (−0.87-0.68)
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