Quantitative tumor perfusion assessment with multidetector CT: are measurements from two commercial software packages interchangeable?

An evaluation of the feasibility of assessment of volume perfusion for the whole lung by 128-slice spiral CT

BACKGROUND

Lung perfusion based on dynamic scanning cannot provide a quantitative assessment of the whole lung because of the limited coverage of the current computed tomography (CT) detector designs.

PURPOSE

To evaluate the feasibility of dynamic volume perfusion CT (VPCT) of the whole lung using a 128-slice CT for the quantitative assessment and visualization of pulmonary perfusion.

MATERIAL AND METHODS

Imaging was performed in a control group of 17 subjects who had no signs of disturbance of pulmonary function or diffuse lung disease, and 15 patients (five patients with acute pulmonary embolism and 10 with emphysema) who constituted the abnormal lung group. Dynamic VPCT was performed in all subjects, and pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time (MTT) were calculated from dynamic contrast images with a coverage of 20.7 cm. Regional and volumetric PBF, PBV, and MTT were statistically evaluated and comparisons were made between the normal and abnormal lung groups.

RESULTS

Regional PBF (94.2 ± 36.5, 161.8 ± 29.6, 185.7 ± 38.1 and 125.5 ± 46.1, 161.9 ± 31.4, 169.3 ± 51.7), PBV (6.7 ± 2.8, 10.9 ± 3.0, 12.9 ± 4.5 and 9.9 ± 4.6, 10.3 ± 2.9, 11.9 ± 4.5), and MTT (5.8 ± 2.4, 4.5 ± 1.3, 4.7 ± 2.1 and 5.6 ± 2.3, 4.3 ± 1.5, 4.9 ± 1.5) demonstrated significant differences in the gravitational and isogravitational directions in the normal lung group (P < 0.05). The PBF (154.2 ± 30.6 vs. 94.9 ± 15.9) and PBV (11.1 ± 4.0 vs. 6.6 ± 1.7) by dynamic VPCT showed significant differences between normal and abnormal lungs (P < 0.05), notwithstanding the four large lungs that had coverage > 20.7 cm.

CONCLUSION

Dynamic VPCT of the whole lung is feasible for the quantitative assessment of pulmonary perfusion by 128-slice CT, and may in future permit the evaluation of both morphological and functional features of the whole lung in a single examination.

Dynamic volume perfusion CT in patients with lung cancer: baseline perfusion characteristics of different histological subtypes

OBJECTIVE

To evaluate dynamic volume perfusion CT (dVPCT) tumor baseline characteristics of three different subtypes of lung cancer in untreated patients.

MATERIALS AND METHODS

173 consecutive patients (131 men, 42 women; mean age 61 ± 10 years) with newly diagnosed lung cancer underwent dVPCT prior to biopsy. Tumor permeability, blood flow (BF), blood volume (BV) and mean transit time (MTT) were quantitatively assessed as well as tumor diameter and volume. Tumor subtypes were histologically determined and compared concerning their dVPCT results. dVPCT results were correlated to tumor diameter and volume.

RESULTS

Histology revealed adenocarcinoma in 88, squamous cell carcinoma in 54 and small cell lung cancer (SCLC) in 31 patients. Tumor permeability was significantly differing between adenocarcinoma, squamous cell carcinoma and SCLC (all p<0.05). Tumor BF and BV were higher in adenocarcinomathan in SCLC (p = 0.001 and p=0.0002 respectively). BV was also higher in squamous cell carcinoma compared to SCLC (p = 0.01). MTT was not differing between tumor subtypes. Regarding all tumors, tumor diameter did not correlate with any of the dVPCT parameters, whereas tumor volume was negatively associated with permeability, BF and BV (r = -0.22, -0.24, -0.24, all p<0.05). In squamous cell carcinoma, tumor diameter und volume correlated with BV (r = 0.53 and r = -0.40, all p<0.05). In SCLC, tumor diameter und volume correlated with MTT (r = 0.46 and r = 0.39, all p<0.05). In adenocarcinoma, no association between morphological and functional tumor characteristics was observed.

CONCLUSIONS

dVPCT parameters are only partially related to tumor diameter and volume and are significantly differing between lung cancer subtypes.

Perfusion CT vascular parameters do not correlate with immunohistochemically derived microvessel density count in colorectal tumors

PURPOSE

To determine whether perfusion computed tomography (CT)-derived vascular parameters-namely, blood flow, mean transit time (MTT), volume transfer constant (K(trans)), permeability-surface area product (PS), extracellular extravascular space volume, and vascular volume-correlate with the immunohistologic markers of angiogenesis in colorectal tumors.

MATERIALS AND METHODS

This prospective study was approved by the Regional Ethics and Research and Development Committees. The perfusion CT protocol was incorporated in the staging CT after informed consent in 29 patients (14 men, 15 women; mean age, 70 years; age range, 55-94 years). The perfusion parameters were calculated over two regions of interest (ROIs), at the invasive and luminal site defined by two radiologists independently. Accurate representative data were captured manually by correcting for motion artifacts and were analyzed by using Matlab software. The vascular heterogeneity between ROIs was assessed by using the Wilcoxon signed rank test. Perfusion CT parameters were correlated with the microvessel density (MVD) count at both corresponding sites obtained by means of immunohistochemical staining of the selected histologic slide with factor VIII and CD105 antigens by using Spearmen rank coefficient.

RESULTS

There was no statistically significant difference found between perfusion CT vascular parameters at the two ROIs by either of the radiologists. The Pearson coefficient for blood flow, MTT, K(trans), and PS at the two ROIs demonstrated good to moderate interobserver variability (for the two ROIs, 0.46 and 0.44; 0.67 and 0.64; 0.41 and 0.72; and 0.86 and 0.56, respectively). None of these parameters correlated with MVD count at the invasive or the luminal site for either of the two antigens.

CONCLUSION

Perfusion CT measurements may measure vascularity of colorectal tumors, however, correlation with MVD, which is a morphologic measure, appears inappropriate. © RSNA, 2013.

Comparison between the deconvolution and maximum slope 64-MDCT perfusion analysis of the esophageal cancer: is conversion possible?

PURPOSE

To estimate if CT perfusion parameter values of the esophageal cancer, which were obtained with the deconvolution-based software and maximum slope algorithm are in agreement, or at least interchangeable.

METHODS

278 esophageal tumor ROIs, derived from 35 CT perfusion studies that were performed with a 64-MDCT, were analyzed. "Slice-by-slice" and average "whole-covered-tumor-volume" analysis was performed. Tumor blood flow and blood volume were manually calculated from the arterial tumor-time-density graphs, according to the maximum slope methodology (BF(ms) and BV(ms)), and compared with the corresponding perfusion values, which were automatically computed by commercial deconvolution-based software (BF(deconvolution) and BV(deconvolution)), for the same tumor ROIs. Statistical analysis was performed using Wilcoxon matched-pairs test, paired-samples t-test, Spearman and Pearson correlation coefficients, and Bland-Altman agreement plots.

RESULTS

BF(deconvolution) (median: 74.75 ml/min/100g, range, 18.00-230.5) significantly exceeded the BF(ms) (25.39 ml/min/100g, range, 7.13-96.41) (Z=-14.390, p<0.001), while BV(deconvolution) (median: 5.70 ml/100g, range: 2.10-15.90) descended the BV(ms) (9.37 ml/100g, range: 3.44-19.40) (Z=-13.868, p<0.001). Both pairs of perfusion measurements significantly correlated with each other: BF(deconvolution), versus BF(ms) (rS=0.585, p<0.001), and BV(deconvolution), versus BV(ms) (rS=0.602, p<0.001). Geometric mean BF(deconvolution)/BF(ms) ratio was 2.8 (range, 1.1-6.8), while geometric mean BV(deconvolution)/BV(ms) ratio was 0.6 (range, 0.3-1.1), within 95% limits of agreement.

CONCLUSIONS

Significantly different CT perfusion values of the esophageal cancer blood flow and blood volume were obtained by deconvolution-based and maximum slope-based algorithms, although they correlated significantly with each other. Two perfusion-measuring algorithms are not interchangeable because too wide ranges of the conversion factors were found.

Tracer-kinetic modeling of dynamic contrast-enhanced MRI and CT: a primer

Dynamic contrast-enhanced computed tomography (DCE-CT) and magnetic resonance imaging (DCE-MRI) are functional imaging techniques. They aim to characterise the microcirculation by applying the principles of tracer-kinetic analysis to concentration-time curves measured in individual image pixels. In this paper, we review the basic principles of DCE-MRI and DCE-CT, with a specific emphasis on the use of tracer-kinetic modeling. The aim is to provide an introduction to the field for a broader audience of pharmacokinetic modelers. In a first part, we first review the key aspects of data acquisition in DCE-CT and DCE-MRI, including a review of basic measurement strategies, a discussion on the relation between signal and concentration, and the problem of measuring reference data in arterial blood. In a second part, we define the four main parameters that can be measured with these techniques and review the most common tracer-kinetic models that are used in this field. We first discuss the models for the capillary bed and then define the most general four-parameter models used today: the two-compartment exchange model, the tissue-homogeneity model, the "adiabatic approximation to the tissue-homogeneity model" and the distributed-parameter model. In simpler tissue types or when the data quality is inadequate to resolve all the features of the more complex models, it is often necessary to resort to simpler models, which are special cases of the general models and hence have less parameters. We discuss the most common of these special cases, i.e. the uptake models, the extended Tofts model, and the one-compartment model. Models for two specific tissue types, liver and kidney, are discussed separately. We conclude with a review of practical aspects of DCE-CT and DCE-MRI data analysis, including the problem of identifying a suitable model for any given data set, and a brief discussion of the application of tracer-kinetic modeling in the context of drug development. Here, an important application of DCE techniques is the derivation of quantitative imaging biomarkers for the assessment of effects of targeted therapeutics on tumors.

Primary colorectal cancer: use of kinetic modeling of dynamic contrast-enhanced CT data to predict clinical outcome

PURPOSE

To compare four different tracer kinetic models for the analysis of dynamic contrast material-enhanced computed tomographic (CT) data with respect to the prediction of 5-year overall survival in primary colorectal cancer.

MATERIALS AND METHODS

This study was approved by the ethical review board. Archival dynamic contrast-enhanced CT data from 46 patients with colorectal cancer, obtained as part of a research study, were analyzed retrospectively by using the distributed parameter, conventional compartmental, adiabatic tissue homogeneity, and generalized kinetic models. Blood flow, blood volume, mean transit time (MTT), permeability-surface area product, extraction fraction, extravascular extracellular volume (v(e)), and volume transfer constant (K(trans)) were compared by using the Friedman test, with statistical significance at 5%. Following receiver operating characteristic analysis, parameters of the different kinetic models and tumor stage were compared with respect to overall survival discrimination, with use of Kaplan Meier analysis and a univariate Cox proportional hazard model, with additional cross-validation and permutation testing.

RESULTS

Blood flow was lower with the distributed parameter model than with the conventional compartmental and adiabatic tissue homogeneity models (P < .0001), and blood flow values determined with the conventional compartmental and adiabatic tissue homogeneity models were similar. Conversely, MTT was longer with the distributed parameter model than with the conventional compartmental and adiabatic tissue homogeneity models (P < .0001). Blood volume, permeability-surface area product, and v(e) were higher with the conventional compartmental model than with the adiabatic tissue homogeneity, distributed parameter, or generalized kinetic models (P < .0001). The extraction fraction was higher with the distributed parameter model than with the adiabatic tissue homogeneity model. With respect to 5-year overall survival, only the distributed parameter model-derived v(e) was predictive of 5-year overall survival with a threshold value of 15.48 mL/100 mL after cross-validation and permutation testing.

CONCLUSION

Parameter values differ significantly between models. Of the models investigated, the distributed parameter model was the best predictor of 5-year overall survival.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120186/-/DC1.

CT perfusion imaging in the diagnosis of esophageal cancer

Esophageal cancer is one of the most common malignant tumors in China. The symptoms of early esophageal cancer often tend to be unspecific and are easily ignored. Diagnosis of esophageal cancer at early stage can improve its therapy and prognosis. Currently, there are still limitations for the application of digestive barium meal examination and endoscopic pathological biopsy in diagnosis of esophageal cancer. CT perfusion imaging, a technique developed in recent years, can assess tissue microcirculation quickly, conveniently, and non-invasively. These unique advantages have led to its gradual application to tumor diagnosis and prognosis evaluation. In this article, we review the application of CT perfusion imaging in the diagnosis of esophageal cancer.

Multicentre imaging measurements for oncology and in the brain

Multicentre imaging studies of brain tumours (and other tumour and brain studies) can enable a large group of patients to be studied, yet they present challenging technical problems. Differences between centres can be characterised, understood and minimised by use of phantoms (test objects) and normal control subjects. Normal white matter forms an excellent standard for some MRI parameters (e.g. diffusion or magnetisation transfer) because the normal biological range is low (<2-3%) and the measurements will reflect this, provided the acquisition sequence is controlled. MR phantoms have benefits and they are necessary for some parameters (e.g. tumour volume). Techniques for temperature monitoring and control are given. In a multicentre study or treatment trial, between-centre variation should be minimised. In a cross-sectional study, all groups should be represented at each centre and the effect of centre added as a covariate in the statistical analysis. In a serial study of disease progression or treatment effect, individual patients should receive all of their scans at the same centre; the power is then limited by the within-subject reproducibility. Sources of variation that are generic to any imaging method and analysis parameters include MR sequence mismatch, B(1) errors, CT effective tube potential, region of interest generation and segmentation procedure. Specific tissue parameters are analysed in detail to identify the major sources of variation and the most appropriate phantoms or normal studies. These include dynamic contrast-enhanced and dynamic susceptibility contrast gadolinium imaging, T(1), diffusion, magnetisation transfer, spectroscopy, tumour volume, arterial spin labelling and CT perfusion.

Diagnosis of hepatocellular carcinoma: newer radiological tools

With the recent dramatic advances in diagnostic modalities, the diagnosis of hepatocellular carcinoma (HCC) is primarily based on imaging. Ultrasound (US) plays a crucial role in HCC surveillance. Dynamic multiphasic multidetector-row CT (MDCT) and magnetic resonance imaging (MRI) are the standard diagnostic methods for the noninvasive diagnosis of HCC, which can be made based on hemodynamic features (arterial enhancement and delayed washout). The technical development of MDCT and MRI has made possible the fast scanning with better image quality and resolution, which enables an accurate CT hemodynamic evaluation of hepatocellular tumor, as well as the application of perfusion CT and MRI in clinical practice. Perfusion CT and MRI can measure perfusion parameters of tumor quantitatively and can be used for treatment response assessment to anti-vascular agents. Besides assessing the hemodynamic or perfusion features of HCC, new advances in MRI can provide a cellular information of HCC. Liver-specific hepatobiliary contrast agents, such as gadoxetic acid, give information regarding hepatocellular function or defect of the lesion, which improves lesion detection and characterization. Diffusion-weighted imaging (DWI) of the liver provides cellular information of HCC and also has broadened its role in lesion detection, lesion characterization, and treatment response assessment to chemotherapeutic agents. In this article, we provide an overview of the state-of-the art imaging techniques of the liver and their clinical role in management of HCC.

Perfusion CT to assess angiogenesis in colon cancer: technical limitations and practical challenges

OBJECTIVE

Perfusion CT may have the potential to quantify the degree of angiogenesis of solid tumours in vivo. This study aims to identify the practical and technical challenges inherent to the technique, and evaluate its feasibility in colorectal tumours.

METHODS

51 patients from 2 institutions prospectively underwent a single perfusion CT on 2 different multidetector scanners. The patients were advised to breath-hold as long as possible, followed by shallow breathing, and were given intravenous buscopan to reduce movement. Numerous steps were explored to identify the challenges.

RESULTS

43 patients successfully completed the perfusion CT as per protocol. Inability to detect the tumour (n=3), misplacement of dynamic sequence co-ordinates (n=2), failure of contrast injection (n=2) and displacement of tumour (n=1) were the reasons for failure. In 14 cases excessive respiratory motion displaced the tumour out of the scanning field along the temporal sequence, leading to erroneous data capture. In nine patients, minor displacements of the tumour were corrected by repositioning the region of interest (ROI) to its original position after reviewing each dynamic sequence slice. In 20 patients the tumour was stable, and data captured from the ROI were representative, and could have been analysed by commercially available Body Tumor Perfusion 3.0® software (GE Healthcare, Waukesha, WI). Hence all data were manually analysed by MATLAB® processing software (MathWorks, Cambridge, UK).

CONCLUSION

Perfusion CT in tumours susceptible to motion during acquisition makes accurate data capture challenging and requires meticulous attention to detail. Motion correction software is essential if perfusion CT is to be used routinely in colorectal cancer.

Digital perfusion phantoms for visual perfusion validation

OBJECTIVE

Despite the increasingly broad use of perfusion applications, we still have no generally accessible means for their verification: The common sense of perfusion maps and "bona fides" of perfusion software vendors remain the only grounds for acceptance. Thus, perfusion applications are one of a very few clinical tools considerably lacking practical objective hands-on validation.

MATERIALS AND METHODS

To solve this problem, we introduce digital perfusion phantoms (DPPs)--numerically simulated DICOM image sequences specifically designed to have known perfusion maps with simple visual patterns. Processing DPP perfusion sequences with any perfusion algorithm or software of choice and comparing the results with the expected DPP patterns provide a robust and straightforward way to control the quality of perfusion analysis, software, and protocols.

RESULTS

The deviations from the expected DPP maps, observed in each perfusion software, provided clear visualization of processing differences and possible perfusion implementation errors.

CONCLUSION

Perfusion implementation errors, often hidden behind real-data anatomy and noise, become very visible with DPPs. We strongly recommend using DPPs to verify the quality of perfusion applications.

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.

Novel oncologic drugs: what they do and how they affect images

Targeted therapies are designed to interfere with specific aberrant biologic pathways involved in tumor development. The main classes of novel oncologic drugs include antiangiogenic drugs, antivascular agents, drugs interfering with EGFR-HER2 or KIT receptors, inhibitors of the PI3K/Akt/mTOR pathway, and hormonal therapies. Cancer cells usurp normal signal transduction pathways used by growth factors to stimulate proliferation and sustain viability. The interaction of growth factors with their receptors activates different intracellular pathways affecting key tumor biologic processes such as neoangiogenesis, tumor metabolism, and tumor proliferation. The response of tumors to anticancer therapy can be evaluated with anatomic response assessment, qualitative response assessment, and response assessment with functional and molecular imaging. Angiogenesis can be measured by means of perfusion imaging with computed tomography and magnetic resonance (MR) imaging. Diffusion-weighted MR imaging allows imaging evaluation of tumor cellularity. The main imaging techniques for studying tumor metabolism in vivo are positron emission tomography and MR spectroscopy. Familiarity with imaging findings secondary to tumor response to targeted therapies may help the radiologist better assist the clinician in accurate evaluation of tumor response to these anticancer treatments. Functional and molecular imaging techniques may provide valuable data and augment conventional assessment of tumor response to targeted therapies. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.317115108/-/DC1.

Current status and guidelines for the assessment of tumour vascular support with dynamic contrast-enhanced computed tomography

Dynamic contrast-enhanced computed tomography (DCE-CT) assesses the vascular support of tumours through analysis of temporal changes in attenuation in blood vessels and tissues during a rapid series of images acquired with intravenous administration of iodinated contrast material. Commercial software for DCE-CT analysis allows pixel-by-pixel calculation of a range of validated physiological parameters and depiction as parametric maps. Clinical studies support the use of DCE-CT parameters as surrogates for physiological and molecular processes underlying tumour angiogenesis. DCE-CT has been used to provide biomarkers of drug action in early phase trials for the treatment of a range of cancers. DCE-CT can be appended to current imaging assessments of tumour response with the benefits of wide availability and low cost. This paper sets out guidelines for the use of DCE-CT in assessing tumour vascular support that were developed using a Delphi process. Recommendations encompass CT system requirements and quality assurance, radiation dosimetry, patient preparation, administration of contrast material, CT acquisition parameters, terminology and units, data processing and reporting. DCE-CT has reached technical maturity for use in therapeutic trials in oncology. The development of these consensus guidelines may promote broader application of DCE-CT for the evaluation of tumour vascularity. Key Points • DCE-CT can robustly assess tumour vascular support • DCE-CT has reached technical maturity for use in therapeutic trials in oncology • This paper presents consensus guidelines for using DCE-CT in assessing tumour vascularity.

Perfusion linearity and its applications in perfusion algorithm analysis

Perfusion analysis computes blood flow parameters (blood volume, blood flow, and mean transit time) from the observed flow of a contrast agent passing through the patient's vascular system. Perfusion deconvolution has been widely accepted as the principal numerical tool for perfusion analysis, and is used routinely in clinical applications. The extensive use of perfusion in clinical decision-making makes numerical stability and robustness of perfusion computations vital for accurate diagnostics and patient safety. The main goal of this paper is to propose a novel approach for validating numerical properties of perfusion algorithms. The approach is based on the Perfusion Linearity Property (PLP), which is fundamental to virtually all perfusion data processing. PLP allows one to study perfusion values as weighted averages of the original imaging data. This, in turn, uncovers hidden problems with the existing perfusion techniques, and may be used to suggest more reliable computational approaches and methodology.

CT hepatic perfusion measurement: comparison of three analytic methods

OBJECTIVES

To compare the efficacy of three analytic methods, maximum slope (MS), dual-input single-compartment model (CM) and deconvolution (DC), for CT measurements of hepatic perfusion and assess the effects of extra-hepatic systemic factors.

MATERIALS AND METHODS

Eighty-eight patients who were suspected of having metastatic liver tumors underwent hepatic CT perfusion. The scans were performed at the hepatic hilum 7-77 s after administration of contrast material. Hepatic arterial and portal perfusions (HAP and HPP, ml/min/100 ml) and arterial perfusion fraction (APF, %) were calculated with the three methods, followed by correlation assessment. Partial correlation analysis was used to assess the effects on hepatic perfusion values by various factors such as age, sex, risk of cardiovascular diseases, arrival time of contrast material at abdominal aorta, transit time from abdominal aorta to hepatic parenchyma, and liver dysfunction.

RESULTS

Mean HAP of MS was significantly higher than DC. HPP of CM was significantly higher than MS and CM, and HPP of MS was significantly higher than DC. There was no significant difference in APF. HAP and APF showed significant and moderate correlations among the methods. HPP showed significant and moderate correlations between CM and DC, and poor correlation between MS and CM or DC. All methods showed weak correlations between HAP or APF and age or sex. Finally, MS showed weak correlations between HAP or HPP and arrival time or cardiovascular risks.

CONCLUSIONS

Hepatic perfusion values arrived at with the three methods are not interchangeable. CM and DC are less susceptible to extra-hepatic systemic factors.

Applications of the repeatability of quantitative imaging biomarkers: a review of statistical analysis of repeat data sets

Repeat imaging data sets performed on patients with cancer are becoming publicly available. The potential utility of these data sets for addressing important questions in imaging biomarker development is vast. In particular, these data sets may be useful to help characterize the variability of quantitative parameters derived from imaging. This article reviews statistical analysis that may be performed to use results of repeat imaging to 1) calculate the level of change in parameter value that may be seen in individual patients to confidently characterize that patient as showing true parameter change, 2) calculate the level of change in parameters value that may be seen in individual patients to confidently categorize that patient as showing true lack of parameter change, 3) determine if different imaging devices are interchangeable from the standpoint of repeatability, and 4) estimate the numbers of patients needed to precisely calculate repeatability. In addition, we recommend a set of statistical parameters that should be reported when the repeatability of continuous parameters is studied.

Perfusion characterization of liver metastases from endocrine tumors: Computed tomography perfusion

AIM: To assess prospectively parameters of computed tomography perfusion (CT p) for evaluation of vascularity of liver metastases from neuroendocrine tumors.

METHODS: This study was approved by the hospital’s institutional review board. All 18 patients provided informed consent. There were 30 liver metastases from neuroendocrine tumors. Patients were divided into three groups depending on the appearance of the liver metastases at the arterial phase of morphological CT (hyperdense, hypodense and necrotic). Sequential acquisition of the liver was performed before and for 2 min after intravenous injection of 0.5 mg/kg contrast medium, at 4 mL/s. Data were analyzed using deconvolution analysis to calculate blood flow (BF), blood volume (BV), mean transit time (MTT), hepatic arterial perfusion index (HAPI) and a bi-compartmental analysis was performed to obtain vascular permeability-surface area product (PS). Post-treatment analysis was performed by a radiologist and regions of interest were plotted on the metastases, normal liver, aorta and portal vein.

RESULTS: At the arterial phase of the morphological CT scan, the aspects of liver metastases were hyperdense (n = 21), hypodense (n = 7), and necrotic (n = 2). In cases of necrotic metastases, none of the CT p parameters were changed. Compared to normal liver, a significant difference in all CT p parameters was found in cases of hyperdense metastases, and only for HAPI and MTT in cases of hypodense metastases. No significant difference was found for MTT and HAPI between hypo- and hyperdense metastases. A significant decrease of PS, BV and BF was demonstrated in cases of patients with hypodense lesions PS (23 ± 11.6 mL/100 g per minute) compared to patients with hyperdense lesions; PS (13.5 ± 10.4 mL/100 g per minute), BF (93.7 ± 75.4 vs 196.0 ± 115.6 mL/100 g per minute) and BV (9.7 ± 5.9 vs 24.5 ± 10.9 mL/100 g).

CONCLUSION: CT p provides additional information compared to the morphological appearance of liver metastases.

Increased blood-brain barrier permeability on perfusion CT might predict malignant middle cerebral artery infarction

BACKGROUND AND PURPOSE

Perfusion CT has been used to assess the extent of blood-brain barrier breakdown. The purpose of this study was to determine the predictive value of blood-brain barrier permeability measured using perfusion CT for development of malignant middle cerebral artery infarction requiring hemicraniectomy (HC).

METHODS

We retrospectively identified patients from our stroke registry who had middle cerebral artery infarction and were evaluated with admission perfusion CT. Blood-brain barrier permeability and cerebral blood volume maps were generated and infarct volumes calculated. Clinical and radiographic characteristics were compared between those who underwent HC versus those who did not undergo HC.

RESULTS

One hundred twenty-two patients (12 HC, 110 no HC) were identified. Twelve patients who underwent HC had developed edema, midline shift, or infarct expansion. Infarct permeability area, infarct cerebral blood volume area, and infarct volumes were significantly different (P < 0.018, P < 0.0211, P < 0.0001, P < 0.0014) between HC and no HC groups. Age (P = 0.03) and admission National Institutes of Health Stroke Scale (P = 0.0029) were found to be independent predictors for HC. Using logistic regression modeling, there was an association between increased infarct permeability area and HC. The OR for HC based on a 5-, 10-, 15-, or 20-cm² increase in infarct permeability area were 1.179, 1.390, 1.638, or 1.932, respectively (95% CI, 1.035 to 1.343, 1.071 to 1.804, 1.108 to 2.423, 1.146 to 3.255, respectively).

CONCLUSIONS

Increased infarct permeability area is associated with an increased likelihood for undergoing HC. Because early HC for malignant middle cerebral artery infarction has been associated with better outcomes, the infarct permeability area on admission perfusion CT might be a useful tool to predict malignant middle cerebral artery infarction and need for HC.

[Advanced NSCLC first pass perfusion at 64-slice CT: reproducibility of volume-based quantitative measurement]

背景与目的

本研究旨在探讨进展期非小细胞肺癌（non-small cell lung cancer, NSCLC）首过法CT灌注（CT perfusion, CTP）的可重复性。

方法

在本院行首过法CTP检查（8×5 mm层厚），且经病理证实的进展期NSCLC患者14例，肿瘤最大径≤3 cm及>3 cm各7例，均在24 h内行第二次CTP扫描。采用组内相关系数（intraclass correlation coefcient, ICC）及Bland-Altman法评价CTP检查的可重复性。

结果

两组进展期NSCLC的血流速度（blood flow, BF）、血容量（blood volume, BV）及表面通透性（permeability surface area product, PS）值的ICC均>0.75；对比剂的平均通过时间（mean transit time, MT）的ICC均 < 0.75。≤3 cm的进展期NSCLC组的BF、BV、MT及PS的可重复系数（repeatability coefficient, RC）及RC值95%变化区间依次为56%（-39%-53%）、45%（-29%-62%）、114%（-83%-145%）、78%（-57%-98%）；>3 cm组的BF、BV、MTT及PS的RC及RC值95%变化区间依次为46%（-48%-45%）、30%（-33%-26%）、-59%（-54%-64%）、33%（-18%-48%）。

结论

去卷积法首过法CTP参数BF及BV可重复性较好，用于评价进展期NSCLC抗血管生成治疗疗效时，可根据肿瘤大小，应用不同的可重复性标准区别对待。

Liver fibrosis in chronic hepatitis C virus infection: differentiating minimal from intermediate fibrosis with perfusion CT

PURPOSE

To prospectively assess the utility of perfusion computed tomography (CT) for differentiating minimal from intermediate fibrosis in treatment-naïve patients with chronic hepatitis C virus (HCV) infection.

MATERIALS AND METHODS

This study was approved by the Institutional Review Board, and informed consent was obtained. Fifty-two patients with treatment-naïve HCV infection underwent perfusion CT and percutaneous liver biopsy on the same day. Portal vein, arterial, and total liver perfusion; mean transit time; and distribution volumes for the right and left liver lobes were measured. Liver samples were scored for fibrosis, and fibrosis area was determined. Differences in quantitative perfusion parameters between patients with minimal fibrosis (score of F1) and those with intermediate fibrosis (score of F2 or F3) were tested.

RESULTS

In patients with intermediate fibrosis (F2 and F3) compared with those with minimal fibrosis (F1), the portal venous perfusion (87 mL min(-1) 100 mL(-1) +/- 27 [standard deviation] vs 138 mL min(-1) 100 mL(-1) +/- 112, P = .042) and total liver perfusion (107 mL min(-1) 100 mL(-1) +/- 31 vs 169 mL min(-1) 100 mL(-1) +/- 137, P = .02) were significantly decreased, and the mean transit time was significantly increased (16 seconds +/- 4 vs 13 seconds +/- 5, P = .025). At multivariate analysis, only the mean transit time was an independent factor (odds ratio, 1.18; 95% confidence interval: 1.02, 1.37; P = .030). Receiver operating characteristic curve analysis showed that a mean transit time threshold of 13.4 seconds allowed discrimination between minimal and intermediate fibrosis with a sensitivity of 71% and a specificity of 65%.

CONCLUSION

The results of this study show that perfusion changes occur early during fibrosis in chronic HCV infection and can be detected with perfusion CT. Perfusion CT may help to discriminate minimal from intermediate fibrosis. Mean transit time appears to be the most promising perfusion parameter for differentiating between fibrosis stages, although the large amount of overlap in the measured parameters limits the clinical utility of this test at present.

Ovarian Cancer: The Role of Functional Imaging as an End Point in Clinical Trials

The Gynaecological Cancer InterGroup conducts collaborative trials in gynecologic cancer and also aims to develop standards that can be used to strengthen all aspects of study methodology. There is an urgent need to develop more refined imaging end points that can be used as early treatment response biomarkers in ovarian cancer. Therefore, the Gynaecological Cancer InterGroup commissioned an expert position paper on the role of functional imaging as an end point in clinical trials in ovarian cancer. In this position paper, we state the limitation of current anatomical imaging methods used in clinical trials, highlight the potential of functional imaging, and provide key recommendations on the use of functional imaging as an end point in ovarian cancer clinical trials.

CT perfusion in solid-body tumours. Part I: Technical issues

Functional imaging is becoming increasingly important in both research and clinical diagnostic radiology. Perfusion computed tomography (CTP) is a readily available and widely used tool that allows an objective measurement of tissue perfusion through the mathematical analysis of data obtained from repeated scans performed after administration of contrast agent. Recently, CTP has been increasingly used in the oncological field, being studied as a potential marker of neoplastic angiogenesis, which is one of the main targets of new tumour therapies. The aim of this paper was to provide the theoretical background and practical guidance for accurately performing CTP and interpreting results of examinations in solid-body tumours. CTP could be a valid tool for functional imaging of tumours if the acquisition technique is robust, if image and data analysis is accurate and if interpretation of results is adequately inserted within a clinical context.

CT perfusion in oncology: how to do it

Robust technique and accurate data analysis are required for reliable computed tomography perfusion (CTp) imaging. Multislice CT is required for high temporal resolution scanning; 16-slice (or 64-slice) scanners are preferred for adequate volume coverage. After tumour localization, the volume of CTp imaging has to be positioned to include the maximum visible area of the tumour and an adequate arterial vessel. Dynamic scans at high temporal resolution (at least 1-s gantry rotation time) are performed to visualize the first pass of contrast agent within the tumour; repeated scans with low temporal resolution can be planned for late enhancement assessment. A short bolus of conventional iodinated contrast agent, preferably with high iodine concentration, is power injected at a high flow rate (>4 ml/s) in the antecubital vein. The breath-hold technique is required for CTp imaging of the chest and upper abdomen to avoid respiratory motion; free breathing is adequate for CTp imaging of the head, neck and pelvis. Using dedicated software, a region of interest (ROI) has to be placed in an adequate artery (as arterial input) to obtain density–time curves; according to different kinetic models, colour maps of different CTp parameters are generated and generally overlaid on CT images. Additional ROIs can be positioned in the tumour, and in all other parts of the CTp volume, to obtain the values of the CTp parameters within the ROI.

Tumor response in patients with advanced non-small cell lung cancer: perfusion CT evaluation of chemotherapy and radiation therapy

OBJECTIVE

The objectives of this study were to prospectively evaluate changes in tumor perfusion after chemoradiation therapy and to investigate the feasibility of perfusion CT for prediction of early tumor response and prognosis of non-small cell lung cancer.

SUBJECTS AND METHODS

Perfusion CT was performed on an MDCT scanner with 50 mL of iodinated contrast material injected at 4 mL/s. The quality of each functional map was rated from 0 to 3 for 123 patients with confirmed lung cancer. A subset of images was independently reviewed by two radiologists to measure interobserver and intraobserver variability. Perfusion parameters and tumor response were assessed for 35 patients with non-small cell lung cancer who underwent chemoradiation therapy. Progression-free survival and overall survival were analyzed for 22 patients who underwent repeated perfusion CT after therapy.

RESULTS

Image quality was graded 2 (moderate) or 3 (good) in 68.2% of cases. High interobserver and intraobserver correlations of perfusion parameters were found on qualified images. The patients who responded to chemoradiation therapy had significantly greater blood flow (p = 0.023) than patients who did not respond. The median progression-free survival period of the patients with an increased permeability-surface area product was 4.7 months, significantly lower than the median progression-free survival period of 19.0 months among patients with a decreased permeability-surface area product (p < 0.001). The median overall survival period was 10.6 months for the group with an increased permeability-surface area product, significantly lower than the 19.3 months for the group with a decreased permeability-surface area product (p = 0.004).

CONCLUSION

Non-small cell lung cancer with higher perfusion is more sensitive to chemoradiation therapy than that with lower perfusion. After chemoradiation therapy, findings at perfusion CT are a significant predictor of early tumor response and overall survival among patients with non-small cell lung cancer.

Optimal duration of acquisition for dynamic perfusion CT assessment of blood-brain barrier permeability using the Patlak model

BACKGROUND AND PURPOSE

A previous study demonstrated the need to use delayed acquisition rather than first-pass data for accurate blood-brain barrier permeability surface product (BBBP) calculation from perfusion CT (PCT) according to the Patlak model, but the optimal duration of the delayed acquisition has not been established. Our goal was to determine the optimal duration of the delayed PCT acquisition to obtain accurate BBBP measurements while minimizing potential motion artifacts and radiation dose.

MATERIALS AND METHODS

We retrospectively identified 23 consecutive patients with acute ischemic anterior circulation stroke who underwent a PCT study with delayed acquisition. The Patlak model was applied for the full delayed acquisition (90-240 seconds) and also for truncated analysis windows (90-210, 90-180, 90-150, 90-120 seconds). Linear regression of Patlak plots was performed separately for the full and truncated analysis windows, and the slope of these regression lines was used to indicate BBBP. The full and truncated analysis windows were compared in terms of the resulting BBBP values and the quality of the Patlak fitting.

RESULTS

BBBP values in the infarct and penumbra were similar for the full 90- to 240-second acquisition (95% confidence intervals for the infarct and penumbra: 1.62-2.47 and 1.75-2.41 mL x100 g(-1) x min(-1), respectively) and the 90- to 210-second analysis window (1.82-2.76 and 2.01-2.74 mL x 100 g(-1) x min(-1), respectively). BBBP values increased significantly with shorter acquisitions. The quality of the Patlak fit was excellent for the full 90- to 240-second and 90- to 210-second acquisitions, but it degraded with shorter acquisitions.

CONCLUSIONS

The duration for the delayed PCT acquisition should be at least 210 seconds, because acquisitions shorter than 210 seconds lead to significantly overestimated BBBP values.

Age- and anatomy-related values of blood-brain barrier permeability measured by perfusion-CT in non-stroke patients

BACKGROUND AND PURPOSE

The goal of this study was to determine blood-brain barrier permeability (BBBP) values extracted from perfusion-CT (PCT) using the Patlak model and possible variations related to age, gender, race, vascular risk factors and their treatment and anatomy in non-stroke patients.

MATERIALS AND METHODS

We retrospectively identified 96 non-stroke patients who underwent a PCT study using a prolonged acquisition time up to 3 minutes. Patients' charts were reviewed for demographic data, vascular risk factors and their treatment. The Patlak model was applied to calculate BBBP values in regions of interest drawn within the basal ganglia and the gray and white matter of the different cerebral lobes. Differences in BBBP values were analyzed using a multivariate analysis considering clinical variables and anatomy.

RESULTS

Mean absolute BBBP values were 1.2 ml 100 g(-1) min(-1) and relative BBBP/CBF values were 3.5%. Statistical differences between gray and white matter were not clinically relevant. BBBP values were influenced by age, history of diabetes and/or hypertension and aspirin intake.

CONCLUSION

This study reports ranges of BBBP values in non-stroke patients calculated from delayed phase PCT data using the Patlak model. These ranges will be useful to detect abnormal BBBP values when assessing patients with cerebral infarction for the risk of hemorrhagic transformation.

Dynamic contrast-enhanced CT of head and neck tumors: comparison of first-pass and permeability perfusion measurements using two different commercially available tracer kinetics models

RATIONALE AND OBJECTIVES

To evaluate the interchangeability of perfusion parameters between two software packages for the postprocessing of dynamic contrast-enhanced (DCE) computed tomographic images of head and neck tumors.

MATERIALS AND METHODS

DCE computed tomographic images of 75 patients with head and neck tumors were postprocessed using a software package based on the maximum-slope approach and Patlak analysis, as well as a software package with deconvolution-based analysis incorporating an adiabatic approximation of tissue homogeneity (ATH) model. The evaluated perfusion parameters included blood flow (F), blood volume (v), and permeability-surface area product (PS). Region-of-interest (ROI) analysis of the tumors and the metastatic lymph nodes was performed. The perfusion parameters were compared using the Wilcoxon matched-pairs test and Bland-Altman plots.

RESULTS

One hundred fifty-two ROIs of tumors and nodes were outlined and analyzed. Moderate to good correlations were demonstrated between the various perfusion values (r = 0.56-0.72, P < .0001). The Wilcoxon test revealed a significant difference between the two methods (P < .001), with the F, v, and PS values obtained using the maximum-slope approach and Patlak analysis higher than those obtained using deconvolution-based analysis with the assumptions of the ATH model. The Bland-Altman plots for F and v values revealed a proportionality trend with outliers, which were strongly associated with the magnitudes of the parameters. Analysis of the PS values did not show any systematic bias.

CONCLUSION

There were significant differences in the perfusion parameters obtained using the two software packages, and thus, these parameters are not directly interchangeable.

Colorectal tumor vascularity: quantitative assessment with multidetector CT--do tumor perfusion measurements reflect angiogenesis?

PURPOSE

To establish the relationships between quantitative perfusion computed tomography (CT) parameters-specifically, primary tumor blood flow, blood volume, transit time, and permeability surface-area product-and immunohistologic markers of angiogenesis in colorectal cancer.

MATERIALS AND METHODS

After institutional review board approval and informed patient consent were obtained for this prospective study, 23 patients (11 men, 12 women; mean age, 68.4 years; age range, 34.8-87.1 years) with colorectal adenocarcinoma underwent a 65-second perfusion CT examination, and tumor blood flow, blood volume, mean transit time, and permeability surface-area product were determined. After surgery, resected specimens were sectioned and stained immunohistochemically to identify CD34 for quantification of microvessel density (MVD), to identify smooth muscle actin for assessment of pericyte coverage index, to identify vascular endothelial growth factor (VEGF), and to identify glucose transporter protein (GLUT-1). Perfusion CT measurements were correlated with MVD, pericyte coverage index, VEGF expression, and GLUT-1 expression by using Pearson or Spearman rank correlation analysis, with significance assigned at the 5% level.

RESULTS

Mean blood flow, blood volume, transit time, and permeability surface-area product values were 72.1 mL/min/100 g of tissue +/- 28.4 (standard deviation), 6.2 mL/100 g of tissue +/- 1.4, 9.3 seconds +/- 3.9, and 13.9 mL/min/100 g of tissue +/- 3.2, respectively. Blood volume (r = 0.59, P = .002) and permeability surface-area product (r = 0.46, P = .03) correlated positively with MVD, but blood flow (r = 0.27, P = .22) and transit time (r = -0.18, P = .44) did not. There were no significant associations between any perfusion CT parameter and pericyte coverage index (r <or= 0.36, P > .05), VEGF score (rho <or= 0.30, P >or= .15), or GLUT-1 score (rho < 0.21, P >or= .33).

CONCLUSION

Tumor permeability surface-area product and blood volume correlate positively with MVD and may reflect the microvascularity of colorectal tumors.

Imaging techniques to evaluate the response to treatment in oncology: current standards and perspectives

Response evaluation in solid tumours currently uses radiological imaging techniques to measure changes under treatment. Imaging requires a well-defined anatomical lesion to be viewed and relies on the measurement of a reduction in tumour size during treatment as the basis for presumed clinical benefit. However, with the development of anti-angiogenesis agents, anatomical imaging has became inappropriate as certain tumours would not reduce in size. Functional studies are therefore necessary and dynamic contrast enhanced magnetic resonance imaging (DCE-MRI), DCE-computed tomography (CT) and DCE-ultrasonography (US) are currently being evaluated for monitoring treatments. Diffusion-weighted MR imaging (DW-MRI) and magnetic resonance spectroscopy (MRS) are also capable of detecting changes in cell density and metabolite content within tumours. In this article, we review anatomical and functional criteria currently used for monitoring therapy. We review the published data on DCE-MRI, DCE-CT, DCE-US, DW-MRI and MRS. This literature review covers the following area: basic principles of the technique, clinical studies, reproducibility and repeatability, limits and perspectives in monitoring therapy. Anatomical criteria such as response evaluation criteria in solid tumours (RECIST) will require adaptation to employ not only new tools but also different complementary techniques such as functional imaging in order to monitor therapeutic effects of conventional and new anti-cancer agents.

Can perfusion CT assessment of primary colorectal adenocarcinoma blood flow at staging predict for subsequent metastatic disease? A pilot study

We aimed to determine whether perfusion CT measurements at colorectal cancer staging may predict for subsequent metastatic relapse. Fifty two prospective patients underwent perfusion CT at staging to estimate tumour blood flow, blood volume, mean transit time, and permeability surface area product. Patients considered metastasis free and suitable for surgery underwent curative resection subsequently. At final analysis, a median of 48.6 months post-surgery, patients were divided into those who remained disease free, and those with subsequent metastases. Vascular parameters for these two groups were compared using t-testing, and receiver operator curve analysis was performed to determine the sensitivity and specificity of these vascular parameters for predicting metastases. Thirty seven (71%) patients underwent curative surgery; data were available for 35: 26 (74%) remained disease free; 9 (26%) recurred (8 metastatic, 1 local). Tumour blood flow differed significantly between disease-free and metastatic patients (76.0 versus 45.7 ml/min/100 g tissue; p = 0.008). With blood flow <64 ml/min/100 g tissue, sensitivity and specificity (95% CI) for development of metastases were 100% (60-100%) and 73% (53-87%), respectively. Our preliminary findings suggest that primary tumour blood flow might potentially be a useful predictor warranting further study.

Dynamic perfusion CT assessment of the blood-brain barrier permeability: first pass versus delayed acquisition

BACKGROUND AND PURPOSE

The Patlak model has been applied to first-pass perfusion CT (PCT) data to extract information on blood-brain barrier permeability (BBBP) to predict hemorrhagic transformation in patients with acute stroke. However, the Patlak model was originally described for the delayed steady-state phase of contrast circulation. The goal of this study was to assess whether the first pass or the delayed phase of a contrast bolus injection better respects the assumptions of the Patlak model for the assessment of BBBP in patients with acute stroke by using PCT.

MATERIALS AND METHODS

We retrospectively identified 125 consecutive patients (29 with acute hemispheric stroke and 96 without) who underwent a PCT study by using a prolonged acquisition time up to 3 minutes. The Patlak model was applied to calculate BBBP in ischemic and nonischemic brain tissue. Linear regression of the Patlak plot was performed separately for the first pass and for the delayed phase of the contrast bolus injection. Patlak linear regression models for the first pass and the delayed phase were compared in terms of their respective square root mean squared errors (square root MSE) and correlation coefficients (R) by using generalized estimating equations with robust variance estimation.

RESULTS

BBBP values calculated from the first pass were significantly higher than those from the delayed phase, both in nonischemic brain tissue (2.81 mL x 100 g(-1) x min(-1) for the first pass versus 1.05 mL x 100 g(-1) x min(-1) for the delayed phase, P < .001) and in ischemic tissue (7.63 mL x 100 g(-1) x min(-1) for the first pass versus 1.31 mL x 100 g(-1) x min(-1) for the delayed phase, P < .001). Compared with regression models from the first pass, Patlak regression models obtained from the delayed data were of better quality, showing significantly lower square root MSE and higher R.

CONCLUSION

Only the delayed phase of PCT acquisition respects the assumptions of linearity of the Patlak model in patients with and without stroke.

Optimization of perfusion CT protocol for imaging of extracranial head and neck tumors

The in vivo assessment of physiological processes associated with microcirculation in the head and neck tissue by means of perfusion computed tomography is widely used in the management of patients with head and neck tumors. However, there is no systematic consideration of the total acquisition duration and placement of the scans. A simulation study for optimizing perfusion studies of extracranial head and neck tumors, with considerations of reducing radiation dose while maintaining accuracy of the perfusion parameters, is demonstrated here. The suggested that dual-phase optimized protocols may provide reliable estimations of the permeability surface area product as well as blood flow and volume without additional radiation burden and serious patient discomfort. These optimized protocols can potentially be useful in the clinical setting of examining patients with extracranial head and neck tumors.

Perfusion CT measurements in healthy cervical spinal cord: feasibility and repeatability of the study as well as interchangeability of the perfusion estimates using two commercially available software packages

Our purpose was to examine the feasibility and reproducibility of perfusion CT studies in the cervical spinal cord and the interchangeability of the values obtained by two post-processing methods. The perfusion CT studies of 40 patients with neck tumours were post-processed using two software packages (Software-1: deconvolution-based analysis with adiabatic tissue homogeneity approach and Software-2: maximum-slope-model with Patlak analysis). Eight patients were examined twice for assessing the reproducibility of the technique. Two neuroradiologists separately post-processed the images with two arterial input functions (AIFs): (1) the internal carotid artery (ICA) and (2) the vertebral artery (VA). Maps of blood flow (F) in ml/min/100 g, blood volume (V) in ml/100 g, mean transit time (MTT) in seconds (s) and permeability (PS) in ml/min/100 g were generated. The mean F, V, MTT and PS (Software-1) with VA-AIF and ICA-AIF were 8.93, 1.12, 16.3, 1.88 and 8.57, 1.19, 16.85 and 1.94, respectively. The reproducibility of the techniques was satisfactory, while the V and MTT values (in Software-1) and the F and V values (in Software-2) were dependent on the site of the AIF (p >or= 0.03 and p=0.02, respectively). The interobserver agreement was very good. The significant differences in measurements for a single patient (%) using Software-1/Software-2 were +/-120%/110%, 90%/80%, 180% and 250%/130% for F, V, MTT and PS, respectively. Only F and PS values in the healthy tissue seemed to be interchangeable. Our results were in essential agreement with those derived by invasive measurements in animals. The cervical spine perfusion CT studies are feasible and reproducible. The present knowledge has to be validated with studies in spinal cord tumours in order to decide the usefulness of the perfusion CT in this field.