Contrast bolus dynamic computed tomography for the measurement of solid organ perfusion

Improving pulmonary perfusion assessment by dynamic contrast-enhanced computed tomography in an experimental lung injury model

Pulmonary perfusion has been poorly characterized in acute respiratory distress syndrome (ARDS). Optimizing protocols to measure pulmonary blood flow (PBF) via dynamic contrast-enhanced (DCE) computed tomography (CT) could improve understanding of how ARDS alters pulmonary perfusion. In this study, comparative evaluations of injection protocols and tracer-kinetic analysis models were performed based on DCE-CT data measured in ventilated pigs with and without lung injury. Ten Yorkshire pigs (five with lung injury, five healthy) were anesthetized, intubated, and mechanically ventilated; lung injury was induced by bronchial hydrochloric acid instillation. Each DCE-CT scan was obtained during a 30-s end-expiratory breath-hold. Reproducibility of PBF measurements was evaluated in three pigs. In eight pigs, undiluted and diluted Isovue-370 were separately injected to evaluate the effect of contrast viscosity on estimated PBF values. PBF was estimated with the peak-enhancement and the steepest-slope approach. Total-lung PBF was estimated in two healthy pigs to compare with cardiac output measured invasively by thermodilution in the pulmonary artery. Repeated measurements in the same animals yielded a good reproducibility of computed PBF maps. Injecting diluted isovue-370 resulted in smaller contrast-time curves in the pulmonary artery (P < 0.01) and vein (P < 0.01) without substantially diminishing peak signal intensity (P = 0.46 in the pulmonary artery) compared with the pure contrast agent since its viscosity is closer to that of blood. As compared with the peak-enhancement model, PBF values estimated by the steepest-slope model with diluted contrast were much closer to the cardiac output (R2 = 0.82) as compared with the peak-enhancement model. DCE-CT using the steepest-slope model and diluted contrast agent provided reliable quantitative estimates of PBF.NEW & NOTEWORTHY Dynamic contrast-enhanced CT using a lower-viscosity contrast agent in combination with tracer-kinetic analysis by the steepest-slope model improves pulmonary blood flow measurements and assessment of regional distributions of lung perfusion.

Considerations for Imaging of Malignant Pleural Mesothelioma: A Consensus Statement from the International Mesothelioma Interest Group

Malignant pleural mesothelioma (MPM) is an aggressive primary malignancy of the pleura that presents unique radiologic challenges with regard to accurate and reproducible assessment of disease extent at staging and follow-up imaging. By optimizing and harmonizing technical approaches to imaging MPM, the best quality imaging can be achieved for individual patient care, clinical trials, and imaging research. This consensus statement represents agreement on harmonized, standard practices for routine multimodality imaging of MPM, including radiography, computed tomography, ¹⁸F-2-deoxy-D-glucose positron emission tomography, and magnetic resonance imaging, by an international panel of experts in the field of pleural imaging assembled by the International Mesothelioma Interest Group. In addition, modality-specific technical considerations and future directions are discussed. A bulleted summary of all technical recommendations is provided.

Mathematical Models for Blood Flow Quantification in Dialysis Access Using Angiography: A Comparative Study

Blood flow rate in dialysis (vascular) access is the key parameter to examine patency and to evaluate the outcomes of various endovascular interve7ntions. While angiography is extensively used for dialysis access–salvage procedures, to date, there is no image-based blood flow measurement application commercially available in the angiography suite. We aim to calculate the blood flow rate in the dialysis access based on cine-angiographic and fluoroscopic image sequences. In this study, we discuss image-based methods to quantify access blood flow in a flow phantom model. Digital subtraction angiography (DSA) and fluoroscopy were used to acquire images at various sampling rates (DSA—3 and 6 frames/s, fluoroscopy—4 and 10 pulses/s). Flow rates were computed based on two bolus tracking algorithms, peak-to-peak and cross-correlation, and modeled with three curve-fitting functions, gamma variate, lagged normal, and polynomial, to correct errors with transit time measurement. Dye propagation distance and the cross-sectional area were calculated by analyzing the contrast enhancement in the vessel. The calculated flow rates were correlated versus an in-line flow sensor measurement. The cross-correlation algorithm with gamma-variate curve fitting had the best accuracy and least variability in both imaging modes. The absolute percent error (mean ± SEM) of flow quantification in the DSA mode at 6 frames/s was 21.4 ± 1.9%, and in the fluoroscopic mode at 10 pulses/s was 37.4 ± 3.6%. The radiation dose varied linearly with the sampling rate in both imaging modes and was substantially low to invoke any tissue reactions or stochastic effects. The cross-correlation algorithm and gamma-variate curve fitting for DSA acquisition at 6 frames/s had the best correlation with the flow sensor measurements. These findings will be helpful to develop a software-based vascular access flow measurement tool for the angiography suite and to optimize the imaging protocol amenable for computational flow applications.

Differences of liver CT perfusion of blunt trauma treated with therapeutic embolization and observation management

Massive hepatic necrosis after therapeutic embolization has been reported. We employed a 320-detector CT scanner to compare liver perfusion differences between blunt liver trauma patients treated with embolization and observation. This prospective study with informed consent was approved by institution review board. From January 2013 to December 2016, we enrolled 16 major liver trauma patients (6 women, 10 men; mean age 34.9 ± 12.8 years) who fulfilled inclusion criteria. Liver CT perfusion parameters were calculated by a two-input maximum slope model. Of 16 patients, 9 received embolization and 7 received observation. Among 9 patients of embolization group, their arterial perfusion (78.1 ± 69.3 versus 163.1 ± 134.3 mL/min/100 mL, p = 0.011) and portal venous perfusion (74.4 ± 53.0 versus 160.9 ± 140.8 mL/min/100 mL, p = 0.008) were significantly lower at traumatic parenchyma than at non-traumatic parenchyma. Among 7 patients of observation group, only portal venous perfusion was significantly lower at traumatic parenchyma than non-traumatic parenchyma (132.1 ± 127.1 vs. 231.1 ± 174.4 mL/min/100 mL, p = 0.018). The perfusion index between groups did not differ. None had massive hepatic necrosis. They were not different in age, injury severity score and injury grades. Therefore, reduction of both arterial and portal venous perfusion can occur when therapeutic embolization was performed in preexisting major liver trauma, but hepatic perfusion index may not be compromised.

Positron Emission Tomography After Ischemic Brain Injury: Current Challenges and Future Developments

Positron emission tomography (PET) is widely used in clinical and animal studies, along with the development of diverse tracers. The biochemical characteristics of PET tracers may help uncover the pathophysiological consequences of cardiac arrest (CA) and ischemic stroke, which include cerebral ischemia and reperfusion, depletion of oxygen and glucose, and neuroinflammation. PubMed was searched for studies of the application of PET for "cardiac arrest," "ischemic stroke," and "targeted temperature management." Available studies were included and classified according to the biochemical properties involved and metabolic processes of PET tracers, and were summarized. The mechanisms of ischemic brain injuries were investigated by PET with various tracers to elucidate the pathological process from the initial decrease of cerebral blood flow (CBF) to the subsequent abnormalities in energy and oxygen metabolism, to the monitoring of inflammation. In general, the trends of cerebral blood flow and oxygen metabolism after ischemic attack are not unidirectional but closely related to the time point of injury and recovery. Glucose metabolism after injury showed significant differences in different brain regions whereas global cerebral metabolic rate of glucose (CMRglc) declined. PET monitoring of neuroinflammation shows comparable efficacy to immunostaining. The technology of PET targeting in brain metabolism and the development of tracers provide new tools to track and evaluate the brain's pathological changes after ischemic brain injury. Despite no existing evidence for an available PET-based prediction method, discoveries of new tracers are expected to provide more possibilities for the whole field.

Estimation of microvascular perfusion after esophagectomy: a quantitative model of dynamic fluorescence imaging

Most common complications of esophagectomy stem from a perfusion deficiency of the gastric conduit at the anastomosis. Fluorescent tracer imaging allows intraoperative visualization of tissue perfusion. Quantitative assessment of fluorescence dynamics has the potential to identify perfusion deficiency. We developed a perfusion model to analyze the relation between fluorescence dynamics and perfusion deficiency. The model divides the gastric conduit into two well-perfused and two anastomosed sites. Hemodynamics and tracer transport were modeled. We analyzed the value of relative time-to-threshold (RTT) as a predictor of the relative remaining flow (RRF). Intensity thresholds for RTT of 20% to 50% of the maximum fluorescence intensity of the well-perfused site were tested. The relation between RTT and RRF at the anastomosed sites was evaluated over large variations of vascular conductance and volume. The ability of RTT to distinguish between sufficient and impaired perfusion was analyzed using c-statistics. We found that RTT was a valuable estimate for low RRF. The threshold of 20% of the maximum fluorescence intensity provided the best prediction of impaired perfusion on the two anastomosed sites (AUC = 0.89 and 0.86). The presented model showed that for low flows, relative time-to-threshold may be used to estimate perfusion deficiency.

New targeted molecular therapies for cancer: radiological response in intrathoracic malignancies and cardiopulmonary toxicity: what the radiologist needs to know

The emergence of new novel therapeutic agents which directly target molecules that are uniquely or abnormally expressed in cancer cells (molecular targeted therapy, MTT) has changed dramatically the treatment of cancer in recent years. The clinical benefit associated with these agents is typically limited to a subset of treated patients, who in many cases are defined by a specific genomic mutations and expression lesion within their tumor cells. All these new therapy modalities represent new challenges to radiologists as their mechanism of action and side effect profiles differ from conventional chemotherapy agents. In this article we will discuss radiological patterns of response to molecular targeted therapies MTT in lung cancer, typical and atypical radiological responses of targeted molecular therapy for other intra thoracic malignancies, cardiopulmonary toxicity and other side effects of molecular targeted therapy MTT in the thorax.

Role of Perfusion CT Differentiating Hemangiomas from Malignant Hepatic Lesions

Objective:

The purpose of the study was to determine the role of computed tomography (CT) perfusion in differentiating hemangiomas from malignant hepatic lesions.

Materials and Methods:

This study was approved by the institutional review board. All the patients provided informed consent. CT perfusion was performed with 64 multidetector CT (MDCT) scanner on 45 patients including 27 cases of metastasis, 9 cases of hepatocellular carcinoma (HCC), and 9 cases of hemangiomas. A 14 cm span of the liver was covered during the perfusion study. Data was analyzed to calculate blood flow (BF), blood volume (BV), permeability surface area product (PS), mean transit time (MTT), hepatic arterial fraction (HAF), and induced residue fraction time of onset (IRFTO). CT perfusion parameters at the periphery of lesions and background liver parenchyma were compared.

Results:

Significant changes were observed in the perfusion parameters at the periphery of different lesions. Of all the perfusion parameters BF, HAF, and IRFTO showed most significant changes. In our study we found: BF of more than 400 ml/100 g/min at the periphery of the hemangiomas showed sensitivity of 88.9%, specificity of 83.3%, positive predictive value (PPV) of 57.1%, and negative predictive value (NPV) of 96.7% in differentiating hemangiomas from hepatic malignancy; HAF of more than 60% at the periphery of hemangiomas showed sensitivity of 77.8%, specificity of 86.1%, PPV of 58.3% and NPV of 93.9% in differentiating hemangiomas from hepatic malignancy; IRFTO of more than 3 s at the periphery of hemangiomas showed sensitivity of 77.8%, specificity of 86.1%, PPV of 58.3%, and NPV of 93.9% in differentiating hemangiomas from hepatic malignancy.

Conclusion:

Perfusion CT is a helpful tool in differentiating hemangiomas from hepatic malignancy by its ability to determine changes in perfusion parameters of the lesions.

How influential is the duration of contrast material bolus injection in perfusion CT? evaluation in a swine model

PURPOSE

To analyze the effect of the duration of contrast material bolus injection on perfusion values in a swine model by using the maximum slope method.

MATERIALS AND METHODS

This study was approved by the institutional animal care committee. Twenty pigs (weight range, 63-77 kg) underwent dynamic volume computed tomography (CT) of the kidneys during suspended respiration. Before the CT examination, a miniature cuff-shaped ultrasonographic flow probe encircling the right renal artery was surgically implanted in each pig to obtain true perfusion values. Two sequential perfusion CT series were performed in 30 seconds, each comprising 30 volumes with identical parameters (100 kV, 200 mAs, 0.5 sec rotation time). The duration of contrast material bolus (0.5 mL/kg of body weight) was 3.8 seconds in the first series (short bolus series) and 11.5 seconds in the second series (long bolus series), and the injection flow rate was adapted accordingly. In each pig, cortical kidney volume was determined by using the volume with the highest cortical enhancement. CT perfusion values were calculated for both series by using the maximum slope method and were statistically compared and correlated with the true perfusion values from the flow probe by using linear regression analysis.

RESULTS

Mean true perfusion and CT perfusion values (in minutes(-1)) for the short bolus series were 1.95 and 2.03, respectively (P = .22), and for the long bolus series, they were 2.02 and 1.92, respectively (P = .12). CT perfusion showed very good correlation with true perfusion in both the short (slope, 1.01; 95% confidence interval: 0.91, 1.11) and long (slope, 0.92; 95% confidence interval: 0.78, 1.04) series. On the basis of the regression analysis, CT perfusion values in the short bolus series were overestimated by 1% and those in the long bolus series were underestimated by 8%.

CONCLUSION

Duration of contrast material bolus injection does not influence CT perfusion values substantially. The longer, clinically preferred intravenous injection scheme is sufficiently accurate for CT perfusion.

Gastric cancer staging with dual energy spectral CT imaging

Purpose

To evaluate the clinical utility of dual energy spectral CT (DEsCT) in staging and characterizing gastric cancers.

Materials and Methods

96 patients suspected of gastric cancers underwent dual-phasic scans (arterial phase (AP) and portal venous phase (PP)) with DEsCT mode. Three types of images were reconstructed for analysis: conventional polychromatic images, material-decomposition images, and monochromatic image sets with photon energies from 40 to 140 keV. The polychromatic and monochromatic images were compared in TNM staging. The iodine concentrations in the lesions and lymph nodes were measured on the iodine-based material-decomposition images. These values were further normalized against that in aorta and the normalized iodine concentration (nIC) values were statistically compared. Results were correlated with pathological findings.

Results

The overall accuracies for T, N and M staging were (81.2%, 80.0%, and 98.9%) and (73.9%, 75.0%, and 98.9%) determined with the monochromatic images and the conventional kVp images, respectively. The improvement of the accuracy in N-staging using the keV images was statistically significant (p<0.05). The nIC values between the differentiated and undifferentiated carcinoma and between metastatic and non-metastatic lymph nodes were significantly different both in AP (p = 0.02, respectively) and PP (p = 0.01, respectively). Among metastatic lymph nodes, nIC of the signet-ring cell carcinoma were significantly different from the adenocarcinoma (p = 0.02) and mucinous adenocarcinoma (p = 0.01) in PP.

Conclusion

The monochromatic images obtained with DEsCT may be used to improve the N-staging accuracy. Quantitative iodine concentration measurements may be helpful for differentiating between differentiated and undifferentiated gastric carcinoma, and between metastatic and non-metastatic lymph nodes.

[Dynamic contrast-enhanced computed tomography. Tracer kinetics and radiation hygienic principles]

Technical innovations in multislice computed tomography (CT) allow for larger volume coverage in ever shorter scan times. This progress has stimulated the clinical application of dynamic contrast-enhanced (DCE) CT techniques, which offer the possibility to noninvasively characterize tissue microcirculation in terms of well-defined physiological quantities. This educational review imparts to radiologists the essential physiological terms and definitions as well as the basic tracer kinetic concepts required for the analysis of DCE-CT data. In particular, four different approaches are presented and exemplified by the analysis of representative DCE data: the steepest-gradient method, model-free algebraic deconvolution in combination with the indicator-dilution theory, two-compartment modelling and the so-called adiabatic approximation to the homogeneity model. Even though DCE-CT offers substantial methodological and practical advantages as compared to DCE-MRI (magnetic resonance imaging), there are also two serious and interconnected shortcomings: the low contrast enhancement in relation to the noise level and the high exposure of patients to ionizing radiation. These limiting aspects are considered in detail from a radiation hygienic point of view, emphasizing the basic principles of justification and optimization. Clinically established as well as potential future applications of DCE-CT will be presented in a subsequent paper.

Assessment of splenic perfusion in patients with malignant hematologic diseases and spleen involvement, liver cirrhosis and controls using volume perfusion CT (VPCT): a pilot study

RATIONALE AND OBJECTIVES

The aim of this study was to assess splenic perfusion in patients with spleen involvement in malignant hematologic diseases and liver cirrhosis and in controls without hepatosplenic disease using volume perfusion computed tomography.

MATERIALS AND METHODS

Between October 2009 and December 2011, 14 hematologic patients with known spleen involvement were recruited. An additional 17 consecutive patients without known splenic or liver disease were enrolled as controls, as well as 29 patients with liver cirrhosis and portal hypertension. A 40-second volume perfusion computed tomographic scan of the upper abdomen was performed. Analysis included measurement of splenic volume, blood flow (BF), blood volume (BV), K(trans), and mean transit time (MTT).

RESULTS

In lymphoma patients, mean splenic volume and perfusion parameters were as follows: splenic volume, 1125.34 mL; BF, 61.24 mL/100 mL/min; BV, 16.53 mL/100 mL; K(trans), 37.00 mL/100 mL/min; and MTT, 12.42 seconds. All perfusion values of patients with lymphoma and cirrhosis differed significantly, except for BV, compared to controls. For patients with lymphoma, significant correlations were found between splenic volume and BF (r = -0.683, P = .000), splenic volume and BV (r = -0.525, P = .002), and splenic volume and MTT (r = 0.543, P = .001). During treatment, significant correlations between the diameters of nodular lymphoma target lesions, splenic volume, and the perfusion parameters were present for splenic volume (r = 0.601, P = .002), BF (r = -0.777, P = .000) and BV (r = -0.500, P = .011).

CONCLUSIONS

Volume perfusion computed tomography represents a novel tool for the assessment of splenic perfusion. Preliminary results in patients with spleen involvement reveal lower perfusion values compared to controls or patients with cirrhosis. Therefore, this technique might provide additional information in clinical routine.

Estimation of glomerular filtration rate in healthy cats using single-slice dynamic CT and Patlak plot analysis

Commonly used clinical indicators of renal disease are either insensitive to early dysfunction or have delayed results. Decreased glomerular filtration rate (GFR) indicates renal dysfunction before there is a loss of 50% of functional nephrons. Most tests evaluate global rather than individual kidney function. Dynamic computed tomography (CT) and Patlak plot analysis allows for individual GFR to be tested. Our objectives were to establish a procedure and provide reference values for determination of global GFR in 10 healthy cats using dynamic CT (CTGFR). This method of GFR determination was compared against serum iohexol clearance (SIC). A single CT slice centered on both kidneys and the aorta was acquired every fifth second during and after a bolus injection of iohexol (240 mgI/ml; 300 mgI/kg) for 115 s. Using data from this dynamic acquisition, Patlak plots were obtained, GFR was calculated, and results were compared to global GFR determined by iohexol clearance. The average global CTGFR estimate was 1.84 ml/min x kg (SD = 0.43; range = [1.22, 2.45]). The average global GFR measured using SIC was 2.45 ml/min x kg (SD = 0.58; range = [1.72, 3.69]). GFR measurements estimated by both dynamic CT and SIC were positively associated (estimated Spearman rank correlation coefficient = 0.72; P = 0.0234). The CTGFR method consistently underestimated GFR with a bias of -0.62 (SE = 0.1307) when compared to SIC (P = 0.0011). In healthy cats, CTGFR was capable of determining individual kidney function and appears clinically promising.

Role of quantitative chest perfusion computed tomography in detecting diabetic pulmonary microangiopathy

AIMS

Aim of the study was to determine the role of perfusion chest computed tomography (pCT) in evaluation of pulmonary diabetic angiopathy.

METHODS

18 never-smoking patients (10 diabetic patients and 8 healthy controls) underwent chest high resolution CT (HRCT) and then pCT scanning. In both groups, blood tests, biochemical analysis, fibrinogen, HbA(1c), spirometry, diffusion capacity for carbon monoxide (DLCO) and body pletysmography were performed.Following parameters of pulmonary perfusion have been analysed: blood volume (BV), blood flow (BF), mean transit time (MTT), time to peak (TTP) and permeability surface (PS).

RESULTS

there were no statistically significant differences between groups in terms of age, sex, BMI, forced expiratory volume in one second (FEV(1)), DLCO. Chest HRCT revealed no pathologies. Significantly higher values of chest pCT for BF (p=0.05), BV (p=0.05) and PS (p=0.01) have been found in diabetics in comparison to controls. No differences were found in MTT.

CONCLUSIONS

significant increase of perfusion parameters in diabetes seems to confirm pulmonary microangiopathy. The results indicate that further studies on application of pCT in diabetic patients may be beneficial for better understanding of lung microangiopathy, its diagnosing and monitoring.

Tracer kinetic modelling of tumour angiogenesis based on dynamic contrast-enhanced CT and MRI measurements

PURPOSE

Technical developments in both magnetic resonance imaging (MRI) and computed tomography (CT) have helped to reduce scan times and expedited the development of dynamic contrast-enhanced (DCE) imaging techniques. Since the temporal change of the image signal following the administration of a diffusible, extracellular contrast agent (CA) is related to the local blood supply and the extravasation of the CA into the interstitial space, DCE imaging can be used to assess tissue microvasculature and microcirculation. It is the aim of this review to summarize the biophysical and tracer kinetic principles underlying this emerging imaging technique offering great potential for non-invasive characterization of tumour angiogenesis.

METHODS

In the first part, the relevant contrast mechanisms are presented that form the basis to relate signal variations measured by serial CT and MRI to local tissue concentrations of the administered CA. In the second part, the concepts most widely used for tracer kinetic modelling of concentration-time courses derived from measured DCE image data sets are described in a consistent and unified manner to highlight their particular structure and assumptions as well as the relationships among them. Finally, the concepts presented are exemplified by the analysis of representative DCE data as well as discussed with respect to present and future applications in cancer diagnosis and therapy.

RESULTS

Depending on the specific protocol used for the acquisition of DCE image data and the particular model applied for tracer kinetic analysis of the derived concentration-time courses, different aspects of tumour angiogenesis can be quantified in terms of well-defined physiological tissue parameters.

CONCLUSIONS

DCE imaging offers promising prospects for improved tumour diagnosis, individualization of cancer treatment as well as the evaluation of novel therapeutic concepts in preclinical and early-stage clinical trials.

Estimation of tissue perfusion by dynamic contrast-enhanced imaging: simulation-based evaluation of the steepest slope method

OBJECTIVE

Tissue perfusion is frequently determined from dynamic contrast-enhanced CT or MRI image series by means of the steepest slope method. It was thus the aim of this study to systematically evaluate the reliability of this analysis method on the basis of simulated tissue curves.

METHODS

9600 tissue curves were simulated for four noise levels, three sampling intervals and a wide range of physiological parameters using an axially distributed reference model and subsequently analysed by the steepest slope method.

RESULTS

Perfusion is systematically underestimated with errors becoming larger with increasing perfusion and decreasing intravascular volume. For curves sampled after rapid contrast injection with a temporal resolution of 0.72 s, the bias was less than 23% when the mean residence time of tracer molecules in the intravascular distribution space was greater than 6 s. Increasing the sampling interval and the noise level substantially reduces the accuracy and precision of estimates, respectively.

CONCLUSIONS

The steepest slope method allows absolute quantification of tissue perfusion in a computationally simple and numerically robust manner. The achievable degree of accuracy and precision is considered to be adequate for most clinical applications.

Quantitative assessment of blood volume and permeability in cerebral mass lesions using dynamic contrast-enhanced computed tomography in the dog

RATIONALE AND OBJECTIVES

To evaluate cerebral blood volume (CBV) and permeability (PS) in spontaneously occurring cerebral neoplastic and non-neoplastic lesions in dogs using dynamic contrast-enhanced computed tomography (DCE-CT).

MATERIALS AND METHODS

Dogs presenting with spontaneous intracranial lesions (n = 16) underwent DCE-CT at the level of the lesion followed by a histologically confirmed diagnosis from a CT-guided stereotactic biopsy. Data post-processing was performed with commercially available CT software (GEMS Advantage Workstation 4.2). Symmetric regions of interest (ROIs) were drawn within the lesion and unaffected areas on the contralateral side. Values were compared between lesion types and ratios of lesion-to-normal brain were calculated.

RESULTS

Dogs with extra-axial lesions (n = 3 meningiomas) had marked elevation of CBV and PS compared to normal brain. All Grade III gliomas (n = 5) had mildly elevated CBV and markedly elevated PS values. All lower Grade II gliomas (n = 2) had minimal elevation in CBV and PS. Dogs with non-neoplastic intra-axial lesions (one each necrotizing, fungal, and lymphoplasmacytic encephalitis) had elevation of PS with normal to mildly elevated CBV. Lesion-to-normal brain ratios for PS separated extra- and intra-axial neoplasms and intra-axial inflammatory/degenerative lesions from each other.

CONCLUSIONS

Low-grade gliomas do not consistently demonstrate elevated vascular parameters, whereas Grade III gliomas and non-neoplastic intra-axial lesions have elevated PS. Ratios between such lesions and normal brain may prove useful for differentiating types of lesions. These findings resemble those previously reported in similar lesions in people indicating that the dog may act as a good model for intracranial masses for the study of lesion angiogenesis and response to therapy.

Perfusion computed tomography could be a new tool for single-session imaging of ureteric obstructive pathology: an experimental study in rats

BACKGROUND/PURPOSE

Perfusion imaging redefines computed tomography (CT) as a technique that can now depict vascular physiology in addition to detailed anatomy. The major clinical applications of perfusion CT are in acute stroke and oncology. Currently, there are very limited data on the application of perfusion CT in urology. The aim of the present study is to investigate the potential value of perfusion CT in anatomic and functional evaluation of obstruction in a single session on experimental hydronephrosis model in rats. Thus, we evaluate the perfusion CT in a new clinical application.

METHODS

Twenty-eight rats were randomly allocated into 4 groups each consisting of 7 rats. At the third week of experimental intervention, postoperative renogram curves and perfusion parameters of the right kidneys' cortex and pelvis were assessed by CT. The right ureter was sutured as proximal complete obstruction in group 1, as distal complete obstruction in group 2, and as proximal partial obstruction in group 3. Group 4 served as the sham control group. Computed tomography was performed with single-slice tomography. Dynamic examination was performed with the help of perfusion software through contrast-enhanced tomography examination.

RESULTS

In all study groups, the aorta time/density curves showed a rapid increase after a rapid decrease, and the duration to reach peak concentration in the normal kidney cortex was observed to be later than the aorta as expected. In groups 1, 2, and 3, the duration to reach peak concentration lengthened and the peak concentration values decreased. The time/density curves gradually increased as a result of the accumulation of the contrast agent in the pelvis, and a peak was observed at the end of the procedure in all study groups. In groups 1, 2, and 3, a statistically significant decrease (P = .01, P = .01, and P = .01, respectively) was observed in the peak concentration values of the contrast agent in comparison to group 4. The flow and blood volume values gradually decreased as the grade of the obstruction increased and the localization of the obstruction or grade of obstruction moved closer to the kidney.

CONCLUSION

In conclusion, perfusion CT technique, performed in a single session, is a useful method for anatomic visualization, together with functional evaluation, in the diagnosis of ureteric obstructive pathology of experimental hydronephrosis model.

Pharmacokinetic analysis of tissue microcirculation using nested models: multimodel inference and parameter identifiability

The purpose of this study is to evaluate the identifiability of physiological tissue parameters by pharmacokinetic modeling of concentration-time curves derived under conditions that are realistic for dynamic-contrast-enhanced (DCE) imaging and to assess the information-theoretic approach of multimodel inference using nested models. Tissue curves with a realistic noise level were simulated by means of an axially distributed multipath reference model using typical values reported in literature on plasma flow, permeability-surface area product, and volume fractions of the intravascular and interstitial space. The simulated curves were subsequently analyzed by a two-compartment model containing these physiological quantities as fit parameters as well as by two reduced models with only three and two parameters formulated for the case of a permeability-limited and a flow-limited scenario, respectively. The competing models were ranked according to Akaike's information criterion (AIC), balancing the bias versus variance trade-off. To utilize the information available from all three models, model-averaged parameters were estimated using Akaike weights that quantify the relative strength of evidence in favor of each model. As compared to the full model, the reduced models yielded equivalent or even superior AIC values for scenarios where the structural information in the tissue curves on either the plasma flow or the capillary permeability was limited. Multimodel inference took effect to a considerable extent in half of the curves and improved the precision of the estimated tissue parameters. As theoretically expected, the plasma flow was subject to a systematic (but largely correctable) overestimation, whereas the other three physiological tissue parameters could be determined in a numerically robust and almost unbiased manner. The presented concept of pharmacokinetic analysis of noisy DCE data using three nested models under an information-theoretic paradigm offers promising prospects for the noninvasive quantification of physiological tissue parameters.

Quantitative measurement of blood flow using perfusion CT for assessing clinicopathologic features and prognosis in patients with rectal cancer

PURPOSE

The ability to evaluate clinicopathologic features and prognosis before surgery by contrast-enhanced CT would be valuable for managing rectal cancer. This study was designed to evaluate the clinical usefulness of perfusion CT in patients with rectal cancer before surgery.

METHODS

Forty-four consecutive patients (27 men, 17 women; median age, 63.6 years) with rectal cancer underwent perfusion CT before surgery. We retrospectively investigated the correlations between tumor blood flow generated by perfusion CT and clinicopathologic features.

RESULTS

There was a significant correlation between blood flow and wall invasion (P = 0.04). Well-differentiated tumors showed significantly higher blood flow than moderately differentiated tumors (P = 0.03). There was a significant tendency for tumors with low blood flow to show lymph node metastasis (P = 0.0005), vascular invasion (P = 0.004), lymphatic invasion (P = 0.04), and distant metastasis (P = 0.0005). For blood flow, accuracy was 75% for detection of tumors with lymph node metastasis if the cutoff point was set at 55 ml/100 g per minute. Patients with high blood flow tumors survived significantly longer than those with low blood flow tumors (P = 0.002).

CONCLUSIONS

Blood flow of rectal cancers may be useful to evaluate pathologic features and prognosis before surgery.

Body perfusion CT: technique, clinical applications, and advances

Perfusion CT has made tremendous progress since its inception and is gradually broadening its applications from the research realm into routine clinical care. This has been particularly noteworthy in the oncological setting, where perfusion CT is emerging as a valuable tool in tissue characterization, risk stratification and monitoring treatment effects especially assessing early response to novel targeted therapies. Recent technological advancements in CT have paved ways to overcome the initial limitations of restricted tissue coverage and radiation dose concerns. In this article, the authors review the basic principles and technique of perfusion CT and discuss its various oncologic and non-oncological clinical applications in body imaging.

Quantitative assessment of early experimental diabetes in rats using dynamic contrast-enhanced computed tomography

PURPOSE

To quantitatively assess the time course of changes of the renal volume and function in the early phase of streptozotocin (STZ)-induced diabetes in rats using dynamic contrast-enhanced computed tomography (DCE-CT).

METHODS

The DCE-CT studies were performed in 24 male Sprague-Dawley rats (n=6 for control and n=18 for STZ-treated group) on days 0, 4, 7, 11, and 14 using a multi-detector row CT. The rats of an STZ-treated group were given intraperitoneally 65mg/kg body weight of STZ on day 0, and were divided into two groups based on the blood glucose concentration on day 4 being less than 300mg/dL [STZ-treated group (L), n=8] or greater than 300mg/dL [STZ-treated group (G), n=10]. The contrast clearance per unit renal volume (K(1)) was estimated from the DCE-CT data using the Patlak model. The renal volume (V(CT)) was calculated by manually delineating the kidney on the contrast-enhanced CT image. The contrast clearance of the entire kidney (K) was obtained by K(1)xV(CT).

RESULTS

V(CT) in the STZ-treated group was significantly enlarged on day 4 compared to that on day 0 and continued until day 14. Although there were no significant changes in the time course of K(1) in all groups, K in the STZ-treated groups (L) and (G) significantly increased on days 7 and 4, respectively, and continued until day 14, suggesting that hyperfiltration occurs in parallel with renal volume enlargement.

CONCLUSION

The present method appears useful for quantitatively evaluating the time course of STZ-induced diabetes in rats, because it allows repeated and simultaneous evaluation of renal morphology and function.

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.

The usefulness of CT perfusion in differentiation between neoplastic and tuberculous disease of the spine

INTRODUCTION

Routine diagnostic techniques are not sufficient to confidently differentiate diseases of the axial skeleton. Purpose of study was to determine whether CT perfusion (CTP) can differentiate inflammatory diseases like tuberculosis from neoplastic diseases of spine.

METHODS

Fifty-one patients with vertebrdraft%freshal body lesions associated with paraspinal mass underwent CT guided bone biopsy and histopathological evaluation. CTP was done before doing bone biopsy. Perfusion parameters like blood volume (BV), blood flow (BF), and time to peak (TTP) were calculated. Values are correlated with histopathological report of bone biopsy. Statistical analysis was done using Mann-Whitney test. P value < .05 was considered significant.

RESULTS

Of 51, 32 had infective osteomyelitis and 19 neoplastic disease (9 metastasis, 5 plasmacytoma, 4 lymphoma and 1 chordoma. Mean rBF was [inflammatory lesions, 1.79 and neoplastic lesions, 9.42 (P < .000)]. Mean rBV was [inflammatory disease, 1.63 and neoplastic lesions, 9.37 (P < .000)].

CONCLUSION

CTP technique has potential for differentiating inflammatory from neoplastic lesions affecting spine associated with paraspinal mass noninvasively.

Advanced gastric cancer and perfusion imaging using a multidetector row computed tomography: correlation with prognostic determinants

Objective

To investigate the relationship between the perfusion CT features and the clinicopathologically determined prognostic factors in advanced gastric cancer cases.

Materials and Methods

A perfusion CT was performed on 31 patients with gastric cancer one week before surgery using a 16-channel multi-detector CT (MDCT) instrument. The data were analyzed with commercially available software to calculate tumor blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS). The microvessel density (MVD), was evaluated by immunohistochemical staining of the surgical specimens with anti- CD34. All of the findings were analyzed prospectively and correlated with the clinicopathological findings, which included histological grading, presence of lymph node metastasis, serosal involvement, distant metastasis, tumor, node, metastasis (TNM) staging, and MVD. The statistical analyses used included the Student's t-test and the Spearman rank correlation were performed in SPSS 11.5.

Results

The mean perfusion values and MVD for tumors were as follows: BF (48.14±16.46 ml/100 g/min), BV (6.70±2.95 ml/100 g), MTT (11.75±4.02 s), PS (14.17±5.23 ml/100 g/min) and MVD (41.7±11.53). Moreover, a significant difference in the PS values was found between patients with or without lymphatic involvement (p = 0.038), as well as with different histological grades (p = 0.04) and TNM stagings (p = 0.026). However, BF, BV, MTT, and MVD of gastric cancer revealed no significant relationship with the clinicopathological findings described above (p > 0.05).

Conclusion

The perfusion CT values of the permeable surface could serve as a useful prognostic indicator in patients with advanced gastric cancer.

Dynamic computed tomographic quantitation of hepatic perfusion in dogs with and without portal vascular anomalies

OBJECTIVE

To compare hepatic, pancreatic, and gastric perfusion on dynamic computed tomography (CT) scans of clinically normal dogs with those of dogs with portal vascular anomalies.

SAMPLE POPULATION

Dynamic computed tomography (CT) scans of 10 clinically normal dogs and 21 dogs with portal vascular anomalies.

PROCEDURES

Retrospective analysis of dynamic CT scans. Hepatic arterial perfusion, hepatic portal perfusion, total hepatic perfusion, hepatic perfusion index, gastric perfusion, and pancreatic perfusion were calculated from time attenuation curves.

RESULTS

Mean +/- hepatic arterial perfusion was significantly higher in affected dogs (0.57 +/- 0.27 mL/min x mL(-1)) than in clinically normal dogs (0.23 +/- 0.11 mL/min x mL(-1)), and hepatic portal perfusion was significantly lower in affected dogs (0.52 +/- 0.47 mL/min x mL(-1)) than in clinically normal dogs (1.08 +/- 0.45 mL/min x mL(-1)). This was reflected in the hepatic perfusion index, which was significantly higher in affected dogs (0.59 +/- 0.34), compared with clinically normal dogs (0.19 +/- 0.07). Gastric perfusion was significantly higher in dogs with portal vascular anomalies (0.72 +/- 0.44 mL/min x mL(-1)) than in clinically normal dogs (0.41 +/- 0.21 mL/min x mL(-1)), but total hepatic perfusion and pancreatic perfusion were not significantly different. Among subgroups, dogs with congenital intrahepatic portosystemic shunts and dogs with arterioportal fistulae had higher hepatic arterial perfusion than did clinically normal dogs. Dogs with congenital intrahepatic portosystemic shunts also had an increase in gastric perfusion and hepatic perfusion index.

CONCLUSIONS AND CLINICAL RELEVANCE

Hepatic perfusion variables measured on CT scans revealed differences in hemodynamics between clinically normal dogs and those with portal vascular anomalies.

CT perfusion for determination of pharmacologically mediated blood flow changes in an animal tumor model

PURPOSE

To prospectively compare single- and multisection computed tomographic (CT) perfusion for tumor blood flow determination in an animal model.

MATERIALS AND METHODS

All animal protocols and experiments were approved by the institutional animal care and use committee before the study was initiated. R3230 mammary adenocarcinoma was implanted in 11 rats. Tumors (18-20 mm) were scanned with dynamic 16-section CT at baseline and after administration of arsenic trioxide, which is known to cause acute reduction in blood flow. The concentration of arsenic was titrated (0-6 mg of arsenic per kilogram of body weight) to achieve a defined blood flow reduction (0%-75%) from baseline levels at 60 minutes, as determined with correlative laser Doppler flowmetry. The mean blood flow was calculated for each of four 5-mm sections that covered the entire tumor, as well as for the entire tumor after multiple sections were processed. Measurements obtained with both methods were correlated with laser Doppler flowmetry measurements. Interobserver agreement was determined for two blinded radiologists, who calculated the percentage of blood flow reduction for the "most representative" single sections at baseline and after arsenic administration. These results were compared with the interobserver variability of the same radiologists obtained by summing blood flow changes for the entire tumor volume.

RESULTS

Overall correlations for acute blood flow reduction were demonstrated between laser Doppler flowmetry and the two CT perfusion approaches (single-section CT, r=0.85 and r(2)=0.73; multisection CT, r=0.93 and r(2)=0.87; pooled data, P=.01). CT perfusion disclosed marked heterogeneity of blood flow, with variations of 36% +/- 13 between adjacent 5-mm sections. Given these marked differences, interobserver agreement was much lower for single-section CT (standard deviation, 0.22) than for multisection CT (standard deviation, 0.10; P=.01).

CONCLUSION

Multisection CT perfusion techniques may provide an accurate and more reproducible method of tumor perfusion surveillance than comparison of single representative tumor sections.

Hemodynamic studies on brain CT perfusion imaging with varied injection rates

OBJECTIVE

This study aimed to determine a contrast medium injection rate that ensures both accuracy for data and safety for operation by comparing hemodynamic parameters of brain CT perfusion imaging with varied injection rates.

METHODS

Twenty-four healthy volunteers were divided into three groups based on contrast medium injection rates (4.5, 6.0, and 7.5 ml/s). For all subjects, CT perfusion scanning was started at 4 s after antecubital venous bolus of contrast media injection. A perfusion-analyzing software package was used to produce a time-density curve in the anterior cerebral artery and the superior sagittal sinus and calculate the regional cerebral blood flow (rCBF) in the gray matter and the white matter. The hemodynamic indices were compared among the three groups, and statistical analysis was carried out using the F test.

RESULTS

The time for the arterial rise to reach the peak value for the 7.5-ml/s group was only 0.2 s ahead of the initiation time for the rise of the superior sagittal sinus. The differences of rCBF in the gray matter and the white matter among the three groups were statistically significant. rCBF in the gray matter and the white matter for the 7.5-ml/s group was 52.8 ml x min(-1) 100 g(-1) . (+/-3.1) and 21.9 ml x min(-1) . 100 g(-1) (+/-2.4), respectively.

CONCLUSIONS

The use of the 7.5-ml/s injection rate can meet the prerequisite of the maximum slope model, and the resulting rCBF can be very close to that measured by positron emission tomography. Therefore, 7.5 ml/s was an ideal contrast medium injection rate.

Imaging tumour angiogenesis

The development of neovasculature via angiogenesis is a vital component of many normal physiological processes and a number of disease states. Neovascularisation is critical for the growth of malignant tumours and for the development and survival of metastases. Recently, the potential of non-invasive imaging for the functional characterisation of neovasculature has become realised. In this review we describe the process of tumour angiogenesis for radiologists and present a summary of the most available computed tomography/magnetic resonance imaging techniques that can depict the functional vascular status of human tumours.

Quantitative assessment of colorectal cancer perfusion using MDCT: inter- and intraobserver agreement

OBJECTIVE

The objective of our study was to determine inter- and intraobserver agreement of MDCT colorectal cancer perfusion measurements.

SUBJECTS AND METHODS

Thirty-one patients (17 men, 14 women; median age, 69 years) with proven colorectal cancer were examined prospectively using MDCT. A 65-sec dynamic study (cine mode, 4 x 5 mm collimation) was acquired through the tumor after i.v. contrast administration (100 mL of iopamidol 350, 5 mL/sec). Tumor blood volume, blood flow, mean transit time, and permeability measurements were determined by two independent observers using commercial software. Inter- and intraobserver agreement was assessed using the Bland-Altman test.

RESULTS

The mean difference for interobserver agreement (95% limits of agreement) was -0.81 mL/100 g tissue (-3.14 to 1.52); -9.94 mL/100 g tissue/min (-51.43 to 32.65); -1.09 sec (-7.05 to 4.86); and -2.90 mL/100 g tissue/min (-11.48 to 5.68) for blood volume, blood flow, mean transit time, and permeability, respectively. The intraclass correlation coefficient was 0.83, 0.89, 0.89, and 0.80, respectively. The mean difference for intraobserver agreement (95% limits of agreement) was 0.12 mL/100 g tissue (-1.90 to 2.14); 0.02 mL/100 g tissue/min (-13.13 to 13.17); -0.19 sec (-3.19 to 2.81); and 0.00 mL/100 g tissue/min (-2.45 to 2.45) for observer 1 and 0.26 mL/100 g tissue (-1.46 to 1.98); 4.47 mL/100 g tissue/min (-26.65 to 35.59); -0.21 sec (-2.48 to 2.06); 1.08 mL/100 g tissue/min (-4.92 to 7.08) for observer 2. The intraclass correlation coefficient was 0.86, 0.98, 0.97, 0.98 for observer 1 and 0.93, 0.96, 0.99, and 0.94, respectively, for observer 2.

CONCLUSION

There is greater inter- than intraobserver agreement for CT vascular perfusion measurements of primary colorectal cancer, which must be addressed for reliable clinical application in therapeutic monitoring.

Effects of TIPS on liver perfusion measured by dynamic CT

OBJECTIVE

Our aim was to measure the arterial, portal venous, and total perfusion of the liver parenchyma with dynamic, single-section CT in patients with liver cirrhosis before and after transjugular intrahepatic portosystemic shunt (TIPS) placement and to compare the results with normal values.

SUBJECTS AND METHODS

Perfusion of the liver parenchyma was measured in 24 healthy volunteers and 41 patients with liver cirrhosis using dynamic single-section CT. Seventeen patients underwent TIPS placement, and CT measurements were repeated within 7 days. CT scans were obtained at a single level comprising the liver, spleen, aorta, and portal vein. Scans were obtained over a period of 88 sec (one baseline scan followed by 16 scans every 2 sec and eight scans every 7 sec) beginning with the injection of a contrast agent bolus (40 mL at 10 mL/sec). Parenchymal and vascular contrast enhancement was measured with regions of interest, and time-density curves were obtained. These data were processed with a pharmaco-dynamic fitting program (TopFit), and the arterial and portal venous component and the total perfusion of the hepatic parenchyma were calculated (milliliters of perfusion per minute per 100 mL of tissue).

RESULTS

Mean normal values for hepatic arterial, portal venous, and total perfusion were 20, 102, and 122 mL/min per 100 mL, respectively. In patients with cirrhosis before TIPS, mean hepatic arterial, portal venous, and total perfusion was 28, 63, and 91 mL/min per 100 mL, respectively, which was statistically significant for all values (p <0.05). After TIPS, hepatic perfusion increased to a mean value of 48, 65, 113 mL/min per 100 mL for arterial (p <0.01), portal venous, and total (p=0.011) perfusion, respectively.

CONCLUSION

In patients with cirrhosis, the hepatic arterial perfusion increased, whereas portal venous and total perfusion decreased compared with that of healthy volunteers. TIPS placement caused a statistically significant increase of the hepatic arterial and total hepatic perfusion. The portal venous parenchymal perfusion remained unchanged.

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.

Perfusion CT for the assessment of tumour vascularity: which protocol?

Perfusion CT is a technique that can be readily incorporated into the existing CT protocols that continue to provide the mainstay for anatomical imaging in oncology to provide an in vivo marker of tumour angiogenesis. By capturing physiological information reflecting the tumour vasculature, perfusion CT can be useful for diagnosis, risk-stratification and therapeutic monitoring. However, a wide range of perfusion CT techniques have evolved and the various commercial implementations advocate different acquisition protocols and processing methods. Acquisition choices include first pass studies or delayed imaging, temporal resolution versus image noise, and single location sequences or multiple spiral acquisitions. Data processing may be semi-quantitative or, using either compartmental analysis or deconvolution, produce results that are quantified in absolute physiological terms such as perfusion, blood volume and permeability. This article discusses the advantages and disadvantages of the more common CT perfusion protocols and offers proposals that could allow for easier comparison between studies employing different techniques.

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.

Quantitative perfusion map of malignant liver tumors, created from dynamic computed tomography data

RATIONALE AND OBJECTIVES

To apply perfusion computed tomography (CT) technique to variable malignant liver tumors, and to define the usefulness of quantitative color mapping.

MATERIALS AND METHODS

Perfusion CT images were created for 36 malignant liver tumors in 28 patients (age, 66.4 +/- 10.1 years; range, 48-85) with metastatic liver tumors (n = 17; nine colorectal carcinomas, eight other malignant tumors) and hepatocellular carcinomas (n = 11). A single-slice dynamic CT was performed after an intravenous bolus injection of 40 mL of contrast material (320 mgI/mL) with 8 mL/sec. The parameters were calculated pixel-by-pixel using maximum slope method, and quantitative maps of arterial and portal perfusion were created. In four patients who underwent transcatheter arterial chemoembolization, perfusion CT was performed before and after transcatheter arterial chemoembolization.

RESULTS

In all patients, liver tumors were shown as hypervascular lesions on arterial perfusion CT. The average arterial perfusion value of the metastatic tumors from the colorectal carcinomas was 0.67 +/- 0.33 mL/min/mL, and that of hepatocellular carcinomas was 0.94 +/- 0.26 mL/min/mL (P = .03). The other metastatic tumors from various primary tumors showed a wide range (0.19-1.45 mL/min/mL) of arterial perfusion. Arterial perfusion of the liver tumors was obviously decreased after successful transcatheter arterial chemoembolization. In 12 of 15 tumors, in which portal perfusion CT images could be created, region-of-interest analysis showed no portal perfusion in the tumors. In two cases, decreased portal perfusion in the segments, which malignant tumors involved, was demonstrated.

CONCLUSION

Perfusion CT can provide quantitative information about arterial and portal perfusion of liver tumors, combined with good anatomic detail in one image. This technique has a potential to evaluate the angiogenesis of liver tumors, to show secondary changes in perfusion, such as decreased portal perfusion in apparently normal liver adjacent to metastases, and to monitor the therapeutic response in vivo.

Assessment of vascular physiology of tumorous livers: comparison of two different methods

RATIONALE AND OBJECTIVES

To evaluate liver and liver tumor perfusions by using two different modelling methods: gamma-variate fitting and a single-compartment model.

MATERIALS AND METHODS

5 New Zealand White rabbits with VX2 tumor implanted into the liver via portal injections were studied. Contrast-enhanced functional CT (fCT) examinations with temporal resolution of 200-500 milliseconds were conducted before tumor inoculation. Thereafter, two or three follow-up studies were conducted. A gamma-variate fitting method was used to determine fractional blood volumes (BV), and a single-compartment model method was used to determine fractional blood volumes (BV), blood flows (BF), and mean transit times (MTT) for normal and tumorous liver regions.

RESULTS

For tumorous regions in liver, the gamma-variate fitting and the single-compartment model methods showed statistically significant increases in arterial perfusions (P < 0.01) and decreases in portal perfusions (P < 0.01 with single-compartment model, and P < 0.05 with gamma-variate fitting) when compared with normal liver regions. The single-compartment model showed statistically significant increases (P < 0.01) in MTTs in tumorous regions. In normal liver regions, portal BFs decreased and MTTs increased after tumor inoculation, but the changes were statistically not significant.

CONCLUSION

The gamma-variate fitting and the single-compartment model methods showed definite differences in perfusions between normal and tumorous regions in liver. The single-compartment model showed slightly more distinction and was faster. More importantly, both methods can easily be applied in the clinical environment in the assessment of liver perfusion.

Glomerular filtration rate measured by using triphasic helical CT with a two-point Patlak plot technique

PURPOSE

To determine the accuracy of the two-point Patlak plot in the calculation of glomerular filtration rate (GFR).

MATERIALS AND METHODS

Fifty patients without acute renal disorder were included. GFR was calculated by using a two-point Patlak plot technique. The computed tomography (CT) protocol consisted of a plain examination followed by two contrast material-enhanced examinations in the arterial and portovenous phase. Each examination included the entire kidneys and was performed after injection of 120 mL iopromide and 300 mg of iodine per milliliter given per 75 kg of body weight. All examinations were performed with a standard abdominal protocol. Section thickness was 4 x 2.5 mm, and table advance was 12.5 mm. Bolus triggering commenced 10 seconds after the start of contrast medium injection. Twelve dynamic scans were obtained with reduced tube current every 3 seconds to obtain sufficient arterial input function data. Correction for hematocrit level was made by using the unenhanced attenuation of the aorta. As a reference method, plasma clearance of the contrast medium injected for CT was calculated from three iodine plasma concentration measurements obtained 3, 4, and 5 hours after injection. Linear correlation was performed.

RESULTS

GFR was calculated from CT data in 48 patients. Two patients were excluded because of breathing errors. Mean GFR was 80 mL/min (range, 17-153 mL/min) as measured with iopromide plasma clearance and 82 mL/min (range, 28-148 mL/min) as measured with CT. Linear correlation between the two methods was r = 0.889; GFR calculated with the two-point Patlak plot was equal to 15 plus 0.83 times GFR (plasma clearance). The mean difference between GFRs as determined with the two methods was -1.2 mL/min (95% CI: -27.1, 24.6).

CONCLUSION

Total GFR can be measured accurately with minimally extended triphasic CT in patients without acute renal disorder by using a two-point Patlak plot technique.

Functional CT imaging of prostate cancer

The purpose of this paper is to investigate the distribution of blood flow (F), mean capillary transit time (Tc), capillary permeability (PS) and blood volume (vb) in prostate cancer using contrast-enhanced CT. Nine stage T2-T3 prostate cancer patients were enrolled in the study. Following bolus injection of a contrast agent, a time series of CT images of the prostate was acquired. Functional maps showing the distribution of F, Tc, PS and vb within the prostate were generated using a distributed parameter tracer kinetic model, the adiabatic approximation to the tissue homogeneity model. The precision of the maps was assessed using covariance matrix analysis. Finally, maps were compared to the findings of standard clinical investigations. Eight of the functional maps demonstrated regions of increased F, PS and vb, the locations of which were consistent with the results of standard clinical investigations. However, model parameters other than F could only be measured precisely within regions of high F. In conclusion functional CT images of cancer-containing prostate glands demonstrate regions of elevated F, PS and Vb. However, caution should be used when applying a complex tracer kinetic model to the study of prostate cancer since not all parameters can be measured precisely in all areas.

Measuring single-kidney glomerular filtration rate on single-detector helical CT using a two-point Patlak plot technique in patients with increased interstitial space

OBJECTIVE

We measured the single-kidney glomerular filtration rate (GFR) with a two-point Patlak plot technique based on multiphasic CT in patients with hydronephrosis or pyelonephritis or both. The question we sought to answer in our study was, Does increased interstitial space as measured with the Patlak plot technique cause overestimation of GFR?

SUBJECTS AND METHODS

Twenty adult patients treated with percutaneous nephrostomy were studied. The CT protocol consisted of an unenhanced scan and three subsequent scans obtained 38, 71, and 102 sec after the initiation of the contrast medium injection. Plasma clearance of the contrast medium was determined and used as the reference. Additionally, single-kidney excretory clearance was determined by separate urine collections from the left and right kidneys. A three-compartment model calculation was made using all data available to estimate volume and transfer rate constant of the interstitial space.

RESULTS

The GFR determined using plasma clearance correlated well with the GFR determined using excretory clearance, with a correlation coefficient of r = 0.94 and a regression line of y = -6 + 0.97 x x. GFR of both kidneys as measured using CT was overestimated according to the GFR determined using plasma clearance, with a correlation coefficient of r = 0.80, and a regression line of y = 35 + 0.79 x x. Single-kidney excretory clearance GFR was similarly overestimated using single-kidney CT GFR, with a correlation coefficient of r = 0.81 and a regression line of y = 20 + 0.84 x x. Single-kidney parenchymal volume was used as an indicator of interstitial space enlargement. The overestimation of excretory clearance GFR using CT correlated significantly with the parenchymal volume of the individual kidneys. A high correlation was also found between overestimation of total GFR determined with CT and interstitial space estimated using a three-compartment model calculation. Relative interstitial space was estimated to be 25% (range, 9-46%) of total kidney volume.

CONCLUSION

Using the interstitial space as a third compartment may introduce an error into the measurement of GFR with the Patlak plot technique. We found that the CT protocol in our study resulted in considerable overestimation of GFR as determined with the Patlak plot in patients with increased interstitial space.

Contrast-assisted destruction-replenishment ultrasound for the assessment of tumor microvasculature in a rat model

Angiogenesis, the development of new blood vessels, is necessary for tumor growth. Anti-angiogenic therapies have recently received attention as a possible cancer treatment. The purpose of this study was to monitor the vascularity of induced tumors in rats using contrast-enhanced ultrasound during anti-angiogenic therapy. Six rats with subcutaneously implanted R3230 murine mammary adenocarcinomas were treated with an orally administered anti-angiogenic agent (SU11657) beginning 28 days after tumor implantation (20 mg/kg BW once daily). Three additional tumor-bearing control rats were treated with an equivalent volume of vehicle alone. Sonographic evaluation of tumor blood flow was performed using a modified Siemens Sonoline Elegra equipped with a 5.0 MHz linear transducer prior to drug administration, during the first 51 hours following initial drug administration, and on days 8 and 15 after initiation of therapy. Tumor volumes were estimated at each time point using a prolate ellipsoid method from linear dimensions measured on the B-mode ultrasound image in the three major axes. A destruction-replenishment technique was used for tumor blood flow evaluation using a constant rate infusion of intravenously delivered ultrasound contrast media (Definity). A destructive pulse was fired first, followed by a chain of non-destructive pulses that allowed for visualization of vascular contrast agent replenishment. Parametric maps of the time required for contrast agent replenishment and the time-integrated intensity were generated for both the tumor and kidney. Following ultrasound examination, contrast-enhanced computed tomography of each tumor was performed in the same imaging plane as that used to acquire the ultrasound images. Fifteen days after the start of treatment, tumors were excised, preserved in 10% formalin, and sectioned in a plane approximating the ultrasound and CT imaging planes. Sections were prepared for light microscopy with H & E, CD31 and factor VIII immunostain to evaluate overall morphology and vessel distribution. Ultrasound measurements of tumor volume, the spatial extent of contrast enhancement, and the time required for contrast replenishment within control tumors were significantly different from those of treated tumors. The time-integrated ultrasound contrast enhancement decreases and the time required for replenishment of the contrast agent within the tumor volume increases over the course of anti-angiogenic therapy. Parametric maps of integrated intensity are shown to correlate with the regions of viable tumor demonstrated on H & E and regions of elevated contrast intensity on CT. Contrast-enhanced ultrasound imaging of implanted tumors provides a tool to assess differences in the microcirculation of treated and control tumors in studies of anti-angiogenic agents.

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.