Rationale and Objectives
The aim of this study was to evaluate increased sampling intervals on cerebral dynamic perfusion computed tomographic (PCT) imaging calculated using software relying on the maximum slope model.
Materials and Methods
PCT data sets from 32 patients with suspected acute stroke were acquired with a sampling interval of 1 image/s. The PCT data sets were modified to simulate sampling intervals of 2, 3, and 4 seconds. Maps of cerebral blood flow (CBF), cerebral blood volume, and time to peak (TTP) were calculated using software relying on the maximum slope model. Parenchymal and vascular peak enhancement; absolute values of CBF, cerebral blood volume, and TTP in the nonischemic hemisphere; and ischemic area in the different perfusion maps were measured.
Results
Parenchymal peak enhancement of the nonischemic hemisphere was statistically significantly decreased in all simulated data sets with >1-second sampling intervals ( P < .001). Absolute CBF and TTP values in the nonischemic hemisphere were increased in all simulated data sets with >1-second sampling intervals ( P = .044–.001 and P = .008–.001, respectively). The ischemic area was significantly underestimated for CBF and TTP in all simulated data sets with >1-second sampling intervals ( P = .022–.005 and P = .019–.005, respectively).
Conclusions
Sampling intervals of >1 second on PCT imaging calculated using software relying on the maximum slope model significantly alter absolute CBF and TTP values and the size of ischemia in CBF and TTP. Thus, increasing the sampling interval on dynamic PCT imaging cannot be recommended in combination with this algorithm.
Computed tomographic (CT) imaging is still the method most widely available for imaging of acute stroke. In the past few years, perfusion CT (PCT) imaging has been increasingly used for the assessment of cerebral hemodynamics and has been implemented in multimodal CT stroke protocols .
On the basis of the calculation of different perfusion parameters from the dynamic data, PCT imaging enables the differentiation of tissue at risk from irreversibly damaged tissue and hence identifies the portion of potentially salvageable brain tissue . Thus, PCT imaging might be applicable for image-based therapy management in the future .
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Materials and methods
Overview
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PCT Protocol
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Simulation of Increased Sampling Intervals
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PCT Postprocessing
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Qualitative Evaluation
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Quantitative Evaluation
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Statistical Analysis
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Results
Qualitative Analysis
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Quantitative Analysis
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Table 1
Parenchymal and Vascular Peak Enhancement for Different Sampling Intervals
Sampling Interval (s) Parameter 1 2 3 4 Peak enhancement, nonischemic hemisphere (HU) Mean ± SD 46.2 ± 2.8 43.7 ± 2.3 43.8 ± 2.3 42.7 ± 2.5 Median (range) 46.3 (37.9–51.5) 43.8 (37.6–49.5) 43.8 (38.1–49.9) 43.2 (37.1–48.5)P <.001 ∗ <.001 ∗ <.001 ∗ Peak enhancement, superior sagittal sinus (HU) Mean ± SD 542.0 ± 121.3 533.6 ± 134.8 536.7 ± 135.0 536.5 ± 134.3 Median (range) 557.6 (295.9–740.2) 548.2 (245.5–776.0) 542.5 (254.2–758.5) 552.5 (282.1–750.7)P .073 .379 .822
HU, Hounsfield units; SD, standard deviation.
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Table 2
Absolute Perfusion Values of the Nonischemic Hemisphere for Different Sampling Intervals
Sampling Interval (s) Perfusion Parameter 1 2 3 4 CBF (mL · 100 g −1 · min −1 )n 32 32 30 23 Mean ± SD 56.8 ± 4.3 58.3 ± 6.4 57.9 ± 6.5 60.4 ± 5.3 Median (range) 56.3 (49.4–73.7) 58.0 (38.4–76.9) 58.4 (29.7–70.4) 59.6 (51.7–73.3)P .030 ∗ .044 ∗ .001 ∗ CBV (mL · 100 g −1 )n 32 32 30 23 Mean ± SD 3.40 ± 0.25 3.47 ± 0.27 3.43 ± 0.47 3.73 ± 0.59 Median (range) 3.38 (3.01–4.36) 3.44 (2.97–4.29) 3.47 (1.37–4.38) 3.66 (2.49–5.80)P .089 .140 <.001 ∗ TTP (s)n 32 32 30 23 Mean ± SD 9.5 ± 2.4 10.3 ± 2.8 10.8 ± 2.8 12.8 ± 3.5 Median (range) 8.8 (6.6–16.6) 9.8 (6.7–19.6) 9.9 (6.0–18.3) 12.2 (4.0–24.0)P .008 ∗ .002 ∗ <.001 ∗
CBF, cerebral blood flow; CBV, cerebral blood volume; SD, standard deviation; TTP, time to peak.
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Table 3
Threshold-Based Ischemic Area for Different Sampling Intervals in Patients with Proven Cerebral Infarctions
Paired Sampling Intervals CBF < 25 mL · 100 g −1 · min −1 (cm 2 ) CBV < 2.0 mL · 100 g −1 (cm 2 ) TTP (Visual) (cm 2 )n 15 15 15 1 s Mean ± SD 21.7 ± 10.8 17.7 ± 10.4 32.2 ± 14.2 Median (range) 18.3 (9.1–41.5) 15.1 (5.0–39.3) 35.2 (7.9–54.9) 2 s Mean ± SD 19.4 ± 11.6 17.1 ± 10.7 28.4 ± 12.3 Median (range) 15.6 (6.4–46.8) 13.1 (5.4–41.1) 32.5 (7.8–43.3)P .022 ∗ .733 .005 ∗ n 14 14 13 1 s Mean ± SD 22.3 ± 11.0 18.0 ± 10.7 32.2 ± 13.8 Median (range) 18.7 (9.1–41.5) 16.7 (5.0 –39.3) 18.3 (6.5–36.1) 3 s Mean ± SD 18.9 ± 10.7 17.5 ± 10.9 25.4 ± 12.0 Median (range) 16.1 (6.5–40.7) 13.7 (6.1–40.8) 17.9 (6.6–32.6)P .005 ∗ .550 .019 ∗ n 8 10 7 1 s Mean ± SD 25.1 ± 10.2 18.4 ± 9.4 33.1 ± 11.3 Median (range) 26.4 (11.2–39.2) 35.2 (7.9–54.9) 32.8 (14.2–50.4) 4 s Mean ± SD 20.9 ± 8.4 18.6 ± 9.6 19.3 ± 4.5 Median (range) 21.2 (9.7–32.9) 27.3 (6.8–42.8) 18.5 (11.9–24.8)P .012 ∗ .959 .018 ∗
CBF, cerebral blood flow; CBV, cerebral blood volume; SD, standard deviation; TTP, time to peak.
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Discussion
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Impact of Sampling Interval on Visual Perfusion Map Quality
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Impact of Sampling Interval on Peak Enhancement and Absolute Perfusion Values
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Impact of Sampling Interval on the Size of the Ischemic Area
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Limitations of This Study
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Conclusions
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