Colorectal cancer: diagnostic potential of CT measurements of hepatic perfusion and implications for contrast enhancement protocols

Hepatic enhancement in colorectal cancer: texture analysis correlates with hepatic hemodynamics and patient survival

RATIONALE AND OBJECTIVES

Perfusion imaging of the liver has attracted interest as a potential means for earlier detection of hepatic metastases, but the techniques are complex and do not form part of routine imaging protocols. This study assesses whether the hemodynamic status of the liver of patients with colorectal cancer but apparently normal hepatic morphology is reflected by texture features within a single portal-phase contrast enhanced computed tomography (CT) image and correlates texture with overall survival.

MATERIALS AND METHODS

Portal-phase CT images from 27 patients with colorectal cancer but no apparent hepatic metastases were processed using a band-pass filter that highlighted image features at different spatial frequencies. A range of parameters reflecting liver texture on filtered images were correlated against CT hepatic perfusion index (HPI) and patient survival.

RESULTS

After image filtration, entropy values from hepatic regions were inversely correlated with HPI (r=-0.503978, P=.007355), and directly correlated with survival (r=0.489642, P=.009533). An entropy value below 2.0 identified four patients who died within 36 months of their CT scan with sensitivity 100% and specificity 65% (P<.03).

CONCLUSION

The hemodynamic status of the liver is reflected by subtle changes in coarse texture on portal phase images that can be revealed by texture analysis. Texture analysis has the potential to identify colorectal cancer patients with an apparently normal portal phase hepatic CT but reduced survival.

Multiphase contrast-enhanced CT imaging in hepatocellular carcinoma correlation with immunohistochemical angiogenic activities

RATIONALE AND OBJECTIVES

To evaluate the correlation between enhancement parameters of multiphase contrast-enhanced computed tomography (CT) and immunohistochemical activities of vascular endothelial growth factor (VEGF), VEGF receptors, and CD34 in hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Twenty-seven patients underwent curative resection for HCC with no preoperative treatment. We defined several CT enhancement parameters by measuring attenuation values of tumor, liver parenchyma, and aorta. The stored tissue blocks were assayed for immunohistochemical activities of VEGF, two VEGF receptors (Flt-1, Flk-1), and CD34, which were correlated with the enhancement parameters of multiphase contrast-enhanced CT.

RESULTS

The VEGF activities in HCC showed moderate positive correlation with phase difference in portal phase, delayed enhancement (DE), tumor-blood ratio, blood pool index, and tumor-parenchyma ratio in arterial phase. The Flk-1 activities in HCC showed moderate positive correlation only with DE. CD34 activity in HCC showed positive correlation with most of the CT parameters except for DE.

CONCLUSION

Our study showed that several CT enhancement parameters representing mainly delayed enhancement features were well correlated with VEGF activity in HCC, and might be valuable indicators for assessing angiogenic activity in HCC.

Hepatic entropy and uniformity: additional parameters that can potentially increase the effectiveness of contrast enhancement during abdominal CT

AIM

To determine how hepatic entropy and uniformity of computed tomography (CT) images of the liver change after the administration of contrast material and to assess whether these additional parameters are more sensitive to tumour-related changes in the liver than measurements of hepatic attenuation or perfusion.

MATERIALS AND METHODS

Hepatic attenuation, entropy, uniformity, and perfusion were measured using multi-phase CT following resection of colorectal cancer. Based on conventional CT and fluorodeoxyglucose positron emission tomography, 12 patients were classified as having no evidence of malignancy, eight with extra-hepatic tumours only, and eight with metastatic liver disease.

RESULTS

Hepatic attenuation and entropy increased after CM administration whereas uniformity decreased. Unlike hepatic attenuation, entropy and uniformity changed maximally in the arterial phase. No significant differences in hepatic perfusion or attenuation were found between patient groups, whereas arterial-phase entropy was lower (p=0.034) and arterial-phase uniformity was higher (p=0.034) in apparently disease-free areas of liver in patients with hepatic metastases compared with those with no metastases.

CONCLUSION

Temporal changes in hepatic entropy and uniformity differ from those for hepatic attenuation. By reflecting the distribution of hepatic enhancement, these additional parameters are more sensitive to tumour-related changes in the liver than measurements of hepatic attenuation or perfusion.

An efficient method for calculating kinetic parameters in a dual-input single-compartment model

Quantitative measurement of hepatic perfusion has the potential to provide important information in the assessment and management of various liver diseases. The utility of hepatic perfusion characterization relies on the resolution of each component of its dual blood supply, i.e. the hepatic artery and portal vein. In this study, a linear equation was derived by integrating the differential equation describing the kinetic behaviour of contrast agent (CA) in a dual-input single-compartment model, from which the kinetic parameters can be easily obtained using the linear least-squares method. The usefulness of this method was investigated using computer simulations, in comparison with the non-linear least-squares (NLSQ) method. This method calculated the kinetic parameters faster than the NLSQ method by a factor of approximately 10, with almost the same accuracy as the NLSQ method. This method will be useful for analysing the kinetic behaviour of CA in the unique liver environment, especially by generating the functional images of kinetic parameters.

Functional imaging of colorectal cancer angiogenesis

Angiogenesis is a key factor in the growth and dissemination of colorectal cancer, with significant implications for its clinical management. Previous trials have provided proof-of-principle that inhibition of angiogenesis has the potential to enhance the effectiveness of treatment for this disease. Characterisation of the angiogenic status of the tumour on an individual patient basis could allow for a more targeted approach to treatment. In vivo imaging techniques that assess tumour microvessel function have the potential to improve the management of treatment for patients with colorectal cancer. This review focuses on MRI and CT assessment of colorectal cancer angiogenesis. We discuss the effects that these two techniques have had in the assessment of this disease, including tumour staging and therapeutic assessment. Their comparability with other imaging techniques, in particular ultrasound, and their limitations are also addressed.

Functional imaging in clinical oncology: magnetic resonance imaging- and computerised tomography-based techniques

Over recent years, advances in cellular biology, molecular biology and genetics have led to a leap forward in our understanding of the biological basis of cancer. Some of these developments have revealed processes and targets that can be visualised and measured by new functional imaging techniques. The resulting images have the potential to improve cancer staging, prognosis and risk assessment, guide radiotherapy planning, direct treatment schedules, improve response assessment and provide new end points for clinical trials. In this review, we have outlined the magnetic resonance imaging- and computerised tomography-based functional techniques and provide evidence for their use.

The use of perfusion CT for the evaluation of therapy combining AZD2171 with gefitinib in cancer patients

The purpose of this study was to determine the feasibility of dynamic contrast-enhanced perfusion CT (CTP) in evaluating the hemodynamic response of tumors in the chest and abdomen treated with a combination of AZD2171 and gefitinib. Thirteen patients were examined just before and every 4-6 weeks after starting therapy. Following intravenous injection of a contrast agent, dynamic image acquisition was obtained at the level of a selected tumor location. To calculate perfusion, the maximum-slope method was used. Pre-treatment average perfusion for extra-hepatic masses was 84 ml/min/100 g, for liver masses arterial perfusion was 25 ml/min/100 g, and a portal perfusion of 30 ml/min/100 g was found. After the administration of AZD2171 and gefitinib, in extra-hepatic masses an initial decrease in perfusion of 18% was followed by a plateau and in liver masses an initial decrease of 39% within the lesions and of 36% within a rim region surrounding the lesions was followed by a tendency to recovery of hepatic artery flow. In conclusion, CTP is feasible in showing changes of perfusion induced by anti-angiogenic therapy.

Imaging tumor angiogenesis: functional assessment using MDCT or MRI?

Functional imaging using multidetector row computed tomography and dynamic contrast-enhanced magnetic resonance imaging are increasingly advocated for assessment of tumor vascularity because these techniques provide excellent anatomic imaging and reliable quantitative perfusion data and are easily incorporated into routine examinations. However, differences in acquisition techniques, mathematical analysis, measurement parameters, and propensity to artifacts influence the choice of imaging modality, which is explored in this review.

Parametric mapping of the hepatic perfusion index with gadolinium-enhanced volumetric MRI

The purpose of this study was to adapt the hepatic perfusion index (HPI) methodology previously developed for MRI to derive 3D parametric maps of HPI, and to investigate apparent differences in HPI maps between a group of colorectal cancer patients and controls. To achieve this, a new and simpler approach to HPI calculation which does not require measurements from the aorta or portal vein is introduced, and assessed with large liver regions of interest (ROIs) in patients and controls. Several example HPI maps showing localized variation are then presented. The subject group consisted of 12 patients with known colorectal metastases, and 13 control subjects referred for routine contrast-enhanced spine imaging with no history of neoplastic disease. HPI was evaluated from serial T1 volume acquisitions acquired over the course of a Gd-DTPA bolus injection. Regions of abnormal perfusion were visible on the HPI maps derived for the patient group, manifested as areas of locally increased HPI extending around the visible margins of known metastases evident on the conventional contrast-enhanced images. This method for MR voxel-based parametric mapping of HPI has the potential to demonstrate regional variations in perfusion at the segmental and subsegmental level.

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Doppler sonographic evaluation of hemodynamic changes in colorectal liver metastases relative to liver size

OBJECTIVE

The mechanisms of hemodynamic alterations in colorectal liver metastases are not clearly understood yet. Considering that an increase in liver size in patients with metastases could also result in an alteration in total liver flow, we aimed to analyze hemodynamic changes relative to the liver volume and to search for the possibility of any intrinsic factors affecting blood flow in patients with metastases.

METHODS

Twenty-eight patients with colorectal liver metastases and 20 control subjects with no liver disease were evaluated sonographically. All patients were examined prospectively by Doppler sonography and helical computed tomography. Hepatic hemodynamic parameters, including blood flow in the hepatic artery and portal vein, total blood flow to the liver, and Doppler perfusion index, were calculated, and values relative to liver volume were obtained. Hepatic perfusion changes in liver metastases were then compared with those in a control group.

RESULTS

The liver volume of the patients with liver metastases was greater than that of the control group (P=.003). Hepatic arterial blood flow rates were higher, whereas portal flow rates were lower, in patients with liver metastases compared with control subjects (P<.05). Total liver blood flow was not significantly different between the two groups. However, total blood flow relative to liver volume was significantly lower in the metastatic group (P<.001). Doppler perfusion index values in the patients with metastasis were significantly higher than in the control group (P=.000).

CONCLUSIONS

Our findings may support the hypothesis that a humoral mediator-induced portal venous flow reduction causes perfusion changes in liver metastases from colorectal disease. However, an additional intrinsic hepatic hemodynamic event should also be present. Doppler perfusion index measurements can provide additional information in the evaluation of patients with colorectal liver metastases.

CT perfusion at early stage of hepatic diffuse disease

AIM: To determine the validity of the non-invasive method of CT perfusion (CTP) in rat model of hepatic diffuse disease.

METHODS: Twenty-eight Wistar rats were divided into two groups. Liver diffuse lesions were induced by diethyln-itrosamine in 14 rats of test group. Rats in control group were bred with pure water. From the 1^st to 12^th wk after the test group was intervened, both groups were studied every week with CTP. CTP parameters of liver parenchyma in different periods and pathologic changes in two groups were compared and analyzed.

RESULTS: The process of hepatic diffuse lesions in test groups was classified into three stages or periods according to the pathologic alterations, namely hepatitis, hepatic fibrosis, and cirrhosis. During this period, hepatic artery flow (HAF) of control group declined slightly, mean transit time (MTT), blood flow (BF) and volume (BV) increased, but there were no significant differences between different periods. In test group, HAF tended to increase gradually, MTT prolonged obviously, BV and BF decreased at the same time. The results of statistical analysis revealed that the difference in the HAF ratio of test group to control group was significant. The ratio of BV and BF in test group to control group in stage of hepatitis and hepatic cirrhosis, hepatic fibrosis and early stage of hepatic cirrhosis was significantly different, but there was no significant difference between hepatitis and hepatic fibrosis. The main pathological changes in stage of hepatitis were swelling of hepatic cells, while sinusoid capillarization and deposition of collagen aggravated gradually in the extravascular Disse’s spaces in stage of fibrosis and early stage of cirrhosis.

CONCLUSION: The technique could reflect some early changes of hepatic blood perfusion in rat with liver diffuse disease and is valuable for their early diagnosis.

Perfusion imaging of the liver: current challenges and future goals

Improved therapeutic options for hepatocellular carcinoma and metastatic disease place greater demands on diagnostic and surveillance tests for liver disease. Existing diagnostic imaging techniques provide limited evaluation of tissue characteristics beyond morphology; perfusion imaging of the liver has potential to improve this shortcoming. The ability to resolve hepatic arterial and portal venous components of blood flow on a global and regional basis constitutes the primary goal of liver perfusion imaging. Earlier detection of primary and metastatic hepatic malignancies and cirrhosis may be possible on the basis of relative increases in hepatic arterial blood flow associated with these diseases. To date, liver flow scintigraphy and flow quantification at Doppler ultrasonography have focused on characterization of global abnormalities. Computed tomography (CT) and magnetic resonance (MR) imaging can provide regional and global parameters, a critical goal for tumor surveillance. Several challenges remain: reduced radiation doses associated with CT perfusion imaging, improved spatial and temporal resolution at MR imaging, accurate quantification of tissue contrast material at MR imaging, and validation of parameters obtained from fitting enhancement curves to biokinetic models, applicable to all perfusion methods. Continued progress in this new field of liver imaging may have profound implications for large patient groups at risk for liver disease.

Assessing Tumor Perfusion and Treatment Response in Rectal Cancer with Multisection CT: Initial Observations

PURPOSE

To use first-pass perfusion computed tomography (CT) to prospectively investigate tumor vascularity in rectal cancer and to determine whether any of the perfusion parameters would predict tumor response to chemotherapy and radiation therapy.

MATERIALS AND METHODS

The institutional review board approved this study, and informed prior consent was obtained from participants. Perfusion CT of rectal cancer was performed with four-section multi-detector row CT in 15 patients (13 men, two women; mean age, 62.1 years; age range, 46-84 years). Five patients with prostate cancer served as controls. All patients with rectal cancer underwent 6-8 weeks of chemotherapy and radiation therapy followed by surgery. In nine patients, perfusion CT was repeated after completion of chemotherapy and radiation therapy. Contrast medium-enhanced dynamic CT was performed with a static table position for 45 seconds, and the data were analyzed by using commercial software to calculate tissue blood flow (BF), blood volume, mean transit time (MTT), and vascular permeability-surface area product. Perfusion parameters of normal rectum and tumor were compared. Perfusion parameters before and after chemotherapy and radiation therapy were compared. A tumor was considered to have responded if its stage at pathologic analysis indicated regression compared with the preoperative stage. Baseline perfusion values were compared between responders and nonresponders. Statistical analysis was performed with the Student t test.

RESULTS

Rectal cancer showed higher BF and shorter MTT compared with those of normal rectum (P < or =.05). After chemotherapy and radiation therapy, tumors showed significant reduction in BF and increase in MTT (P < or =.05). There was a significant difference in baseline BF and MTT values between responders and nonresponders (P < or =.05). Tumors in three patients with high initial BF and short MTT showed poor response.

CONCLUSION

Perfusion CT of rectal cancer can enable assessment of tumor vascularity and perfusion changes that result from chemotherapy and radiation therapy. In this small patient sample, tumors with initial high BF and short MTT values tended to respond poorly to chemotherapy and radiation therapy.

Quantitative measurement of hepatic portal perfusion by multidetector row CT with compensation for respiratory misregistration

Our purpose was to determine whether hepatic portal perfusion assessed by multidetector row CT using compensation for respiratory misregistration can predict the severity of chronic liver disease. We carried out dynamic CT in 43 patients (chronic hepatitis: n=9; cirrhosis: n=24; normal liver: n=10). In this series, 20 patients had liver tumours. The CT protocol was designed to avoid respiratory artefacts and included two interscan breathing periods during the study. To compensate for respiratory misregistration, image sets in the same z-axis position were acquired from four-slice data on each scan, and the portal perfusion calculations were made according to the maximum slope method. Portal perfusion was compared with and without compensation for respiratory misregistration, and the different types of hepatic disease. In the liver tumour patients in particular, portal perfusion was compared with the degree of hepatic fibrosis in the liver sections. Portal perfusion in the patients without compensation for respiratory misregistration (1.10 ml min(-1)ml(-1)) was higher than that of those with compensation (0.99 ml min(-1)ml(-1); p=0.036). Hepatic portal perfusion of patients with chronic hepatitis (0.97 ml min(-1)ml(-1)) and liver cirrhosis (0.88 ml min(-1)ml(-1)) was less than that of patients with normal liver (1.32 ml min(-1)ml(-1); p=0.03, 0.001). Moderate correlation was seen between portal perfusion and the percentage of fibrosis in patients with liver tumours (r=0.55). Hepatic portal perfusion obtained by multidetector row dynamic CT using compensation for respiratory misregistration has the potential to improve non-invasive assessment of the degree of chronic liver disease.

Functional CT imaging in oncology

The two-compartment pharmacokinetics exhibited by iodinated contrast media makes these agents well suited to the study of tumour angiogenesis in which new vessels are not only produced in greater number but also are abnormally permeable to circulating molecules. The temporal changes in contrast enhancement of tumours on CT have been shown to correlate with histopathological assessments of angiogenesis with the intravascular and extravascular phases of contrast enhancement reflecting microvessel density and vascular permeability, respectively. By quantifying tumour contrast enhancement to capture physiological information about the vascular system, functional CT can provide a useful adjunct to the anatomical information afforded by MDCT in oncology, aiding with tumour diagnosis, risk stratification and therapy monitoring. By simultaneously assessing tumour vascularity and metabolic demand, the broader expansion of integrated MDCT/PET imaging will support highly sophisticated assessments of tumour biology within a single examination.

Liver metastases in cancer: detection with contrast-enhanced ultrasonography

In patients with known or suspected malignancy, ultrasonography (US) is often the first choice for liver imaging because of its widespread availability and low cost. Compared with contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI), the sensitivity of conventional US for detecting hepatic metastases is relatively poor. The advent of microbubble contrast agents changed this situation. Sensitivity and specificity increased substantially with the use of these contrast agents and contrast-specific imaging modes in recent years. Currently, numerous US imaging methods exist, based on Doppler techniques or harmonic imaging. They exploit the complex nonlinear behavior of microbubbles in a sound field to achieve marked augmentation of the US signal. Although microbubble contrast agents are essentially blood pool agents, some have a hepatosplenic specific late phase. Imaging during this late phase is particularly useful for improving the detection of malignant liver lesions and allows US to perform similarly to spiral CT as shown by recent studies. In addition, this late phase imaging is very helpful for lesion characterization. Low mechanical index imaging with the newer perfluor agents permits real-time imaging of the dynamic contrast behavior during the arterial, portal venous, and late phases and is particularly helpful for lesion characterization. The use of US for hemodynamic studies of the liver transit time may detect blood flow changes induced by micrometastases even before they become visible on imaging. In this field of functional imaging, further research is required to achieve conclusive results, which are not yet available.

Ultrasonographic detection of focal liver lesions: increased sensitivity and specificity with microbubble contrast agents

Ultrasonography (US) is the first choice for screening patients with suspected liver lesions. However, due to a lack of contrast agents, US used to be less sensitive and specific compared with computed tomography (CT) and magnet resonance imaging (MRI). The advent of microbubble contrast agents increased both sensitivity and specificity dramatically. Rapid developments of the contrast agents as well as of special imaging techniques were made in recent years. Today numerous different US imaging methods exist which based either on Doppler or on harmonic imaging. They are using the particular behaviour of microbubbles in a sound field which varies depending on the energy of insonation (low/high mechanical index, MI) as well as on the properties of the agent themselves. Apart from just blood pool enhancement some agents have a hepatosplenic specific late phase. US imaging during this late phase using relatively high MI in phase inversion mode (harmonic imaging) or stimulated acoustic emission (SAE; Doppler method) markedly improves the detection of focal liver lesions and is also very helpful for lesion characterisation. With regards to detection, contrast enhanced US performs similarly to CT as shown by recent studies. Early results of studies using low MI imaging and the newer perfluor agents are also showing promising results for lesion detection. Low MI imaging with these agents has the advantage of real time imaging and is particularly helpful for characterisation of focal lesions based on their dynamic contrast behaviour. Apart from the techniques which based on the morphology of liver lesions there were some attempts for the detection of occult metastases or micrometastases by means of liver blood flow changes. Also in this field the use of US contrast agents appears to have advantages over formerly used non contrast-enhanced methods although no conclusive results are available yet.

Capillarization of the sinusoids in liver fibrosis: noninvasive assessment with contrast-enhanced MRI in the rabbit

Sinusoidal capillarization induces microcirculatory changes in liver cirrhosis and fibrosis. The purpose of this study was to assess whether contrast-enhanced MRI can be used to demonstrate the effects of sinusoidal capillarization in liver fibrosis. Dynamic MRI after injection of a low-molecular-weight contrast agent of 0.56 kDa (Gd-DOTA), and two high-molecular-weight contrast agents of 6.47 kDa and 52 kDa (P792 and P717) was performed in rabbits with liver fibrosis induced by cholesterol and diethylstilbestrol. The hepatic distribution volume accessible to the high-molecular-weight agents decreased in the rabbits with liver fibrosis (P792: 7.8% +/- 1.7% vs. 10.1% +/- 1.8% in normal rabbits, P =.038; P717: 6.2% +/- 2.1% vs. 9.7% +/- 1.6% in normal rabbits, P =.007), whereas the hepatic mean transit time (MTT) of the low-molecular-weight agent was increased (15.9 +/- 8.0 s vs. 8.8 +/- 2.6 s in normal rabbits, P =.015). In rabbits with liver fibrosis, the clearance of indocyanine green (ICG) was correlated with the volume accessible to the high-molecular-weight agents (P792: r = 0.810, P =.015; P717: r = 0.857, P =.007). The collagen content of the liver was inversely correlated with the distribution volume of P717 (r = -.833, P =.010) and with the ICG clearance (r = -.810, P =.015). It was concluded that the microcirculatory changes induced by sinusoidal capillarization in liver fibrosis can be demonstrated noninvasively with MRI.

Functional computed tomography in oncology

Functional Computed Tomography (CT) describes the use of existing technologies and conventional contrast agents to capture physiological parameters that reflect the vasculature within tumours and other tissues. The technique is readily incorporated into routine conventional CT examinations and, in tumours, the physiological parameters obtained provide an in-vivo marker of angiogenesis. As well as providing a research tool, functional CT has clinical applications in tumour diagnosis, staging, risk stratification and therapy monitoring, including the characterisation of pulmonary nodules, detection of occult hepatic metastases, grading of cerebral glioma and monitoring of anti-angiogenesis drugs. With the recent commercial availability of appropriate software and the development of multislice CT systems, functional CT is poised to make a significant impact upon the imaging of patients with cancer.

Assessment of perfusion of facial microvascular transplants and early detection of ischemia by perfusion-CT scan

OBJECTIVE

Perfusion-computed tomography (CT) is a promising new technique to assess ischemic lesions caused by ischemic brain stroke. In this study, the use of perfusion-CT scans to predict ischemia in microvascular transplants of the face was examined.

STUDY DESIGN

Thirty-eight patients with microvascular latissimus dorsi transplants after tumor surgery were assessed by perfusion-CT scan 34 to 72 hours after surgery. In these cases, clinical examination of the transplant and examination by means of O(2)-probes were either unsuccessful or impossible. An electron beam tomography of the region of interest was performed by using an intravenous nonionic iodine-containing contrast medium (Ultravist 300, Nycomed, Germany) that was applied with an injector at a flow rate of 5 mL/min. Twenty scans with a scanning time of 300 ms and an interscanning time of 3 seconds were carried out. Changes in the Houndsfield units within the transplant as well as the region of the contralateral erector spinae muscle were measured.

RESULTS

Central malperfusion resulting in later complete transplant loss was detected in 2 cases. Peripheral malperfusion was found in 6 cases, resulting in localized resection and secondary wound closure. When no malperfusion was registered, the straightforward healing process took place.

CONCLUSION

Perfusion-CT scans are of great aid in the assessment of microvascular transplant perfusion in the face, when adequate perfusion is not verifiable clinically or by O(2)-probe because of removal or malfunction.

Special techniques for imaging blood flow to tumors

In this review, the current imaging methods of assessing tumor perfusion are discussed and compared. Because most of the techniques depend on the administration of contrast agents, we first consider some general principles underlying the fate of contrast agents and their behavior inside the unique vascular environment of tumors.

Measuring portal venous perfusion with contrast-enhanced CT: comparison of direct and indirect methods

RATIONALE AND OBJECTIVES

Two algorithms can be used to measure portal venous perfusion (PVP) with contrast material-enhanced single-level liver computed tomography. The "direct" and "indirect" algorithms use data from the portal vein and aorta, respectively. This study compared PVP values obtained with direct and with indirect algorithms in a series of patients.

MATERIALS AND METHODS

Both techniques were applied in 27 patients with cirrhosis (14 men and 13 women; mean age, 56.1 years +/- 9.4) and 18 control patients (seven men and 11 women; 52.8 years +/- 12.3). A single section through the liver was scanned after intravenous injection of ioversol (40-mL bolus; 320 mg of iodine per milliliter).

RESULTS

Both techniques showed reduced PVP in patients with cirrhosis (0.63 for direct and 0.17 for indirect method) compared with control patients (1.06 and 0.26, respectively), but only the direct method agreed with physiologic expectations based on animal and human studies. In separating cirrhotic and control patients, the area under the receiver operating characteristic curve was significantly greater for the direct method (0.91 vs 0.78; P = .03).

CONCLUSION

Both direct and indirect methods are feasible and distinguish well between cirrhotic and control patients, but the direct method is more physiologic and is preferable if portal venous data are available.

Hepatic haemodynamics: interrelationships between contrast enhancement and perfusion on CT and Doppler perfusion indices

This study compares three techniques that evaluate hepatic haemodynamics for the detection of metastatic liver disease to determine the interrelationships between the techniques and to assess their equivalence. The three techniques studied were dedicated CT measurements of hepatic enhancement, CT measurements of perfusion and Doppler perfusion indices. 53 patients with proven malignancies of either breast or colon underwent a single location dynamic CT for measurement of hepatic perfusion and enhancement, whilst a subset of 12 patients underwent both CT perfusion and Doppler perfusion studies. Statistically significant correlations were found between CT arterial phase enhancement and CT arterial perfusion (r=0.612, p<0.001), and between both of these parameters and Doppler arterial flow (r=0.867, p<0.001 and r=0.842, p<0.001, respectively). Significant correlations were also found between both the ratio of CT arterial enhancement to peak enhancement and the CT arterial perfusion with the Doppler perfusion index (r=0.797, p=0.002 and r=0.725, p=0.008, respectively). Combined CT arterial and portal perfusion correlated with peak liver enhancement (r=0.614, p< 0.001), but Doppler measurements of portal flow did not correlate with any CT parameter. Increased arterial enhancement, perfusion or flow are valuable additional radiological signs for the presence of hepatic metastases that can be elicited by incorporating any one of these methods into existing imaging protocols.

Assessment of hepatic perfusion parameters with dynamic MRI

Quantification of hepatic perfusion parameters greatly contributes to the assessment of liver function. The purpose of this study was to describe and validate the use of dynamic MRI for the noninvasive assessment of hepatic perfusion parameters. The signal from a fast T(1)-weighted spoiled gradient-echo sequence preceded by a nonslice-selective 90 degrees pulse and a spoiler gradient was calibrated in vitro with tubes filled with various gadolinium concentrations. Dynamic images of the liver were obtained after intravenous bolus administration of 0.05 mmol/kg of Gd-DOTA in rabbits with normal liver function. Hepatic, aortic, and portal venous signal intensities were converted to Gd-DOTA concentrations according to the in vitro calibration curve and fitted with a dual-input one-compartmental model. With MRI, hepatic blood flow was 100 +/- 35 mL min(-1) 100 mL(-1), the arterial fraction 24 +/- 11%, the distribution volume 13.0 +/- 3.7%, and the mean transit time 8.9 +/- 4.1 sec. A linear relationship was observed between perfusion values obtained with MRI and with radiolabeled microspheres (r = 0.93 for hepatic blood flow [P < 0.001], r = 0.79 for arterial blood flow [P = 0.01], and r = 0.91 for portal blood flow [P < 0.001]). Our results indicate that hepatic perfusion parameters can be assessed with dynamic MRI and compartmental modeling.

Standardized perfusion value: universal CT contrast enhancement scale that correlates with FDG PET in lung nodules

The standardized enhancement value and standardized perfusion value allow comparison between different methods for quantification of contrast enhancement during computed tomography (CT). Standard perfusion values calculated from CT measurements of perfusion within pulmonary nodules compared favorably with those derived from previously reported enhancement data and correlated with standardized uptake values obtained from positron emission tomographic images (r = 0.8, P <.01).

Reproducibility of quantitative CT perfusion imaging

The ability to demonstrate regions of abnormal cerebral blood flow in the setting of acute stroke is of diagnostic and prognostic importance. It may also influence therapeutic strategies. The advantage of CT perfusion imaging is its ability to give quantifiable measurements of cerebral blood flow on any modern CT machine without the need to buy specialized equipment. The aim was to assess day-to-day variability of values of cerebral blood volume obtained with this technique. Seven patients with cerebral gliomas were studied using dynamic CT perfusion imaging on two occasions, approximately 24 h apart to reduce variability from diurnal variations. Regions of interest were produced in predominately middle cerebral artery locations in both hemispheres on the first and second CT perfusion studies. Absolute values for cerebral blood flow were produced for these regions and were correlated with flows obtained in the same regions of interest on the follow-up study. The Pearson correlation coefficient obtained was 0.884. CT perfusion imaging is easily performed on conventional modern CT equipment and demonstrates little variability in measures of absolute cerebral blood flow within individuals when studied on two occasions within 24 h.

Early changes in liver perfusion caused by occult metastases in rats: detection with quantitative CT

PURPOSE

To determine whether computed tomography (CT) can depict liver hemodynamic changes caused by occult hepatic micrometastases in rat.

MATERIALS AND METHODS

Liver micrometastases (mean diameter, 500 micrometer +/- 300) were produced in seven BD IX rats by injecting 10(7) DHDK12 PROb colorectal carcinoma cells into the spleen. Macrometastases (mean diameter, 7 mm +/- 3) were produced in four other rats. Five normal rats were studied as controls. CT images were obtained every 300 msec for 30 seconds during the injection of 1 mL per kilogram of body weight of contrast medium. The time-attenuation curves of the aorta, portal vein, and liver were used to calculate liver perfusion with a deconvolution model designed for the dual blood supply.

RESULTS

Micrometastases in an apparently normal liver caused a 34% decrease in portal blood flow and a 25% increase in the mean transit time for the blood to pass through the liver. These findings suggest increased resistance in the sinusoidal capillaries. Similar but greater changes were found in the macrometastases.

CONCLUSION

Occult liver micrometastases in rats generate changes in liver perfusion that can be detected with CT.

Correlation between angiographically assessed vascularity and blood flow in hepatic metastases in patients with colorectal carcinoma

BACKGROUND

The correlation between vascularity and blood flow in hepatic metastases in patients with colorectal carcinoma was studied in 22 metastatic liver tumors.

METHODS

Hepatic metastases were categorized into Grades A-C, in order of increasing vascularity, as determined by hepatic angiography. Of the 22 metastatic liver tumors from 15 patients that showed on angiography, 5 tumors had slightly increased tumor vascularization (Grade A), 10 tumors had vascularization similar to normal (Grade B), and 7 tumors showed decreased vascularization relative to liver parenchyma (Grade C). Blood flow in these metastatic liver tumors was calculated quantitatively by positron emission tomography (PET) scanning using the C(15)O(2) steady-state method and the H(2)(15)O dynamic method.

RESULTS

Using the H(2)(15)O method, blood flow value in Grade A tumors was 52.9 +/- 17.0 mL per 100 g per minute (mean +/- standard error), that in Grade B tumors was 35.7 +/- 3.8 mL per 100 g per minute, and that in Grade C tumors was 31.7 +/- 6.6 mL per 100 g per minute.

CONCLUSIONS

A significant difference was found between blood flows in Grade A metastatic liver tumors and Grade B or C tumors (P < 0.002). There was no significant difference between blood flows in Grade B and C tumors. PET scan quantification results were almost parallel with the angiographic results. Even Grade C tumors had sufficient blood flow, about 32 mL per 100 g per minute on dynamic PET scans. These findings suggest that blood flow in hepatic metastases from colorectal carcinoma is greater than generally is believed.

Alterations in hepatic perfusion resulting from splanchnic venous luminal compromise caused by pancreatic carcinoma

OBJECTIVE

We determined whether alterations in hepatic enhancement exist on dual phase helical CT of the liver in patients with splanchnic venous luminal compromise resulting from pancreatic adenocarcinoma.

SUBJECTS AND METHODS

We examined the extent of hepatic enhancement on dual phase helical CT in 22 patients with pancreatic adenocarcinoma. Eleven patients had splanchnic venous luminal narrowing (flattening along at least 120 degrees of the circumference) of the superior mesenteric vein with (n = 3) or without (n = 8) portal vein involvement caused by tumor. In the remaining patients, splanchnic vasculature appeared normal. An additional 16 patients without pancreatic or hepatic abnormality who underwent dual phase helical CT served as control subjects. We compared the extent of arterial phase and portal venous phase enhancement among the three groups.

RESULTS

The group of patients with splanchnic venous luminal compromise had significantly higher hepatic enhancement during the arterial phase (p < 0.01) and lower enhancement during the portal venous phase (p < 0.05) compared with the other two groups of patients. No significant difference in hepatic enhancement during either phase was noted between the control subjects and the patients with normal vasculature.

CONCLUSION

Because hepatic enhancement correlates with perfusion, splanchnic venous luminal compromise resulting from pancreatic adenocarcinoma likely causes decreased portal venous flow and compensatory increased hepatic arterial flow. This finding supports other evidence of a homeostatic mechanism that maintains hepatic perfusion.

Imaging liver metastases: current limitations and future prospects

The diagnosis of liver metastasis relies on imaging. The sensitivity of ultrasound, CT and magnetic resonance techniques for detecting liver metastases can only be assessed in comparison with surgical inspection, intraoperative ultrasound and pathological examination, all methods that are of uncertain accuracy in detecting very small lesions. With current imaging technology, we should detect virtually all liver metastases 2 cm or larger in size, and most of those 1-2 cm in size. Even with optimum imaging, at present we detect only about one-half of metastatic nodules smaller than 1 cm in patients undergoing liver resection and pathological correlation. Improvements in the earlier detection of metastases will probably require a fundamentally different approach from that of conventional anatomical methods. Micrometastases produce alterations in blood flow that may be recognized by radionuclide or Doppler perfusion methods.

CT measurement of perfusion and permeability within lymphoma masses and its ability to assess grade, activity, and chemotherapeutic response

PURPOSE

Structural CT criteria such as nodal size and appearance have a poor correlation with the grade and activity of a lymphoma mass. This study investigates the potential for functional CT perfusion and permeability measurements to assess lymphoma grade and activity.

METHOD

Thirty-nine patients with proven lymphoma underwent 47 dynamic contrast-enhanced CT studies. Lymphoma grade was classified as low or intermediate/high. In seven patients who underwent repeated studies, measurements were correlated against change in disease activity in the intervening period.

RESULTS

Median perfusion values were higher in active disease (0.55 vs. 0.37 ml/min/ml) and intermediate/high-grade lymphoma (0.56 vs. 0.46 ml/min/ml). Perfusion below 0.2 ml/min/ml implied inactive disease (p < 0.03), whereas > 0.5 ml/min/ml suggested intermediate/high-grade lymphoma (p = 0.11). Median values of permeability were little different between patient groups. Only perfusion fell when disease became inactive.

CONCLUSION

Only CT perfusion measurements of nodes have potential for assessing lymphoma grade, activity, and treatment response.

Tumour angiogenesis and its relation to contrast enhancement on computed tomography: a review

Angiogenesis describes the formation of new blood vessels within tumours. The process is essential for tumour growth and metastasis. The development of new vessels leads to physiological changes, specifically increased perfusion, blood volume and capillary permeability, that alter contrast enhancement during computed tomography (CT). Functional CT techniques that quantify these physiological changes can provide greater insight into how angiogenesis alters contrast enhancement in routine practice and also serve as diagnostic tools in their own right. The functional information obtained can aid with tissue characterisation, such as type or grade of tumour, improve the detection of hepatic metastases, produce clearer delineation of tumours with benefits for radiotherapy planning and biopsy, and provide prognostic information. By providing a marker for tumour angiogenesis, quantitative contrast enhanced CT can improve the diagnostic assessment of patients with cancer.

Imaging of tumour therapy responses by dynamic CT

The objective of this study was to investigate whether functional CT with Patlak analysis could be used to demonstrate acute changes associated with radiotherapy. Patlak analysis yields fractional vascular volume and contrast clearance per unit volume (a measure of permeability). Four tumour types (prostate, bronchus, breast and cervix) were studied pre-radiotherapy and at 1-2 weeks and 6-12 weeks post-therapy. Significant rises in fractional vascular volume and contrast clearance were shown at 1-2 weeks. These indices were still significantly elevated at 6-12 weeks post-therapy. In the prostates perfusion values were also elevated reflecting a hyperemic response to radiotherapy. Dynamic CT with Patlak analysis can be used to measure important pathophysiological indices which may prove useful in assessing response to therapy of tumours.

Hepatic metastases: the value of quantitative assessment of contrast enhancement on computed tomography

OBJECTIVE

Occult and overt hepatic metastases have been the target of research in an effort to improve detection and characterisation of cancer spread and, consequently, guidance of treatment. This paper aims to illustrate the value of two quantitative techniques for assessing contrast enhancement during CT in the detection of hepatic metastases. It outlines the applications to which they can be put, and the ease of incorporation into current protocols.

METHODS AND MATERIAL

The first technique, perfusion CT, uses a single location dynamic CT sequence to obtain time attenuation data whilst a short, high concentration IV bolus of contrast passes through the abdominal vasculature. Quantitative hepatic arterial and portal values are calculated, along with a perfusion image map. The second technique uses densitometric analysis during a modified contrast enhanced dual-phase liver CT examination. Semi-quantitative values are calculated from the images obtained at the 25 and 40 s times.

RESULTS

Both perfusion CT and densitometric analysis have been to shown to differentiate between normal and tumour-bearing liver as defined by structural CT. Hepatic metastases are associated with increased arterial perfusion and arterial phase enhancement. Increased arterial phase enhancement on densitometric analysis in the absence of overt lesions heralds the onset of visible metastases in the liver in the ensuing 18 months. Perfusion CT has also demonstrated a correlation between high arterial perfusion around a visible metastasis and increased survival.

CONCLUSION

Both techniques can provide more information than is available from conventional enhanced CT scans alone. An algorithm for the clinical application of perfusion CT is proposed. The ease with which these quantitative techniques can be performed and the extra information they provide could lead to improved staging of cancer and more appropriate patient management.