MR characterization of focal liver lesions: pearls and pitfalls

From Phantoms to Patients: Improved Fusion and Voxel-Wise Analysis of Diffusion-Weighted Imaging and FDG-Positron Emission Tomography in Positron Emission Tomography/Magnetic Resonance Imaging for Combined Metabolic-Diffusivity Index (cDMI)

Hybrid positron emission tomography/magnetic resonance imaging (PET/MR) opens new possibilities in multimodal multiparametric (m2p) image analyses. But even the simultaneous acquisition of positron emission tomography (PET) and magnetic resonance imaging (MRI) does not guarantee perfect voxel-by-voxel co-registration due to organs and distortions, especially in diffusion-weighted imaging (DWI), which would be, however, crucial to derive biologically meaningful information. Thus, our aim was to optimize fusion and voxel-wise analyses of DWI and standardized uptake values (SUVs) using a novel software for m2p analyses. Using research software, we evaluated the precision of image co-registration and voxel-wise analyses including the rigid and elastic 3D registration of DWI and [18F]-Fluorodeoxyglucose (FDG)-PET from an integrated PET/MR system. We analyzed DWI distortions with a volume-preserving constraint in three different 3D-printed phantom models. A total of 12 PET/MR-DWI clinical datasets (bronchial carcinoma patients) were referenced to the T1 weighted-DIXON sequence. Back mapping of scatterplots and voxel-wise registration was performed and compared to the non-optimized datasets. Fusion was rated using a 5-point Likert scale. Using the 3D-elastic co-registration algorithm, geometric shapes were restored in phantom measurements; the measured ADC values did not change significantly (F = 1.12, p = 0.34). Reader assessment showed a significant improvement in fusion precision for DWI and morphological landmarks in the 3D-registered datasets (4.3 ± 0.2 vs. 4.6 ± 0.2, p = 0.009). Most pronounced differences were noted for the chest wall (p = 0.006), tumor (p = 0.007), and skin contour (p = 0.014). Co-registration increased the number of plausible ADC and SUV combinations by 25%. The volume-preserving elastic 3D registration of DWI significantly improved the precision of fusion with anatomical sequences in phantom and clinical datasets. The research software allowed for a voxel-wise analysis and visualization of [18F]FDG-PET/MR data as a "combined diffusivity-metabolic index" (cDMI). The clinical value of the optimized PET/MR biomarker can thus be tested in future PET/MR studies.

MR Imaging of Pediatric Neuroblastoma: Is Gadolinium Enhancement Necessary for Evaluation of Image-Defined-Risk Factors?

Background: Pre-treatment stratification and outcomes of neuroblastoma patients often depend on the assessment of image-defined risk factors (IDRFs) on MR Imaging, usually using Gadolinium-contrast materials which are cautioned in pediatrics. We aimed to address whether gadolinium contrast-enhanced sequences are necessary to identify the presence/absence of IDRFs. Methods: Patients with neuroblastoma with MR imaging were retrospectively identified from 2005 to 2021. Ninety confirmed IDRFs were evaluated in 23 patients. Corresponding MR studies were anonymized, randomized, and independently evaluated by 3 fellowship-trained pediatric radiologists. Each radiologist assessed the studies twice. At the first reading, all enhanced sequences were omitted, while in the second reading, the full study with enhanced sequences were included. Consensus reading was obtained among readers. Inter- and intra-rater agreements using Kappa statistics (κ) as well as the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of non-enhanced MR in assessing IDRFs with respect to enhanced MR were calculated. Results: There were substantial (ĸ: 0.64-0.73) intra-reader agreements, and moderate to substantial (ĸ: 0.57-0.62) inter-reader agreements among radiologists in identifying IDRFs using non-enhanced MR. Non-enhanced MR had a sensitivity of 87.8% (95% CI [79-94]), specificity of 93% (89-96), PPV of 82.3 (73-89), NPV of 95.4 (92-98), and accuracy of 91.6 (88-94) in identifying IDRFs. However, 5/23 patients (21.7%) had a change in staging with the inclusion of contrast sequences. Conclusion: Although contrast sequences have a role in IDRF assessment, the majority can be adequately assessed on MR without gadolinium-contrast enhancement. Validation in a larger cohort is an important next step.

Morphological, dynamic and functional characteristics of liver pseudolesions and benign lesions

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide and one of the most common causes of death among patients with cirrhosis, developing in 1-8% of them every year, regardless of their cirrhotic stage. The radiological features of HCC are almost always sufficient for reaching the diagnosis; thus, histological confirmation is rarely needed. However, the study of cirrhotic livers remains a challenge for radiologists due to the developing of fibrous and regenerative tissue that cause the distortion of normal liver parenchyma, changing the typical appearances of benign lesions and pseudolesions, which therefore may be misinterpreted as malignancies. In addition, a correct distinction between pseudolesions and malignancy is crucial to allow appropriate targeted therapy and avoid treatment delays.The present review encompasses technical pitfalls and describes focal benign lesions and pseudolesions that may be misinterpreted as HCC in cirrhotic livers, providing the imaging features of regenerative nodules, large regenerative nodules, siderotic nodules, hepatic hemangiomas (including rapidly filling and sclerosed hemangiomas), segmental hyperplasia, arterioportal shunts, focal confluent fibrosis and focal fatty changes. Lastly, the present review explores the most promising new imaging techniques that are emerging and that could help radiologists differentiate benign lesions and pseudolesions from overt HCC.

Is IV contrast necessary for MRI follow-up in children with abdominal neuroblastoma?

PURPOSE

The safety of multiple doses of gadolinium-based MRI IV contrast has recently been called in to question. While the long-term safety is being investigated, here, we seek to determine if there is added value to the use of IV contrast for improving detection of tumoral recurrences in children with a history of abdominal neuroblastoma.

METHODS

This is a retrospective review of children who underwent abdominal MRI with gadolinium contrast. One radiologist reviewer determined presence or absence of tumor, both before and after administration of IV contrast material and documented level of confidence when a finding was encountered. Change in reader confidence after the use of contrast was measured and fraction of missed lesions on pre-contrast was calculated. Liver and spleen lesions were documented separately.

RESULTS

453 MRI scans in 110 unique patients were reviewed. 65 patients were documented to have a total of 125 lesions, excluding liver, spleen and bones. There were 23 instances of contrast altering the radiologist's confidence and one lesion was missed without the use of contrast. Among liver and spleen, several hepatic lesions were seen only after contrast, but all were benign lesions.

CONCLUSION

In selected patients who are undergoing MRI for neuroblastoma, it may be reasonable to forgo the use of IV contrast.

Gd-EOB-DTPA-enhanced MR findings in chemotherapy-induced sinusoidal obstruction syndrome in colorectal liver metastases

Background

We assessed the clinical presentations, biomarkers, and Gd-EOB-DTPA-enhanced MRI features that were associated with oxaliplatin-induced sinusoidal obstruction syndrome (SOS) to detect chemotherapy-associated SOS in a timely manner.

Methods

Fifty-seven patients who underwent oxaliplatin-based chemotherapy and Gd-EOB-DTPA-enhanced MRI were included. Post-oxaliplatin heterogeneity in liver parenchyma was scored on a grading scale of 0 to 3. Abnormal clinical findings, including splenomegaly, hepatomegaly, gall bladder wall thickening, and hepatic vein narrowing, were also assessed. Additionally, alanine transaminase (ALT) levels, aspartate aminotransferase (AST) levels, and platelet counts were measured.

Results

For SOS, 21 patients were scored grade 0, 24 were grade 1, seven were grade 2, and five were grade 3. Hepatomegaly, splenomegaly, gall bladder wall thickening, and hepatic vein narrowing were significantly correlated with the grade for non-tumorous hepatic parenchymal heterogeneity. For laboratory findings, ALT and AST levels, the AST-to-platelet ratio index score, and platelet counts were significantly associated with a high grade (≥2) of non-tumorous hepatic parenchymal heterogeneity.

Conclusions

We assessed the clinical presentations, biomarkers, and Gd-EOB-DTPA-enhanced MRI features that were associated with oxaliplatin-induced sinusoidal obstruction syndrome (SOS) to detect chemotherapy-associated SOS in a timely manner. Additionally, specific laboratory findings were significantly associated with a high grade (≥2).

MRI in pregnant patients with suspected abdominal and pelvic cancer: a practical guide for radiologists

The incidence of abdominal and pelvic cancer in pregnancy is low, but it is rising as the population of pregnant women gets older. Depending on disease stage, gestational age and patient's preference, active surveillance as well as surgery and chemotherapy are feasible options during pregnancy. Correct diagnosis and staging of the tumor is crucial for choosing the best therapeutic approach. Moreover, a reproducible modality to assess the treatment response is requested. Magnetic resonance imaging (MRI) is commonly used with good results for the local staging and treatment response evaluation of most abdominal and pelvic cancers in nonpregnant patients, and it is considered relatively safe during pregnancy. The purpose of this article is to analyze the most relevant topics regarding the use of MRI in pregnant women with abdominal and pelvic cancer. We discuss MRI safety during pregnancy, including the use of gadolinium-based contrast agents (GBCAs), how to prepare the patient for the exam and MRI technique. This will be followed by a brief review on the most common malignancies diagnosed during pregnancy and their MRI appearance.

Multifocal Nodular Fatty Infiltration of the Liver: A Rare Benign Disorder That Mimics Metastatic Liver Disease

Fatty liver disease is a frequent diagnosis. Rarely, it adopts a multifocal nodular pattern mimicking multiple liver metastases. Multifocal nodular fatty infiltration of the liver entails a challenging problem that must be included as a differential diagnosis when dealing with healthy patients with an incidental finding of multiple liver lesions, even in the absence of obesity or metabolic syndrome. A complete clinical examination and high-quality imaging, including magnetic resonance imaging, might help to confirm diagnosis and to avoid unnecessary liver biopsies.

Imaging-based diagnosis of benign lesions and pseudolesions in the cirrhotic liver

Liver cirrhosis is a leading cause of death worldwide, with 1-year mortality rates of up to 57% in decompensated patients. Hepatocellular carcinoma (HCC) is the most common primary tumor in cirrhotic livers and the second leading cause of cancer-related mortality worldwide. Annually, up to 8% of patients with cirrhosis develop HCC. The diagnosis of HCC rarely requires histological confirmation: in fact, according to the most recent guidelines, the imaging features of HCC are almost always sufficient for a certain diagnosis. Thus, the role of the radiologist is pivotal because the accurate detection and characterization of focal liver lesions in patients with cirrhosis are essential in improving clinical outcomes. Despite recent technical innovations in liver imaging, several issues remain for radiologists regarding the differentiation of HCC from other hepatic lesions, particularly benign lesions and pseudolesions. It is important to avoid misdiagnosis of benign liver lesions as HCC (false-positive cases) because this diagnostic misinterpretation may lead to ineligibility of a patient for potentially curative treatments or inappropriate assignment of high priority scores to patients on waiting lists for liver transplantation. This review presents a pocket guide that could be useful for the radiologist in the diagnosis of benign lesions and pseudolesions in cirrhotic livers, highlighting the imaging features that help in making the correct diagnosis of macroregenerative nodules; siderotic nodules; arterioportal shunts; hemangiomas, including fast-filling hemangiomas, hemangiomas with pseudowashout, and sclerosed hemangiomas; confluent fibrosis; pseudomasses in chronic portal vein thrombosis; and focal fatty changes.

Spectrum of Pitfalls, Pseudolesions, and Potential Misdiagnoses in Cirrhosis

OBJECTIVE

The purposes of this article are to review a variety of pitfalls in liver imaging that can lead to the inaccurate diagnosis of focal hepatic lesions in cirrhosis, to describe the pathophysiologic processes of these pitfalls, and to provide specific clues for achieving the correct diagnoses.

CONCLUSION

Cirrhosis complicates liver imaging. The distortion and replacement of normal liver parenchyma by fibrous and regenerative tissue can change the typical appearance of many benign lesions, causing them to be misinterpreted as malignancy. In addition, the high incidence and prevalence of hepatocellular carcinoma among patients with cirrhosis put radiologists on high alert for any suspicious findings, especially because not all hepatocellular carcinomas have a typical imaging appearance.

Comparison of gadoxetic acid versus gadopentetate dimeglumine for the detection of hepatocellular carcinoma at 1.5 T using the liver imaging reporting and data system (LI-RADS v.2017)

PURPOSE

The goal of this study was to investigate the Liver Imaging Reporting and Data System (LI-RADS) v.2017 for the categorization of hepatocellular carcinomas (HCCs) with gadoxetic acid compared with gadopentetate dimeglumine-enhanced 1.5-T magnetic resonance imaging (MRI).

MATERIAL AND METHODS

We included 141 high-risk patients with 145 pathologically-confirmed HCCs who first underwent gadopentetate dimeglumine-enhanced 1.5-T followed by gadoxetic acid-enhanced 1.5-T MRI. Two independent radiologists evaluated the presence or absence of major HCC features and assigned LI-RADS categories after considering ancillary features on both MRIs. Finally, the sensitivity of LI-RADS category 5 (LR-5) and the frequencies of major HCC features were compared between gadoxetic acid- and gadopentetate dimeglumine-enhanced 1.5-T MRI using the Wilcoxon test.

RESULTS

The sensitivity of LR-5 for diagnosing HCCs was significantly different between gadoxetic acid- and gadopentetate dimeglumine-enhanced MRI (73.8% [107/145] vs 26.2% [38/145], P < 0.001; 71% [103/145] vs 29% [42/145], P < 0.001 for reviewers 1 and 2, respectively). Among the major HCC LI-RADS features, capsule appearance was less frequently demonstrated on gadoxetic acid-enhanced MRI than on gadopentetate dimeglumine-enhanced MRI (3.4% [5/145] vs 5.5% [8/145], P = 0.793; 4.1% [6/145] vs 5.5% [8/145], P = 0.87 for reviewers 1 and 2, respectively), and the frequency of arterial hyperenhancement was not significantly different between gadoxetic acid and gadopentetate dimeglumine (89% [129/145] vs 89% [129/145], P = 1.000). In addition, the frequency of a washout appearance was less in the transitional phase (TP) than in the portal venous phase (PVP) on gadoxetic acid-enhanced MRI (43% [46/107] vs 57% [61/107], P = 0.367).

CONCLUSION

Gadoxetic acid-enhanced MRI showed a comparable sensitivity to gadopentetate dimeglumine-enhanced MRI for the diagnosis of HCCs, and LI-RADS category 4 (LR-4) hepatic nodules were upgraded to LR-5 when taking into account the major features according to LI-RADS v.2017.

Fat-Containing Liver Lesions on Imaging: Detection and Differential Diagnosis

OBJECTIVE

The purpose of this article is to review how fat is detected on imaging and to discuss the differential diagnosis of fat-containing liver lesions.

CONCLUSION

Fat is a highly useful feature in characterizing liver lesions on imaging. Although a variety of liver lesions can show fat on cross-sectional imaging, the presence of fat usually indicates that the lesion is of hepatocellular origin. Less commonly, nonhepatocellular fatty lesions may be distinguished by ancillary clinical and imaging features.

Interpreting body MRI cases: what you need to know to get started

Interpreting body MRI cases can seem overwhelming to an uninitiated radiologist. The standard study includes a variety of pulse sequences, the names of which vary depending on the MR vendor. Pulse sequences may be displayed haphazardly on the picture archiving and communication system (PACS), frequently not synchronized with the imaging protocol. Adding to the complexity is the use of different gadolinium-based contrast agents, which may affect the timing and diagnostic yield of each sequence. The following introductory primer for interpreting body MRI cases is meant to create a basic framework for efficiently reviewing body MRI cases to provide high quality interpretations, fully utilizing the diagnostic information of the modality. There are 4 components that need to be mastered when interpreting body MRI cases including: (1) recognizing the key sequences in a basic body MRI protocol, (2) learning how to best display the key pulse sequences on PACS, (3) understanding the technique and clinical utility of each sequence and learning how to utilize sequences to be an "MR Pathologist", and (4) understanding the key features of the different gadolinium based contrast agents.

Current role of body MRI in pediatric oncology

Magnetic resonance imaging (MRI) plays an important role in the imaging of children with non-central nervous system malignancies, and it is increasingly replacing or complementing CT in many cases. MRI has several advantages over CT, including superior contrast resolution as well as superior tissue characterization with the use of novel pulse sequences and functional or organ-specific contrast agents. In addition, the lack of ionizing radiation - an important consideration in children - allows for multiphase dynamic post-contrast imaging, which can be useful for lesion detection and characterization. Several challenges remain in the performance of MRI in pediatric oncology patients, including the frequent need for sedation or anesthesia in young children because of long imaging times, as well as the suboptimal imaging of the lungs in the evaluation for pulmonary metastatic disease. However, despite these challenges, with continued improvements in MRI image quality and the development of novel sequences, contrast agents and quantitative imaging techniques, MRI is expected to play an ever increasing role in the imaging of pediatric oncology patients.

Combined 18F-NaF and 18F-FDG PET/CT in the Evaluation of Sarcoma Patients

PURPOSE

The combined administration of F-NaF and F-FDG in a single PET/CT scan has the potential to improve patient convenience and cancer detection. Here we report the use of this approach for patients with sarcomas.

PATIENTS AND METHODS

This is a retrospective review of 21 patients (12 men, 9 women; age, 19-66 years) with biopsy-proven sarcomas who had separate F-NaF PET/CT, F-FDG PET/CT, and combined F-NaF/F-FDG PET/CT scans for evaluation of malignancy. Two board-certified nuclear medicine physicians and 1 board-certified musculoskeletal radiologist were randomly assigned to review the scans. Results were analyzed for sensitivity and specificity, using linear regression and receiver operating characteristics.

RESULTS

A total of 13 patients had metastatic disease on F-NaF PET/CT, F-FDG PET/CT, and combined F-NaF/F-FDG PET/CT. Skeletal disease was more extensive on the F-NaF PET/CT scan than on the F-FDG PET/CT in 3 patients, whereas in 1 patient, F-FDG PET/CT showed skeletal disease and the F-NaF PET/CT was negative. Extraskeletal lesions were detected on both F-FDG and combined F-NaF/F-FDG PET/CT in 20 patients, with 1 discordant finding in the lung.

CONCLUSIONS

The combined F-NaF/F-FDG PET/CT scan allows for accurate evaluation of sarcoma patients. Further evaluation of this proposed imaging modality is warranted to identify the most suitable clinical scenarios, including initial treatment strategy and evaluation of response to therapy.

[Modern diagnostics of cystic liver lesions and hemangiomas]

CLINICAL ISSUE

Cystic liver lesions incorporate a broad heterogeneous group of mostly benign but also malignant abnormalities. The radiological aim is the non-invasive diagnosis with the use of different imaging modalities to determine the type of lesion.

STANDARD RADIOLOGICAL METHODS

The common generally asymptomatic incidental findings of cystic lesions on ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) must be classified on the basis of specific imaging features. Such a differentiation is essential because the clinical consequences and the appropriate therapy can vary depending on the underlying pathology. Due to the morphological overlap of many cystic lesions, conventional radiological methods are often insufficient.

METHODICAL INNOVATIONS

The huge advances in cross-sectional imaging (multidetector CT, MRI with special sequences and different contrast agents and MR cholangiopancreatography) in combination with the clinical history usually enable a non-invasive diagnosis. Pathognomonic morphological and hemodynamic lesion features, as well as a knowledge of the pathomechanisms, help to differentiate this broad spectrum of entities.

ACHIEVEMENTS

In this article the different entities of cystic liver lesions, together with the appropriate diagnostic method for detection and distinction and including their strengths and limitations, are demonstrated.

PRACTICAL RECOMMENDATIONS

A well-founded knowledge about the development of various cystic liver lesions and the suitable choice of imaging method facilitate a non-invasive diagnosis.

Errors in multidetector row computed tomography

Multidetector row computed tomography (MDCT) represents the technique of choice for the majority of pathologies today and is responsible for the majority of diagnoses. However, despite the low number of studies dedicated to errors in MDCT, CT reporting seems especially prone to generating errors and errors are an inevitable part of MDCT practice. Most of these arise during image interpretation but, differently from other radiological techniques, the awareness of radiologists regarding technical CT aspects and pathologies substantially contribute in generating errors, in particular because CT technology expands rapidly and radiologists do not routinely receive specific and appropriate training for its use and because CT examinations are not the same for each patient and each pathology and the choice of the most appropriate CT examination (including the dose exposure to the patient) presumes a very large awareness from radiologists. This review is aimed at increasing awareness regarding the type of errors in MDCT and in particular to also highlight technical and procedural errors.

Magnetic resonance imaging and endorectal ultrasound for diagnosis of rectal lesions

Endorectal ultrasonography (ERUS) and magnetic resonance imaging (MRI) allow exploring the morphology of the rectum in detail. Use of such data, especially assessment of the rectal wall, is an important tool for ascertaining the perianal fistula localization as well as stage of the cancer and planning it appropriate treatment, as stage T3 tumors are usually treated with neoadjuvant therapy, whereas T2 tumors are initially managed surgically. The only advantage of ERUS over MRI is the possibility of assessing T1 tumors that could be treated by transanal endoscopic microsurgery. However, MRI is better for visualizing most radiological prognostic features in rectal or anal cancer such as a circumferential resection margin less than 1 mm, T stage at T1-T2 or T3 tumors with extramural extension less than 5 mm, absence of extramural vascular invasion, N stage at N0/N1, and tumors located in the middle or upper third of the rectum. It can also evaluate the intersphincteric space or levator ani muscle involvement. Increased signal on diffusion weighted imaging (DWI) and low apparent diffusion coefficient (ADC) values as well as an irregular contour and heterogeneous internal signal intensity seem to predict the involvement of pelvic lymphatic nodes better than their size alone. Computed tomography as well as other examination techniques, including digital rectal examination, contrast edema, recto- and colonoscopy, are less useful in staging of rectal cancer but still are very important screening tools.