Quantitative hepatic CT perfusion measurement: comparison of Couinaud's hepatic segments with dual-source 128-slice CT

A simplified computational liver perfusion model, with applications to organ preservation

Advanced liver preservation strategies could revolutionize liver transplantation by extending preservation time, thereby allowing for broader availability and better matching of transplants. However, developing new cryopreservation protocols requires exploration of a complex design space, further complicated by the scarcity of real human livers to experiment upon. We aim to create computational models of the liver to aid in the development of new cryopreservation protocols. Towards this goal, we present an approach for generating 3D models of the liver vasculature by building upon the space colonization algorithm. Additionally, we introduce the concept of a super lobule which enables a computational abstraction of biological liver lobules. User-tunable parameters allow for vasculatures of varying depth and topology to be generated. In each model, we solve for a common lumped resistance value assigned to the super lobules, allowing the overall physiological blood pressure and flow rate through the liver to be preserved. We demonstrate our approach's ability to maintain consistency between models of varying depth. Finally, we simulate steady state machine perfusion of the generated models and demonstrate how they can be used to quickly test the effect of different boundary conditions when designing organ preservation protocols.

Role of Computed Tomography Perfusion in Patients with Liver Cirrhosis and Hepatocellular Carcinoma

Background

There is a lack of data on computed tomography (CT) perfusion parameters in patients with cirrhosis and the vascular changes that occur with increasing severity of cirrhosis, as well as changes that can occur in the remote/background liver parenchyma when hepatocellular carcinoma (HCC) develops. This study aimed to evaluate the association between CT perfusion parameters in the background liver parenchyma in cirrhotic patients with and without HCC.

Methods

This prospective study comprised consecutive patients with cirrhosis with or without HCC. A CT perfusion scan of the whole liver was done on a 128-detector row CT scanner in the four-dimensional spiral mode. Arterial liver perfusion (ALP), portal venous perfusion (PVP), hepatic perfusion index (HPI), blood flow (BF), blood volume (BV), and time to peak (TTP) were assessed. The perfusion parameters of the background liver parenchyma (bALP, bPVP, bHPI, bBF, bBV, and bTTP) were compared between the patients with cirrhosis (group I) and cirrhosis with HCC (group II). Perfusion parameters were also compared between the background liver parenchyma and the HCC in group II.

Results

Of the 93 patients evaluated during the study period, 60 patients (30 in group I and 30 in group II, mean age, 54.5 years, 53 men) were included in the analysis. Among the perfusion parameters in the background parenchyma, bPVP was lower and bHPI was higher in group II, suggesting increased hepatic arterial perfusion of even the remote background liver parenchyma in patients with HCC (P = 0.001 and P = 0.01, respectively). Perfusion parameters were significantly altered with increasing severity of cirrhosis (based on Child-Pugh class) both within and between groups. Additionally, there were significant differences in all the perfusion parameters between HCC and the background cirrhotic liver.

Conclusion

HPI and PVP of background liver parenchyma were significantly different in cirrhosis with and without HCC and also showed a worsening trend with increasing grades of cirrhosis.

Non-contrast enhanced magnetic resonance imaging for characterization of Fontan associated liver disease

OBJECTIVES

To evaluate the ability of non-contrast enhanced magnetic resonance imaging (MRI) techniques to characterize Fontan associated liver disease (FALD) in adolescent and adult Fontan patients.

METHODS

Fontan patients (n = 29) and healthy controls (n = 13) underwent an MRI protocol with T₁, T₂ and Apparent Diffusion Coefficient (ADC) mapping. Routine FALD screening included abdominal ultrasound and laboratory testing.

RESULTS

Median follow-up after Fontan operation was 15.1 (IQR 12.0-16.8) years. Distinct differences in tissue characteristics were visualized. T₁ and T₂ relaxation times were prolonged in Fontan patients, particularly of the right lobe (T₁: 745 (IQR 715-784) ms vs. 586 (IQR 555-602) ms, p < 0.001; T₂: 63 (IQR 59-64) ms vs. 58 (IQR 56-60) ms, p = 0.002). Left lobe ADC was lower in Fontan patients (1.10 (IQR 1.06-1.18) x 10^-3 mm²/s vs. 1.23 (IQR 1.19-1.29) x 10^-3 mm²/s, p < 0.001). T₂ mapping was able to differentiate between controls and Fontan patients with different FALD severity. Right lobe T₂ was higher in patients with moderate or severe in comparison to those with no or mild changes and healthy controls (64 (IQR 61-67) ms vs. 60 (IQR 59-63) ms vs. 58 (IQR 56-60) ms, p = 0.001).

CONCLUSIONS

Non-contrast enhanced MRI methods are able to visualize regional differences in liver tissue characteristics. T₁ and T₂ relaxation times were prolonged in Fontan patients suggestive of fibrosis or congestive hepatopathy, while reduced ADC might reflect impaired microperfusion. These methods have promising clinical potential for detection of liver abnormalities in Fontan patients. The usefulness of T₂ mapping to grade FALD severity merits further investigation.

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

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

The effect of tumor location on long-term results of microwave ablation for early-stage hepatocellular carcinoma

BACKGROUND

To analyze the influence of tumor location, including tumor adjacency and located segments on long-term survival outcomes for patients with solitary hepatocellular carcinoma (HCC) after microwave ablation (MWA).

METHODS

This retrospective study evaluated 850 patients. The hepatic segments where the tumor is located, tumor adjacency (important tissues adjacent to tumor) and other clinical characteristics were collected. Overall survival (OS), local tumor progression (LTP) and disease-free survival (DFS) were compared and analyzed. Influence of tumor location was evaluated by multi-models and the effect of adjacency for OS, LTP, and DFS in different segments was analyzed by stratification analysis.

RESULTS

The OS, LTP, and DFS rates were similar in different hepatic segments, so were in high risk and safe locations. In multi-models, HCC in segment 8 showed lower death rate of 43% than that in segment 2 (HR 0.57; P = 0.01) and tumors in segment 6 seemed to have lower LTP rate. Tumors in high-risk locations were risk factors for OS, LTP, and DFS compared with tumors in safe locations, but all differences were not significant in different models. The effects of tumor adjacency on survival outcomes among subgroups of segments were limited.

CONCLUSION

The tumor adjacency was not a prognostic factor of survival outcomes for patients with solitary tumors after MWA, but tumors in segment 8 seemed to better OS rate than tumors in other segments.

Diffusion kurtosis imaging in liver: a preliminary reproducibility study in healthy volunteers

OBJECTIVES

To systematically test the reproducibility of DKI technique in normal liver and report a complete set of DKI measurement data.

MATERIALS AND METHODS

Thirty-two healthy volunteers were examined with liver DKI twice on the GE 3.0 T MRI scanner and reviewed by three professional experts. DKI-derived parameters fractional anisotropy of kurtosis (FAk), mean diffusivity (Md), axial diffusivity (Da), radial diffusivity (Dr), mean kurtosis (Mk), axial kurtosis (Ka), and radial kurtosis (Kr) in eight segments divided by Couinaud octagonal method were collected. Inter-class correlation coefficient (ICC) was used to assess the agreement between three experts. For each expert, the reproducibility of twice scans was evaluated by Bland-Altman method. Multivariate analysis of variance was to explore the regional distribution characteristics of DKI-derived parameters, and showed with box-plot graph.

RESULTS

Using ICC analysis, except for FAk (ICC 0.312, 0.307), other DKI metric values showed high reproducibility (0.716 < ICC < 0.907) between three experts for each of two DKI measurements. With Bland-Altman method, liver segment 5 (S5) showed the best reproducibility between two DKI measurement, and the reproducibility of segment 4 (S4) was the worst. The reproducibility of the right lobe was significantly higher than the left lobe. The values of diffusion metrics (Md, Da, and Dr) and kurtosis metrics (Mk, Ka, and Kr) existed significantly difference between the right and left hepatic lobes.

CONCLUSION

DKI has shown excellent reproducibility in liver imaging. The range of values for multiple DKI parameters, derived from the normal liver, was reported, and may provide data reference for further clinical DKI applications. Additionally, DKI technique is a non-invasive method to reflect the perfusion or structural differences between the left and right hepatic lobes from the molecular level.

Computed tomography-based evaluation of segmental variation of liver density and its implications

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has become a major health concern. Focal fat deposition frequently seems to involve segment IV b. This indicates a consistent pattern of fat deposition in the liver. The present study evaluates the pattern of fat distribution in the liver using computed tomogram (CT) attenuation index.

METHODS

Two radiologists evaluated 517 non-contrast CT scan images of the abdomen and pelvis. Two 40-mm² regions of interest (ROIs) were selected from each segment. The hepatic segmental densities (HSDs) were obtained by calculating the mean densities of areas of corresponding liver segments. The mean hepatic attenuation (MHA) was quantified by obtaining the mean segmental densities. Densities were compared between the segments and with the MHA.

RESULTS

The mean age (SD) of the patients was 55.5 year (15.6), and 276 (53.4%) were males. The overall mean hepatic density was 53.05 (95% CI, 52.95-53.15) Hounsfield units (HU). The lowest mean HSD was observed in segment IV b and the highest mean HSD was observed in segment V. Segments I, IV a and IV b showed significantly lower mean HSDs and segments V, VI and VIII showed significantly higher mean HSDs compared with the overall mean MHA/mean hepatic density (MHD), whereas mean HSDs of segments II, III and VII were not significantly different from the overall mean MHA/MHD.

CONCLUSION

Segment IV b seems to be the most vulnerable site for fat deposition; focal lesions here should be carefully evaluated. Segments II, III and VII seem to closely represent MHD.

Computational Modeling in Liver Surgery

The need for extended liver resection is increasing due to the growing incidence of liver tumors in aging societies. Individualized surgical planning is the key for identifying the optimal resection strategy and to minimize the risk of postoperative liver failure and tumor recurrence. Current computational tools provide virtual planning of liver resection by taking into account the spatial relationship between the tumor and the hepatic vascular trees, as well as the size of the future liver remnant. However, size and function of the liver are not necessarily equivalent. Hence, determining the future liver volume might misestimate the future liver function, especially in cases of hepatic comorbidities such as hepatic steatosis. A systems medicine approach could be applied, including biological, medical, and surgical aspects, by integrating all available anatomical and functional information of the individual patient. Such an approach holds promise for better prediction of postoperative liver function and hence improved risk assessment. This review provides an overview of mathematical models related to the liver and its function and explores their potential relevance for computational liver surgery. We first summarize key facts of hepatic anatomy, physiology, and pathology relevant for hepatic surgery, followed by a description of the computational tools currently used in liver surgical planning. Then we present selected state-of-the-art computational liver models potentially useful to support liver surgery. Finally, we discuss the main challenges that will need to be addressed when developing advanced computational planning tools in the context of liver surgery.

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.

Diminished liver microperfusion in Fontan patients: A biexponential DWI study

It has been demonstrated that hepatic apparent diffusion coefficients (ADC) are decreasing in patients with a Fontan circulation. It remains however unclear whether this is a true decrease of molecular diffusion, or rather reflects decreased microperfusion due to decreased portal blood flow. The purpose of this study was therefore to differentiate diffusion and microperfusion using intravoxel incoherent motion (IVIM) modeled diffusion-weighted imaging (DWI) for different liver segments in patients with a Fontan circulation, compare to a control group, and relate with liver function, chronic hepatic congestion and hepatic disease. For that purpose, livers of 59 consecutively included patients with Fontan circulation (29 men; mean-age, 19.1 years) were examined (Oct 2012─Dec 2013) with 1.5T MRI and DWI (b = 0,50,100,250,500,750,1500,1750 s/mm²). IVIM (D_slow, D_fast, f_fast) and ADC were calculated for eight liver segments, compared to a control group (19 volunteers; 10 men; mean-age, 32.9 years), and correlated to follow-up duration, clinical variables, and laboratory measurements associated with liver function. The results demonstrated that microperfusion was reduced (p<0.001) in Fontan livers compared to controls with ─38.1% for D_fast and ─32.6% for f_fast. Molecular diffusion (D_slow) was similar between patients and controls, while ADC was significantly lower (─14.3%) in patients (p<0.001). ADC decreased significantly with follow-up duration after Fontan operation (r = ─0.657). D_slow showed significant inverse correlations (r = ─0.591) with follow-up duration whereas D_fast and f_fast did not. From these results it was concluded that the decreasing ADC values in Fontan livers compared with controls reflect decreases in hepatic microperfusion rather than any change in molecular diffusion. However, with the time elapsed since the Fontan operation molecular diffusion and ADC decreased while microperfusion remained stable. This indicates that after Fontan operation initial blood flow effects on the liver are followed by intracellular changes preceding the formation of fibrosis and cirrhosis.

Perfusion CT imaging of the liver: review of clinical applications

Perfusion computed tomography (CT) has a great potential for determining hepatic and portal blood flow; it offers the advantages of quantitative determination of lesion hemodynamics, distinguishing malignant and benign processes, as well as providing morphological data. Many studies have reported the use of this method in the assessment of hepatic tumors, hepatic fibrosis associated with chronic liver disease, treatment response following radiotherapy and chemotherapy, and hepatic perfusion changes after radiological or surgical interventions. The main goal of liver perfusion imaging is to improve the accuracy in the characterization of liver disorders. In this study, we reviewed the clinical application of perfusion CT in various hepatic diseases.

CT Perfusion Imaging Can Predict Patients' Survival and Early Response to Transarterial Chemo-Lipiodol Infusion for Liver Metastases from Colorectal Cancers

Objective

To prospectively evaluate the performance of computed tomography perfusion imaging (CTPI) in predicting the early response to transarterial chemo-lipiodol infusion (TACLI) and survival of patients with colorectal cancer liver metastases (CRLM).

Materials and Methods

Computed tomography perfusion imaging was performed before and 1 month after TACLI in 61 consecutive patients. Therapeutic response was evaluated on CT scans 1 month and 4 months after TACLI; the patients were classified as responders and non-responders based on 4-month CT scans after TACLI. The percentage change of CTPI parameters of target lesions were compared between responders and non-responders at 1 month after TACLI. The optimal parameter and cutoff value were determined. The patients were divided into 2 subgroups according to the cutoff value. The log-rank test was used to compare the survival rates of the 2 subgroups.

Results

Four-month images were obtained from 58 patients, of which 39.7% were responders and 60.3% were non-responders. The percentage change in hepatic arterial perfusion (HAP) 1 month after TACLI was the optimal predicting parameter (p = 0.003). The best cut-off value was -21.5% and patients who exhibited a ≥ 21.5% decrease in HAP had a significantly higher overall survival rate than those who exhibited a < 21.5% decrease (p < 0.001).

Conclusion

Computed tomography perfusion imaging can predict the early response to TACLI and survival of patients with CRLM. The percentage change in HAP after TACLI with a cutoff value of -21.5% is the optimal predictor.

Preoperative hepatic CT perfusion as an early predictor for the recurrence of esophageal squamous cell carcinoma: initial clinical results

Reports suggest that hepatic blood flow may have an association with cancer progression. The aim of the present study was to evaluate whether the hepatic blood flow measured by CT perfusion (CTP) may identify patients at high‑risk for postoperative recurrence of esophageal squamous cell carcinoma (ESCC). Prior to surgery, hepatic CTP images were obtained using a 320-row area detector CT. The data were analyzed by a commercially available software based on the dual input maximum slope method, and arterial blood flow (AF, ml/min/100 ml tissue), portal blood flow (PF, ml/min/100 ml tissue) and perfusion index [PI (%) = AF/AF + PF x 100] were measured. These parameters were compared with the pathological stage and outcome of the ESCC patients. Forty-five patients with ESCC were eligible for this study. The median follow-up period was 17 months, and recurrences were observed in 9 patients (20%). The preoperative PI values of the 9 patients with recurrence were significantly higher than those of the 36 patients without recurrence (23.9 vs. 15.9, P=0.0022). Patients were categorized into the following two groups; high PI (>20) and low PI (<20). The recurrence-free survival of the low PI group was significantly better than that of the high PI group (P<0.0001). A multivariate analysis showed that a high PI was an independent risk factor for recurrence (odds ratio, 19.1; P=0.0369).Therefore, the preoperative PI of the liver may be a useful imaging biomarker for predicting the recurrence of patients with esophageal cancer.

Characterization of incidental cardiac masses in oncological patients using a new CT-based tumor volume perfusion technique

Cardiac masses are challenging for non-invasive diagnostic procedures and therapy, respectively. In tumor patients differentiation between primary or secondary cardiac neoplasm and thrombus is a frequent and knowingly difficult task to manage. To avoid complex and unnecessary surgical diagnostic procedures non-invasive methods are in favor. For initiation of adequate therapy and evaluation of prognosis, however, early and reliable diagnosis is mandatory. So far, echocardiography and magnetic resonance imaging represent the mainstay for cardiac imaging diagnosis. Recently, the new technique of CT-based tumor volume perfusion (VPCT) measurement has advanced to a potent, reliable, and easy to perform alternative for cardiac imaging. The purpose of this study was to review the existing spectrum of diagnostic modalities for characterization of cardiac masses in an oncologic patient cohort with emphasis on their strengths and limitations and to present the benefit from using the novel technique called VPCT for this purpose.