Rationale and Objectives
To assess the effect of measurement time on blood flow (BF), blood volume (BV), and k-trans-values (flow extraction product) in patients undergoing volume perfusion computed tomography (VPCT) for lung cancer.
Materials and Methods
This prospective study was approved by our local Research Ethics Committee and informed consent was obtained in all patients. Between December 2009 and December 2010, 75 VPCT scans were obtained in 54 consecutive patients (15 women, 39 men) with histologically confirmed lung cancer. A 64-second VPCT of the tumor (80 kV, 60 mAs) using 128 × 0.6-mm collimation, 6.9-cm z-axis coverage and a total of 26 volume measurements, was performed. BF, BV, and K trans were determined. Data evaluation was performed for different measurement times (64 seconds, 45 seconds, 39 seconds, and 36 seconds) by removing the last two, four, and five scans and repeating the analysis. A one-way repeated-measures analysis of variance was used to test for effects of measurement time on BF, BV, and k-trans and unpaired/paired Student t -tests were applied for comparisons within/between groups, respectively.
Results
No effect of measurement time on BF values was noted ( P > .05), whereas a significant decrease of BV values (at 39 seconds: 71% ± 2% of 64-second values) and a significant increase of k-trans-values (at 39 seconds: 146% ± 8% of 64-second values) were observed with progressively shortened measurement time ( P < .05, respectively). Additionally, with reduced measurement time, the increase in k-trans-values was significantly more pronounced in those patient groups with higher BV (at 39 seconds: 171% ± 15% versus 120% ± 3% of 64-second measurements), and those with lower k-trans (at 39 seconds: 167% ± 16% versus 126% ± 4% of 64-second measurements) ( P < .05, respectively).
Conclusion
Whereas estimation of BF in lung cancer was independent from VPCT measurement time within the chosen ranges, approximation of both BV and k-trans was affected by measurement duration. A fixed measurement time of 40 seconds is recommended.
In the functional assessment of a tumor, two properties are best prone for evaluation: its metabolic activity, which is readily appreciated by molecular imaging techniques, such as positron emission tomography (PET), and its vascular characteristics (ie, perfusion and vessel wall permeability), which can be approximated by volume perfusion computed tomography (VPCT) as well as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and DCE ultrasound (DCE-US) . Whereas PET imaging and its applications in oncology have been extensively investigated , the significance of VPCT has scarcely been explored.
Contrast-enhanced VPCT measures changes in tissue density over time. After intravenous injection of contrast material, repeated CT scans of the tissue volume being studied are performed. The density/time curves of two structures are compared: a region of interest (ROI) is placed on the afferent artery, and a volume of interest (VOI) on the tumor being analyzed . A two-compartment model (Patlak analysis) can be used to evaluate dynamics of contrast medium. Initially, the contrast material remains predominantly intravascular and therefore can be used to measure perfusion . Over time, it leaks out of the intravascular space into the interstitium, which can be used to estimate permeability also known as transit constant (k-trans or flow extraction product, defined as the sum of the flow within the microvasculature and capillary permeability) . Only 1%–2% of an administered dose enters the intracellular space, an amount that can readily be neglected .
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Materials and methods
Patients and Lesions
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CT Protocol
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Quantitative Perfusion Assessment
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Tumor Size and Location
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Statistics
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Results
Mean BF, BV, and k-trans
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BF, BV, and k-trans Values—Changes Through Different Measurement Times
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Changes in k-trans Values—Dependence on Absolute BV and K-trans
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Discussion
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Conclusion
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