Perfusion CT and US of colorectal cancer liver metastases: a correlative study of two dynamic imaging modalities

Radiomics Response Signature for Identification of Metastatic Colorectal Cancer Sensitive to Therapies Targeting EGFR Pathway

BACKGROUND

The authors sought to forecast survival and enhance treatment decisions for patients with liver metastatic colorectal cancer by using on-treatment radiomics signature to predict tumor sensitiveness to irinotecan, 5-fluorouracil, and leucovorin (FOLFIRI) alone (F) or in combination with cetuximab (FC).

METHODS

We retrospectively analyzed 667 metastatic colorectal cancer patients treated with F or FC. Computed tomography quality was classified as high (HQ) or standard (SD). Four datasets were created using the nomenclature (treatment) - (quality). Patients were randomly assigned (2:1) to training or validation sets: FCHQ: 78:38, FCSD: 124:62, FHQ: 78:51, FSD: 158:78. Four tumor-imaging biomarkers measured quantitative radiomics changes between standard of care computed tomography scans at baseline and 8 weeks. Using machine learning, the performance of the signature to classify tumors as treatment sensitive or treatment insensitive was trained and validated using receiver operating characteristic (ROC) curves. Hazard ratio and Cox regression models evaluated association with overall survival (OS).

RESULTS

The signature (area under the ROC curve [95% confidence interval (CI)]) used temporal decrease in tumor spatial heterogeneity plus boundary infiltration to successfully predict sensitivity to antiepidermal growth factor receptor therapy (FCHQ: 0.80 [95% CI = 0.69 to 0.94], FCSD: 0.72 [95% CI = 0.59 to 0.83]) but failed with chemotherapy (FHQ: 0.59 [95% CI = 0.44 to 0.72], FSD: 0.55 [95% CI = 0.43 to 0.66]). In cetuximab-containing sets, radiomics signature outperformed existing biomarkers (KRAS-mutational status, and tumor shrinkage by RECIST 1.1) for detection of treatment sensitivity and was strongly associated with OS (two-sided P < .005).

CONCLUSIONS

Radiomics response signature can serve as an intermediate surrogate marker of OS. The signature outperformed known biomarkers in providing an early prediction of treatment sensitivity and could be used to guide cetuximab treatment continuation decisions.

Dynamic Contrast-Enhanced Ultrasound of Gastric Cancer: Correlation with Perfusion CT and Histopathology

Objective

To assess the relationship between contrast-enhanced ultrasound (CEUS) parameters and perfusion CT (PCT) parameters of gastric cancers and their correlation with histologic features.

Materials and Methods

This prospective study was approved by our Institutional Review Board. We included 43 patients with pathologically-proven gastric cancers undergoing CEUS using SonoVue® (Bracco) and PCT on the same day. Correlation between the CEUS parameters (peak intensity [PI], area under the curve [AUC], rise time [RT] from 10% to 90% of PI, time to peak [TTP_US], and mean transit time [MTT_US]) and PCT parameters (blood flow, blood volume, TTP_CT, MTT_CT, and permeability surface product) of gastric cancers were analyzed using Spearman's rank correlation test. In cases of surgical resection, the CEUS and PCT parameters were compared according to histologic features using Mann-Whitney test.

Results

CEUS studies were of diagnostic quality in 88.4% (38/43) of patients. Among the CEUS parameters of gastric cancers, RT and TTP_US showed significant positive correlations with TTP_CT (rho = 0.327 and 0.374, p = 0.045 and 0.021, respectively); PI and AUC were significantly higher in well-differentiated or moderately-differentiated tumors (n = 4) than poorly-differentiated tumors (n = 18) (p = 0.026 and 0.033, respectively), whereas MTT_CT showed significant differences according to histologic types (poorly cohesive carcinoma [PCC] vs. non-PCC), T-staging (≤ T2 vs. ≥ T3), N-staging (N0 vs. N-positive), and epidermal growth factor receptor expression (≤ faint vs. ≥ moderate staining) (p values < 0.05).

Conclusion

In patients with gastric cancers, CEUS is technically feasible for the quantification of tumor perfusion and may provide correlative and complementary information to that of PCT, which may allow prediction of histologic features.

Better understanding of acute gouty attack using CT perfusion in a rabbit model

OBJECTIVE

To assess hemodynamic changes related to acute gouty knee arthritis in a rabbit with CT perfusion (CTP) METHODS: Forty-two rabbits were randomly separated into two groups: the treated group of 30 and the control group of 12. The right knee was injected with monosodium urate solution and polymyxin in the treated group and saline and polymyxin in the control group. At 2, 16, 32, 48, 60, and 72 h after injection, five rabbits from the treated group and two rabbits from the control group were selected for CTP. At each time point, blood flow (BF), blood volume (BV), and clearance rate (CL) were measured, and microvessel density (MVD) was evaluated with a microscope.

RESULTS

In the treated group, BF, BV, CL, and MVD were significantly higher than in the control group (p < 0.001). Differences within paired comparison of BV, BF, CL, and MVD were all significant (all p < 0.001). Peak time of BV, BF, and MVD was 32 h and 48 h for CL. After multivariate stepwise linear regression analysis, BV was linearly associated with MVD and vice versa, which also applied to BF with MVD and BF with CL, separately. The ascending rate of MVD was the highest among that of all parameters; so was the descending rate of CL.

CONCLUSION

CTP in this rabbit knee model accurately detected hemodynamic changes during a gouty attack.

KEY POINTS

• Acute gouty arthritis can be evaluated with CTP in a rabbit knee model. • Following injection of MSU crystals, producing an acute gouty attack, CTP successfully assessed hemodynamic changes. • The ascending rate of MVD was the highest among that of all parameters; so was the descending rate of CL.

Dynamic Three-Dimensional Contrast-Enhanced Ultrasound to Predict Therapeutic Response of Radiofrequency Ablation in Hepatocellular Carcinoma: Preliminary Findings

BACKGROUND & AIMS

To investigate the value of dynamic three-dimensional contrast-enhanced ultrasound (3D-CEUS) in the assessment of therapeutic response of hepatocellular carcinoma (HCC) treated with radiofrequency ablation (RFA).

METHODS

Forty-two patients (31 men and 11 women; mean age (52.1 ± 13.1 years)) with 42 clinical diagnosed HCC lesions (size range 14-48 mm; mean size 28.4 ± 9.9 mm) treated by RFA were included. All patients underwent two-dimensional contrast-enhanced ultrasound (2D-CEUS) and 3D-CEUS 1 month after treatment. Two radiologists assessed the absence (complete response, CR) or presence (residual tumor, RT) of any arterially hyperenhancing nodules within or along the margin of the treated HCC lesions. Complete response on magnetic resonance (MR) imaging acted as standard of reference (SOR).

RESULTS

After RFA treatment, 3D-CEUS was successfully conducted in 34 HCC lesions. CR was observed on both 2D-CEUS and 3D-CEUS in 25/42 (59.5%) HCC and RT in 6/42 (14.3%) HCC lesions. In 3/42 (7.1%) HCC lesion, RT was documented by SOR and 3D-CEUS, but it was not appreciable at 2D-CEUS. In 3/42 (7.1%) HCC lesion, the presence of peripheral RT was suspected by both 2D-CEUS and 3D-CEUS, but it was not confirmed by SOR. No statistically significant difference between 2D-CEUS and 3D-CEUS in depicting either CR or RT was found (P = 0.25). Combined with dynamic 3D-CEUS, the diagnostic accuracy was improved from 85.7% to 92.9%.

CONCLUSIONS

3D-CEUS might be helpful in better diagnostic performance in the assessment of therapeutic response of HCC treated after RFA.

Advanced Imaging Techniques in Evaluation of Colorectal Cancer

Imaging techniques are clinical decision-making tools in the evaluation of patients with colorectal cancer (CRC). The aim of this article is to discuss the potential of recent advances in imaging for diagnosis, prognosis, therapy planning, and assessment of response to treatment of CRC. Recent developments and new clinical applications of conventional imaging techniques such as virtual colonoscopy, dual-energy spectral computed tomography, elastography, advanced computing techniques (including volumetric rendering techniques and machine learning), magnetic resonance (MR) imaging-based magnetization transfer, and new liver imaging techniques, which may offer additional clinical information in patients with CRC, are summarized. In addition, the clinical value of functional and molecular imaging techniques such as diffusion-weighted MR imaging, dynamic contrast material-enhanced imaging, blood oxygen level-dependent imaging, lymphography with contrast agents, positron emission tomography with different radiotracers, and MR spectroscopy is reviewed, and the advantages and disadvantages of these modalities are evaluated. Finally, the future role of imaging-based analysis of tumor heterogeneity and multiparametric imaging, the development of radiomics and radiogenomics, and future challenges for imaging of patients with CRC are discussed. Online supplemental material is available for this article. ^©RSNA, 2018.

Perfusion imaging of colorectal liver metastases treated with bevacizumab and stereotactic body radiotherapy

Stereotactic body radiotherapy (SBRT) and bevacizumab are used in the treatment of colorectal liver metastases. This study prospectively evaluated changes in perfusion of liver metastases in seven patients treated with both bevacizumab and SBRT. Functional imaging using dynamic contrast-enhanced CT perfusion and contrast-enhanced ultrasound were performed at baseline, after bevacizumab, and after SBRT. After bevacizumab, a significant decrease was found in permeability (−28%, p < .05) and blood volume (−47%, p < .05), while SBRT led to a significant reduction in permeability (−22%, p < .05) and blood flow (−37%, p < .05). This study demonstrates that changes in perfusion can be detected after bevacizumab and SBRT.

Three-dimensional Dynamic Contrast-enhanced US Imaging for Early Antiangiogenic Treatment Assessment in a Mouse Colon Cancer Model

PURPOSE

To evaluate feasibility and reproducibility of three-dimensional (3D) dynamic contrast material-enhanced (DCE) ultrasonographic (US) imaging by using a clinical matrix array transducer to assess early antiangiogenic treatment effects in human colon cancer xenografts in mice.

MATERIALS AND METHODS

Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. Three-dimensional DCE US imaging with two techniques (bolus and destruction-replenishment) was performed in human colon cancer xenografts (n = 38) by using a clinical US system and transducer. Twenty-one mice were imaged twice to assess reproducibility. Seventeen mice were scanned before and 24 hours after either antiangiogenic (n = 9) or saline-only (n = 8) treatment. Data sets of 3D DCE US examinations were retrospectively segmented into consecutive 1-mm imaging planes to simulate two-dimensional (2D) DCE US imaging. Six perfusion parameters (peak enhancement [PE], area under the time-intensity curve [AUC], time to peak [TTP], relative blood volume [rBV], relative blood flow [rBF], and blood flow velocity) were measured on both 3D and 2D data sets. Percent area of blood vessels was quantified ex vivo with immunofluorescence. Statistical analyses were performed with the Wilcoxon rank test by calculating intraclass correlation coefficients and by using Pearson correlation analysis.

RESULTS

Reproducibility of both 3D DCE US imaging techniques was good to excellent (intraclass correlation coefficient, 0.73-0.86). PE, AUC, rBV, and rBF significantly decreased (P ≤ .04) in antiangiogenic versus saline-treated tumors. rBV (r = 0.74; P = .06) and rBF (r = 0.85; P = .02) correlated with ex vivo percent area of blood vessels, although the statistical significance of rBV was not reached, likely because of small sample size. Overall, 2D DCE-US overestimated and underestimated treatment effects from up to 125-fold to170-fold compared with 3D DCE US imaging. If the central tumor plane was assessed, treatment response was underestimated up to threefold or overestimated up to 57-fold on 2D versus 3D DCE US images.

CONCLUSION

Three-dimensional DCE US imaging with a clinical matrix array transducer is feasible and reproducible to assess tumor perfusion in human colon cancer xenografts in mice and allows for assessment of early treatment response after antiangiogenic therapy.

Three-dimensional Dynamic Contrast-enhanced US Imaging for Early Antiangiogenic Treatment Assessment in a Mouse Colon Cancer Model

PURPOSE

To evaluate feasibility and reproducibility of three-dimensional (3D) dynamic contrast material-enhanced (DCE) ultrasonographic (US) imaging by using a clinical matrix array transducer to assess early antiangiogenic treatment effects in human colon cancer xenografts in mice.

MATERIALS AND METHODS

Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. Three-dimensional DCE US imaging with two techniques (bolus and destruction-replenishment) was performed in human colon cancer xenografts (n = 38) by using a clinical US system and transducer. Twenty-one mice were imaged twice to assess reproducibility. Seventeen mice were scanned before and 24 hours after either antiangiogenic (n = 9) or saline-only (n = 8) treatment. Data sets of 3D DCE US examinations were retrospectively segmented into consecutive 1-mm imaging planes to simulate two-dimensional (2D) DCE US imaging. Six perfusion parameters (peak enhancement [PE], area under the time-intensity curve [AUC], time to peak [TTP], relative blood volume [rBV], relative blood flow [rBF], and blood flow velocity) were measured on both 3D and 2D data sets. Percent area of blood vessels was quantified ex vivo with immunofluorescence. Statistical analyses were performed with the Wilcoxon rank test by calculating intraclass correlation coefficients and by using Pearson correlation analysis.

RESULTS

Reproducibility of both 3D DCE US imaging techniques was good to excellent (intraclass correlation coefficient, 0.73-0.86). PE, AUC, rBV, and rBF significantly decreased (P ≤ .04) in antiangiogenic versus saline-treated tumors. rBV (r = 0.74; P = .06) and rBF (r = 0.85; P = .02) correlated with ex vivo percent area of blood vessels, although the statistical significance of rBV was not reached, likely because of small sample size. Overall, 2D DCE-US overestimated and underestimated treatment effects from up to 125-fold to170-fold compared with 3D DCE US imaging. If the central tumor plane was assessed, treatment response was underestimated up to threefold or overestimated up to 57-fold on 2D versus 3D DCE US images.

CONCLUSION

Three-dimensional DCE US imaging with a clinical matrix array transducer is feasible and reproducible to assess tumor perfusion in human colon cancer xenografts in mice and allows for assessment of early treatment response after antiangiogenic therapy.

Update on the role of imaging in management of metastatic colorectal cancer

Evolution in the treatment of metastatic colorectal cancer (mCRC) has led to significant improvement in the survival of these patients. Surgery is useful in patients with resectable disease. Liver-directed therapies such as hepatic arterial infusion, transarterial radio- and chemoembolization, and percutaneous ablation are sometimes used by oncologists when the liver is the only site of metastatic disease. Unresectable mCRC is typically treated with systemic chemotherapy. First-line systemic chemotherapeutic regimens for mCRC are FOLFOX (combination of 5-fluorouracil/leucovorin [5-FU/LV] and oxaliplatin) and FOLFIRI (combination of 5-FU/LV and irinotecan) combined with molecular targeted drugs. Molecular targeted therapies that are effective in treating mCRC include antiangiogenic agents such as bevacizumab-an antibody against vascular endothelial growth factor-and antibodies directed against epidermal growth factor receptor (EGFR). EGFR-directed antibodies such as cetuximab and panitumumab have been shown to produce activity only in wild-type KRAS tumors. Imaging modalities such as multidetector computed tomography (CT), magnetic resonance imaging, and positron emission tomography/CT play a major role in the selection of appropriate treatment strategies. Assessment of treatment response in patients who undergo liver-directed and systemic therapy requires imaging at regular intervals. Recent studies have shown that alternative treatment response criteria may be more predictive of pathologic response in mCRC than conventional criteria such as Response Evaluation Criteria in Solid Tumors. Awareness of unusual response patterns, as well as of complications and toxicities, is helpful in guiding patient management.

CT perfusion of the liver: principles and applications in oncology

With the introduction of molecularly targeted chemotherapeutics, there is an increasing need for defining new response criteria for therapeutic success because use of morphologic imaging alone may not fully assess tumor response. Computed tomographic (CT) perfusion imaging of the liver provides functional information about the microcirculation of normal parenchyma and focal liver lesions and is a promising technique for assessing the efficacy of various anticancer treatments. CT perfusion also shows promising results for diagnosing primary or metastatic tumors, for predicting early response to anticancer treatments, and for monitoring tumor recurrence after therapy. Many of the limitations of early CT perfusion studies performed in the liver, such as limited coverage, motion artifacts, and high radiation dose of CT, are being addressed by recent technical advances. These include a wide area detector with or without volumetric spiral or shuttle modes, motion correction algorithms, and new CT reconstruction technologies such as iterative algorithms. Although several issues related to perfusion imaging-such as paucity of large multicenter trials, limited accessibility of perfusion software, and lack of standardization in methods-remain unsolved, CT perfusion has now reached technical maturity, allowing for its use in assessing tumor vascularity in larger-scale prospective clinical trials. In this review, basic principles, current acquisition protocols, and pharmacokinetic models used for CT perfusion imaging of the liver are described. Various oncologic applications of CT perfusion of the liver are discussed and current challenges, as well as possible solutions, for CT perfusion are presented.

Functional imaging of the liver

Anatomical-based imaging is used widely for the evaluation of diffuse and focal liver, including detection, characterization, and therapy response assessment. However, a limitation of anatomical-based imaging is that structural changes may occur relatively late in a disease process. By applying conventional anatomical-imaging methods in a more functional manner, specific pathophysiologic alterations of the liver may be assessed and quantified. There has been an increasing interest in both the clinical and research settings, with the expectation that functional-imaging techniques may help solve common diagnostic dilemmas that conventional imaging alone cannot. This review considers the most common functional magnetic resonance imaging, computed tomography, and ultrasound imaging techniques that may be applied to the liver.

Effect of dual vascular input functions on CT perfusion parameter values and reproducibility in liver tumors and normal liver

OBJECTIVE

To assess the impact on absolute values and reproducibility of adding portal venous (PV) to arterial input functions in computed tomographic perfusion (CTp) evaluations of liver tumors and normal liver.

METHODS

Institutional review board approval and written informed consent were obtained; the study complied with Health Insurance Portability and Accountability Act regulations. Computed tomographic perfusion source data sets, obtained from 7 patients (containing 9 liver tumors) on 2 occasions, 2 to 7 days apart, were analyzed by deconvolution modeling using dual ("Liver" protocol: PV and aorta) and single ("Body" protocol: aorta only) vascular inputs. Identical tumor, normal liver, aortic and, where applicable, PV regions of interest were used in corresponding analyses to generate tissue blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability (PS) values. Test-retest variability was assessed by within-patient coefficients of variation.

RESULTS

For liver tumor and normal liver, median BF, BV, and PS were significantly higher for the Liver protocol than for the Body protocol: 171.3 to 177.8 vs 39.4 to 42.0 mL/min per 100 g, 17.2 to 18.7 vs 3.1 to 4.2 mL/100 g, and 65.1 to 78.9 vs 50.4 to 66.1 mL/min per 100 g, respectively (P < 0.01 for all). There were no differences in MTT between protocols. Within-patient coefficients of variation were lower for all parameters with the Liver protocol than with the Body protocol: BF, 7.5% to 11.2% vs 11.7% to 20.8%; BV, 10.1% to 14.4% vs 16.6% to 30.1%; MTT, 4.2% to 5.5% vs 10.4% to 12.9%; and PS, 7.3% to 12.1% vs 12.6% to 20.3%, respectively.

CONCLUSION

Utilization of dual vascular input CTp liver analyses has substantial impact on absolute CTp parameter values and test-retest variability. Incorporation of the PV inputs may yield more precise results; however, it imposes substantial practical constraints on acquiring the necessary data.

Correlation and agreement between contrast-enhanced ultrasonography and perfusion computed tomography for assessment of liver metastases from endocrine tumors: normalization enhances correlation

We studied correlation and agreement between perfusion parameters derived from contrast-enhanced ultrasonography (CEUS) and computed tomography (CT). Both techniques were performed in 16 patients with proven liver metastases from endocrine tumor. Replenishment study after ultrasound-induced destruction of microbubbles was used for CEUS quantification. CEUS-derived relative values of blood flow, blood volume and mean transit time were compared with perfusion CT-derived parameters measured in the same tumors. Significant correlation was observed between CEUS normalized values and CT absolute tumor values for blood flow (r = 0.58; p = 0.018), blood volume (r = 0.61; p = 0.012) and mean transit time (r = 0.52; p = 0.037). Correlation was not significant for non-normalized values. Agreement between CEUS normalized values and perfusion CT relative values was significant (p < 0.04). Estimated bias between CEUS and CT for relative perfusion values was -1.38 (-5.02; 2.27) for blood flow, +0.26 (-0.79; 1.31) for blood volume and +0.21 (-0.46; 0.87) for mean transit time. We conclude that normalization markedly increased correlation between CEUS- and CT-derived perfusion values and allowed agreement assessment.

Quantitative perfusion analysis of malignant liver tumors: dynamic computed tomography and contrast-enhanced ultrasound

OBJECTIVE

To prospectively analyze the correlation between quantitative parameters of perfusion derived from dynamic contrast-enhanced CT (DCE-CT) and contrast-enhanced ultrasound (DCE-US) in patients with malignant liver tumors.

MATERIALS AND METHODS

Thirty patients (mean age: 59.4 ± 12.3 years) with primary malignant liver tumors or hepatic metastases of various origin underwent DCE-CT (4D spiral mode, scan range, 14.8 cm; 15 scans; cycle time, 3 seconds) and DCE-US (low mechanical index, <0.1, 2.4 mL microbubbles). DCE-CT and DCE-US images were evaluated by 2 radiologists regarding quantitative perfusion parameters including arterial liver perfusion (ALP), portal-venous perfusion (PVP), and total perfusion (P = ALP + PVP) from DCE-CT, as well as blood inflow velocity (B) and the normalized slope within the calculation range (CVan) from DCE-US.

RESULTS

Quantitative assessment was possible with DCE-CT in 12/30 (40%) patients before and in all patients after automated motion correction. With DCE-US, quantitative assessment could not be performed in 9/30 (30.0%) patients due to respiratory motion. Interreader agreements for quantitative perfusion analysis were good with DCE-CT (r = 0.640-0.892, each P < 0.001) and DCE-US (r = 0.761-0.909, each P < 0.001). Moderate significant correlations were found between the perfusion parameters from DCE-CT (P, ALP) and DCE-US (B, CVan) (r = 0.446-0.621, each P < 0.05). No significant correlations were found between PVP from CT and perfusion parameters from DCE-US (B, CVan; each P = nonsignificant).

CONCLUSIONS

Quantitative evaluation of DCE-CT data was feasible in all patients after automated motion correction, whereas DCE-US data could not be quantitatively evaluated in 30% of patients due to respiratory motion and lack of motion correction software. Quantitative arterial perfusion analysis showed moderate significant correlations for blood flow parameters among modalities.

Perfusion CT assessment of tissue hemodynamics following hepatic arterial infusion of increasing doses of angiotensin II in a rabbit liver tumor model

PURPOSE

To investigate the effects of increasing doses of angiotensin II on hepatic hemodynamics in the normal rabbit liver and in hepatic VX2 tumors by using dynamic contrast material-enhanced perfusion computed tomography (CT).

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Solitary hepatic VX2 tumors were implanted into 12 rabbits. In each animal, perfusion CT of the liver was performed before (at baseline) and after hepatic arterial infusion of varying doses (0.1-50.0 μg/mL) of angiotensin II. Images were acquired continuously for 80 seconds after the start of the intravenous contrast material administration. Blood flow (BF), blood volume (BV), mean transit time (MTT), and capillary permeability-surface area product were calculated for the tumor and the adjacent and distant normal liver tissue. Generalized linear mixed models were used to estimate the effects of angiotensin II dose on outcome measures.

RESULTS

Angiotensin II infusion increased contrast enhancement of the tumor and distal liver vessels. Tumor BF increased in a dose-dependent manner after administration of 0.5-25.0 μg/mL angiotensin II, but only the 2.5 μg/mL dose induced a significant increase in tumor BF compared with BF in the adjacent (68.0 vs 26.3 mL/min/100 g, P < .0001) and distant (68.0 vs 28.3 mL/min/100 g, P = .02) normal liver tissue. Tumor BV varied with angiotensin II dose but was greater than the BV of the adjacent and distant liver tissue at only the 2.5 μg/mL (4.8 vs 3.5 mL/100 g for adjacent liver [P < .0001], 4.8 vs 3.3 mL/100 g for distant liver [P = .0006]) and 10.0 μg/mL (4.9 vs 4.4 mL/100 g for adjacent liver [P = .007], 4.9 vs 4.3 mL/100 g for distant liver [P = .04]) doses. Tumor MTT was significantly shorter than the adjacent liver tissue MTT at angiotensin II doses of 2.5 μg/mL (9.7 vs 15.8 sec, P = .001) and 10.0 μg/mL (5.1 vs 13.2 sec, P = .007) and significantly shorter than the distant liver tissue MTT at 2.5 μg/mL only (9.7 vs 15.3 sec, P = .0006). The capillary permeability-surface area product for the tumor was higher than that for the adjacent liver tissue at the 2.5 μg/mL angiotensin II dose only (11.5 vs 8.1 mL/min/100 g, P = .01).

CONCLUSION

Perfusion CT enables a mechanistic understanding of angiotensin II infusion in the liver and derivation of the optimal effective dose. The 2.5 μg/mL angiotensin II dose increases perfusion in hepatic VX2 tumors versus that in adjacent and distant normal liver tissue primarily by constricting normal distal liver vessels and in turn increasing tumor BF and BV.