Rationale and Objectives
The aim of this study was to investigate the effect of scan duration on the measurement of blood flow (BF), blood volume (BV), and permeability–surface area product (PS) in patients undergoing computed tomography (CT) perfusion for brain tumors.
Materials and Methods
CT perfusion scans were performed in 14 patients with malignant glioma. Patients were scanned for 150 seconds, and BF, BV, and PS were assessed for scan durations of 150, 120, 90, and 60 seconds. Systematic, random, and percentage errors associated with shorter scan durations were calculated. Repeated-measures analyses of variance with paired t tests were used to compare the perfusion values measured from different scan durations. Systematic and random errors were correlated with scan duration.
Results
No effect of scan duration on BF and BV values was noted ( P > .05). PS values were not affected by scan duration except in the tumor rim, in which they were significantly higher at 60 seconds ( P < .01). Median percentage error was highest at 60 seconds for tumor core PS (median, 32.1%; interquartile range, 16.5%–43.0%). Tumor rim BV and PS and tumor core BF were correlated with scan durations ( r = 0.42, −0.50, and −0.50, respectively; P < .01). Random errors were negatively correlated with scan durations for all tissue types ( P ≤ .01) except for white matter BV.
Conclusions
A scan duration of ≤60 seconds is not warranted for the measurement of PS in brain tumors. A scan duration of ≥90 seconds is recommended.
Malignant gliomas are highly aggressive brain tumors that are characterized by increased vascularity with immature and highly permeable blood vessels . Given that blood-brain barrier disruption and neovascularity play an essential role in the progression of malignant gliomas, recent studies have investigated the use of perfusion imaging for evaluating brain tumors. Blood flow (BF), blood volume (BV), and permeability–surface area product (PS) obtained from computed tomography (CT) perfusion studies have been demonstrated to be useful in differentiating glioma grade and distinguishing treatment-induced necrosis from recurrent or progressive tumors . CT perfusion parameters have also demonstrated correlations with microvascular cellular proliferation and proangiogenic gene expressions .
Although CT perfusion may be helpful in providing important physiologic information for evaluating brain tumors, there is no consensus regarding the optimal scan protocol. A scan duration of ≥2 minutes has been suggested for accurate calculation of tumor permeability , but scan durations in the range of 45 to 199 seconds have been used to evaluate tumor perfusion parameters for brain and other tumor sites . For example, a 65-second scan was recommended when the Johnson-Wilson model was used for the calculation of permeability (ie, PS) in colorectal cancer , while a scan duration of ≥40 seconds was recommended when the Patlak method was used to calculate permeability (ie, K trans , flow-extraction product) in lung cancer .
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Materials and methods
CT Perfusion Imaging
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Image Analysis
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Measurement Errors of Perfusion Parameters Due to Truncation
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Statistical Analysis
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Results
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Table 1
Median (Interquartile Range) Percentage Errors Associated with Scan Durations of <150 Seconds
Parameter Scan Duration (seconds) Gray Matter White Matter Tumor Rim Tumor Core Blood flow 60 2.7 (1.9–4.5) 4.3 (3.3–5.9) 7.9 (6.0–10.3) 10.6 (8.7–16.8) 90 2.4 (1.5–3.3) 2.9 (2.6–4.4) 4.7 (3.1–6.3) 6.1 (5.2–7.1) 120 1.6 (1.2–2.2) 2.3 (2.0–2.9) 3.2 (2.5–3.8) 4.0 (2.6–6.6) Blood volume 60 1.0 (0.7–2.0) 2.1 (1.5–3.1) 5.8 (4.8–7.5) 13.9 (8.1–21.4) 90 0.9 (0.6–1.1) 1.6 (1.1–3.0) 3.3 (2.4–4.3) 7.6 (4.7–9.6) 120 0.5 (0.4–0.9) 0.9 (0.7–1.6) 2.0 (1.4–2.4) 4.2 (2.4–6.9) Permeability–surface area product 60 29.2 (21.3–32.8) 28.7 (24.2–34.3) 21.9 (17.1–28.6) 32.1 (16.5–43.0) 90 22.0 (15.4–30.5) 21.7 (12.5–27.6) 11.3 (7.9–16.0) 19.3 (11.3–24.3) 120 15.5 (13.3–17.6) 16.6 (11.0–20.3) 6.4 (4.0–8.1) 9.6 (4.9–12.7)
Table 2
Spearman’s Rank Correlation of Systematic and Random Errors with Scan Duration
Error Type Tissue Type Blood Flow Blood Volume Permeability–Surface Area Product Systematic error Gray matter −0.01 −0.09 −0.19 White matter −0.12 −0.06 −0.19 Tumor rim −0.30 0.42 † −0.50 † Tumor core −0.50 † 0.15 −0.13 Random error Gray matter −0.43 † −0.34 ∗ −0.54 † White matter −0.47 † −0.25 −0.56 † Tumor rim −0.50 † −0.53 † −0.62 † Tumor core −0.60 † −0.46 † −0.64 †
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Discussion
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Conclusions
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