Article Figures & Data
Figures
- Fig 1.
Region-of-interest placement. Lesion (red) and contralateral (green) regions of interest from 1 patient are superimposed on the diffusion-weighted image that was used for their placement (left) and the perfusion source image to which they were subsequently transferred (right).
- Fig 2.
Visual appearance of truncation artifacts resulting from scans of different durations. Sample perfusion maps produced from a single patient's perfusion data, which have been truncated to simulate perfusion scans of 2 different durations that are similar to those in common clinical use: 45.5 seconds (top row) and 90.5 seconds (bottom row) following contrast injection. The CBV map from the shorter 45.5-second scan shows a low-CBV lesion in the right frontal lobe (arrows, top row). However, the more accurate CBV map produced from the longer scan shows elevated rather than reduced CBV (arrows, bottom row). CBF maps produced from the 2 scan durations show little appreciable difference. The MTT map from the truncated scan shows almost no lesion, but there is a sizeable lesion with prolonged MTT in the map produced from the longer scan. The Tmax maps produced from the 2 scan durations show subjectively appreciable lesions of similar sizes. However, the color legend at the right of the figure shows that the abnormal Tmax values produced by the shorter scan are <6 seconds, so this tissue would not be classified as “at risk” by studies that use that threshold, whereas the longer scan produced a large lesion with Tmax values above the 6-second threshold.
- Fig 3.
Quantitative measurement of truncation artifacts caused by scans of different durations. Mean values of the 3 different CBV measurements (A), the 2 different CBF measurements (B), the 4 different MTT measurements (C), and the 2 different Tmax measurements (D), averaged across all patients, for scan durations ranging from 39.5 to 110 seconds after contrast injection. The curves in each graph were fitted by logarithmic regression, which showed a significant (P < .001) decrease in every calculated parameter with decreasing scan time. However, the magnitude of this reduction was much smaller for CBF than for the other parameters.
- Fig 4.
Artifactual effect of truncation on Tmax lesion volumes. Volumes of tissue with calculated Tmax values of >6 seconds averaged across all patients, for scan durations ranging from 39.5 to 110 seconds after contrast injection. The curves in each graph were fitted by logarithmic regression, which showed a significant (P < .001) reduction in both sTmax and oTmax with decreasing scan duration.
- Fig 5.
Change in Tmax lesion volume resulting from truncation artifacts. Tmax maps produced from a single patient's perfusion data, which have been truncated to simulate perfusion scans of 2 different durations that are similar to those in common clinical use: 45.5 seconds (left) and 90.5 seconds (right) following contrast injection. High-contrast window settings were used to depict pixels with a Tmax of >6 seconds as white and other pixels as black. The 90.5-second scan demonstrates a large lesion that would be considered “at risk” by using the 6-second criterion and could potentially make the patient eligible for thrombolytic therapy. The 45.5-second scan shows a much smaller Tmax lesion. Tmax lesion sizes measured across all image sections for this patient were 430.2 mL for the 90.5-second scan and 79.2 mL for the 45.5-second scan.
Tables
Hemodynamic Measurement Deconvolution Algorithm Function Used for CBV Integration t-statistic Slopea Potential Truncation Effectb Lesion Reversal Frequency CBVc None Concentration 41.53 1.08/log10(s) 47.6% 37% (21/57) sCBVr sSVD Response 17.99 1.46/log10(s) 64.2% 35% (20/57) oCBVr oSVD Response 16.72 1.17/log10(s) 51.4% 46% (26/57) sCBF sSVD NA 9.62 0.09/log10(s) 4.10% 4% (2/57) oCBF oSVD NA 3.58 0.04/log10(s) 1.96% 2% (1/57) sMTTc sSVD Concentration 34.49 3.03/log10(s) 133% 47% (27/57) sMTTr sSVD Response 35.57 3.73/log10(s) 164% 28% (16/57) oMTTc oSVD Concentration 42.50 3.79/log10(s) 166% 54% (31/57) oMTTr oSVD Response 51.15 4.67/log10(s) 205% 39% (22/57) sTmax sSVD NA 25.91 14.10/log10(s) 6.19 seconds 44% (25/57) oTmax oSVD NA 28.62 18.2/log10(s) 8.00 seconds 42% (24/57) Note:—NA indicates not applicable.
↵a The slopes of all 11 hemodynamic parameters with respect to the logarithm of scan duration were significantly greater than zero (P < .001). Therefore, t-statistics rather than P values are reported.
↵b “Potential truncation effect” refers to the expected reduction in the calculated parameter value that would result from decreasing the scan duration from 110 seconds to 40 seconds postinjection. For example, if the CBVc value derived from a 110-second scan were 107.6% of normal, the expected CBVc using a 40-second scan would be 60.0% of normal.
- Table 2:
Regression-derived effects of scan duration on the volume of brain tissue with Tmax greater than 6 seconds
Hemodynamic Measurement Deconvolution Algorithm t-statistic Lesion Volume Slopea Potential Truncation Effectb sTmax sSVD 44.21 162.7 mL/log10(s) 71.5 mL oTmax oSVD 47.94 213.4 mL/log10(s) 93.8 mL ↵a The slopes of sTmax and oTmax lesion volumes with respect to the logarithm of scan duration were both significantly greater than zero with P < .001. Therefore, t-statistics rather than P values are reported.
↵b “Potential truncation effect” reflects the expected decrease in the lesion volume that would result from decreasing the scan duration from 110 seconds to 40 seconds postinjection. For example, if the volume of an oTmax lesion were measured to be 150 mL using a 110-second scan, the expected lesion volume derived from a 40-second scan would be 56.2 mL.
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