Computed tomography perfusion imaging for therapeutic assessment: has it come of age as a biomarker in oncology? Invest Radiol. 2012;47:2-4. [PMID: 21808202 DOI: 10.1097/rli.0b013e318229ff3e]

Automated Quantitative Analysis of CT Perfusion to Classify Vascular Phenotypes of Pancreatic Ductal Adenocarcinoma

CT perfusion (CTP) analysis is difficult to implement in clinical practice. Therefore, we investigated a novel semi-automated CTP AI biomarker and applied it to identify vascular phenotypes of pancreatic ductal adenocarcinoma (PDAC) and evaluate their association with overall survival (OS).

METHODS

From January 2018 to November 2022, 107 PDAC patients were prospectively included, who needed to undergo CTP and a diagnostic contrast-enhanced CT (CECT). We developed a semi-automated CTP AI biomarker, through a process that involved deformable image registration, a deep learning segmentation model of tumor and pancreas parenchyma volume, and a trilinear non-parametric CTP curve model to extract the enhancement slope and peak enhancement in segmented tumors and pancreas. The biomarker was validated in terms of its use to predict vascular phenotypes and their association with OS. A receiver operating characteristic (ROC) analysis with five-fold cross-validation was performed. OS was assessed with Kaplan-Meier curves. Differences between phenotypes were tested using the Mann-Whitney U test.

RESULTS

The final analysis included 92 patients, in whom 20 tumors (21%) were visually isovascular. The AI biomarker effectively discriminated tumor types, and isovascular tumors showed higher enhancement slopes (2.9 Hounsfield unit HU/s vs. 2.0 HU/s, p < 0.001) and peak enhancement (70 HU vs. 47 HU, p < 0.001); the AUC was 0.86. The AI biomarker's vascular phenotype significantly differed in OS (p < 0.01).

CONCLUSIONS

The AI biomarker offers a promising tool for robust CTP analysis. In PDAC, it can distinguish vascular phenotypes with significant OS prognostication.

Effect of scan duration on CT perfusion values in metastases from renal cell carcinoma

Objective

CT perfusion (CTp) values are affected by CT scan acquisition duration (tacq); their reproducibility is adversely affected by uncertainty in their measurement. The objectives were to assess the effects of tacq on CTp parameter values in metastases from renal cell carcinoma (mRCC) in thoracic and abdominal locations.

Materials and Methods

131 CTp evaluations in 53 patients with mRCC were retrospectively analyzed by distributed parameter modeling to yield tissue blood flow (BF), blood volume (BV), mean transit time (MTT), permeability (PS), and also hepatic arterial perfusion (HAP) and hepatic arterial fraction (HAF) for liver metastases and normal liver, with tacq from 25 to 590 s. Penalized piecewise polynomial regression (SPLINE) characterized functional relationships between CTp parameters and acquisition duration, tacq. Evidence for time-invariance was evaluated for each parameter at multiple time points by conducting inference on the fitted derivative to assess its proximity to zero as a function of acquisition time. Equivalence testing was implemented with three levels of confidence (low (20%), moderate (70%), high (95%)).

Results

Systematic and non-systematic variability was observed for CTp parameter values with limited tacq. All parameters in all locations approached increasing stability with increasing tacq. PS, HAP and HAF required longer acquisition times than BF, BV and MTT to attain comparable levels of stability. Stabilization tended to require longer acquisition in liver than other tissues. tacq=380 s was required to obtain at least moderate level of confidence for all parameters and organs.

Conclusion

Increasing tacq yields increasingly more stable CT perfusion parameters, and thereby better reproducibility.

Dual-energy computed tomography as a lower radiation dose alternative to perfusion computed tomography in tumor viability assessment

To present the utility of dual-energy computed tomography (DECT) in the assessment of angiogenesis of focal lesions as an example of a solitary pulmonary nodule (SPN). This prospective study comprised 28 patients with SPN who underwent DECT and perfusion computed tomography (CTP), according to a proprietary protocol. Two radiologists independently analyzed four perfusion parameters, namely blood flow (BF), blood volume (BV), the time to maximum of the tissue residue function (Tmax), permeability surface area product (PS) from CTP, in addition to the iodine concentration (IC) and normalized iodine concentration (NIC) of the SPN from DECT. We used the Pearson R correlation and interclass correlation coefficients (ICC_s). Statistical significance was assumed at p < 0.05. The mean tumor size was 23.5 ± 6.5 mm. We observed good correlations between IC and BF (r = 0.78, p < 0.000) and NIC and BF (r = 0.71, p < 0.000) as well as between IC and BV (r = 0.73, p < 0.000) and NIC and BV (r = 0.73, p < 0.000) and poor correlation between IC and PS (r = 0.38, p = 0.044).There was no correlation between NIC and PS (r = 0.35, p = 0.064), IC content and Tmax (r = - 0.28, p = 0.147) and NIC and Tmax (r = - 0.21, p = 0.266). Inter-reader agreement on quantitative parameters at CTP (ICC_PS = 0.97, ICC_Tmax = 0.96, ICC_BV = 0.98, and ICC_BF = 0.99) and DECT (ICC_IC = 0.98) were excellent. The radiation dose was significantly lower in DECT than that in CTP (4.84 mSv vs. 9.07 mSv, respectively). DECT is useful for the functional assessment of oncological lesions with less exposure to radiation compared to perfusion computed tomography.

Basis and current state of computed tomography perfusion imaging: a review

Computed tomography perfusion (CTP) is a functional imaging that allows for providing capillary-level hemodynamics information of the desired tissue in clinics. In this paper, we aim to offer insight into CTP imaging which covers the basics and current state of CTP imaging, then summarize the technical applications in the CTP imaging as well as the future technological potential. At first, we focus on the fundamentals of CTP imaging including systematically summarized CTP image acquisition and hemodynamic parameter map estimation techniques. A short assessment is presented to outline the clinical applications with CTP imaging, and then a review of radiation dose effect of the CTP imaging on the different applications is presented. We present a categorized methodology review on known and potential solvable challenges of radiation dose reduction in CTP imaging. To evaluate the quality of CTP images, we list various standardized performance metrics. Moreover, we present a review on the determination of infarct and penumbra. Finally, we reveal the popularity and future trend of CTP imaging.

A Systematic Review on the Role of the Perfusion Computed Tomography in Abdominal Cancer

Background and purpose

Perfusion Computed Tomography (CTp) is an imaging technique which allows quantitative and qualitative evaluation of tissue perfusion through dynamic CT acquisitions. Since CTp is still considered a research tool in the field of abdominal imaging, the aim of this work is to provide a systematic summary of the current literature on CTp in the abdominal region to clarify the role of this technique for abdominal cancer applications.

Materials and Methods

A systematic literature search of PubMed, Web of Science, and Scopus was performed to identify original articles involving the use of CTp for clinical applications in abdominal cancer since 2011. Studies were included if they reported original data on CTp and investigated the clinical applications of CTp in abdominal cancer.

Results

Fifty-seven studies were finally included in the study. Most of the included articles (33/57) dealt with CTp at the level of the liver, while a low number of studies investigated CTp for oncologic diseases involving UGI tract (8/57), pancreas (8/57), kidneys (3/57), and colon–rectum (5/57).

Conclusions

Our study revealed that CTp could be a valuable functional imaging tool in the field of abdominal oncology, particularly as a biomarker for monitoring the response to anti-tumoral treatment.

Current Imaging Evaluation of Tumor Response to Advanced Medical Treatment in Metastatic Renal-Cell Carcinoma: Clinical Implications

The present review is focused on the role of diagnostic tomographic imaging such as computed tomography and magnetic resonance imaging to assess and predict tumor response to advanced medical treatments in metastatic renal cell carcinoma (RCC) patients. In this regard, antiangiogenic agents and immune checkpoint inhibitors (ICIs) have developed as advanced treatment options replacing the conventional therapy based on interferon-alpha and interleuchin-2 which had unfavorable toxicity profile and low response rates. In clinical practice, the imaging evaluation of treatment response in cancer patients is based on dimensional changes of tumor lesions in sequential scans; in particular, Response Evaluation Criteria in Solid Tumors (RECIST) have been defined for this purpose and also applied in patients with metastatic RCC. However, these new drugs with predominant cytostatic effect make RECIST insufficient to realize an adequate response imaging evaluation. Therefore, new imaging criteria (mCHOI and iRECIST) have been proposed to assess tumor response to advanced medical treatments of metastatic RCC, they correlate better than RECIST with the progression-free survival and overall survival. Finally, a potential role of radiomics and machine learning models has been suggested to predict tumor response.

Dynamic Measurement of Arterial Liver Perfusion With an Interventional C-Arm System

PURPOSE

Objective intraprocedural measurement of hepatic blood flow could provide a quantitative treatment end point for locoregional liver procedures. This study aims to validate the accuracy and reproducibility of cone-beam computed tomography perfusion (CBCTp) measurements of arterial liver perfusion (ALP) against clinically available computed tomography perfusion (CTp) measurements in a swine embolization model.

METHODS

Triplicate CBCTp measurements using a selective arterial contrast injection were performed before and after complete embolization of the left lobe of the liver in 5 swine. Two CBCTp protocols were evaluated that differed in sweep duration (3.3 vs 4.5 seconds) and the number of acquired projection images (166 vs 248). The mean ALP was measured within identical volumes of interest selected in the embolized and nonembolized regions of the perfusion map generated from each scan. Postembolization CBCTp values were also compared with CTp measurements.

RESULTS

The 2 CBCTp protocols demonstrated high concordance correlation (0.90, P < 0.001). Both CBCTp protocols showed higher reproducibility than CTp in the nontarget lobe, with an intraclass correlation of 0.90 or greater for CBCTp and 0.83 for CTp (P < 0.001 for all correlations). The ALP in the embolized lobe was nearly zero and hence excluded for reproducibility. High concordance correlation was observed between the CTp and each CBCTp protocol, with the shorter CBCTp protocol reaching a concordance correlation of 0.75 and the longer achieving 0.87 (P < 0.001 for both correlations).

CONCLUSIONS

Dynamic blood flow measurement using an angiographic C-arm system is feasible and produces quantitative results comparable to CTp.

Assessment of prostate cancer with integrated CT-perfusion using a sector-wise approach

OBJECTIVE

The role of computed tomography perfusion (CTP) in characterizing primary prostate cancer (PCa) is not definitely known. The aim of the present study was to investigate the relationship between CTP parameters and histopathological features of PCa tissue, using a sector-wise approach.

MATERIAL AND METHODS

Fifty-one patients with biopsy-proven PCa underwent prospectively a CTP scan prior to radical prostatectomy. Blood flow (BF), mean blood volume (BV) and mean transit time (MTT) were calculated, with the prostate being divided into eight sectors. Corresponding sector-wise histopathological analysis of whole-mount prostatectomy specimens was performed to determine tumoral area (mm²), mean microvessel density (MVD), Gleason patterns (primary, secondary) and total Gleason score. Spearman's rank correlation coefficient was used to analyze the association between CTP and histopathological parameters.

RESULTS

BF correlated weakly with tumoral area [ρs coefficient (p-value): 0.25 (0.00)] and MVD [ρs coefficient (p-value): 0.23 (0.00)]. No valuable correlation was found between CTP parameters and primary and secondary Gleason patterns, whereas total Gleason score was weakly correlated with BV [ρs coefficient (p-value): 0.22 (0.00)] and MTT [ρs coefficient (p-value): 0.25 (0.00)].

CONCLUSION

BF correlates weakly with size and vascularity of PCa. There is a need for further studies to elucidate the association between CTP parameters and other histopathological parameters.

320-row CT renal perfusion imaging in patients with aortic dissection: A preliminary study

OBJECTIVE

To investigate the clinical value of renal perfusion imaging in patients with aortic dissection (AD) using 320-row computed tomography (CT), and to determine the relationship between renal CT perfusion imaging and various factors of aortic dissection.

METHODS

Forty-three patients with AD who underwent 320-row CT renal perfusion before operation were prospectively enrolled in this study. Diagnosis of AD was confirmed by transthoracic echocardiography. Blood flow (BF) of bilateral renal perfusion was measured and analyzed. CT perfusion imaging signs of AD in relation to the type of AD, number of entry tears and the false lumen thrombus were observed and compared.

RESULTS

The BF values of patients with type A AD were significantly lower than those of patients with type B AD (P = 0.004). No significant difference was found in the BF between different numbers of intimal tears (P = 0.288), but BF values were significantly higher in cases with a false lumen without thrombus and renal arteries arising from the true lumen than in those with thrombus (P = 0.036). The BF values measured between the true lumen, false lumen and overriding groups were different (P = 0.02), with the true lumen group having the highest. Also, the difference in BF values between true lumen and false lumen groups was statistically significant (P = 0.016), while no statistical significance was found in the other two groups (P > 0.05). The larger the size of intimal entry tears, the greater the BF values (P = 0.044).

CONCLUSIONS

This study shows a direct correlation between renal CT perfusion changes and AD, with the size, number of intimal tears, different types of AD, different renal artery origins and false lumen thrombosis, significantly affecting the perfusion values.

Multislice Analysis of Blood Flow Values in CT Perfusion Studies of Lung Cancer

Objectives. Tumour heterogeneity represents a key issue in CT perfusion (CTp), where all studies are usually based on global mean or median values of perfusion maps, often computed on whole tumour. We sought to determine whether, and to what extent, such global values can be representative of tumour heterogeneity, with respect to single slices, and could be used for therapy assessment. Materials and Methods. Twelve patients with one primary non-small cell lung cancer lesion were enrolled in this study, for a total amount of 26 CTp examinations and 118 slices. Mean and median blood flow (BF) values, calculated voxel-based, were computed on each slice and the whole tumour. To measure functional heterogeneity, entropy was calculated on BF values as well. Results. Most of the slices were not represented by the global BF values computed on the whole tumour. In addition, there are a number of lesions having equivalent global BF values, but they are composed of slices having very different heterogeneity distributions, that is, entropy values. Conclusions. Global mean/median BF values of the single slices separately should be considered for clinical assessment, only if interpreted through entropy computed on BF values. The numerical equivalence between global BF values of different lesions may correspond to different clinical status, thus inducing possible errors in choice of therapy when considering global values only.

Assessing Tumor Response to Treatment in Patients with Lung Cancer Using Dynamic Contrast-Enhanced CT

The aim of this study was to provide an overview of the literature available on dynamic contrast-enhanced computed tomography (DCE-CT) as a tool to evaluate treatment response in patients with lung cancer. This systematic review was compiled according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Only original research articles concerning treatment response in patients with lung cancer assessed with DCE-CT were included. To assess the validity of each study we implemented Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2). The initial search yielded 651 publications, and 16 articles were included in this study. The articles were divided into groups of treatment. In studies where patients were treated with systemic chemotherapy with or without anti-angiogenic drugs, four out of the seven studies found a significant decrease in permeability after treatment. Four out of five studies that measured blood flow post anti-angiogenic treatments found that blood flow was significantly decreased. DCE-CT may be a useful tool in assessing treatment response in patients with lung cancer. It seems that particularly permeability and blood flow are important perfusion values for predicting treatment outcome. However, the heterogeneity in scan protocols, scan parameters, and time between scans makes it difficult to compare the included studies.

Feasibility of 4D perfusion CT imaging for the assessment of liver treatment response following SBRT and sorafenib

Objectives

To evaluate the feasibility of 4-dimensional perfusion computed tomography (CT) as an imaging biomarker for patients with hepatocellular carcinoma and metastatic liver disease.

Methods and materials

Patients underwent volumetric dynamic contrast-enhanced CT on a 320-slice scanner before and during stereotactic body radiation therapy and sorafenib, and at 1 and 3 months after treatment. Quiet free breathing was used in the CT acquisition and multiple techniques (rigid or deformable registration as well as outlier removal) were applied to account for residual liver motion. Kinetic modeling was performed on a voxel-by-voxel basis in the gross tumor volume and normal liver resulting in 3-dimensional parameter maps of blood perfusion, capillary permeability, blood volume, and mean transit time. Perfusion characteristics in the tumor and adjacent liver were correlated with radiation dose distributions to evaluate dose-response. Paired t tests assessed change in spatial and histogram parameters from baseline to different time points during and after treatment. Technique reproducibility as well as the impact of arterial and portal vein input functions was also investigated using intra- and inter-subject variance and Bland-Altman analysis.

Results

Quantitative perfusion parameters were reproducible (±5.7%; range, 2%-10%) depending on tumor/normal liver type and kinetic parameter. Statistically significant reductions in tumor perfusion were measurable over the course of treatment and as early as 1 week after sorafenib administration (P < .05). Marked liver parenchyma perfusion reduction was seen with a strong dose-response effect (R² = 0.95) that increased significantly over the course treatment.

Conclusions

The proposed methodology demonstrated feasibility of evaluating spatiotemporal changes in liver tumor perfusion and normal liver function following antiangiogenic therapy and radiation treatment warranting further evaluation of biomarker prognostication.

Comparison of organ-specific-radiation dose levels between 70 kVp perfusion CT and standard tri-phasic liver CT in patients with hepatocellular carcinoma using a Monte-Carlo-Simulation-based analysis platform

Purpose

The aim of this study was to systematically compare organ-specific-radiation dose levels between a radiation dose optimized perfusion CT (dVPCT) protocol of the liver and a tri-phasic standard CT protocol of the liver using a Monte-Carlo-Simulation-based analysis platform.

Methods and materials

The complete CT data of 52 patients (41 males; mean age 65 ± 12) with suspected HCC that underwent dVPCT examinations on a 3rd generation dual-source CT (Somatom Force, Siemens) with a dose optimized tube voltage of 70 kVp or 80 kVp were exported to an analysis platform (Radimetrics, Bayer). The dVPCT studies were matched with a reference group of 50 patients (35 males; mean age 65 ± 14) that underwent standard tri-phasic CT (sCT) examinations of the liver with 130 kVp using the calculated water-equivalent-diameter of the patients. The analysis platform was used for the calculation of the organ-specific effective dose (ED) as well as global radiation-dose parameters (ICRP103).

Results

The organ-specific ED of the dVPCT protocol was statistically significantly lower when compared to the sCT in 14 of 21, and noninferior in a total of 18 of 21 examined items (all p < 0.05). The EDs of the dVPCT examinations were especially in the dose sensitive organs such as the red marrow (17.3 mSv vs 24.6 mSv, p = < 0.0001) and the liver (33.3 mSv vs 46.9 mSv, p = 0.0003) lower when compared to the sCT.

Conclusion

Our results suggest that dVPCT performed at 70 or 80 kVp compares favorably to sCT performed with 130 kVp with regard to effective organ dose levels, especially in dose sensitive organs, while providing additional functional information which is of paramount importance in patients undergoing novel targeted therapies.

Advances in computed tomography and magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver cancer. Imaging is important for establishing a diagnosis of HCC and early diagnosis is imperative as several potentially curative treatments are available when HCC is small. Hepatocarcinogenesis occurs in a stepwise manner on a background of chronic liver disease or cirrhosis wherein multiple genes are altered resulting in a range of cirrhosis-associated nodules. This progression is related to increased cellularity, neovascularity and size of the nodule. An understanding of the stepwise progression may aid in early diagnosis. Dynamic and multiphase contrast-enhanced computed tomography and magnetic resonance imaging still form the cornerstone in the diagnosis of HCC. An overview of the current diagnostic standards of HCC in accordance to the more common practicing guidelines and their differences will be reviewed. Ancillary features contribute to diagnostic confidence and has been incorporated into the more recent Liver Imaging Reporting and Data System. The use of hepatocyte-specific contrast agents is increasing and gradually changing the standard of diagnosis of HCC; the most significant benefit being the lack of uptake in the hepatocyte phase in the earlier stages of HCC progression. An outline of supplementary techniques in the imaging of HCC will also be reviewed.

Early biomarkers from dynamic contrast-enhanced magnetic resonance imaging to predict the response to antiangiogenic therapy in high-grade gliomas

INTRODUCTION

The aim of this study is to investigate whether early changes in tumor volume and perfusion measurements derived from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may predict response to antiangiogenic therapy in recurrent high-grade gliomas.

METHODS

Twenty-seven patients who received bevacizumab every 3 weeks were enrolled in the study. For each patient, three MRI scans were performed: at baseline, after the first dose, and after the fourth dose of bevacizumab. The entire tumor volume (V(tot)), as well as contrast-enhanced and noncontrast-enhanced tumor subvolumes (V(CE-T1) and V(NON-CE-T1), respectively) were outlined using post-contrast T1-weighted images as a guide for the tumor location. Histogram analysis of normalized IAUGC (nIAUGC) and transfer constant K(trans) maps were performed. Each patient was classified as a responder patient if he/she had a partial response or a stable disease or as a nonresponder patient if he/she had progressive disease.

RESULTS

Responding patients showed a larger reduction in V(NON-CE-T1) after a single dose, compared to nonresponding patients. Tumor subvolumes with increased values of nIAUGC and K(trans), after a single dose, significantly differed between responders and nonresponders. The radiological response was found to be significantly associated to the clinical outcome. After a single dose, V(tot) was predictive of overall survival (OS), while V(CE-T1) showed a tendency of correlation with OS.

CONCLUSION

Tumor subvolumes with increased nIAUGC and K(trans) showed the potential for improving the diagnostic accuracy of DCE. Early assessments of the entire tumor volume, including necrotic areas, may provide complementary information of tumor behavior in response to anti-VEGF therapies and is worth further investigation.

Multiparametric imaging of patient and tumour heterogeneity in non-small-cell lung cancer: quantification of tumour hypoxia, metabolism and perfusion

Purpose

Multiple imaging techniques are nowadays available for clinical in-vivo visualization of tumour biology. FDG PET/CT identifies increased tumour metabolism, hypoxia PET visualizes tumour oxygenation and dynamic contrast-enhanced (DCE) CT characterizes vasculature and morphology. We explored the relationships among these biological features in patients with non-small-cell lung cancer (NSCLC) at both the patient level and the tumour subvolume level.

Methods

A group of 14 NSCLC patients from two ongoing clinical trials (NCT01024829 and NCT01210378) were scanned using FDG PET/CT, HX4 PET/CT and DCE CT prior to chemoradiotherapy. Standardized uptake values (SUV) in the primary tumour were calculated for the FDG and hypoxia HX4 PET/CT scans. For hypoxia imaging, the hypoxic volume, fraction and tumour-to-blood ratio (TBR) were also defined. Blood flow and blood volume were obtained from DCE CT imaging. A tumour subvolume analysis was used to quantify the spatial overlap between subvolumes.

Results

At the patient level, negative correlations were observed between blood flow and the hypoxia parameters (TBR >1.2): hypoxic volume (−0.65, p = 0.014), hypoxic fraction (−0.60, p = 0.025) and TBR (−0.56, p = 0.042). At the tumour subvolume level, hypoxic and metabolically active subvolumes showed an overlap of 53 ± 36 %. Overlap between hypoxic sub-volumes and those with high blood flow and blood volume was smaller: 15 ± 17 % and 28 ± 28 %, respectively. Half of the patients showed a spatial mismatch (overlap <5 %) between increased blood flow and hypoxia.

Conclusion

The biological imaging features defined in NSCLC tumours showed large interpatient and intratumour variability. There was overlap between hypoxic and metabolically active subvolumes in the majority of tumours, there was spatial mismatch between regions with high blood flow and those with increased hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-015-3169-4) contains supplementary material, which is available to authorized users.

Effect on perfusion values of sampling interval of computed tomographic perfusion acquisitions in neuroendocrine liver metastases and normal liver

OBJECTIVE

This study aimed to assess the effects of sampling interval (SI) of computed tomographic (CT) perfusion acquisitions on CT perfusion values in normal liver and liver metastases from neuroendocrine tumors.

METHODS

Computed tomographic perfusion in 16 patients with neuroendocrine liver metastases was analyzed using distributed-parameter modeling to yield tissue blood flow, blood volume, mean transit time, permeability, and hepatic arterial fraction for tumor and normal liver. Computed tomographic perfusion values for the reference SI of 0.5 s (SI0.5) were compared with those of SI data sets of 1 second, 2 seconds, 3 seconds, and 4 seconds using mixed-effects model analyses.

RESULTS

Increases in SI beyond 1 second were associated with significant and increasing departures of CT perfusion parameters from the reference values at SI0.5 (P ≤ 0.0009). Computed tomographic perfusion values deviated from the reference with increasing uncertainty with increasing SIs. Findings for normal liver were concordant.

CONCLUSIONS

Increasing SIs beyond 1 second yield significantly different CT perfusion parameter values compared with the reference values at SI0.5.

Technical prerequisites and imaging protocols for CT perfusion imaging in oncology

The aim of this review article is to define the technical prerequisites of modern state-of-the-art CT perfusion imaging in oncology at reasonable dose levels. The focus is mainly on abdominal and thoracic tumor imaging, as they pose the largest challenges with respect to attenuation and patient motion. We will show that low kV dynamic scanning in conjunction with detection technology optimized for low photon fluxes has the highest impact on reducing dose independently of other choices made in the protocol selection. We discuss, derived from relatively simple first principles, on what appropriate temporal sampling and total scan duration depend on and why optimized contrast medium injection protocols are also essential in limiting dose. Finally we will examine the possibility of simultaneously extracting standard morphological and functional information from one single 4D examination as a potential enabler for a more widespread use of dynamic contrast enhanced CT in oncology.

Inferring Stable Acquisition Durations for Applications of Perfusion Imaging in Oncology

Tissue perfusion plays a critical role in oncology. Growth and migration of cancerous cells requires proliferation of networks of new blood vessels through the process of tumor angiogenesis. Many imaging technologies developed recently attempt to measure characteristics pertaining to the passage of fluid through blood vessels, thereby providing a noninvasive means for cancer detection, as well as treatment prognostication, prediction, and monitoring. However, because these techniques require a sequence of successive imaging scans under administration of intravenous imaging tracers, the quality of the resulting perfusion data depends on the acquisition protocol. In this paper, we explain how to infer stability for stochastic curve estimation. The topic is motivated by two recent attempts to determine stable acquisition durations for acquiring perfusion characteristics using dynamic computed tomography, wherein inference used inappropriate statistical methods. Notably, when appropriate statistical techniques are used, the resulting conclusions deviate substantially from those previously reported in the literature.

Revised Choi imaging criteria correlate with clinical outcomes in patients with metastatic renal cell carcinoma treated with sunitinib

PURPOSE

To compare revised Choi criteria that incorporate concurrent size and attenuation changes at early follow-up imaging with Response Evaluation Criteria in Solid Tumors ( RECIST Response Evaluation Criteria in Solid Tumors ) 1.1 and original Choi criteria in stratification of clinical outcomes in patients with metastatic renal cell carcinoma ( mRCC metastatic renal cell carcinoma ) treated with sunitinib.

MATERIALS AND METHODS

Institutional review board approved this retrospective study and waived informed consent. Baseline and first follow-up computed tomographic scans in 69 patients (50 men, 19 women; mean age, 60.3 years; range, 19-83 years) with mRCC metastatic renal cell carcinoma treated with sunitinib from October 1, 2008, to March 1, 2013, were evaluated for tumor response by using RECIST Response Evaluation Criteria in Solid Tumors 1.1, original Choi criteria, and revised Choi criteria. Correlations with overall survival ( OS overall survival ) and progression-free survival ( PFS progression-free survival ) were compared and stratified according to each radiologic criteria with Kaplan-Meier and multivariate Cox regression analysis.

RESULTS

Median follow-up time was 29.7 months (95% confidence interval [ CI confidence interval ]: 18.9, 45.9). Response according to revised Choi criteria was independently correlated with OS overall survival (hazard ratio, 0.47 [95% CI confidence interval : 0.23, 0.99]; P = .046) and PFS progression-free survival (hazard ratio, 0.53 [95% CI confidence interval : 0.29, 0.99]; P = .047). Response according to RECIST Response Evaluation Criteria in Solid Tumors was not significantly correlated with OS overall survival (hazard ratio, 0.65 [95% CI confidence interval : 0.27, 1.58]; P = .344) or PFS progression-free survival (hazard ratio, 0.89 [95% CI confidence interval : 0.42, 1.91]; P = .768). Response according to original Choi criteria was not significantly correlated with OS overall survival (hazard ratio, 0.60 [95% CI confidence interval : 0.32, 1.11]; P = .106) or PFS progression-free survival (hazard ratio, 0.59 [95% CI confidence interval : 0.34, 1.02]; P = .060). Median OS overall survival and PFS progression-free survival in responders according to revised Choi criteria was 39.4 months (95% CI confidence interval : 9.1, upper limit not estimated) and 13.7 months (95% CI confidence interval : 6.4, 24.6), respectively, compared with 12.8 months (95% CI confidence interval : 8.7, 18.0) and 5.3 months (95% CI confidence interval : 3.9, 8.4), respectively, in nonresponders.

CONCLUSION

Contemporaneous reduction in tumor size and attenuation were correlated with favorable clinical outcomes. Response according to revised Choi criteria showed better correlation with clinical outcomes compared with that according to RECIST Response Evaluation Criteria in Solid Tumors or original Choi criteria in patients with mRCC metastatic renal cell carcinoma treated with sunitinib.

Metastatic renal cell carcinoma: radiologic findings and assessment of response to targeted antiangiogenic therapy by using multidetector CT

Recent advances in treatment of metastatic renal cell carcinoma (RCC), such as new molecular therapies that use novel antiangiogenic agents, have led to revision of the most frequently used guideline to evaluate tumor response to therapy: Response Evaluation Criteria in Solid Tumors (RECIST 1.1). Assessment of the response of metastatic RCC to therapy has traditionally been based on changes in target lesion size. However, the mechanism of action of newer antiangiogenic therapies is more cytostatic than cytotoxic, which leads to disease stabilization rather than to tumor regression. This change in tumor response makes RECIST 1.1--a system whose criteria are based exclusively on tumor size--inadequate to discriminate patients with early tumor progression from those with more progression-free disease and prolonged survival. New criteria such as changes in attenuation, morphology, and structure, as seen at contrast-enhanced multidetector computed tomography (CT), are being incorporated into new classifications used to assess response of metastatic RCC to antiangiogenic therapies. The new classifications provide better assessments of tumor response to the new therapies, but they have some limitations. The authors provide a practical review of these systems--the Choi, modified Choi, and Morphology, Attenuation, Size, and Structure (MASS) criteria--by explaining their differences and limitations that may influence the feasibility and reproducibility of these classifications. The authors review the use of multidetector CT in the detection of metastatic RCC and the different appearances and locations of these lesions. They also provide an overview of the new antiangiogenic therapies and their mechanisms of action and a brief introduction to functional imaging techniques. Functional imaging techniques, especially dynamic contrast-enhanced CT, seem promising for assessing response of metastatic RCC to treatment. Nonetheless, further studies are needed before functional imaging can be used in routine clinical practice.

Study of 320-slice dynamic volume CT perfusion in different pathologic types of kidney tumor: preliminary results

Objective

To investigate microcirculatory differences between pathologic types of kidney tumor using 320-slice dynamic volume CT perfusion.

Methods

Perfusion imaging with 320-slice dynamic volume CT was prospectively performed in 85 patients with pathologically proven clear cell renal cell carcinoma (RCC) (n = 66), papillary RCC (n = 7), chromophobe RCC (n = 5), angiomyolipoma (AML) with minimal fat (n = 7), or RCC (n = 78). Equivalent blood volume (Equiv BV), permeability surface-area product (PS; clearance/unit volume = permeability), and blood flow (BF) of tumor and normal renal cortex were measured and analyzed. Effective radiation dose was calculated.

Results

There was a significant difference in all three parameters between tumor and normal renal cortex (P<0.001). Equiv BV was significantly different between RCC and AML with minimal fat (P = 0.038) and between clear cell RCC and AML with minimal fat (P<0.001). Mean Equiv BV and BF were significantly higher in clear cell RCC than in papillary RCC (P<0.001 for both) and mean Equiv BV was higher in clear cell RCC than in chromophobe RCC (P<0.001). The effective radiation dose of the CT perfusion protocol was 18.5 mSv.

Conclusion

Perfusion imaging using 320-slice dynamic volume CT can be used to evaluate hemodynamic features of the whole kidney and kidney tumors, which may be useful in the differential diagnosis of these four pathologic types of kidney tumor.

Recommendations for the clinical and radiological evaluation of response to treatment in metastatic renal cell cancer

The evaluation of response to treatment is a critical step for determining the effectiveness of oncology drugs. Targeted therapies such as tyrosine kinase inhibitors and mammalian target of rapamycin inhibitors are active drugs in patients with metastatic renal cell carcinoma (mRCC). However, treatment with this type of drugs may not result in significant reductions in tumor size, so standard evaluation criteria based on tumor size, such as Response Evaluation Criteria in Solid Tumors (RECIST), may be inappropriate for evaluating response to treatment in patients with mRCC. In fact, targeted therapies apparently yield low response rates that do not reflect increased disease control they may cause and, consequently, the benefit in terms of time to progression. To improve the clinical and radiological evaluation of response to treatment in patients with mRCC treated with targeted drugs, a group of 32 experts in this field have reviewed different aspects related to this issue and have put together a series of recommendations with the intention of providing guidance to clinicians on this matter.

Characterization of tumor heterogeneity using dynamic contrast enhanced CT and FDG-PET in non-small cell lung cancer

PURPOSE

Dynamic contrast-enhanced CT (DCE-CT) quantifies vasculature properties of tumors, whereas static FDG-PET/CT defines metabolic activity. Both imaging modalities are capable of showing intra-tumor heterogeneity. We investigated differences in vasculature properties within primary non-small cell lung cancer (NSCLC) tumors measured by DCE-CT and metabolic activity from FDG-PET/CT.

METHODS

Thirty three NSCLC patients were analyzed prior to treatment. FDG-PET/CT and DCE-CT were co-registered. The tumor was delineated and metabolic activity was segmented on the FDG-PET/CT in two regions: low (<50% maximum SUV) and high (≥50% maximum SUV) metabolic uptake. Blood flow, blood volume and permeability were calculated using a maximum slope, deconvolution algorithm and a Patlak model. Correlations were assessed between perfusion parameters for the regions of interest.

RESULTS

DCE-CT provided additional information on vasculature and tumor heterogeneity that was not correlated to metabolic tumor activity. There was no significant difference between low and high metabolic active regions for any of the DCE-CT parameters. Furthermore, only moderate correlations between maximum SUV and DCE-CT parameters were observed.

CONCLUSIONS

No direct correlation was observed between FDG-uptake and parameters extracted from DCE-CT. DCE-CT may provide complementary information to the characterization of primary NSCLC tumors over FDG-PET/CT imaging.

Diagnosis of hepatocellular carcinoma: newer radiological tools

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

Multiparametric PET/CT in oncology

The standardized uptake value (SUV) and other measurements of tumour uptake of fluorodeoxyglucose (FDG) on positron emission tomography (PET) can potentially be supplemented by additional imaging parameters derived either from the PET images or from the computed tomography (CT) component of integrated PET/CT examinations including tumour size, CT attenuation, texture (reflecting tumour heterogeneity) and blood flow. This article illustrates the emerging benefits of such a multiparametric approach. Example benefits include greater diagnostic accuracy in characterization of adrenal masses achieved by using both the SUV and measured CT attenuation. Tumour size combined with the SUV can potentially improve the prognostic information available from PET/CT in oesophageal and lung cancer. However, greater improvements may be realized through using CT measurements of texture instead of size. Studies in breast and lung cancer suggest that combined PET/CT measurements of glucose metabolism and blood flow provide correlates for tumour proliferation and angiogenesis, respectively. These combined measurements can be utilized to determine vascular-metabolic phenotypes, which vary with tumour type. Uncoupling of blood flow and metabolism suggests a poor prognosis for larger more advanced tumours, high-grade lesions and tumours responding poorly to treatment. Vascular-metabolic imaging also has the potential to subclassify tumour response to treatment. The additional biomarkers described can be readily incorporated in existing FDG-PET examinations thereby improving the ability of PET/CT to depict tumour biology, characterize potentially malignant lesions, and assess prognosis and therapeutic response.

Imaging-based tumor treatment response evaluation: review of conventional, new, and emerging concepts

Tumor response may be assessed readily by the use of Response Evaluation Criteria in Solid Tumor version 1.1. However, the criteria mainly depend on tumor size changes. These criteria do not reflect other morphologic (tumor necrosis, hemorrhage, and cavitation), functional, or metabolic changes that may occur with targeted chemotherapy or even with conventional chemotherapy. The state-of-the-art multidetector CT is still playing an important role, by showing high-quality, high-resolution images that are appropriate enough to measure tumor size and its changes. Additional imaging biomarker devices such as dual energy CT, positron emission tomography, MRI including diffusion-weighted MRI shall be more frequently used for tumor response evaluation, because they provide detailed anatomic, and functional or metabolic change information during tumor treatment, particularly during targeted chemotherapy. This review elucidates morphologic and functional or metabolic approaches, and new concepts in the evaluation of tumor response in the era of personalized medicine (targeted chemotherapy).

Early perfusion changes in patients with recurrent high-grade brain tumor treated with Bevacizumab: preliminary results by a quantitative evaluation

BACKGROUND

To determine whether early monitoring of the effects of bevacizumab in patients with recurrent high-grade gliomas, by a Perfusion Computed Tomography (PCT), may be a predictor of the response to treatment assessed through conventional MRI follow-up.

METHODS

Sixteen patients were enrolled in the present study. For each patient, two PCT examinations, before and after the first dose of bevacizumab, were acquired. Areas of abnormal Cerebral Blood Volume (CBV) were manually defined on the CBV maps, using co-registered T1- weighted images, acquired before treatment, as a guide to the tumor location. Different perfusion metrics were derived from the histogram analysis of the normalized CBV (nCBV) maps; both hyper and hypo-perfused sub-volumes were quantified in the lesion, including tumor necrosis. A two-tailed Wilcoxon test was used to establish the significance of changes in the different perfusion metrics, observed at baseline and during treatment. The relationships between changes in perfusion and morphological MRI modifications at first follow-up were investigated.

RESULTS

Significant reductions in mean and median nCBV were detected throughout the entire patient population, after only a single dose of bevacizumab. The nCBV histogram modifications indicated the normalization effect of bevacizumab on the tumor abnormal vasculature. An improvement in hypoxia after a single dose of bevacizumab was predictive of a greater reduction in T1-weighted contrast-enhanced volumes at first follow-up.

CONCLUSIONS

These preliminary results show that a quantification of changes in necrotic intra-tumoral regions could be proposed as a potential imaging biomarker of tumor response to anti-VEGF therapies.