Dynamic contrast-enhanced CT of head and neck tumors: perfusion measurements using a distributed-parameter tracer kinetic model. Initial results and comparison with deconvolution-based analysis

Variations of quantitative perfusion measurement on dynamic contrast enhanced CT for colorectal cancer: implication of standardized image protocol

Tumor angiogenesis is considered an important prognostic factor. With an increasing emphasis on imaging evaluation of the tumor microenvironment, dynamic contrast enhanced-computed tomography (DCE-CT) has evolved as an important functional technique in this setting. Yet many questions remain as to how and when these functional measurements should be performed for each agent and tumor type, and what quantitative models should be used in the fitting process. In this study, we evaluated the variations of perfusion measurement on DCE-CT for rectal cancer patients from (1) different tracer kinetic models, (2) different scan acquisition lengths, and (3) different scan intervals. A total of seven commonly used models were studied: the adiabatic approximation to the tissue homogeneity (AATH) model, adiabatic approximation to the homogeneity tissue with fixed transit time (AATHFT) model, the Tofts model (TM), the extended Tofts model (ETM), Patlak model, Logan model, and the model-free deconvolution method. Akaike's information criterion was used to identify the best fitting model. The interchangeability of different models was further evaluated using Bland-Altman analysis. All models gave comparable blood volume (BV) measurements except the Patlak method. While for the volume transfer constant (K_trans) estimation, AATHFT, AATH, and ETM generated reasonable agreement among each other but not for the other models. Regarding the blood flow (BF) measurement, no two models were interchangeable. In addition, the perfusion parameters were compared with four acquisition times (45, 65, 85, and 105 s) and four temporal intervals (1, 2, 3, and 4 s). No significant difference was observed in the volume transfer constant (K_trans), BV, and BF measurements when comparing data acquired over 65 s with data acquired over 105 s using any of the DCE models in this study. Yet increasing the temporal interval led to a significant overestimation of BF in the deconvolution method. In conclusion, the perfusion measurement is indeed model dependent and the image acquisition/processing technique is dependent. The radiation dose of DCE-CT was an average of 1.5-2 times an abdomen/pelvic CT, which is not insubstantial. To take the DCE-CT forward as a biomarker in oncology, prospective studies should be carefully designed with the optimal image acquisition and analysis technique.

Advanced Hepatocellular Carcinoma: Perfusion Computed Tomography-Based Kinetic Parameter as a Prognostic Biomarker for Prediction of Patient Survival

OBJECTIVE

The aim of this study was to find prognostic biomarkers in perfusion computed tomography (PCT)-based kinetic parameters for advanced hepatocellular carcinoma (HCC) treated with antiangiogenic chemotherapy.

METHODS

Twenty-two patients with advanced HCC underwent PCT imaging and subsequently received bevacizumab in combination with gemcitabine and oxaliplatin. Pretreatment PCT data within advanced HCC were analyzed using the Tofts-Kety, 2-compartment exchange, adiabatic approximation to the tissue homogeneity (AATH), and distributed parameter models. Blood flow, blood volume, extraction fraction (E), and other 3 parameters were calculated. Kinetic parameters in each model were evaluated with 1-year survival discrimination using Kaplan-Meier analysis and with overall survival using univariate Cox regression analysis.

RESULTS

Only the AATH model-derived E was statistically significantly prognostic for 1-year survival. The increased AATH model-derived E was significantly associated with longer overall survival (P = 0.005).

CONCLUSIONS

The AATH model-derived E was an effective prognostic biomarker for advanced HCC.

Patient characteristics influencing the variability of distributed parameter-based models in DCE-CT kinetic analysis

Kinetic parameter variability may be sensitive to kinetic model choice, kinetic model implementation or patient-specific effects. The purpose of this study was to assess their impact on the variability of dynamic contrast-enhanced computed tomography (DCE-CT) kinetic parameters. A total of 11 canine patients with sinonasal tumours received high signal-to-noise ratio, test-double retest DCE-CT scans. The variability for three distributed parameter (DP)-based models was assessed by analysis of variance. Mixed-effects modelling evaluated patient-specific effects. Inter-model variability (CV_inter ) was comparable to or lower than intra-model variability (CV_intra ) for blood flow (CV_inter :[4-28%], CV_intra :[28-31%]), fractional vascular volume (CV_inter :[3-17%], CV_intra :[16-19%]) and permeability-surface area product (CV_inter :[5-12%], CV_intra :[14-15%]). The kinetic models were significantly (P<0.05) impacted by patient characteristics for patient size, area underneath the curve of the artery and of the tumour. In conclusion, DP-based models demonstrated good agreement with similar differences between models and scans. However, high variability in the kinetic parameters and their sensitivity to patient size may limit certain quantitative applications.

A comparative analysis of water-soluble and blood-pool contrast agents for in vivo vascular imaging with micro-CT

RATIONALE AND OBJECTIVES

In recent years, micro-computed tomography (micro-CT) has emerged as a high-resolution modality for vascular exploration in vivo. Several x-ray contrast agents for in vivo imaging are on the market and are based on different formulations. The objective of this study was to compare contrast-related and pharmacokinetic properties of a water-soluble compound containing iomeprol (Iomeron 400) and blood-pool agents (eXIA160XL, AuroVist 15 nm, and ExiTron nano 12000) for the identification of suitable in vivo vascular imaging applications.

MATERIALS AND METHODS

Forty-four healthy C57BL/6J mice were used in this study. Iomeprol was administered with a continuous infusion protocol; the other agents as a bolus. Anatomical micro-CT was applied at the head, neck, and lower hind limb before (baseline) and immediately after contrast injection, and used to quantify contrast-related properties of the agents. Dynamic micro-CT was applied at the same regions to characterize the agents pharmacokinetics.

RESULTS

All contrast media revealed safe, except for eXIA160XL, which caused death in four of eight tested animals and was therefore excluded early from the study. AuroVist 15 nm provided the highest attenuation (2.33/mm) as compared to iomeprol (1.97/mm) and ExiTron nano 12000 (1.58/mm) and a maximum temporal variation of contrast of 20% after 30 minutes, but the appearance of a dark skin staining did not allow multiple injections of the agent. Iomeprol passively diffused across capillary membranes, and after 30 minutes doubled the tissue contrast with respect to its initial levels. ExiTron nano 12000 revealed temporal variations of contrast below 10% and significantly reduced clearance rates after the third consecutive injection.

CONCLUSION

AuroVist 15 nm is best suited for anatomical investigation of the vascular network, while the high extravasation levels of iomeprol can be exploited for perfusion analysis. ExiTron nano 12000 is indicated for use in longitudinal monitoring with repeated injections.

Head and neck cancer: value of perfusion CT in depicting primary tumor spread

Background

The aim of this study was to assess head and neck squamous cell cancer and surrounding tissue in computed tomography contrast enhanced and perfusion studies, and to examine the role of perfusion imaging in depiction of tissue infiltration.

Material/Methods

We prospectively evaluated 43 primary malignant head and neck tumors, using standard CT followed by perfusion. Blood flow, blood volume, mean transit time, and permeability values were obtained using regions of interest (ROIs) over lesions and surrounding tissue. Results were compared with histological analysis of resected tissue. Sensitivity, specificity, accuracy, positive and negative predictive values were calculated for both methods.

Results

We found significant differences between infiltrated and non-infiltrated tissue, especially with regard to muscles. In case of bone and salivary gland infiltration, change in perfusion parameters did not allow proper diagnosis.

Conclusions

CTP shows promise in depicting malignant infiltration. The combined use of CECT plus CTP results in correct staging of the majority of head and neck tumors.

Standardization of Stroke Perfusion CT for Reperfusion Therapy

With the advances in terms of perfusion imaging, the "time is brain" approach used for acute reperfusion therapy in ischemic stroke patients is slowly being replaced by a "penumbra is brain" or "imaging is brain" approach. But the concept of penumbra-guided reperfusion therapy has not been validated. The lack of standardization in penumbral imaging is one of the main contributing factors for this absence of validation. This article reviews the issues underlying the lack of standardization of perfusion-CT for penumbra imaging, and offers avenues to remedy this situation.

The challenges of integrating molecular imaging into the optimization of cancer therapy

We review novel, in vivo and tissue-based imaging technologies that monitor and optimize cancer therapeutics. Recent advances in cancer treatment centre around the development of targeted therapies and personalisation of treatment regimes to individual tumour characteristics. However, clinical outcomes have not improved as expected. Further development of the use of molecular imaging to predict or assess treatment response must address spatial heterogeneity of cancer within the body. A combination of different imaging modalities should be used to relate the effect of the drug to dosing regimen or effective drug concentration at the local site of action. Molecular imaging provides a functional and dynamic read-out of cancer therapeutics, from nanometre to whole body scale. At the whole body scale, an increase in the sensitivity and specificity of the imaging probe is required to localise (micro)metastatic foci and/or residual disease that are currently below the limit of detection. The use of image-guided endoscopic biopsy can produce tumour cells or tissues for nanoscopic analysis in a relatively patient-compliant manner, thereby linking clinical imaging to a more precise assessment of molecular mechanisms. This multimodality imaging approach (in combination with genetics/genomic information) could be used to bridge the gap between our knowledge of mechanisms underlying the processes of metastasis, tumour dormancy and routine clinical practice. Treatment regimes could therefore be individually tailored both at diagnosis and throughout treatment, through monitoring of drug pharmacodynamics providing an early read-out of response or resistance.

The evaluation of anti-angiogenic treatment effects for implanted rabbit VX2 breast tumors using functional multi-slice spiral computed tomography (f-MSCT)

OBJECTIVE

Investigate the benefit of functional multi-slice spiral computed tomography (f-MSCT) perfusion imaging in the non-invasive assessment of targeted anti-angiogenesis therapy on an implanted rabbit VX2 breast tumor model.

METHOD

69 female pure New Zealand white rabbits were randomly assigned to one of the 4 groups and received treatment accordingly: control (saline), Endostar, neoadjuvant chemotherapy (Cyclophosphamide, Epirubicin and 5-Fluorouracil, CEF), combination therapy (Endostar and CEF). After 2 weeks of treatment, f-MSCT perfusion scannings were performed for all rabbits and information about blood flow (BF), blood volume (BV), mean transit time (MTT) and surface permeability (SP) was collected. After perfusion imaging, tumor tissues were sampled for immunohistochemistry and the Western blot test of VEGF protein expression.

RESULTS

(1) The VEGF expression level, measured by immunohistochemistry and Western blot, decreased by treatment group (control > Endostar > CEF > combination therapy). The same was true for the mean BF, BV, MTT and PS, which decreased from the control group to the combination therapy group gradually. The mean MTT level increased in reverse order from the control to the combination therapy group. The difference between any 2 groups on these measures was statistically significant (P < 0.05). (2) There was moderate positive correlation between VEGF expression and BE, BV, or PS level (P < 0.05) and a negative correlation between VEGF expression and MTT level for all 4 groups (P < 0.05).

CONCLUSION

Therefore, f-MSCT can be used as a non-invasive approach to evaluate the effect of anti-angiogenic therapy for implanted rabbit VX2 breast tumors.

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.

Response and progression-free survival in oropharynx squamous cell carcinoma assessed by pretreatment perfusion CT: comparison with tumor volume measurements

BACKGROUND AND PURPOSE

Perfusion CT (PCT) provides a rapid, reliable, and non-invasive technique for assessing tumor vascularity. The purpose of this study was to assess whether pretreatment dynamic perfusion CT (PCT) may predict response to induction chemotherapy and midterm progression-free survival (PFS) in advanced oropharynx squamous cell carcinoma (SCCA) and to compare the results with those derived by tumor volume measurements.

MATERIALS AND METHODS

Nineteen patients underwent routine contrast-enhanced CT (CECT), pretreatment PCT, and conventional endoscopy. Tumor response was determined according to radiologic (RECIST) criteria. The PCT parameters, tumor volume, radiologic response, and PFS were analyzed with use of Cox-proportional hazards model, receiver operating characteristic (ROC), and Kaplan-Meier analysis.

RESULTS

The baseline blood flow (BF), blood volume (BV), and permeability surface area product (PS) were significantly higher, whereas mean transit time (MTT) was significantly lower in the responders than in the nonresponders (P < or = .002). BV showed 100% sensitivity, MTT and PS had the highest specificity (100%), and BF showed 84.2% sensitivity and 66.7% specificity for prediction of tumor response after induction chemotherapy. The pretreatment tumor volume correlated with PFS in the pooled patients group (r = 0.4; P < .0001), whereas postinduction tumor volume correlated significantly with PFS in the responders and nonresponders (r = 0.22-0.64; P < or = .006). Pretreatment tumor volume (P = .0001) and BF (P = .001) were significant predictors for PFS.

CONCLUSIONS

Pretreatment PCT parameters may predict response after induction chemotherapy. Tumor volume and BF values may predict PFS in patients with advanced oropharyngeal SCCA.

PET Imaging of Angiogenesis

Angiogenesis is a highly-controlled process that is dependent on the intricate balance of both promoting and inhibiting factors, involved in various physiological and pathological processes. A comprehensive understanding of the molecular mechanisms that regulate angiogenesis has resulted in the design of new and more effective therapeutic strategies. Due to insufficient sensitivity to detect therapeutic effects by using standard clinical endpoints or by looking for physiological improvement, a multitude of imaging techniques have been developed to assess tissue vasculature on the structural, functional and molecular level. Imaging is expected to provide a novel approach to noninvasively monitor angiogenesis, to optimize the dose of new antiangiogenic agents and to assess the efficacy of therapies directed at modulation of the angiogenic process. All these methods have been successfully used preclinically and will hopefully aid in antiangiogenic drug development in animal studies. In this review article, the application of PET in angiogenesis imaging at both functional and molecular level will be discussed. For PET imaging of angiogenesis related molecular markers, we emphasize integrin alpha(v)beta(3), VEGF/VEGFR, and MMPs.

Whole-tumor perfusion CT parameters and glucose metabolism measurements in head and neck squamous cell carcinomas: a pilot study using combined positron-emission tomography/CT imaging

BACKGROUND AND PURPOSE

Previous (separately performed) perfusion CT (PCT) and PET studies have been inconclusive regarding the correlation of functional tumor characteristics. The purpose of this study was to perform dual assessment of head and neck squamous cell carcinomas (SCCAs) to examine the relationship between perfusion measurements derived from PCT and glucose standardized uptake values (SUV).

MATERIALS AND METHODS

We prospectively evaluated 15 primary and recurrent SCCAs using combined positron-emission tomography (PET) and CT of the head and neck. SUV(mean), SUV(max), blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability (PS) values were calculated with use of manually drawn regions of interest (ROIs) over the lesions and the healthy muscle tissue. Parametric comparison test, correlation coefficients, and regression analysis were performed.

RESULTS

The mean (+/- SD) SUV(mean), SUV(max), BF, BV, MTT, and PS values in the tumor tissue were 6.26 (+/- 1.48), 15.25 (+/- 3.81), 91.50 (+/- 24.69), 5.08 (+/- 1.17), 7.51 (+/- 2.24), and 23.08 (+/- 8.77), respectively. All PET/CT and PCT parameters of muscle versus tumor tissue were statistically different (.0001 < P < .001). There were significant correlations between BF and SUV(max) as well as SUV(mean) (r = 0.57; P = .02 and r = 0.63; P = .011, respectively) in the tumors. Significant correlation was also found between PS and SUV(mean) (r = 0.53; P = .04) in the tumors. Regression analysis showed: SUV(max) = 0.09 x BF + 7.2 (R(2) = 0.33; P = .02), SUV(mean) = 0.05 x BF + 2.22 (R(2) = 0.45; P = .011), and SUV(mean) = 0.05 x PS + 5.36 (R(2) = 0.35; P = .04). The tumor to nontumor (muscle) SUV(mean) and SUV(max) ratio was 9.45 (+/- 3.55) and 17.58 (+/- 4.32), respectively. BF-ratio SUV(mean) and BF-ratio SUV(max) showed significant correlations (r = 0.64; P = .01 and r = 0.53; P = .04, respectively). Regression analysis showed ratio SUV(mean) = 0.14 x BF-3.48 (R(2) = 0.42; P = .01) and ratio SUV(max) = 0.14 x BF + 4.51 (R(2) = 0.29; P = .04).

CONCLUSION

Tissue perfusion-metabolic coupling is evident in head and neck SCCAs and may provide additional diagnostic information in patients undergoing PET/CT studies.

CT coronary angiography: quantitative assessment of myocardial perfusion using test bolus data-initial experience

The aim of this study is to quantify myocardial perfusion during coronary CT angiography using data from a modified timing test-bolus acquisition. Institutional review board approval and informed consent were obtained. Nineteen patients with suspected coronary artery disease underwent combined coronary CT angiography and cardiac (82)Rubidium-PET perfusion. Prior to the CT angiogram a retrospectively ECG-gated dynamic test bolus was obtained following 25 mls of IV contrast medium injected at 5 ml/s. Images were acquired every 1.5 s for 30 s using 4 x 1.25-mm slices at 120 kV, 35 mAs. Regions of interest were drawn to delineate the myocardium and aorta on the resulting transaxial images. Time density curves were created and perfusion calculated using two simple approaches: maximum-slope method and peak method. In patients with normal PET myocardial perfusion, the mean (SD) resting myocardial perfusion estimated by CT using the maximum-slope method was 0.89 (+/-0.27) ml/min/g and 0.93 (+/-0.21) ml/min/g at end-systole and end-diastole, respectively, and 0.69 (+/-0.11) ml/min/g and 0.79 (+/-0.19) at end-systole and end-diastole, respectively, for the peak method. Thus quantification of myocardial perfusion from a routine coronary CT angiography test bolus is possible. CT-derived myocardial perfusion values are consistent with published values derived from other techniques.

Chapter 7. Molecular imaging of tumor vasculature

Cancer, with more than 10 million new cases a year worldwide, is the third leading cause of death in developed countries. One critical requirement during cancer progression is angiogenesis, the formation of new blood vessels. Structural and functional imaging of tumor vasculature has been studied using various imaging modalities such as magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound. Molecular imaging, a key component of the 21st-century cancer-patient management strategy, takes advantage of these traditional imaging techniques and introduces molecular probes to determine the expression of indicative molecular markers at different stages of cancer development. In this chapter, we will focus on two tumor vasculature-related targets: integrin alpha(v)beta(3) and vascular endothelial growth factor receptor (VEGFR). For imaging of integrin alpha(v)beta(3) on the tumor vasculature, only nanoparticle-based probes will be discussed. VEGFR imaging will be discussed in depth, and we will give a detailed example of positron emission tomography (PET) imaging of VEGFR expression using radio-labeled VEGF(121) protein. Future clinical translation will be critical for maximum patient benefit from these agents. To achieve this goal, multidisciplinary approaches and cooperative efforts from many individuals, institutions, industries, and organizations are needed to quickly translate multimodality tumor vasculature imaging into multiple facets of cancer patient management.