Characterization of hepatocellular carcinoma (HCC) lesions using a novel CT-based volume perfusion (VPCT) technique. Eur J Radiol. 2015;84:1029-1035. [PMID: 25816994 DOI: 10.1016/j.ejrad.2015.02.020]

Photon-counting computed tomography - clinical application in oncological, cardiovascular, and pediatric radiology

BACKGROUND

 Photon-counting detector computed tomography (PCD-CT) is a promising new technology with the potential to fundamentally change workflows in the daily routine and provide new quantitative imaging information to improve clinical decision-making and patient management.

METHOD

 The contents of this review are based on an unrestricted literature search of PubMed and Google Scholar using the search terms "photon-counting CT", "photon-counting detector", "spectral CT", "computed tomography" as well as on the authors' own experience.

RESULTS

 The fundamental difference with respect to the currently established energy-integrating CT detectors is that PCD-CT allows for the counting of every single photon at the detector level. Based on the identified literature, PCD-CT phantom measurements and initial clinical studies have demonstrated that the new technology allows for improved spatial resolution, reduced image noise, and new possibilities for advanced quantitative image postprocessing.

CONCLUSION

 For clinical practice, the potential benefits include fewer beam hardening artifacts, a radiation dose reduction, and the use of new or combinations of contrast agents. In particular, critical patient groups such as oncological, cardiovascular, lung, and head & neck as well as pediatric patient collectives benefit from the clinical advantages.

KEY POINTS

  · Photon-counting computed tomography (PCD-CT) is being used for the first time in routine clinical practice, enabling a significant dose reduction in critical patient populations such as oncology, cardiology, and pediatrics.. · Compared to conventional CT, PCD-CT enables a reduction in electronic image noise.. · Due to the spectral data sets, PCD-CT enables fully comprehensive post-processing applications..

CITATION FORMAT

· Hagen F, Soschynski M, Weis M et al. Photon-counting computed tomography - clinical application in oncological, cardiovascular, and pediatric radiology. Fortschr Röntgenstr 2024; 196: 25 - 34.

Arterial enhancement fraction in evaluating the therapeutic effect and survival for hepatocellular carcinoma patients treated with DEB-TACE

BACKGROUND

Arterial enhancement fraction (AEF), derived from triphasic CT scans, is considered to indirectly reflect the ratio of hepatic arterial perfusion to total perfusion. The purpose of this study was to retrospectively investigate the relationship between AEF and treatment response and survival in hepatocellular carcinoma (HCC) patients treated with drug-eluting bead (DEB) TACE.

METHODS

AEF of primary lesion (AEF_pre) and residual tumor (AEF_post) in 158 HCC patients were obtained from triphasic liver CT examinations pre- and post-treatment. Wilcoxon-signed rank test was used to compare the AEF_pre and AEF_post for different response groups. Survival curves for overall survival (OS) in patients with different AEF were created by using Kaplan-Meier method. Cox regression analyses were used to determine the association between AEF and OS.

RESULTS

There was no correlation between AEF_pre and treatment response. After DEB-TACE, AEF_post was significantly lower than AEF_pre either in the partial response group (38.9% vs. 52.7%, p <  0.001) or in the stable disease group (49.3% vs. 52.1%, p = 0.029). In the progression disease group, AEF_post was numerically higher than AEF_pre (55.5% vs. 53.0%, p = 0.604). Cox regression analyses showed that risk of death increased in patients with AEF_pre > 57.95% (HR = 1.66, p = 0.019) or AEF_post > 54.85% (HR = 2.47, p <  0.001), and the risk reduced in patients with any reduction in tumor AEF (decrease ratio ≥ 0) and with increased AEF but not exceeding the ratio of 0.102 (increase ratio <  0.102) (HR = 0.32, p <  0.001).

CONCLUSIONS

The change in AEF of viable tumor is correlated with response of HCC to DEB-TACE. In addition, the AEF could be a helpful predictor in future studies on the embolization treatment for HCC.

Rim Enhancement after Technically Successful Transarterial Chemoembolization in Hepatocellular Carcinoma: A Potential Mimic of Incomplete Embolization or Reactive Hyperemia?

Contrast enhancement at the margins/rim of embolization areas in hepatocellular-carcinoma (HCC) lesions treated with transarterial chemoembolization (TACE) might be an early prognostic indicator for HCC recurrence. The aim of this study was to evaluate the predictive value of rim perfusion for TACE recurrence as determined by perfusion CT (PCT). A total of 52 patients (65.6 ± 9.3 years) underwent PCT directly before, immediately after (within 48 h) and at follow-up (95.3 ± 12.5 days) after TACE. Arterial-liver perfusion (ALP), portal-venous perfusion (PVP) and hepatic-perfusion index (HPI) were evaluated in normal liver parenchyma, and on the embolization rim as well as the tumor bed. A total of 42 lesions were successfully treated, and PCT measurements showed no residually vascularized tumor areas. Embolization was not entirely successful in 10 patients with remaining arterialized focal nodular areas (ALP 34.7 ± 10.1 vs. 4.4 ± 5.3 mL/100 mL/min, p < 0.0001). Perfusion values at the TACE rim were lower in responders compared to normal adjacent liver parenchyma and edges of incompletely embolized tumors (ALP liver 16.3 ± 10.1 mL/100 mL/min, rim responder 8.8 ± 8.7 mL/100 mL/min, rim non-responder 23.4 ± 8.6 mL/100 mL/min, p = 0.005). At follow-up, local tumor relapse was observed in 17/42, and 15/42 showed no recurrence (ALP 39.1 ± 10.1 mL/100 mL/min vs. 10.0 ± 7.4 mL/100 mL/min, p = 0.0008); four patients had de novo disseminated disease and six patients were lost in follow-up. Rim perfusion was lower compared to adjacent recurring HCC and not different between groups. HCC lesions showed no rim perfusion after TACE, neither immediately after nor at follow-up at three months, both for mid-term responders and mid-term relapsing HCCs, indicating that rim enhancement is not a sign of reactive hyperemia and not predictive of early HCC recurrence.

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.

CT hepatic arterial perfusion index does not allow stratification of the degree of esophageal varices and bleeding risk in cirrhotic patients in Child-Pugh classes A and B

Purpose

To evaluate if the hepatic arterial perfusion index (HPI) in liver parenchyma of cirrhotic patients can serve as a surrogate parameter for stratifying the degree of esophageal varices and related bleeding risks.

Methods

CT image data of sixty-six patients (59 men; mean age 68 years ± 10 years) with liver cirrhosis (Child–Pugh class A (35/66, 53%), B (25/66, 38%), and C (6/66, 9%) who underwent perfusion CT (PCT) for hepatocellular carcinoma (HCC) screening between April 2010 and January 2019 were retrospectively identified. HPI, a parameter calculated by a commercially available CT liver perfusion analysis software that is based on the double maximum slope model, using time attenuation curve to determine perfusion, was correlated with the degree of esophageal varices diagnosed at endoscopy and the number of bleeding events.

Results

Eta correlation coefficient for HPI/presence of esophageal varices was very weak (0.083). Spearman-Rho for HPI/grading of esophageal varices was very weak (0.037 (p = 0.804)). Kendall-Tau-b for HPI/grading of esophageal varices was very weak (0.027 (p = 0.807)). ANOVA and Bonferroni post-hoc-tests showed no significant difference of HPI between different grades of esophageal varices (F (3, 62) = 1.676, p = 0.186). Eta correlation coefficient for HPI/bleeding event was very weak (0.126).

Conclusion

The stratification of the degree of esophageal varices and the related bleeding risk by correlation with the HPI as a surrogate parameter for portal venous hypertension was not possible for patients with liver cirrhosis in Child–Pugh class A and B.

Graphic abstract

Dynamic contrast-enhanced CT-derived blood flow measurements enable early prediction of long term outcome in metastatic renal cell cancer patients on antiangiogenic treatment

PURPOSE

To evaluate the role of dynamic contrast-enhanced CT (DCE-CT) as an independent non-invasive biomarker in predicting long term outcome in patients with metastatic renal cell carcinoma (mRCC) on antiangiogenic treatment.

MATERIAL AND METHODS

Eighty two mRCC patients were prospectively enrolled from 09/2011 to 04/2015, out of which 71 were included in the final data analysis; the population was observed until 12/2020 to obtain complete overall survival data. DCE-CT imaging was performed at baseline and 10 to 12 weeks after start of treatment with targeted therapy. DCE-CT included a dynamic acquisition after injection of 50 ml of nonionic contrast agent at 6 ml/s using a 4D spiral mode (10 cm z-axis coverage, acquisition time 43 sec, 100 kVp (abdomen), 80 kVp (chest), 80-100 mAs) on a dual source scanner (Definition FLASH, Siemens). Blood flow (BF) was calculated for target tumor volumes using a deconvolution model. Progression free survival (PFS) and overall survival (OS) were analyzed using Kaplan-Meier statistics (SPSS version 24).

RESULTS

Patients were treated with either sunitinib, pazopanib, sorafenib, tivozanib, axitinib, or cabozantinib. A cut-off value of 50% blood flow reduction at follow-up allowed for identification of patients with favorable long-term outcome: Median OS in n = 42 patients with an average blood flow reduction of >50% (mean, 79%) was 34 (range, 14-54) months, while n = 21 patients with an average reduction of less than 50% (mean, 28%) showed a median OS of 12 (range, 6-18) months, and n = 8 patients with an increase in blood flow survived for a median of 7 (range, 3-11) months.

CONCLUSION

Blood flow in metastases measured with DCE-CT at first follow-up is a strong predictor of overall survival in mRCC patients on antiangiogenic treatment.

Correlation of C-arm CT acquired parenchymal blood volume (PBV) with 99mTc-macroaggregated albumin (MAA) SPECT/CT for radioembolization work-up

OBJECTIVE

SPECT/CT with 99mTc-macroaggregated albumin (MAA) is generally used for diagnostic work-up prior to transarterial radioembolization (TARE) to exclude shunts and to provide additional information for treatment stratification and dose calculation. C-arm CT is used for determination of lobular vascular supply and assessment of parenchymal blood volume (PBV). Aim of this study was to correlate MAA-uptake and PBV-maps in hepatocellular carcinoma (HCC) and hepatic metastases of the colorectal carcinoma (CRC).

MATERIALS AND METHODS

34 patients underwent a PBV C-arm CT immediately followed by 99mTc-MAA injection and a SPECT/CT acquisition after 1 h uptake. MAA-uptake and PBV-maps were visually assessed and semi-quantitatively analyzed (MAA-tumor/liver-parenchyma = MAA-TBR or PBV in ml/100ml). In case of a poor match, tumors were additionally correlated with post-TARE 90Y-Bremsstrahlung-SPECT/CT as a reference.

RESULTS

102 HCC or CRC metastases were analyzed. HCC presented with significantly higher MAA-TBR (7.6 vs. 3.9, p<0.05) compared to CRC. Tumors showed strong intra- and inter-individual dissimilarities between TBR and PBV with a weak correlations for capsular HCCs (r = 0.45, p<0.05) and no correlation for CRC. The demarcation of lesions was slightly better for both HCC and CRC in PBV-maps compared to MAA-SPECT/CT (exact match: 52%/50%; same intensity/homogeneity: 38%/39%; insufficient 10%/11%). MAA-SPECT/CT revealed a better visual correlation with post-therapeutic 90Y-Bremsstrahlung-SPECT/CT.

CONCLUSION

The acquisition of PBV can improve the detectability of small intrahepatic tumors and correlates with the MAA-Uptake in HCC. The results indicate that 99mTc-MAA-SPECT/CT remains to be the superior method for the prediction of post-therapeutic 90Y-particle distribution, especially in CRC. However, intra-procedural PBV acquisition has the potential to become an additional factor for TARE planning, in addition to improving the determination of segment and tumor blood supply, which has been demonstrated previously.

Assessment of Hepatic Perfusion Using GRASP MRI: Bringing Liver MRI on a New Level

PURPOSE

The aim of this study was to demonstrate the feasibility of hepatic perfusion imaging using dynamic contrast-enhanced (DCE) golden-angle radial sparse parallel (GRASP) magnetic resonance imaging (MRI) for characterizing liver parenchyma and hepatocellular carcinoma (HCC) before and after transarterial chemoembolization (TACE) as a potential alternative to volume perfusion computed tomography (VPCT).

METHODS AND MATERIALS

Between November 2017 and September 2018, 10 patients (male = 8; mean age, 66.5 ± 8.6 years) with HCC were included in this prospective, institutional review board-approved study. All patients underwent DCE GRASP MRI with high spatiotemporal resolution after injection of liver-specific MR contrast agent before and after TACE. In addition, VPCT was acquired before TACE serving as standard of reference. From the dynamic imaging data of DCE MRI and VPCT, perfusion maps (arterial liver perfusion [mL/100 mL/min], portal liver perfusion [mL/100 mL/min], hepatic perfusion index [%]) were calculated using a dual-input maximum slope model and compared with assess perfusion measures, lesion characteristics, and treatment response using Wilcoxon signed-rank test. To evaluate interreader agreement for measurement repeatability, the interclass correlation coefficient (ICC) was calculated.

RESULTS

Perfusion maps could be successfully generated from all DCE MRI and VPCT data. The ICC was excellent for all perfusion maps (ICC ≥ 0.88; P ≤ 0.001). Image analyses revealed perfusion parameters for DCE MRI and VPCT within the same absolute range for tumor and liver tissue. Dynamic contrast-enhanced MRI further enabled quantitative assessment of treatment response showing a significant decrease (P ≤ 0.01) of arterial liver perfusion and hepatic perfusion index in the target lesion after TACE.

CONCLUSIONS

Dynamic contrast-enhanced GRASP MRI allows for a reliable and robust assessment of hepatic perfusion parameters providing quantitative results comparable to VPCT and enables characterization of HCC before and after TACE, thus posing the potential to serve as an alternative to VPCT.

Dose Optimization of Perfusion-derived Response Assessment in Hepatocellular Carcinoma Treated with Transarterial Chemoembolization: Comparison of Volume Perfusion CT and Iodine Concentration

RATIONALE AND OBJECTIVES

We assessed the value of iodine concentration (IC) as a perfusion-derived response marker for hepatocellular carcinoma (HCC) treated with transarterial chemoembolization (TACE) in comparison with volume perfusion computed tomography (VPCT) parameters.

MATERIALS AND METHODS

Forty-one HCC lesions in 32 patients examined before and after TACE were analyzed retrospectively. VPCT-parameters were calculated and lesion iodine-maps were computed using subtraction of the baseline and the scan 7 seconds after aortic peak enhancement from the corresponding 80 kVp-VPCT data set. Modified RECIST was used as standard response criteria. Comparisons were performed using Student's t test for normal distributed data and Mann-Whitney U test for non-normal distributed data. Additionally, correlation analysis, receiver operating characteristics (ROC) and interreader agreement were assessed.

RESULTS

In responding lesions, mean pre-TACE IC and blood flow (BF) were 131.2 mg/100 mL and 96.7 mL/100 mL/min, decreasing to IC 25.6 mg/100 mL (P < 0.001) and BF 28.5 mL/100 mL/min (P < 0.001) post-TACE. In nonresponding lesions, the values remained almost unchanged: pre-TACE: mean BF 79.3 mL/100 mL/min and mean IC 90.4 mg/100 mL; post-TACE: mean BF 71.3 mL/100 mL/min (n.s.) and mean IC 105.4 mg/100 mL (n.s.). Differences in IC-values revealed a high sensitivity/specificity of 96.7%/81.8%. IC and VPCT-parameters showed strong, positive correlations. Mean volume CT dose index for VPCT was 63.4 mGy and 4.9 mGy for iodine maps.

CONCLUSION

Thus, IC is a meaningful perfusion marker for local therapy response monitoring in HCC that can be acquired with low radiation dose. This information is important for further therapy response applications using dual and single energy CT.

Perfusion-CT analysis for assessment of hepatocellular carcinoma lesions: diagnostic value of different perfusion maps

BACKGROUND

Computed tomography liver perfusion (CTLP) has been improved in recent years, offering a variety of perfusion-parametric maps. A map that better discriminates hepatocellular carcinoma (HCC) is still to be found.

PURPOSE

To compare different CTLP maps, regarding their ability to differentiate cirrhotic or non-cirrhotic parenchyma from malignant HCC.

MATERIAL AND METHODS

Twenty-six patients (11 cirrhotic) with 50 diagnosed HCC lesions, underwent CTLP on a 128-row dual-energy CT system. Nine different maps were generated. Regions of interest (ROIs) were positioned on non-tumorous parenchyma and on HCCs found on previous magnetic resonance imaging. Perfusion parameters for non-cirrhotic and cirrhotic livers were compared. Receiver operating characteristic (ROC) analysis was employed to evaluate each map's ability to discriminate HCCs from non-tumorous livers. Comparison of ROC curves was performed to evaluate statistical significance of differences in the discriminating efficiency of derived perfusion maps.

RESULTS

Perfusion parameters for non-tumorous liver and HCCs recorded in cirrhotic patients did not significantly differ from corresponding values recorded in non-cirrhotic patients ( P > 0.05). The highest power for HCC discrimination was found for the maximum-slope-of-increase (MSI) parametric map, with estimated the area under ROC curve of 0.997. An MSI cut-off criterion of 2.2 HU/s was found to provide 96% sensitivity and 100% specificity. Time to peak, blood flow, and transit time to peak were also found to have high discriminating power.

CONCLUSION

Among available CTLP-derived perfusion parameters, MSI was found to provide the highest diagnostic accuracy in discriminating HCCs from non-tumorous parenchyma. Perfusion parameters for non-tumorous livers and HCCs were not found to significantly differ between cirrhotic and non-cirrhotic patients.

Can cone-beam CT tumor blood volume predicts the response to chemoembolization of colorectal liver metastases? Results of an observational study

PURPOSE

To determine whether intraprocedural C-arm cone-beam CT (CBCT) parenchymal blood volume (PBV) can predict the response of colorectal cancer liver metastases (CRCLM) 2 months after irinotecan drug-eluting bead (DEBIRI) chemoembolization.

MATERIALS AND METHODS

This single-center observational study was compliant with the Helsinki Declaration and approved by our institutional review board. Thirty-four consecutive CRCLM patients referred for DEBIRI chemoembolization were enrolled between March 2015 and December 2016. Tumor size was assessed at baseline and 2 months after DEBIRI chemoembolization by multidetector CT (Response Evaluation Criteria in Solid Tumors RECIST 1.0), and PBV was measured before and after DEBIRI chemoembolization. Two independent readers reviewed all data. We determined the potential correlation (Spearman's rank correlation) between intraprocedural PBV values and tumor response at 2 months. The relationship between tumor response and PBV was studied using a mixed model. A logistic regression model was applied to study the relationship between patient "Responder/Non-responder" and PBV.

RESULTS

There was a strong correlation between baseline PBV or the percent change of PBV and the 2-month tumor response (rho = - 0.8587 (p = 0.00001) and rho = 0.8027 (p = 0.00001), respectively). The mixed model showed that an increase of 1 ml/1000 ml in PBV of a tumor before DEBIRI chemoembolization led to a 0.54 mm decrease in diameter (p < 0.005). A 1% decrease in PBV after DEBIRI chemoembolization resulted in tumor shrinkage of 0.75 mm (p < 0.005). The logistic regression model showed that patients with a 1% smaller mean decrease of PBV after DEBIRI chemoembolization had a 10% lower likelihood of achieving disease control (OR = 0.9, 95% confidence interval (CI) = 0.81-1; p = 0.0493).

CONCLUSION

Intraprocedural PBV may predict tumor response to DEBIRI chemoembolization.

KEY POINTS

• There is a strong relationship between the parenchymal blood volume (PBV) of colorectal liver metastases before DEBIRI chemoembolization and tumor response at 2 months. • Higher PBV values before DEBIRI chemoembolization correlate with greater tumor shrinkage, but only if the PBV decreases by more than 70% after DEBIRI chemoembolization. • Each increase of 1% in the mean decrease of PBV after DEBIRI chemoembolization resulted in a 10% lower likelihood of achieving disease control (OR = 0.9, 95% confidence interval (CI) = 0.81-1; p = 0.0493).

Comparison of patient dose from routine multi-phase and dynamic liver perfusion CT studies taking into account the effect of iodinated contrast administration

OBJECTIVES

To accurately determine and compare patient radiation burden from routine multi-phase CT (MPCT) and dynamic CT liver perfusion (CTLP) studies taking into account the effect of iodine uptake of exposed tissues/organs.

MATERIALS AND METHODS

40 consecutive MPCT of upper abdomen and 40 consecutive CTLP studies performed on a modern CT scanner were retrospectively studied. Iodine uptake of radiosensitive tissues at the time of acquisition was calculated through the difference of tissues' CT numbers between NECT and CECT images. Monte Carlo simulation and mathematical anthropomorphic phantoms were employed to derive patient-size-specific organ dose data from each scan involved taking into account the effect of iodinated contrast uptake on absorbed dose. Effective dose estimates were derived for routine multiphase CT and CTLP by summing up the contribution of NECT and CECT scans involved.

RESULTS

The mean underestimation error in organ doses from CECT exposures if iodine uptake is not encountered was found to be 2.2%-38.9%. The effective dose to an average-size patient from routine 3-phase CT, 4-phase CT and CTLP studies was found to be 20.6, 27.7 and 25.8 mSv, respectively. Effective dose from CTLP was found lower than 4-phase CT of upper abdomen irrespective of patient body size. Compared to 3-phase CT, the radiation burden from CTLP was found to be higher for average size-patients but again lower for overweight patients.

CONCLUSIONS

Modern CT technology allows CTLP studies at comparable or even lower patient radiation burden compared to routine multi-phase liver CT imaging.

Diagnostic Value of Quantitative Perfusion Computed Tomography Technique in the Assessment of Tumor Response to Sorafenib in Patients With Advanced Hepatocellular Carcinoma

AIM

The aim of this study was to assess the role of dynamic contrast-enhanced perfusion computed tomography (pCT) imaging in the early detection of blood flow changes related to antiangiogenic treatment with sorafenib, in patients with advanced hepatocellular carcinoma (HCC), being the modified Response Evaluation Criteria in Solid Tumors (mRECIST) criteria the standard of reference.

METHODS

Between 2012 and 2016, 43 cirrhotic patients (male, n = 39; female, n = 4) with biopsy-proven multifocal HCC underwent multi-detector-row computed tomography, and pCT examinations were performed before and every 2 months after sorafenib administration. Perfusion CT technique is based on the acquisition of 16 dynamic slices/scan per 40 scans, performed on a 256-slice multi-detector-row computed tomography scanner, after intravenous bolus injection of 50 mL of iodinated contrast agent (350 mg I/mL) at a flow rate of 5 mL/s. According to mRECIST, patients were stratified into complete (CR) or partial response (PR) and stable (SD) or progressive disease (PD). The following pCT parameters were calculated: hepatic perfusion (mL/s per 100 g), time to peak (seconds), arterial perfusion (mL/s), and hepatic perfusion index (%). Perfusion CT values at baseline and first follow-up were reported for all mRECIST groups and then compared between the nonprogressor (CR, PR, SD) and progressor groups (PD).

RESULTS

Most pCT values were significantly higher (P < 0.01) between baseline and follow-up in the CR and PR groups, whereas nonsignificant differences were found among SD patients, and a nonsignificant trend (P > 0.05) toward increase was observed among PD patients. Moreover, pCT values were significantly higher (P = 0.05) at baseline in the nonprogressor group compared with the progressor.

CONCLUSION

Preliminary results suggest that pCT adds quantitative data of vascularization, thus demonstrating its usefulness in the assessment of therapeutic response to sorafenib in advanced HCC, in line with mRECIST criteria, offering 1-step information on tissue cellularity and vascularization.

Evaluation of the effect of image noise on CT perfusion measurements using digital perfusion phantoms

OBJECTIVES

To assess the influence of image noise on computed tomography (CT) perfusion studies, CT perfusion software algorithms were evaluated for susceptibility to image noise and results applied to clinical perfusion studies.

METHODS

Digital perfusion phantoms were generated using a published deconvolution model to create time-attenuation curves (TACs) for 16 different combinations of blood flow (BF; 30/60/90/120 ml/100 ml/min) and flow extraction product (FEP; 10/20/30/40 ml/100 ml/min) corresponding to values encountered in clinical studies. TACs were distorted with Gaussian noise at 50 different strengths to approximate image noise, performing 200 repetitions for each noise level. A total of 160,000 TACs were evaluated by measuring BF and FEP with CT perfusion software, comparing results for the maximum slope and Patlak models with those obtained with a deconvolution model. To translate results to clinical practice, data of 23 patients from a CT perfusion study were assessed for image noise, and the accuracy of reported CT perfusion measurements was estimated.

RESULTS

Perfusion measurements depend on image noise as means and standard deviations of BF and FEP over repetitions increase with increasing image noise, especially for low BF and FEP values. BF measurements derived by deconvolution show larger standard deviations than those performed with the maximum slope model. Image noise in the evaluated CT perfusion study was 26.46 ± 3.52 HU, indicating possible overestimation of BF by up to 85% in a clinical setting.

CONCLUSIONS

Measurements of perfusion parameters depend heavily upon the magnitude of image noise, which has to be taken into account during selection of acquisition parameters and interpretation of results, e.g., as a quantitative imaging biomarker.

KEY POINTS

• CT perfusion results depend heavily upon the magnitude of image noise. • Different CT perfusion models react differently to the presence of image noise. • Blood flow may be overestimated by 85% in clinical CT perfusion studies.

Prognostic value of perfusion CT in hepatocellular carcinoma treatment with sorafenib: comparison with mRECIST in longitudinal follow-up

Background Targeted therapies are of increasing clinical importance and classic radiologic therapy response-criteria often fail to detect early therapeutic response or failure. For hepatocellular carcinoma (HCC), this is of major importance as therapeutic options are limited. Purpose To investigate the impact of sorafenib-treatment on intralesional perfusion using perfusion computed tomography (PCT) in HCC and to correlate the observed changes with mRECIST and the course of serum alpha-fetoprotein (AFP) for identification of their prognostic value. Material and Methods PCT was performed before and after two months of sorafenib treatment in 28 consecutive HCC patients and AFP levels were registered. Changes in tumor perfusion parameters blood flow (BF), blood volume (BV), mean transit time (MTT), volume transfer constant (K^trans), arterial liver perfusion (ALP), and hepatic perfusion index (HPI) were registered in one target lesion. mRECIST measurements were performed at baseline and after two and four months during sorafenib treatment. Results According to mRECIST, after two months of treatment, all patients showed stable disease (SD), whereas after four months, 13 patients (46%) showed SD and 15 patients (54%) showed progressive disease (PD). A significant decrease was found in perfusion parameters BF, BV, K^trans, ALP, and HPI in patients with SD as well as a significant increase in MTT ( P < 0.05) after two months compared to baseline, while patients with PD showed a significant increase in HPI, BF, and BV. There were no correlations between AFP and mRECIST or perfusion parameters. Conclusion Decreased intralesional BF and HPI after two months of sorafenib treatment predicts disease stabilization after four months, whereas AFP dynamics were of limited value.

Correlation between acoustic radiation force impulse (ARFI)-based tissue elasticity measurements and perfusion parameters acquired by perfusion CT in cirrhotic livers: a proof of principle

PURPOSE

To investigate whether liver stiffness measured by acoustic radiation force impulse (ARFI) sonoelastography always correlates with the liver perfusion parameters quantified by perfusion CT in patients with known liver cirrhosis.

METHODS

Sonoelastography and perfusion CT were performed in 50 patients (mean age 65.5; range 45-87 years) with liver cirrhosis, who were classified according to Child-Pugh into class A (30/50, 60%), B (17/50, 34%), and C (3/50, 6%). For standardized ARFI measurements in the left liver lobe at a depth of 4 cm, a convex 6-MHz probe was used. CT examinations were performed using 80 kV, 100 mAs, and 50 ml of iodinated contrast agent injected at 5 ml/s. Using standardized region-of-interest measurements, we quantified arterial, portal venous, and total liver perfusion.

RESULTS

There was a significant linear correlation between tissue stiffness and arterial liver perfusion (p = 0.015), and also when limiting the analysis to patients with histology (p = 0.019). In addition, there was a positive correlation between the total blood supply (arterial + portal-venous liver perfusion) to the liver and tissue stiffness (p = 0.001; with histology, p = 0.027). Shear wave velocity increased with higher Child-Pugh stages (p = 0.013).

CONCLUSION

The degree of tissue stiffness in cirrhotic livers correlates expectedly-even if only moderately-with the magnitude of arterial liver perfusion and total liver perfusion. As such, liver elastography remains the leading imaging tool in assessing liver fibrosis.

Use of patient outcome endpoints to identify the best functional CT imaging parameters in metastatic renal cell carcinoma patients

OBJECTIVE

To use the patient outcome endpoints overall survival and progression-free survival to evaluate functional parameters derived from dynamic contrast-enhanced CT.

METHODS

69 patients with metastatic renal cell carcinoma had dynamic contrast-enhanced CT scans at baseline and after 5 and 10 weeks of treatment. Blood volume, blood flow and standardized perfusion values were calculated using deconvolution (BV_deconv, BF_deconv and SPV_deconv), blood flow and standardized perfusion values using maximum slope (BF_max and SPV_max) and blood volume and permeability surface area product using the Patlak model (BV_patlak and PS). Histogram data for each were extracted and associated to patient outcomes. Correlations and agreements were also assessed.

RESULTS

The strongest associations were observed between patient outcome and medians and modes for BV_deconv, BV_patlak and BF_deconv at baseline and during the early ontreatment period (p < 0.05 for all). For the relative changes in median and mode between baseline and weeks 5 and 10, PS seemed to have opposite associations dependent on treatment. Interobserver correlations were excellent (r ≥ 0.9, p < 0.001) with good agreement for BF_deconv, BF_max, SPV_deconv and SPV_max and moderate to good (0.5 < r < 0.7, p < 0.001) for BV_deconv and BV_patlak. Medians had a better reproducibility than modes.

CONCLUSION

Patient outcome was used to identify the best functional imaging parameters in patients with metastatic renal cell carcinoma. Taking patient outcome and reproducibility into account, BV_deconv, BV_patlak and BF_deconv provide the most clinically meaningful information, whereas PS seems to be treatment dependent. Standardization of acquisition protocols and post-processing software is necessary for future clinical utilization. Advances in knowledge: Taking patient outcome and reproducibility into account, BV_deconv, BV_patlak and BF_deconv provide the most clinically meaningful information. PS seems to be treatment dependent.

Can dual-energy CT replace perfusion CT for the functional evaluation of advanced hepatocellular carcinoma?

OBJECTIVES

To determine the degree of relationship between iodine concentrations derived from dual-energy CT (DECT) and perfusion CT parameters in patients with advanced HCC under treatment.

METHODS

In this single-centre IRB approved study, 16 patients with advanced HCC treated with sorafenib or radioembolization who underwent concurrent dynamic perfusion CT and multiphase DECT using a single source, fast kV switching DECT scanner were included. Written informed consent was obtained for all patients. HCC late-arterial and portal iodine concentrations, blood flow (BF)-related and blood volume (BV)-related perfusion parameters maps were calculated. Mixed-effects models of the relationship between iodine concentrations and perfusion parameters were computed. An adjusted p value (Bonferroni method) < 0.05 was considered significant.

RESULTS

Mean HCC late-arterial and portal iodine concentrations were 22.7±12.7 mg/mL and 18.7±8.3 mg/mL, respectively. Late-arterial iodine concentration was significantly related to BV (mixed-effects model F statistic (F)=28.52, p<0.0001), arterial BF (aBF, F=17.62, p<0.0001), hepatic perfusion index (F=28.24, p<0.0001), positive enhancement integral (PEI, F=66.75, p<0.0001) and mean slope of increase (F=32.96, p<0.0001), while portal-venous iodine concentration was mainly related to BV (F=29.68, p<0.0001) and PEI (F=66.75, p<0.0001).

CONCLUSIONS

In advanced HCC lesions, DECT-derived late-arterial iodine concentration is strongly related to both aBF and BV, while portal iodine concentration mainly reflects BV, offering DECT the ability to evaluate both morphological and perfusion changes.

KEY POINTS

• Late-arterial iodine concentration is highly related to arterial BF and BV. • Portal iodine concentration mainly reflects tumour blood volume. • Dual-energy CT offers significantly decreased radiation dose compared with perfusion CT.

Multi-detector CT: Liver protocol and recent developments

Multi-detector computed tomography is today the workhorse in the evaluation of the vast majority of patients with known or suspected liver disease. Reasons for that include widespread availability, robustness and repeatability of the technique, time-efficient image acquisitions of large body volumes, high temporal and spatial resolution as well as multiple post-processing capabilities. However, as the technique employs ionizing radiation and intravenous iodine-based contrast media, the associated potential risks have to be taken into account. In this review article, liver protocols in clinical practice are discussed with emphasis on optimisation strategies. Furthermore, recent developments such as perfusion CT and dual-energy CT and their applications are presented.

Computed Tomography Perfusion Following Transarterial Chemoembolization of Hepatocellular Carcinoma: A Feasibility Study in the Early Period

OBJECTIVES

The aim of this study was to assess the feasibility of computed tomography (CT) perfusion in early follow-up after transarterial chemoembolization (TACE) of hepatocellular carcinoma (HCC).

METHODS

Fifteen patients with a total of 16 HCC who were referred to our institution for TACE were included in the study. Computed tomography perfusion was performed within 1 to 3 days before and 4 to 7 days after TACE. Multiphase contrast-enhanced CT was performed 35 (SD, 20) days after TACE. Hepatic arterial blood flow and portal venous blood flow, as well as the perfusion index (PI), were calculated for each HCC using the dual input maximum slope method. Visual grading of the PI and visual grading of the amount of deposition of embolic material within the HCC were performed using a 6-step scale. Differences in perfusion before and after TACE and correlation of perfusion before TACE with the amount of embolization material depositions 1 week and 1 month after TACE were tested.

RESULTS

No statistically significant correlation was found between pre-TACE perfusion parameters and the amount of embolization material deposition in the post-TACE studies. There was no statistically significant difference between pre- and post-TACE arterial blood flow and portal venous blood flow, whereas PI was significantly lower after TACE. Congruently, visual grading of PI was statistically significantly lower after TACE. There was no statistically significant difference in quantitative pre-TACE and post-TACE PI between tumors, which showed hypervascularization in the multiphase follow-up CT and tumors that did not show hypervascularization. However, tumors that showed hypervascularization in the multiphase follow-up CT had significantly higher visual grading of PI after TACE than tumors that did not show hypervascularization.

CONCLUSIONS

Our findings indicate that visual interpretation of the PI of HCC derived from dual-input maximum slope CT perfusion may be an early predictor of response to TACE.

Impact of transjugular intrahepatic portosystemic shunt implantation on liver perfusion measured by volume perfusion CT

Background Implantation of a transjugular intrahepatic portosystemic shunt (TIPS) induces changes of liver perfusion. Purpose To determine the changes in arterial, portal venous, and total perfusion of the liver parenchyma induced by TIPS using the technique of volume perfusion computed tomography (VPCT) and compare results with invasively measured hepatic intravascular pressure values. Material and Methods VPCT quantification of liver perfusion was performed in 23 patients (mean age, 62.5 ± 8.8 years) with portal hypertension in the pre-TIPS and post-TIPS setting, respectively. A commercially available software package was used for post-processing, enabling separate calculation of the dual (arterial [ALP] and portal venous [PVP]) blood supply and additionally of the hepatic perfusion index (HPI) (HPI = ALP/(ALP + PVP)*100%). Invasive pressure measurements were performed during the intervention, before and after TIPS placement. Liver function tests performed before and after the procedure were compared. Results Mean decrease of pressure gradient through TIPS was 13.3 mmHg. Mean normal values for ALP, PVP, and total perfusion (ALP + PVP) before TIPS were 15.9, 37.7, and 53.5 mL/100 mL/min, respectively, mean HPI was 35.4%. After TIPS, ALP increased to a mean value of 37.7 mL/100 mL/min, PVP decreased (15.7 mL/100 mL/min, P < 0.05), whereas total perfusion remained unchanged (53.4 mL/100 mL/min, P = 0.97). HPI increased (71.9%; P < 0.05). No correlation between invasive pressure measurement and VPCT parameters was observed. After TIPS, liver function tests were found to worsen with a significant increase of bilirubin ( P < 0.05). Conclusion Following TIPS placement, ALP and HPI increased in all patients, whereas PVP markedly decreased. Interestingly, the magnitude of decrease in portosystemic pressure gradients was not found to correlate with VPCT parameters.

Is liver perfusion CT reproducible? A study on intra- and interobserver agreement of normal hepatic haemodynamic parameters obtained with two different software packages

OBJECTIVE

To evaluate the agreement between the measurements of perfusion CT parameters in normal livers by using two different software packages.

METHODS

This retrospective study was based on 78 liver perfusion CT examinations acquired for detecting suspected liver metastasis. Patients with any morphological or functional hepatic abnormalities were excluded. The final analysis included 37 patients (59.7 ± 14.9 y). Two readers (1 and 2) independently measured perfusion parameters using different software packages from two major manufacturers (A and B). Arterial perfusion (AP) and portal perfusion (PP) were determined using the dual-input vascular one-compartmental model. Inter-reader agreement for each package and intrareader agreement between both packages were assessed with intraclass correlation coefficients (ICC) and Bland-Altman statistics.

RESULTS

Inter-reader agreement was substantial for AP using software A (ICC = 0.82) and B (ICC = 0.85-0.86), fair for PP using software A (ICC = 0.44) and fair to moderate for PP using software B (ICC = 0.56-0.77). Intrareader agreement between software A and B ranged from slight to moderate (ICC = 0.32-0.62) for readers 1 and 2 considering the AP parameters, and from fair to moderate (ICC = 0.40-0.69) for readers 1 and 2 considering the PP parameters.

CONCLUSION

At best there was only moderate agreement between both software packages, resulting in some uncertainty and suboptimal reproducibility. Advances in knowledge: Software-dependent factors may contribute to variance in perfusion measurements, demanding further technical improvements. AP measurements seem to be the most reproducible parameter to be adopted when evaluating liver perfusion CT.

Monitoring Disease Activity in Patients with Aortitis and Chronic Periaortitis Undergoing Immunosuppressive Therapy by Perfusion CT

RATIONALE AND OBJECTIVES

To evaluate the role of perfusion CT for monitoring inflammatory activity in patients with aortitis and chronic periaortitis undergoing immunosuppressive therapy.

MATERIALS AND METHODS

Seventeen symptomatic patients (median age 68.5 years) who underwent perfusion-based computed tomography (CT) monitoring after diagnostic contrast-enhanced CT were retrospectively included in this study. Blood flow (BF), blood volume (BV), volume transfer constant (k-trans), time to peak, and mean transit time were determined by setting circular regions of interest in prominently thickened parts of the vessel wall or perfused surrounding tissue at sites where the perfusion CT color maps showed a maximum BF value. Differences in CT perfusion and, morphological parameters, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were tested for significance during therapy.

RESULTS

In all patients BF and BV dropped at second perfusion CT (P < 0.05). In aortitis patients, CRP dropped from 3.86 ± 5.31 mg/dL to 0.9 ± 1.37 mg/dL and in periaortitis patients from 1.78 ± 2.25 mg/dL to 0.79 ± 1.55 mg/dL, whereas ESR dropped from 45.71 ± 37.59 seconds to 8.57 ± 3.1 seconds and 36.78 ± 34.67 seconds to 17.22 ± 21.82 seconds in aortitis and in periaortitis, respectively.

CONCLUSIONS

The course of perfusion CT parameters in aortitis and chronic periaortitis undergoing immunosuppressive therapy dropped at different extent after therapy.

Comparison between acoustic radiation force impulse quantification data and perfusion-CT parameters in hepatocellular carcinoma

OBJECTIVE

To find out, if ultrasound elastography of hepatocellular carcinoma (HCC) can predict patterns of tumor perfusion in volume perfusion computed tomography (VPCT).

MATERIAL AND METHODS

25 consecutive patients (mean age, 68.9; range, 51-85 years) with liver cirrhosis suspected of HCC underwent VPCT and acoustic radiation force impulse (ARFI) elastography the same day. Quantitative elasticity values were registered, while blood flow (BF), blood volume (BV) and hepatic perfusion index (HPI) of the HCC lesions were calculated. Additionally, we identified histologic WHO grading, lesion size and localization. The Siemens Acuson S 3000 HELX-System with Virtual Touch™-Software and Siemens Somatom Definition Flash with Syngo^® software were used.

RESULTS

A total of 43 HCC lesions were assessed. Mean shear wave velocity was 2.6m/s (range, 1.1-4.3m/s). There was no significant linear correlation between the elasticity values and BF (p=0.751), BV (p=0.426) and HPI (p=0.437). However, elasticity values were higher, the larger the tumor was (p=0.008). Shear wave velocity declined with increasing distance of the HCC to the skin surface (p=0.028) and depending on liver segment. In addition, elasticity values were higher in less differentiated HCCs. This trend was not statistically significant (p=0.842).

CONCLUSION

Tissue elasticity in HCC does not correlate with the degree of tumor vascularization, but calculated values are influenced both by the tumor size and localization inside the liver.

Radiological biomarkers for assessing response to locoregional therapies in hepatocellular carcinoma: From morphological to functional imaging (Review)

Many hepatocellular carcinoma (HCC) patients do not qualify for curative surgical intervention and are instead treated with locoregional therapies (LRTs) including ablative and endovascular therapies. Assessment of imaging response is essential in the management of HCC for determining efficacy of therapy and as a surrogate marker for improved survival. The established morphological image biomarkers for tumor burden measurement continue to be applied, as size measurement can easily be used in clinical practice. However, in the setting of liver-directed LRTs for HCC, simple tumor morphological changes can be less informative and usually appear later than biologic changes. Functional imaging (such as perfusion and diffusion imaging, PET-CT/MR and MR spectroscopy) has the potential to be a promising technique for assessment of HCC response to LRTs. Although promising, none of these functional imaging biomarkers have gone through all the required steps of standardization and validation and established accepted criteria for clinical practice.

Correlation of magnetic resonance signal characteristics and perfusion parameters assessed by volume perfusion computed tomography in hepatocellular carcinoma: Impact on lesion characterization

AIM: To find out if magnetic resonance (MR)-signal characteristics of hepatocellular carcinomas (HCC) correlate with perfusion parameters assessed by volume perfusion computed tomography (VPCT).

METHODS: From October 2009 to January 2014, 26 (mean age, 69.3 years) patients with 36 HCC lesions who underwent both VPCT and MR liver imaging were analysed. We compared signal intensity in the T1w- and T2w-images and wash-in/wash-out kinetics on post-contrast MR images with mean values of blood flow (BF, mL/100 mL per minute), blood volume (BV, mL/100 mL), k-trans (mL/100 mL per minute), arterial liver perfusion (mL/100 mL per minute), portal venous perfusion and hepatic perfusion index (HPI, %) obtained by VPCT. Signal intensity on magnetic resonance imaging (MRI) was classified hyper/iso/hypointense compared with surrounding liver parenchyma.

RESULTS: Signal intensity on native T1w- and T2w-images was hyper/iso/hypo in 4/16/16 and 21/14/1 lesions, respectively. Wash-in and wash-out contrast kinetics were found on MRI in 33 of 36 lesions (91.7%) and 25 of 36 lesions (69.4%), respectively. The latter was observed significantly more often in higher graded lesions (P < 0.005). HPI was 94.7% ± 6.5%. There was no significant relationship between lesion’s MR-signal intensity, MR signal combinations, size and any of the VPCT-perfusion parameters. However HPI was constantly high in all HCC lesions.

CONCLUSION: VPCT parameters add limited value to MR-lesion characterization. However in HCC lesions with atypical MR signal characteristics HPI can add a parameter to ensure HCC diagnosis.

Advanced imaging techniques in the therapeutic response of transarterial chemoembolization for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the major causes of morbidity and mortality in patients with chronic liver disease. Transarterial chemoembolization (TACE) can significantly improve the survival rate of patients with HCC and is the first treatment choice for patients who are not suitable for surgical resections. The evaluation of the response to TACE treatment affects not only the assessment of the therapy efficacy but also the development of the next step in the treatment plan. The use of imaging to examine changes in tumor volume to assess the response of solid tumors to treatment has been controversial. In recent years, the emergence of new imaging technology has made it possible to observe the response of tumors to treatment prior to any morphological changes. In this article, the advances in studies reporting the use of computed tomography perfusion imaging, diffusion-weighted magnetic resonance imaging (MRI), intravoxel incoherent motion, diffusion kurtosis imaging, magnetic resonance spectroscopy, magnetic resonance perfusion-weighted imaging, blood oxygen level-dependent MRI, positron emission tomography (PET)/computed tomography and PET/MRI to assess the TACE treatment response are reviewed.

Iodine concentration as a perfusion surrogate marker in oncology: Further elucidation of the underlying mechanisms using Volume Perfusion CT with 80 kVp

OBJECTIVES

To assess the value of iodine concentration (IC) in computed tomography data acquired with 80 kVp, as a surrogate for perfusion imaging in hepatocellular carcinoma (HCC) and lymphoma by comparing iodine related attenuation (IRA) with quantitative Volume Perfusion CT (VPCT)-parameters.

METHODS

VPCT-parameters were compared with intra-tumoral IC at 5 time points after the aortic peak enhancement (APE) with a temporal resolution of 3.5 sec in untreated 30 HCC and 30 lymphoma patients.

RESULTS

Intra-tumoral perfusion parameters for HCC showed a blood flow (BF) of 52.7 ± 17.0 mL/100 mL/min, blood volume (BV) 12.6 ± 4.3 mL/100 mL, arterial liver perfusion (ALP) 44.4 ± 12.8 mL/100 mL/min. Lesion IC 7 sec after APE was 133.4 ± 57.3 mg/100 mL. Lymphoma showed a BF of 36.8 ± 13.4 mL/100 mL/min, BV of 8.8 ± 2.8 mL/100 mL and IC of 118.2 ± 64.5 mg/100 mL 3.5 sec after APE. Strongest correlations exist for VPCT-derived BF and ALP with IC in HCC 7 sec after APE (r = 0.71 and r = 0.84) and 3.5 sec after APE in lymphoma lesions (r = 0.77). Significant correlations are also present for BV (r = 0.60 and r = 0.65 for HCC and lymphoma, respectively).

CONCLUSIONS

We identified a good, time-dependent agreement between VPCT-derived flow values and IC in HCC and lymphoma. Thus, CT-derived ICs 7 sec after APE in HCC and 3.5 sec in lymphoma may be used as surrogate imaging biomarkers for tumor perfusion with 80 kVp.

KEY POINTS

• Iodine concentration derived from low kVp CT is regarded as perfusion surrogate • Correlation with Perfusion CT was performed to elucidate timing and histology dependencies • Highest correlation was present 7 sec after aortic peak enhancement in hepatocellular carcinoma • In lymphoma, highest correlation was calculated 3.5 sec after aortic peak enhancement • With these results, further optimization of Dual energy CT protocols is possible.

Imaging of HCC-Current State of the Art

Early diagnosis of hepatocellular carcinoma (HCC) is crucial for optimizing treatment outcome. Ongoing advances are being made in imaging of HCC regarding detection, grading, staging, and also treatment monitoring. This review gives an overview of the current international guidelines for diagnosing HCC and their discrepancies as well as critically summarizes the role of magnetic resonance imaging (MRI) and computed tomography (CT) techniques for imaging in HCC. The diagnostic performance of MRI with nonspecific and hepatobililiary contrast agents and the role of functional imaging with diffusion-weighted imaging will be discussed. On the other hand, CT as a fast, cheap and easily accessible imaging modality plays a major role in the clinical routine work-up of HCC. Technical advances in CT, such as dual energy CT and volume perfusion CT, are currently being explored for improving detection, characterization and staging of HCC with promising results. Cone beam CT can provide a three-dimensional analysis of the liver with tumor and vessel characterization comparable to cross-sectional imaging so that this technique is gaining an increasing role in the peri-procedural imaging of HCC treated with interventional techniques.