Diagnosis of liver metastases: value of diffusion-weighted MRI compared with gadolinium-enhanced MRI. Eur Radiol. 2010;20:1431-1441. [PMID: 20148251 DOI: 10.1007/s00330-009-1695-9]

Psychophysical Evaluation of Visual vs. Computer-Aided Detection of Brain Lesions on Magnetic Resonance Images

BACKGROUND

Magnetic resonance imaging (MRI) diagnosis is usually performed by analyzing contrast-weighted images, where pathology is detected once it reached a certain visual threshold. Computer-aided diagnosis (CAD) has been proposed as a way for achieving higher sensitivity to early pathology.

PURPOSE

To compare conventional (i.e., visual) MRI assessment of artificially generated multiple sclerosis (MS) lesions in the brain's white matter to CAD based on a deep neural network.

STUDY TYPE

Prospective.

POPULATION

A total of 25 neuroradiologists (15 males, age 39 ± 9, 9 ± 9.8 years of experience) independently assessed all synthetic lesions.

FIELD STRENGTH/SEQUENCE

A 3.0 T, T₂ -weighted multi-echo spin-echo (MESE) sequence.

ASSESSMENT

MS lesions of varying severity levels were artificially generated in healthy volunteer MRI scans by manipulating T₂ values. Radiologists and a neural network were tasked with detecting these lesions in a series of 48 MR images. Sixteen images presented healthy anatomy and the rest contained a single lesion at eight increasing severity levels (6%, 9%, 12%, 15%, 18%, 21%, 25%, and 30% elevation in T₂ ). True positive (TP) rates, false positive (FP) rates, and odds ratios (ORs) were compared between radiological diagnosis and CAD across the range lesion severity levels.

STATISTICAL TESTS

Diagnostic performance of the two approaches was compared using z-tests on TP rates, FP rates, and the logarithm of ORs across severity levels. A P-value <0.05 was considered statistically significant.

RESULTS

ORs of identifying pathology were significantly higher for CAD vis-à-vis visual inspection for all lesions' severity levels. For a 6% change in T₂ value (lowest severity), radiologists' TP and FP rates were not significantly different (P = 0.12), while the corresponding CAD results remained statistically significant.

DATA CONCLUSION

CAD is capable of detecting the presence or absence of more subtle lesions with greater precision than the representative group of 25 radiologists chosen in this study.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 3.

One-stop local and whole-body staging of children with cancer

Accurate staging and re-staging of cancer in children is crucial for patient management. Currently, children with a newly diagnosed cancer must undergo a series of imaging tests, which are stressful, time-consuming, partially redundant, expensive, and can require repetitive anesthesia. New approaches for pediatric cancer staging can evaluate the primary tumor and metastases in a single session. However, traditional one-stop imaging tests, such as CT and positron emission tomography (PET)/CT, are associated with considerable radiation exposure. This is particularly concerning for children because they are more sensitive to ionizing radiation than adults and they live long enough to experience secondary cancers later in life. In this review article we discuss child-tailored imaging tests for tumor detection and therapy response assessment - tests that can be obtained with substantially reduced radiation exposure compared to traditional CT and PET/CT scans. This includes diffusion-weighted imaging (DWI)/MRI and integrated [F-18]2-fluoro-2-deoxyglucose (18F-FDG) PET/MRI scans. While several investigators have compared the value of DWI/MRI and 18F-FDG PET/MRI for staging pediatric cancer, the value of these novel imaging technologies for cancer therapy monitoring has received surprisingly little attention. In this article, we share our experiences and review existing literature on this subject.

Seeing the whole picture: Added value of MRI for extraperitoneal findings in CRS-HIPEC candidates

PURPOSE

In colorectal cancer (CRC) patients the selection of suitable cytoreductive surgery and hyperthermic peritoneal chemotherapy (CRS-HIPEC) candidates is based on the location and extent of peritoneal metastases (PM) and presence of extraperitoneal metastases. MRI is increasingly being used to accurately assess the extent of PM, however, the significance of extraperitoneal findings in these scans has never been evaluated before.

METHODS

CRC patients who had undergone an additional MRI scan after standard work-up with CT for preoperative staging between January 2016-January 2020 were selected. CT and MRI reports were reviewed for new abdominopelvic extra-peritoneal findings on MRI (MR-EPF) and MR-EPFs concerning lesions previously indicated as equivocal (uncertain benign/malignant) on CT. Reference standard were surgical results or follow-up imaging.

RESULTS

In 158 included patients 60 MR-EPFs (in 58/158 patients) were noted: twenty-six (43%) were new findings and thirty-four (57%) were equivocal findings on CT. Of the 34 equivocal findings 27 were 'rejected/less likely malignant' and 7 'confirmed/more likely malignant' based on MRI. In 29 patients (18%) the MR-EPFs had direct influence on treatment planning. Three patients (2%), eligible for CRS-HIPEC on CT, were deemed inoperable due to MR-EPFs.

CONCLUSION

MRI had an added value in more than a third of the patients due to abdominopelvic extraperitoneal findings that were undetected or indeterminate on CT and therefore influenced the treatment in a substantial part of the patients. Combined with the known accurate detection of peritoneal disease on MRI, MRI seems a logical addition to the diagnostic workup of potential CRS-HIPEC candidates.

The Feasibility of a Fast Liver MRI Protocol for Lesion Detection of Adults at 3.0-T

Purpose

To investigate the feasibility of a fast liver magnetic resonance imaging (MRI) protocol for lesion detection in adults using 3.0-T MRI.

Methods

A fast liver MRI exam protocol was proposed. The protocol included motion-resistant coronal T2-w sequence, axial T2-w fast spin echo sequence with fat suppression, axial in-op phase gradient recalled echo (GRE) T1, axial diffusion weighted imaging (DWI), and axial contrast-enhanced T1 sequences. To evaluate the diagnostic capacity of the proposed protocol, 31 consecutive patients (20 males and 11 females; mean age, 53.2 years) underwent a liver MRI exam with conventional sequences, including the proposed protocol as a subset. Images from the conventional protocol and extracted abbreviated protocol were independently read, and the diagnostic concordance rate was assessed for each patient. The concordance analysis is presented as the proportion of concordant cases between the two protocols.

Results

The net measurement time of the fast liver MRI protocol without adjustment and waiting time were 4 min and 28 s. In the 31 patients included in this study, 139 suspicious findings were found from both the conventional liver MR protocol and the fast liver MRI protocol. The diagnostic concordance rate was 96.4%.

Conclusions

The fast liver MRI protocol is feasible at 3.0-T, with a shorter exam time and high diagnostic concordance compared to the conventional liver MRI workflow.

Diagnostic performance of contrast-enhanced ultrasound and magnetic resonance imaging for detecting colorectal liver metastases: A systematic review and meta-analysis

OBJECTIVES

To determine the diagnostic performance of contrast-enhanced ultrasound, diffusion-weighted magnetic resonance imaging and contrast-enhanced magnetic resonance imaging for detecting colorectal liver metastases.

METHODS

We performed comprehensive searches of the MEDLINE, EMBASE, and Cochrane Library databases to identify studies reporting the per-lesion diagnostic accuracy of contrast-enhanced ultrasound, diffusion-weighted magnetic resonance imaging, and contrast-enhanced magnetic resonance imaging for detecting colorectal liver metastases. Studies published between January 2003 and December 2018 with reference standards, including histopathology and intraoperative observation, and/or follow-up, were included. Sources of bias were assessed using the QUADAS-2 tool. A linear mixed-effects regression model was used to determine sensitivity estimates.

RESULTS

Overall, 47 articles were included. The sensitivity estimates for contrast-enhanced ultrasound, diffusion-weighted magnetic resonance imaging, and contrast-enhanced magnetic resonance imaging for detecting colorectal liver metastases were 85.3%, 83.0%, and 90.1%, respectively. For lesions ≥10 mm in diameter, the sensitivities were 93.1%, 92.9%, and 94.5%, respectively. In 21 articles using histopathology as the only reference standard, the sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio for contrast-enhanced ultrasound/contrast-enhanced magnetic resonance imaging were 86%/91%, 91%/95%, 9.2/16.6, 0.15/0.10, and 61/170, respectively.

CONCLUSIONS

CEUS showed a diagnostic ability comparable to that of DWI and CEMRI, particularly for lesions ≥10 mm in diameter.

Improving preoperative detection of synchronous liver metastases in pancreatic cancer with combined contrast-enhanced and diffusion-weighted MRI

PURPOSE

To explore the value of gadolinium-enhanced MRI combined with diffusion-weighted MRI (Gd-enhanced MRI with DWI) in addition to contrast-enhanced CT (CECT) for detection of synchronous liver metastases for potentially resectable pancreatic cancer.

METHODS

By means of a retrospective cohort study we included patients with potentially resectable pancreatic cancer on CECT, who underwent Gd-enhanced MRI with DWI between January 2012 and December 2016. A single observer evaluated MRI and CT and was blinded to imaging, pathology, and surgery reports. Liver lesions were scored in both modalities, using a 3-point scale: 1-benign, 2-indeterminate, 3- malignant (i.e., metastasis). The primary outcome parameters were the presence of liver metastases on Gd-enhanced MRI with DWI and the sensitivity of Gd-enhanced MRI with DWI for synchronous liver metastases.

RESULTS

We included 66 patients (42 men, 24 women; median age 65 years, range 36-82 years). In 19 patients, liver metastases were present, which were confirmed by histopathology (n = 12), ¹⁸FDG-PET (n = 6), or surgical inspection (n = 1). Gd-enhanced MRI with DWI showed metastases in 16/19 patients (24%), which resulted in a sensitivity of 84% (95% CI 60-97%). Contrast-enhanced MRI showed 156 and DWI 397 metastases (p = 0.051), and 339 were particularly small (< 5 mm).

CONCLUSIONS

In this study, Gd-enhanced MRI with DWI detected synchronous liver metastases in 24% of patients with potentially resectable pancreatic cancer on CECT with a sensitivity of 84%. Diffusion-weighted MRI showed a greater number of metastases than any other sequence, particularly small metastases (< 5 mm).

Detection of liver metastases on gadobenate dimeglumine-enhanced MRI: systematic review, meta-analysis, and similarities with gadoxetate-enhanced MRI

OBJECTIVES

To determine the sensitivity and positive predictive value (PPV) of gadobenate-enhanced MR imaging for the detection of liver metastases.

METHODS

This systematic review and meta-analysis was conducted according to PRISMA guidelines. A comprehensive search (EMBASE, PubMed) was performed to identify relevant articles up to December 2017. Studies eligible for inclusion were performed using appropriate methodology with complete verification by means of histopathology, intraoperative observation and/or follow-up, and sufficient information to permit determination of true-positive (TP), false-negative (FN), and false-positive (FP) values. Sources of bias were assessed using the QUADAS-2 tool. An inverse variance-weighted random-effects model was used to obtain sensitivity and PPV estimates. Information was analyzed and presented using Cochran's Q statistic, funnel plots, and modified Deeks' analysis.

RESULTS

Ten articles (256 patients, 562 metastases) were included. Sensitivity estimates for pre-contrast (unenhanced) imaging, gadobenate-enhanced dynamic imaging, and combined unenhanced, dynamic, and delayed hepatobiliary phase imaging for detecting liver metastases on a per-lesion basis were 77.8% (95% CI 71.4-84.3%, 7 assessments), 88.1% (95% CI, 84.0-92.2%, 13 assessments), and 95.1% (95% CI 93.1-97.1%, 15 assessments), respectively. The addition of hepatobiliary phase images significantly improved the detection of liver metastases. The overall PPV was 90.9% (95% CI 86.6-95.1%, 11 assessments). Deeks' funnel analysis revealed no association between sample size and sensitivity (β = 0.02, p = 0.814) indicating no significant publication bias.

CONCLUSIONS

Gadobenate-enhanced MR imaging has high sensitivity and PPV for the detection of liver metastases on a per-lesion basis. The sensitivity and PPV for detection is comparable to reported values for the pure liver-specific agent gadoxetate.

KEY POINTS

• Gadobenate dimeglumine is a hepatobiliary MR contrast agent that permits acquisition of contrast-enhanced liver images during the immediate post-injection dynamic phase, like any extracellular agent, and in the delayed hepatobiliary phase, after specific uptake by the hepatocytes. • The hepatobiliary phase improves detection of liver metastases when compared either to pre-contrast unenhanced images alone or to pre-contrast + gadobenate-enhanced dynamic phase images. • The meta-analysis showed an overall sensitivity of 95.1% and PPV of 90.9% of gadobenate-enhanced MRI for the detection of metastases, when based on the evaluation of all available acquisitions.

Imaging strategies in the management of gastric cancer: current role and future potential of MRI

Accurate preoperative staging of gastric cancer and the assessment of tumor response to neoadjuvant treatment is of importance for treatment and prognosis. Current imaging techniques, mainly endoscopic ultrasonography (EUS), computed tomography (CT) and ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET), have their limitations. Historically, the role of magnetic resonance imaging (MRI) in gastric cancer has been limited, but with the continuous technical improvements, MRI has become a more potent imaging technique for gastrointestinal malignancies. The accuracy of MRI for T- and N-staging of gastric cancer is similar to EUS and CT, making MRI a suitable alternative to other imaging strategies. There is limited evidence on the performance of MRI for M-staging of gastric cancer specifically, but MRI is widely used for diagnosing liver metastases and shows potential for diagnosing peritoneal seeding. Recent pilot studies showed that treatment response assessment as well as detection of lymph node metastases and systemic disease might benefit from functional MRI (e.g. diffusion weighted imaging and dynamic contrast enhancement). Regarding treatment guidance, additional value of MRI might be expected from its role in better defining clinical target volumes and setup verification with MR-guided radiation treatment.

MRI assessment of hepatocellular carcinoma after locoregional therapy

Liver cirrhosis and hepatocellular carcinoma (HCC) constitute one of the major causes of morbidity, mortality, and high health care costs worldwide. Multiple treatment options are available for HCC depending on the clinical status of the patient, size and location of the tumor, and available techniques and expertise. Locoregional treatment options are multiple. The most challenging part is how to assess the treatment response by different imaging modalities, but our scope will be assessing the response to locoregional therapy for HCC by MRI. This will be addressed by conventional MR methods using LI-RADS v2018 and by functional MR using diffusion-weighted imaging, perfusion, and highlighting the value of the novel intravoxel incoherent motion (IVIM).

[Importance of diffusion imaging in liver metastases]

CLINICAL/METHODICAL ISSUE

Detection and characterization of focal liver lesions.

STANDARD RADIOLOGICAL METHODS

Due to its excellent soft tissue contrast, the availability of liver-specific contrast agents and the possibility of functional imaging, magnetic resonance imaging (MRI) is the method of choice for the evaluation of focal liver lesions.

METHODICAL INNOVATIONS

Diffusion-weighted imaging (DWI) enables generation of functional information about the microstructure of a tissue besides morphological information.

PERFORMANCE

In the detection of focal liver lesions DWI shows a better detection rate compared to T2w sequences and a slightly poorer detection rate compared to dynamic T1w sequences. In principle, using DWI it is possible to distinguish malignant from benign liver lesions and also to detect a therapy response at an early stage.

ACHIEVEMENTS

For both detection and characterization of focal liver lesions, DWI represents a promising alternative to the morphological sequences; however, a more detailed characterization with the use of further sequences should be carried out particularly for the characterization of solid benign lesions. For the assessment and prognosis of therapy response, DWI offers advantages compared to morphological sequences.

PRACTICAL RECOMMENDATIONS

For the detection of focal liver lesions DWI is in principle sufficient. After visual detection of a solid liver lesion a more detailed characterization should be carried out using further sequences (in particular dynamic T1w sequences). The DWI procedure should be used for the assessment and prognosis of a therapy response.

Added value of diffusion-weighted imaging in hepatic tumors and its impact on patient management

Background

To investigate the added diagnostic value of diffusion-weighted imaging (DWI) of the liver and its impact on therapy decisions in patients with hepatic malignancy.

Methods

Interdisciplinary gastrointestinal tumorboard cases concerning patients with hepatic malignancies discussed between 11/2015 and 06/2016 were included in this retrospective, single-center study. Two radiologists independently reviewed the respective liver MR-examination first without, then with DWI. The readers were blinded regarding number, position and size of hepatic malignancies. Cases in which DWI revealed additional findings concerning the hepatic tumor status as compared to conventional sequences alone were presented to experienced members of the interdisciplinary tumor board. In this retrospective setting changes in treatment decisions based on these additional findings in the DWI sequences were recorded.

Results

A total of 87 patients were included. DWI revealed additional findings in 12 patients (13,8%). These new findings had a direct effect on the therapy in 8 patients (9,2%): In 6 patients (6,9%) the surgical/interventional treatment was adapted (n = 5: extended resection, n = 1: with transarterial chemoembolization of a single hepatocellular carcinoma only detectable in DWI); 2 patients (2,3%) received systemic therapy (n = 1: neo-adjuvant, n = 1: palliative) based on the additional findings in DWI. In 4 patients (4.6%) additional DWI findings did not affect the therapeutic decision.

Conclusions

DWI is a relevant diagnostic tool in oncologic imaging of the liver. By providing further information regarding tumor load in hepatic malignancies it can lead to a significant change in treatment.

Liver metastases: Detection and staging

The liver is more often involved with metastatic disease than primary liver tumors. The accurate detection and characterization of liver metastases are crucial since patient management depends on it. The imaging options, mainly consisting of contrast-enhanced ultrasound (CEUS), multidetector computed tomography (CT), magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI), extra-cellular contrast media and liver-specific contrast media as well as positron emission tomography/computed tomography (PET/CT), are constantly evolving. PET/MRI is a more recent hybrid method and a topic of major interest concerning liver metastases detection and characterization. This review gives a brief overview about the spectrum of imaging findings and focus on an update about the performance, advantages and potential limitations of each modality as well as current developments and innovations.

Diffusion weighted magnetic resonance imaging of liver: Principles, clinical applications and recent updates

Diffusion-weighted imaging (DWI), a functional imaging technique exploiting the Brownian motion of water molecules, is increasingly shown to have value in various oncological and non-oncological applications. Factors such as the ease of acquisition and ability to obtain functional information in the absence of intravenous contrast, especially in patients with abnormal renal function, have contributed to the growing interest in exploring clinical applications of DWI. In the liver, DWI demonstrates a gamut of clinical applications ranging from detecting focal liver lesions to monitoring response in patients undergoing serial follow-up after loco-regional and systemic therapies. DWI is also being applied in the evaluation of diffuse liver diseases such as non-alcoholic fatty liver disease, hepatic fibrosis and cirrhosis. In this review, we intend to review the basic principles, technique, current clinical applications and future trends of DW-MRI in the liver.

Focal Liver Lesions Classification and Characterization: What Value Do DWI and ADC Have?

OBJECTIVE

The aim of this work was to analyze the value of diffusion-weighted imaging (DWI) in the classification/characterization of focal liver lesions (FLLs).

METHODS

Retrospective study, approved by ethical board, of 100 proven FLLs (20 hemangiomas, 20 focal nodular hyperplasia, 20 dysplastic nodules, 20 hepatocellular carcinomas, and 20 metastases) was performed by 1.5-T MR. For each lesion, 2 readers, blinded of medical history, have evaluated 6 sets of images: set A (T1/T2-weighted images), set B (set A + DWI), set C (set B + apparent diffusion coefficient [ADC] map), set D (set A + dynamic and hepatobiliary phases), set E (set D + DWI), set F (set E + ADC map).

RESULTS

In unenhanced images, the evaluation of the ADC improves the accuracy in classification/characterization (+9%/14%, respectively), whereas in enhanced images the accuracy was increased by DWI (+7%/12%, respectively) and ADC (+13%/19%, respectively). Diffusion-weighted imaging does not improve classification/characterization of hemangiomas, may be useful in focal nodular hyperplasia/dysplastic nodules vs metastases/hepatocellular carcinoma differentiation, and increases the classification/characterization of metastases in both unenhanced and enhanced images.

CONCLUSIONS

Diffusion-weighted imaging may improve classification/characterization of FLLs at unenhanced/enhanced examinations.

Standard-b-Value Versus Low-b-Value Diffusion-Weighted Imaging in Hepatic Lesion Discrimination: A Meta-analysis

OBJECTIVE

We sought to determine the comparative diagnostic performance of standard-b-value (500-1000s/mm) versus low-b-value (≤500 s/mm) diffusion-weighted imaging (DWI) in the discrimination of hepatic lesions.

METHODS

A total of 1775 hepatic malignant lesions and 1120 benign hepatic lesions from 21 studies were included.

RESULTS

(1) The global sensitivity was 0.86 (95% confidence interval [CI], 0.847-0.879), the specificity was 0.82 (95% CI, 0.797-0.842), the positive likelihood ratio (PLR) was 6.234 (95% CI, 4.260-9.123), the negative likelihood ratio (NLR) was 0.175 (95% CI, 0.135-0.227), and diagnostic odds ratio (DOR) was 42.836 (95% CI, 24.134-76.031). The area under the curve (AUC) and Q* index were 0.93 and 0.87. Publication bias was not present (P > 0.05). (2)The sensitivity of a subgroup meta-analysis of standard-b-value DWI was 0.858 (95% CI, 0.835-0.880), the specificity was 0.836 (95% CI, 0.807-0.863), the PLR was 6.527 (95% CI, 3.857-11.046), the NLR was 0.168 (95% CI, 0.123-0.239), and the DOR was 49.716 (95% CI, 22.897-107.98). The AUC and Q* index were 0.941 and 0.88. (3)The sensitivity of a subgroup meta-analysis of low-b-value DWI was 0.87 (95% CI, 0.84-0.89), the specificity was 0.80 (95% CI, 0.76-0.83), the PLR was 6.22 (95% CI, 3.29-11.76), the NLR was 0.19 (95% CI, 0.12-0.29), and the DOR was 37.14 (95% CI, 14.80-93.18). The AUC and Q* index were 0.922 and 0.86.

CONCLUSIONS

Hepatic DWI is useful in differentiating between malignant and benign hepatic lesions. Standard-b-value DWI displayed an overall superior diagnostic accuracy over low-b-value DWI. Further trials needed to determine whether increasing b values beyond 1000 s/mm affects the diagnostic accuracy of hepatic lesion discrimination.

The role of apparent diffusion coefficient values in characterization of solid focal liver lesions: a prospective and comparative clinical study

We evaluated and compared the diagnostic accuracy (DA) of apparent diffusion coefficient (ADC) values with that of lesion-to-liver ADC ratios in the characterization of solid focal liver lesions (FLLs). This prospective study was approved by the Institutional Human Ethics Board, after waiving written informed consent. Diffusion-weighted imaging and other routine magnetic resonance imaging were performed on 142 consecutive patients with suspected liver disease. The mean ADC values and lesion-to-liver ADC ratios were compared between benign and malignant solid FLLs. Receiver operating characteristic analysis was performed. The study participants included 46 patients (28 men, 18 women; mean age, 52.5 years) with 57 solid FLLs (32 malignant and 25 benign FLLs). The mean ADC values and ADC ratios of benign solid FLLs were significantly higher than those of malignant lesions (P&lt;0.01). The difference between the area under the receiver operating characteristic curve of the ADC values (0.699) and ADC ratios (0.752) was not significant. Our study suggests that the DA of the ADC ratio is not significantly higher than that of ADC in characterizing solid FLLs.

Prevalence of hepatic lesion types defined by T2-weighted and dynamic gadolinium-enhanced MR imaging in patients with metastasized neuroendocrine tumors

PURPOSE

Identifying liver metastases from neuroendocrine tumors (NETs) is a pretherapeutic challenge in patients who are candidates for liver resection. The aims of our study are to characterize and determine the frequency of different MRI characteristics of liver metastases caused by NETs in a lesion-by-lesion analysis and to determine the frequency of monomorphous and polymorphous metastases in a patient-by-patient analysis.

METHODS

This retrospective study involved 47 patients with liver metastases arising from histologically confirmed NETs. In a lesion-by-lesion analysis, we classified these metastases according to their MRI characteristics as follows: hypervascular lesions with homogeneous or peripheral enhancement, hypovascular lesions, pure cystic lesions, and mixed solid/cystic lesions. In the patient-by-patient analysis, we distinguished patients whose metastases had the same MRI characteristics from patients with mixed lesion characteristics.

RESULTS

A total of 376 metastases were analyzed. Of these, 84.3% (n = 317) were hypervascular, with 51.9% showing homogeneous enhancement and 32.4% (n = 122) showing peripheral enhancement. Another 7.4% (n = 28) were hypovascular, 5.3% (n = 20) were pure cystic, and 2.9% (n = 11) were mixed solid/cystic. After excluding three patients with solitary lesions, 40.9% of patients (n = 18) had mixed-type lesions, consisting of hypervascular lesions with either homogeneous or peripheral enhancement in 27.3% of cases (n = 12), while 59.1% of patients (n = 26) had identical lesions.

CONCLUSION

Approximately 15% of metastases have atypical MRI characteristics and are either hypovascular or cystic. Metastases with different MRI characteristics coexist in 40% of patients.

Diffusion weighted imaging: Technique and applications

Diffusion weighted imaging (DWI) is a method of signal contrast generation based on the differences in Brownian motion. DWI is a method to evaluate the molecular function and micro-architecture of the human body. DWI signal contrast can be quantified by apparent diffusion coefficient maps and it acts as a tool for treatment response evaluation and assessment of disease progression. Ability to detect and quantify the anisotropy of diffusion leads to a new paradigm called diffusion tensor imaging (DTI). DTI is a tool for assessment of the organs with highly organised fibre structure. DWI forms an integral part of modern state-of-art magnetic resonance imaging and is indispensable in neuroimaging and oncology. DWI is a field that has been undergoing rapid technical evolution and its applications are increasing every day. This review article provides insights in to the evolution of DWI as a new imaging paradigm and provides a summary of current role of DWI in various disease processes.

Current evidence for the diagnostic value of gadoxetic acid-enhanced magnetic resonance imaging for liver metastasis

A variety of imaging techniques, including ultrasonography (US), multidetector computed tomography (MDCT), magnetic resonance imaging (MRI) and positron emission tomography combined with CT scan (PET/CT), are available for diagnosis and treatment planning in liver metastasis. Contrast-enhanced MDCT is a relatively non-invasive, widely available and standardized method for hepatic work-up. Gadoxetic acid (gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid; EOB Primovist®]) is a recently developed liver-specific hepatobiliary MR contrast agent that offers both dynamic imaging as well as liver-specific static hepatocyte imaging, referred to as the hepatobiliary phase. Following contrast injection, this technique reveals dynamic vascular phases (arterial, portal venous and delayed phases), in addition to the hepatobiliary phase upon uptake by functional hepatocytes. The overall sensitivity of gadoxetic acid-enhanced MRI was significantly higher than that of contrast-enhanced CT. Specifically, the higher sensitivity of gadoxetic acid-enhanced MRI was observed in lesions smaller than 1 cm in diameter. Gadoxetic acid-enhanced MRI is considered an extremely useful tool for the diagnosis of liver metastases. Future studies will focus on diagnostic algorithms involving combinations of modalities such as MRI, MDCT and/or (18) F-fluorodeoxyglucose PET/CT, which may impact the treatment plan for these patients.

Added value of diffusion-weighted magnetic resonance imaging for the detection of pancreatic fluid collection infection

OBJECTIVES

To investigate the added value of diffusion-weighted (DW) magnetic resonance (MR) imaging in the detection of infection in pancreatic fluid collections (PFC).

METHODS

Forty-patients with PFC requiring endoscopic-transmural drainage underwent conventional-MR and DW-MR imaging (b = 1000 s/mm²) before endoscopy. MR images were divided into two sets (set1, conventional-MR; set2, conventional-MR, DW-MR and ADC maps) and randomized. Two independent readers performed qualitative and quantitative (apparent diffusion coefficient, ADC) image analysis. Bacteriological analysis of PFC content was the gold standard. Non-parametric tests were used for comparisons. Sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV) and accuracy were calculated for the two sets for both readers. Receiver operating characteristic curves (ROC) were drawn to assess quantitative DW-MR imaging diagnostic performance.

RESULTS

For both readers, sensitivity, specificity, NPV, PPV and accuracy for infected PFCs were higher for set2 (P > .05). ADC were lower in infected versus non-infected PFCs (P ≤ .031). Minimum ADC cut-off: 1,090×10^-3 mm²/s for reader 1 and 1,012×10^-3 mm²/s for reader 2 (sensitivity and specificity 67 % and 96 % for both readers).

CONCLUSION

Qualitative information provided by DW-MR may help to assess PFCs infection. Infected PFCs show significantly lower ADCs compared to non-infected ones.

KEY POINTS

• DW improves MR diagnostic accuracy to detect infection of PFC • Infected PFCs show lower ADC compared to non-infected ones (P < .031) • DW-MR images are easy to interpret especially for non-experienced radiologist.

The efficacy of diffusion weighted imaging and apparent diffusion coefficients mapping for liver metastasis of colonic adenocarcinomas

Objectives:

To establish retrospectively the relation between the histopathologic grade of colorectal liver metastasis and apparent diffusion coefficient (ADC) values of hepatic metastases of colorectal adenocarcinomas.

Methods:

The diagnoses of liver metastases were confirmed with biopsy, surgery, and follow-up imaging findings. Twenty-six patients with 94 liver metastasis were included in the study. Of 94 masses, 59 were poorly-differentiated adenocarcinoma, 18 were moderately-differentiated adenocarcinoma, and 17 were well-differentiated regarding the diameters, ADC values, and ratio index (RI) values. Kolmogorov-smirnov normality test, Kruskal-wallis analysis of variance, Mann-Whitney U test with Bonferroni correction, Spearman correlation analysis, and receiver operating characteristics curve methods were applied to evaluate the statistical relations.

Results:

There was a statistically significant difference in terms of ADC values and RI between poorly-differentiated adenocarcinoma and moderately-differentiated adenocarcinoma plus well-differentiated adenocarcinomas. Poorly-differentiated adenocarcinomas have the lowest ADC values and highest RI values among other groups.

Conclusion:

Use of ADC values alone can be executed for the diagnosis of focal hepatic masses and also can aid in the differentiation of benign and malignant hepatic lesions.

Diffusion-Weighted Imaging with Two Different b-Values in Detection of Solid Focal Liver Lesions

One hundred and eighty-two consecutive patients with suspected liver disease were recruited to receive diffusion-weighted imaging (DWI) with two different b-values, in comparison with T2-weighted imaging (T2WI). The detection rate of three MR sequences in solid focal liver lesions (FLLs) and subgroup analyses were performed. Our prospective study found that DWI600 was equivalent to DWI100 and T2WI for the detection of solid FLLs overall but was significantly more accurate in the detection of malignant solid FLLs and lesions larger than 10 mm.

The role of diffusion-weighted imaging in the detection of hepatic metastases from colorectal cancer: A comparison with unenhanced and Gd-EOB-DTPA enhanced MRI

OBJECTIVES

To compare the role of DWI vs. gadoxetic-acid-disodium enhanced MRI in the detection of colorectal hepatic metastases.

METHODS

Fifty-four patients with 115 hepatic metastases were included in this retrospective study, approved by the Ethical Board. All patients underwent intraoperative-ultrasound and surgical resection within two weeks after MRI. Images were grouped in 4 sets, which were analyzed by two radiologists in different sessions: unenhanced T1-T2w (set A), set A plus DWI (set B), set A plus gadoxetic-acid-disodium (set C), set A plus DWI plus gadoxetic-acid-disodium (set D). For each set, metastases presence/size/site was reported. Interobserver agreement and statistical significance were assessed by Cohen's kappa and Mc-Nemar's test, respectively.

RESULTS

Readers' agreement was always very good (k>0.80). Mean sensitivity values were 84.3/92.1/95.6/97.3% for set A/B/C/D, respectively. Mean specificity, positive predicted, negative predicted, and accuracy values strongly and progressively increased in the various set too: from 62.5% (set A) to 85.0% as for specificity, from 92.8% to 97.3% as for positive predicted value, from 41.0% to 85.1% as for negative predicted value, and from 81.1% to 95.5% as for accuracy. For each reader from set A to D, the number of false negatives progressively decreases.

CONCLUSIONS

For both readers, DWI improved all statistical parameters in the unenhanced examinations, as for nodules either smaller or greater than 1cm, while in the EOB-enhanced examinations DWI prevalently increased specificity/negative predictive value.

Multiparametric MR Imaging in Abdominal Malignancies

Modern MR imaging protocols can yield both anatomic and functional information for the assessment of hepatobiliary and pancreatic malignancies. Diffusion-weighted imaging is fully integrated into state-of-the-art protocols for tumor detection, characterization, and therapy monitoring. Hepatobiliary contrast agents have gained ground in the evaluation of focal liver lesions during the last years. Perfusion MR imaging is expected to have a central role for monitoring therapy in body tumors treated with antivascular drugs. Approaches such as Magnetic resonance (MR) elastography and (1)H-MR spectroscopy are still confined to research centers, but with the potential to grow in a short time frame.

Technical advancements and protocol optimization of diffusion-weighted imaging (DWI) in liver

An area of rapid advancement in abdominal MRI is diffusion-weighted imaging (DWI). By measuring diffusion properties of water molecules, DWI is capable of non-invasively probing tissue properties and physiology at cellular and macromolecular level. The integration of DWI as part of abdominal MRI exam allows better lesion characterization and therefore more accurate initial diagnosis and treatment monitoring. One of the most technical challenging, but also most useful abdominal DWI applications is in liver and therefore requires special attention and careful optimization. In this article, the latest technical developments of DWI and its liver applications are reviewed with the explanations of the technical principles, recommendations of the imaging parameters, and examples of clinical applications. More advanced DWI techniques, including Intra-Voxel Incoherent Motion (IVIM) diffusion imaging, anomalous diffusion imaging, and Diffusion Kurtosis Imaging (DKI) are discussed.

A comparative study of apparent diffusion coefficient and intravoxel incoherent motion-derived parameters for the characterization of common solid hepatic tumors

BACKGROUND

The performance of diffusion-weighted imaging parameters for characterizing hepatic tumors is controversial.

PURPOSE

To compare the performances of apparent diffusion coefficient (ADC) and intravoxel incoherent motion (IVIM)-derived parameters, including the pure diffusion coefficient (D), perfusion coefficient (D*), and perfusion fraction (f), in the characterization of common solid hepatic tumors.

MATERIAL AND METHODS

Twelve healthy volunteers and 43 patients underwent free-breath diffusion-weighted magnetic resonance imaging (DW-MRI) of the liver using eight b values (10-800 s/mm(2)). Twelve regions of interest (ROIs) of normal liver tissue in healthy volunteers and 49 hepatic lesions (23 hepatocellular carcinomas [HCCs], 16 hemangiomas, and 10 metastases) were measured. Conventional ADC(0,500) and ADCtotal obtained by the mono-exponential model, as well as D, D*, and f were calculated. Student t-tests and receiver operating characteristic (ROC) analysis were also performed.

RESULTS

ADC(0,500), ADCtotal, and D were significantly lower in the malignant group ([1.48 ± 0.35] × 10(-3) mm(2)/s; [1.35 ± 0.30] × 10(-3) mm(2)/s; [1.18 ± 0.33] × 10(-3) mm(2)/s) compared to the hemangioma group ([2.74 ± 1.03] × 10(-3) mm(2)/s; [2.61 ± 0.81] × 10(-3) mm(2)/s; [1.97 ± 0.79] × 10(-3) mm(2)/s]. D* did not differ among multiple comparisons. For the area under the ROC curve (AUC-ROC), the maximum value was attained with ADCtotal (0.983) and was closely followed by ADC(0,500) (0.967), with lower values obtained for D (0.837), f (0.649), and D* (0.599). Statistically significant differences were found between the AUC-ROC of both ADCs (ADCtotal and ADC(0,500)) and D. There was no statistically significant difference between the AUC-ROC of ADCtotal and ADC(0,500).

CONCLUSION

ADCs showed superior diagnostic performance compared to IVIM-derived parameters in detecting differences between the malignant group and hemangioma group.

Morphologic and Functional Imaging of Non-Colorectal Liver Metastases

Liver metastases are the most frequent malignant liver lesions. Besides colorectal carcinoma, gastric carcinoma, pancreatic carcinoma, breast cancer, lung cancer, and neuroendocrine tumors are the most common entities that metastasize to the liver. The morphology of these metastases depends on the primary tumor. For morphologic and functional imaging of non-colorectal liver metastases, multiple imaging techniques such as ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography coupled with CT or MRI are available. This review summarizes morphologic and functional characteristics of different non-colorectal liver metastases.

Focal liver lesions detection: Comparison of respiratory-triggering, triggering and tracking navigator and tracking-only navigator in diffusion-weighted imaging

PURPOSE

To compare low b value (10s/mm(2)) spin-echo echo-planar (SE-EP) diffusion-weighted imaging (DWI) acquired with respiratory-triggering (RT), triggering and tracking navigator (TT), tracking only navigator (TRON) techniques for image quality and focal liver lesions (FLL) detection in non-cirrhotic patients.

MATERIAL AND METHODS

This bi-centric study was approved by the institutional review boards; informed consent was obtained. Eighty-three patients were prospectively included and SE-EP-DWI with RT, TT and TRON techniques were performed. DWI sequences were randomized and independently analyzed by two readers. The qualitative evaluation was based on a 3-point score for axial artifacts (motion, ghost, susceptibility artifacts and distortion) and stair-step artifacts. Sensitivity of FLL detection was calculated for all lesions together and after lesion size stratification (≤ 10 mm, >10-20mm and >20mm). The standard of reference consisted of a retrospective reading of the conventional MRI, the three DWI sequences and by follow-up (12 months): a total of 409 FLL were detected. Data between sequences was compared with non-parametric tests. Cohen's kappa coefficient was used for inter-observer agreement.

RESULTS

Image quality was comparable for RT and TT. TRON showed statistically significantly more axial artifacts for the two readers (p<0.05). Stair-step artifacts were not statistically significantly different between DWI sequences. Overall sensitivities for RT, TT, TRON were 85%, 86%, 82% and 86%, 89% 83%, respectively, for readers 1 and 2. The inter-observer agreement was very good.

CONCLUSION

Image quality was better for RT and TT compared to TRON. Overall sensitivities for FLL detection were comparable between techniques and readers.

New imaging techniques for liver diseases

Newly developed or advanced methods of ultrasonography and MR imaging provide combined anatomical and quantitative functional information about diffuse and focal liver diseases. Ultrasound elastography has a central role for staging liver fibrosis and an increasing role in grading portal hypertension; dynamic contrast-enhanced ultrasonography may improve tumor characterization. In clinical practice, MR imaging examinations currently include diffusion-weighted and dynamic MR imaging, enhanced with extracellular or hepatobiliary contrast agents. Moreover, quantitative parameters obtained with diffusion-weighted MR imaging, dynamic contrast-enhanced MR imaging and MR elastography have the potential to characterize further diffuse and focal liver diseases, by adding information about tissue cellularity, perfusion, hepatocyte transport function and visco-elasticity. The multiparametric capability of ultrasonography and more markedly of MR imaging gives the opportunity for high diagnostic performance by combining imaging biomarkers. However, image acquisition and post-processing methods should be further standardized and validated in multicenter trials.

Differential diagnosis between hepatic metastases and benign focal lesions using DWI with parallel acquisition technique: a meta-analysis

We aim to investigate the diagnostic capability of diffusion-weighted imaging using parallel acquisition technique for the differentiation between hepatic metastases and benign focal lesions with a meta-analysis. The meta-analysis included a total of 858 hepatic metastases and 440 benign liver lesions from nine studies. The pooled sensitivity and specificity of diffusion-weighted imaging (DWI) were 0.87 (95% CI, 0.84-0.89) and 0.90 (95% CI, 0.87-0.93), respectively. The positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were 8.50 (95% CI, 4.97-14.52) and 0.17 (95% CI, 0.11-0.26), respectively. The P value for χ (2) heterogeneity for all pooled estimates was <0.05. From the fitted summary receiver operating characteristics (SROC), the area under the curve (AUC) and Q* index were 0.95 and 0.88, respectively. Publication bias is not present (t = -0.76, P = 0.471). The meta-regression analysis indicated that evaluated covariates included patient number, patient population, mean age, maximum of b factor, number of cysts, number of hemangiomas, and field were not sources of heterogeneity (all P value >0.05). Diffusion-weighted imaging was useful for differentiation between hepatic metastases and benign focal lesions. The diffusion characteristics of the benign hepatocellular lesions, including cases of focal nodular hyperplasia (FNH) and adenoma, have rarely been reported and need further studies. The diagnostic capability of DWI with parallel acquisition technique for differentiation between metastases and benign hepatic focal lesions might be overestimated.

Incremental value of liver MR imaging in patients with potentially curable colorectal hepatic metastasis detected at CT: a prospective comparison of diffusion-weighted imaging, gadoxetic acid-enhanced MR imaging, and a combination of both MR techniques

PURPOSE

To prospectively compare diagnostic performance of diffusion-weighted (DW) imaging, gadoxetic acid-enhanced magnetic resonance (MR) imaging, both techniques combined (combined MR imaging), and computed tomography (CT) for detecting colorectal hepatic metastases and evaluate incremental value of MR for patients with potentially curable colorectal hepatic metastases detected with CT.

MATERIALS AND METHODS

In this institutional review board-approved prospective study, with informed consent, 51 patients (39 men, 12 women; mean age, 62 years) with potentially resectable hepatic metastases detected with CT underwent liver MR, including DW imaging and gadoxetic acid-enhanced MR. Two independent readers reviewed DW, gadoxetic acid-enhanced, combined MR, and CT image sets to detect hepatic metastases. The figure-of-merit (FOM) value representing overall diagnostic performance, sensitivity, and positive predictive value (PPV) for each image set were analyzed by using free-response receiver operating characteristic analysis and generalized estimating equations.

RESULTS

There were 104 hepatic metastases in 47 patients. The pooled FOM values, sensitivities, and PPVs of combined MR (FOM value, 0.93; sensitivity, 98%; and PPV, 88%) and gadoxetic acid-enhanced MR (FOM value, 0.92; sensitivity, 95%; and PPV, 90%) were significantly higher than those of CT (FOM value, 0.82; sensitivity, 85%; and PPV, 73%) (P < .006). The pooled FOM value and sensitivity of combined MR (FOM value, 0.92; sensitivity, 95%) was also significantly higher than that of DW imaging (FOM value, 0.82; sensitivity, 79%) for metastases (≤1-cm diameter) (P ≤ .003). DW imaging showed significantly higher pooled sensitivity (79%) and PPV (60%) than CT (sensitivity, 50%; PPV, 33%) for the metastases (≤1-cm diameter) (P ≤ .004). In 47 patients with hepatic metastases, combined MR depicted more metastases than CT in 10 and 14 patients, respectively, according to both readers.

CONCLUSION

Gadoxetic acid-enhanced MR and combined MR are more accurate than CT in detecting colorectal hepatic metastases, have an incremental value when added to CT alone for detecting additional metastases, and can be routinely performed in patients with potentially curable hepatic metastases detected with CT.

Presurgical planning for hepatobiliary malignancies: clinical and imaging considerations

There are many considerations in the evaluation of liver malignancy before planned surgical treatment. This article focuses on interpretation of MR imaging of the liver for surgical treatment planning of hepatocellular carcinoma, colorectal cancer metastases, and hilar cholangiocarcinoma. Clinical status, anatomic variants, future liver remnant, and underlying liver disease are all important factors in the decision to proceed with liver resection. The primary objective of preoperative imaging is to correctly identify patients who are candidates for curative intervention and to accurately stage their disease. Treatment planning for these complex patients is best done with a multidisciplinary team approach.

Diffusion-weighted imaging of the liver: techniques and applications

Diffusion-weighted imaging (DWI) is a technique that assesses the cellularity, tortuosity of the extracellular/extravascular space, and cell membrane density based on differences in water proton mobility in tissues. The strength of the diffusion weighting is reflected by the b value. DWI using several b values enables the quantification of the apparent diffusion coefficient. DWI is increasingly used in liver imaging for multiple reasons: it can add useful qualitative and quantitative information to conventional imaging sequences; it is acquired relatively quickly; it is easily incorporated into existing clinical protocols; and it is a noncontrast technique.

Functional MR imaging of the abdomen

In this article, functional magnetic resonance (MR) imaging techniques in the abdomen are discussed. Diffusion-weighted imaging (DWI) increases the confidence in detecting and characterizing focal hepatic lesions. The potential uses of DWI in kidneys, adrenal glands, bowel, and pancreas are outlined. Studies have shown potential use of quantitative dynamic contrast-enhanced MR imaging parameters, such as K(trans), in predicting outcomes in cancer therapy. MR elastography is considered to be a useful tool in staging liver fibrosis. A major issue with all functional MR imaging techniques is the lack of standardization of the protocol.

The effect of respiratory and cardiac motion in liver diffusion tensor imaging (DTI)

OBJECTIVE

To evaluate the effect of respiratory and cardiac motion on diffusion tensor imaging (DTI) metrics in healthy human liver.

METHODS

Fifteen healthy subjects, participating in either part of this study, were scanned using a 1.5-T magnetic resonance imaging (MRI) device. Coronal liver DTI (6 diffusion-encoding directions; b, 300 mm/s) during breath holding was compared to free breathing. Cardiac motion effects were evaluated by comparing breath-held DTI scans acquired during both diastole and systole.

RESULTS

Free breathing resulted in a significantly increased mean diffusivity (P < 0.05), λ1 (P < 0.01), λ2 (P < 0.05), and λ3 (P < 0.01) compared to breath holding. During systole significant increases in fractional anisotropy (P < 0.05), mean diffusivity (P < 0.05), and λ1 (P < 0.05), compared to systole, were found in the left lobe. The right lobe, which is less affected by cardiac motion, showed no significant change in DTI metrics over the cardiac cycle.

CONCLUSIONS

Respiratory and cardiac motion tends to increase liver DTI metrics.

Diffusion-weighted MRI and optimal b-value for characterization of liver lesions

BACKGROUND

Diffusion-weighted imaging (DWI) is commonly used to distinguish between benign and malignant liver lesions. However, different b-values are recommended.

PURPOSE

To determine the most suitable b-value in DWI for differentiation of benign and malignant liver lesions.

MATERIAL AND METHODS

A total of 124 lesions in 89 consecutive patients (43 men, 46 women; age, mean ± standard deviation, 58 ± 14 years) with a pathological or radiological diagnosis of malignant or benign focal liver lesions after magnetic resonance imaging (MRI) were included in this study. Routine abdominal MRI and DWI were performed using seven b-values (0, 50, 200, 400, 600, 800, 1000 s/mm(2)). Lesions were analyzed for benignity/malignity using apparent diffusion coefficient (ADC) values with 10 b-value combinations and by measuring the lesion/normal parenchyma ADC ratio.

RESULTS

Mean ADC values were significantly different between malignant and benign lesions for all b-value combinations (P=0.000). The best b-value combination was 0 and 800 (Az=0.935). Using lower b-values such as 0 and 50 together with higher b-values ≥ 600 s/mm(2) was beneficial (Az=0.928 and 0.927). Mean ADC values were approximately 13% (1-15%) higher in total when b=0 and b=50 s/mm(2) were included in multiple b-value combinations.

CONCLUSION

In DWI, we recommend the use of b-values of 0 and 800 s/mm(2) as two b-values, or b=0, 50, 600, 800, and 1000 s/mm(2) as multiple b-values for distinguishing between benign and malignant liver lesions. Mean ADC value is 13% higher in total by additional use of b=0 and b=50 s/mm(2) in multiple b-value combinations.

Hepatocellular carcinoma and other hepatic malignancies: MR imaging

Magnetic resonance (MR) imaging surpasses all other imaging modalities in characterizing liver lesions by virtue of the exquisite tissue contrast, specificity for various tissue types, and extreme sensitivity to contrast enhancement. In addition to differentiating benign from malignant lesions, MR imaging generally discriminates between the various malignant liver lesions. Hepatocellular carcinoma constitutes most primary malignant liver lesions and usually arises in the setting of cirrhosis. Intrahepatic cholangiocarcinoma is a distant second and features distinctly different imaging features. Overall, metastases are the most common malignant liver lesions and arise from several primary neoplasms; most commonly gastrointestinal, lung, breast, and genitourinary.

Determination of malignancy and characterization of hepatic tumor type with diffusion-weighted magnetic resonance imaging: comparison of apparent diffusion coefficient and intravoxel incoherent motion-derived measurements

OBJECTIVE

The objective of this study was to compare the value of the apparent diffusion coefficient (ADC) determined with 3 b values and the intravoxel incoherent motion (IVIM)-derived parameters in the determination of malignancy and characterization of hepatic tumor type.

MATERIALS AND METHODS

Seventy-six patients with 86 solid hepatic lesions, including 8 hemangiomas, 20 lesions of focal nodular hyperplasia, 9 adenomas, 30 hepatocellular carcinomas, 13 metastases, and 6 cholangiocarcinomas, were assessed in this prospective study. Diffusion-weighted images were acquired with 11 b values to measure the ADCs (with b = 0, 150, and 500 s/mm) and the IVIM-derived parameters, namely, the pure diffusion coefficient and the perfusion-related diffusion fraction and coefficient. The diffusion parameters were compared between benign and malignant tumors and between tumor types, and their diagnostic value in identifying tumor malignancy was assessed.

RESULTS

The apparent and pure diffusion coefficients were significantly higher in benign than in malignant tumors (benign: 2.32 [0.87] × 10 mm/s and 1.42 [0.37] × 10 mm/s vs malignant: 1.64 [0.51] × 10 mm/s and 1.14 [0.28] × 10 mm/s, respectively; P < 0.0001 and P = 0.0005), whereas the perfusion-related diffusion parameters did not differ significantly between the 2 groups. The apparent and pure diffusion coefficients provided similar accuracy in assessing tumor malignancy (areas under the receiver operating characteristic curve of 0.770 and 0.723, respectively). In the multigroup analysis, the ADC was found to be significantly higher in hemangiomas than in hepatocellular carcinomas, metastases, and cholangiocarcinomas. In the same manner, it was higher in lesions of focal nodular hyperplasia than in metastases and cholangiocarcinomas. However, the pure diffusion coefficient was significantly higher only in hemangiomas versus hepatocellular and cholangiocellular carcinomas.

CONCLUSIONS

Compared with the ADC, the diffusion parameters derived from the IVIM model did not improve the determination of malignancy and characterization of hepatic tumor type.

Magnetic resonance imaging in cirrhosis: what's new?

Cirrhosis is the main risk factor for the development of hepatocellular carcinoma (HCC). The major causative factors of cirrhosis in the United States and Europe are chronic hepatitis C infection and excessive alcohol consumption with nonalcoholic steatohepatitis emerging as another important risk factor. Magnetic resonance imaging is the most sensitive imaging technique for the diagnosis of HCC, and the sensitivity can be further improved with the use of diffusion-weighted imaging and hepatocyte-specific contrast agents. The combination of arterial phase hyperenhancement, venous or delayed phase hypointensity "washout feature," and capsular enhancement are features highly specific for HCC with reported specificities of 96% and higher. When these features are present in a mass in the cirrhotic liver, confirmatory biopsy to establish the diagnosis of HCC is not necessary. Other tumors, such as cholangiocarcinoma, sometimes occur in the cirrhotic at a much lower rate than HCC and can mimic HCC, as do other benign lesions such as perfusion abnormalities. In this article, we discuss the imaging features of cirrhosis and HCC, the role of magnetic resonance imaging in the diagnosis of HCC and other benign and malignant lesions that occur in the cirrhotic liver, and the issue of nonspecific arterially hyperenhancing nodules often seen in cirrhosis.

P4 radiology of hepatobiliary diseases with gadoxetic acid-enhanced MRI as a biomarker

A recent paradigm shift in radiology has focused on the globalization of so-called P4 radiology. P4 radiology represents delivery of imaging results that are predictive, personalized, pre-emptive and participatory. The combination of the P4 approach and biomarkers is particularly pertinent to MRI, especially with technological advances such as diffusion-weighted imaging. The development of new liver-specific MRI contrast media, particularly gadoxetic acid, demonstrate specific pharmacokinetic properties, which provide combined morphologic and functional information in the same setting. The evaluation of hepatobiliary pathology beyond morphology gives rise to the possibilty of using gadoxetic acid-enhanced MRI as an imaging biomarker of hepatobiliary diseases. The integration of functional imaging with an understanding of complex disease mechanisms forms the basis for P4 radiology, which may ultimately lead to individualized, cost-effective, targeted therapy for patients. This will enable radiologists to determine the prognosis of the disease and estimate early response to treatment, with the participation of all the required medical disciplines.

Chemotherapy-induced focal hepatopathy in patients with gastrointestinal malignancy: gadoxetic acid--enhanced and diffusion-weighted MR imaging with clinical-pathologic correlation

PURPOSE

To retrospectively evaluate findings of chemotherapy-induced focal hepatopathy (CIFH) on gadoxetic acid-enhanced magnetic resonance (MR) and diffusion-weighted (DW) images and to determine imaging features that are most helpful in differentiating CIFH from metastasis.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, and informed consent was waived. MR images, including DW images and gadoxetic acid-enhanced images, from 12 patients (four men, eight women; age range, 25-64 years) with 15 CIFHs were reviewed independently and in consensus by two radiologists and were compared with those obtained in 20 control patients (12 men, eight women; age range, 32-84 years) with 30 hepatic metastasis who were matched for tumor size, primary organ, and chemotherapy regimen. Interobserver agreement was assessed with κ statistics, and univariate analysis was performed for comparisons. For quantitative analyses, apparent diffusion coefficients (ADCs) and lesion-to-liver contrast ratios (CRs) were measured. Histopathologic examinations were performed for CIFHs.

RESULTS

Histopathologic examination revealed that the development of CIFHs was attributable to accentuated manifestations of sinusoidal obstruction syndrome. Interobserver agreement was excellent (κ > 0.85). An ill-defined margin on hepatobiliary phase (HBP) images was the most discriminating independent variable in the differentiation of CIFH from metastasis (odds ratio, 16; P = .009). ADC and CR values in CIFH group were significantly higher than those in metastasis group (P < .001 and P = .041).

CONCLUSION

CIFH should be considered a mimicker of metastasis in patients with gastrointestinal malignancy during chemotherapy. CIFH can be differentiated from metastasis on the basis of gadoxetic acid-enhanced MR and DW imaging findings; an ill-defined margin on HBP images was especially characteristic.

Noncontrast MRI with diffusion-weighted imaging as the sole imaging modality for detecting liver malignancy in patients with high risk for hepatocellular carcinoma

PURPOSE

To compare the diagnostic performance of the noncontrast MRI including DWI to the standard MRI for detecting hepatic malignancies in patients with chronic liver disease.

MATERIALS AND METHODS

We included 135 patients with 136 histologically-confirmed hepatocellular carcinomas (HCCs), 12 cholangiocarcinomas, and 34 benign lesions (≤ 2.0 cm), and 22 patients with cirrhosis but no focal liver lesion who underwent 3.0 T liver MRI. Noncontrast MRI set (T1- and T2-weighted images and DWI) and standard MRI set (gadoxetic acid-enhanced and noncontrast MRI) were analyzed independently by three observers to detect liver malignancies using receiver operating characteristic analysis.

RESULTS

The Az value of the noncontrast MRI (mean, 0.906) was not inferior to that of the combined MRI (mean, 0.924) for detecting malignancies by all observers (P>0.05). For each observer, no significant difference was found in the sensitivity and specificity between the two MRI sets for detecting liver malignancies and distinguishing them from benign lesions (P>0.05), whereas negative predictive value was higher with the combined MRI than with the noncontrast MRI (P=0.0001). When using pooled data, the sensitivity of the combined MRI (mean 94.8%) was higher than that of the noncontrast MRI (mean, 91.7%) (P =0.001), whereas specificity was equivalent (78.6% vs 77.5%).

CONCLUSION

Noncontrast MRI including DWI showed reasonable performance compared to the combined gadoxetic acid-enhanced and noncontrast MRI set for detecting HCC and cholangiocarcinoma and differentiating them from benign lesions in patients with chronic liver disease.

Liver lesion detection and characterization: role of diffusion-weighted imaging

Diffusion-weighted imaging (DWI) plays an emerging role for the assessment of focal and diffuse liver diseases. This growing interest is due to that fact that DWI is a noncontrast technique with inherent high contrast resolution, with promising results for detection and characterization of focal liver lesions. Recent advances in diffusion image quality have also added interest to this technique in the abdomen. The purpose of this review is to describe the current clinical roles of DWI for the detection and characterization of focal liver lesions, and to review pitfalls, limitations, and future directions of DWI for assessment of focal liver disease.