Low-Field-Strength Body MRI: Challenges and Opportunities at 0.55 T.

Advances in MRI technology have led to the development of low-field-strength (hereafter, "low-field") (0.55 T) MRI systems with lower weight, fewer shielding requirements, and lower cost than those of traditional (1.5-3 T) systems. The trade-offs of lower signal-to-noise ratio (SNR) at 0.55 T are partially offset by patient safety and potential comfort advantages (eg, lower specific absorption rate and a more cost-effective larger bore diameter) and physical advantages (eg, decreased T2* decay, shorter T1 relaxation times). Image reconstruction advances leveraging developing technologies (such as deep learning-based denoising) can be paired with traditional techniques (such as increasing the number of signal averages) to improve SNR. The overall image quality produced by low-field MRI systems, although perhaps somewhat inferior to 1.5-3 T MRI systems in terms of SNR, is nevertheless diagnostic for a broad variety of body imaging applications. Effective low-field body MRI requires (a) an understanding of the trade-offs resulting from lower field strengths, (b) an approach to modifying routine sequences to overcome SNR challenges, and (c) a workflow for carefully selecting appropriate patients. The authors describe the rationale, opportunities, and challenges of low-field body MRI; discuss important considerations for low-field imaging with common body MRI sequences; and delineate a variety of use cases for low-field body MRI. The authors also include lessons learned from their preliminary experience with a new low-field MRI system at a tertiary care center. Finally, they explore the future of low-field MRI, summarizing current limitations and potential future developments that may enhance the clinical adoption of this technology. ©RSNA, 2023 Supplemental material is available for this article. Quiz questions for this article are available through the Online Learning Center. See the invited commentary by Venkatesh in this issue.

Quality Control of Magnetic Resonance Elastography Using Percent Measurable Liver Volume Estimation.

BACKGROUND: Although studies have described factors associated with failed magnetic resonance elastography (MRE), little is known about what factors influence usable elastography data. PURPOSE: To identify factors that have a negative impact on percent measurable liver volume (pMLV), defined as the proportion of usable liver elastography data relative to the volume of imaged liver in patients undergoing MRE. STUDY TYPE: Retrospective. SUBJECTS: A total of 264 patients (n = 132 males, n = 132 females; mean age = 57 years) with suspected or known chronic liver disease underwent MRE paired with a liver protocol MRI. FIELD STRENGTH/SEQUENCE: MRE was performed on a single 1.5 T scanner using a two-dimensional gradient-recalled echo phase-contrast sequence with a passive acoustic driver overlying the right hemiliver. ASSESSMENT: Stiffness maps (usable data at 95% confidence) and liver contours on magnitude images of the MRE acquisition were manually traced and used to assess mean stiffness and pMLV. Hepatic fat fraction and R2 * values were also calculated. The distance from the acoustic wave generator on the skin surface to the liver edge was measured. Two radiologists performed the MR analyses with 50 overlapping cases for inter-reader analysis. STATISTICAL TESTS: Linear regression was performed to identify factors significantly associated with pMLV. Intraclass correlation was performed for inter-reader reliability. RESULTS: pMLV was 31% ± 20% (range 0%-86%). Complete MRE failure (i.e. pMLV = 0%) occurred in 10 patients (4%). Multivariate linear regression identified higher hepatic fat fraction, R2 *, BMI, and driver-to-liver surface distance; male sex; and lower mean liver stiffness was significantly independently associated with lower pMLV. Intraclass correlation for pMLV was 0.96, suggestive of excellent reliability. DATA CONCLUSION: Higher fat fraction, R2 *, BMI, driver-to-liver surface distance, male sex, and lower mean liver stiffness were associated with lower pMLV. Optimization of image acquisition parameters and driver placement may improve MRE quality, and pMLV likely serves as a diagnostic utility quality control metric. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 2.

Imaging Biomarkers of Hepatic Fibrosis: Reliability and Accuracy of Hepatic Periportal Space Widening and Other Morphologic Features on MRI.

OBJECTIVE. The purpose of this article was to assess the reliability and accuracy of hepatic periportal space widening and other qualitative imaging features for the prediction of hepatic fibrosis. MATERIALS AND METHODS. This single-center retrospective study identified consecutive patients who had undergone liver MR elastography. Two abdominal radiologists independently reviewed anatomic images, assessing multiple qualitative features of chronic liver disease (CLD) including periportal space widening. Each reader also measured the periportal space at the main portal vein (MPV) and right portal vein (RPV). Interrater reliability analysis was then performed. Sensitivity and specificity were determined for the detection of any hepatic fibrosis (stage I or higher) and of advanced fibrosis (stage III or higher) using stiffness on MR elastography as the reference standard. RESULTS. Of 229 subjects, 157 (69%) had fibrosis and 78 (34%) had advanced fibrosis. Agreement for periportal space widening was moderate (κ = 0.47), and agreement for remaining features was moderate to substantial (κ = 0.42-0.80). Agreement for the periportal space at the MPV was moderate (ICC, 0.55), and agreement for the periportal space at the RPV was near perfect (ICC, 0.83). Periportal space widening had the highest sensitivity (83.0%) for any fibrosis, with limited specificity (61.3%). Surface nodularity had the highest specificity (94.4%) for any fibrosis, with limited sensitivity (51.6%). Periportal space widening plus one or more additional imaging feature of CLD or the presence of surface nodularity alone had sensitivity of 72.6% and specificity of 76.1%. A periportal space at the MPV greater than 9.5 mm had substantial agreement with qualitative periportal space widening (κ = 0.74). CONCLUSION. Periportal space widening has a high sensitivity for hepatic fibrosis, with moderate specificity when combined with additional anatomic features of CLD.

Large-Scale Assessment of Scan-Time Variability and Multiple-Procedure Efficiency for Cross-Sectional Neuroradiological Exams in Clinical Practice.

Scheduling of CT and MR exams requires reasonable estimates for expected scan duration. However, scan-time variability and efficiency gains from combining multiple exams are not quantitatively well characterized. In this work, we developed an informatics approach to quantify typical duration, duration variability, and multiple-procedure efficiency on a large scale, and used the approach to analyze 48,766 CT- and MR-based neuroradiological exams performed over one year. We found MR exam durations demonstrated higher absolute variability, but lower relative variability and lower multiple-procedure efficiency, compared to CT exams (p < 0.001). Our approach enables quantification of real-world operational performance and variability to inform optimal patient scheduling, efficient resource utilization, and sustainable service planning.

JOURNAL CLUB: Hepatopancreaticobiliary Imaging Second-Opinion Consultations: Is There Value in the Second Reading?

OBJECTIVE: Tertiary care practices increasingly provide second-opinion consultations on reports from outside practices or institutions. This practice of providing a second opinion has been studied in a variety of subspecialties; however, its potential effect on the management of hepatopancreaticobiliary (HPB) disease is not known. The purpose of this study was to assess the rate of significant discrepancies between the initial report and the consultation report, the source of discrepancies, and the frequency of repeat imaging recommendations. MATERIALS AND METHODS: Retrospective chart review was performed for 480 consecutive CT and MRI consultation reports interpreted between January 2014 and December 2015 for patients with HPB diseases whose initial CT and MRI reports were generated at outside facilities. The initial report and the consultation report were independently reviewed and compared by two abdominal radiologists. Discrepancies between the initial report and the consultation report were divided into minor and major differences in the detection or interpretation of abnormalities. Clinical importance was defined as a change in a finding or interpretation that directly impacted management of the patient. RESULTS: A major discrepancy between the reports was identified in 27-28% of cases split evenly between detection and interpretation of abnormalities. Interreader agreement for categorization was moderate (weighted kappa value, 0.49). In consensus review, the rate of a major discrepancy occurring increased to 32%. Common sources of discrepancy were interpretation of findings as malignant versus benign (49% of cases) and accuracy of staging (15% of cases). Imaging limitations were described in 16% of cases, commonly as a result of an insufficient protocol or poor image quality. CONCLUSION: Discrepancies in interpretation resulting in direct implications for clinical management are seen in almost one-third of HPB consultation cases. Second-opinion imaging consultation in the tertiary care setting can frequently impact management.

Utility of a multidisciplinary tumor board in the management of pancreatic and upper gastrointestinal diseases: an observational study.

BACKGROUND & OBJECTIVES: Multidisciplinary tumor boards (MDTBs) are frequently employed in cancer centers but their value has been debated. We reviewed the decision-making process and resource utilization of our MDTB to assess its utility in the management of pancreatic and upper gastrointestinal tract conditions. METHODS: A prospectively-collected database was reviewed over a 12-month period. The primary outcome was change in management plan as a result of case discussion. Secondary outcomes included resources required to hold MDTB, survival, and adherence to treatment guidelines. RESULTS: Four hundred seventy cases were reviewed. MDTB resulted in a change in the proposed plan of management in 101 of 402 evaluable cases (25.1%). New plans favored obtaining additional diagnostic workup. No recorded variables were associated with a change in plan. For newly-diagnosed cases of pancreatic ductal adenocarcinoma (n = 33), survival time was not impacted by MDTB (p = .154) and adherence to National Comprehensive Cancer Network guidelines was 100%. The estimated cost of physician time per case reviewed was $190. CONCLUSIONS: Our MDTB influences treatment decisions in a sizeable number of cases with excellent adherence to national guidelines. However, this requires significant time expenditure and may not impact outcomes. Regular assessments of the effectiveness of MDTBs should be undertaken.

Imaging of tailgut cysts.

Tailgut cysts are congenital lesions that arise from the primitive hindgut in the true embryonic tail but fail to regress during gestation. These lesions are rare and more frequently encountered later in life and more commonly in women, and are the most common primary retrorectal tumor. Tailgut cysts may be asymptomatic or cause rectal bleeding, pain, or symptoms related to mass effect on the rectum or bladder. Pathologically, tailgut cysts are typically multilocular, lined with a variety of epithelial cell types, and are most frequently benign. Imaging is the linchpin of diagnosis due risks associated with biopsy. The purpose of this pictorial review is to present the spectrum of imaging findings associated with tailgut cysts on CT and MRI with focus on the use of advanced MRI and diffusion-weighted imaging. We present case examples of tailgut cysts, their CT and MR imaging findings, and diagnostic and management considerations.

Whole-body simultaneous positron emission tomography (PET)-MR: optimization and adaptation of MRI sequences.

The purpose of this article is to introduce the underlying challenges associated with the incorporation of magnetic resonance imaging (MRI) into the new hybrid imaging modality simultaneous positron emission tomography (PET)/MR and their impact on attenuation correction, sequence optimization, and protocol development. Many adjustments to MR sequences are necessary for optimal whole-body and fused image results.

Combined hepatocellular-cholangiocarcinoma: what the radiologist needs to know about biphenotypic liver carcinoma.

Combined hepatocellular-cholangiocarcinoma (CHC), also referred to as primary liver carcinoma (PLC) with biphenotypic differentiation, is an increasingly recognized subtype of malignant PLC encompassing varying morphologic forms thought to arise either from progenitor cell lineage or dedifferentiation of mature liver cells. Tumor cells express both biliary and hepatocellular markers by immunohistochemistry, and may also express progenitor cell and stem cell markers. Due to the relative rarity of this tumor type, little is known about the risk factors, imaging appearance, or prognosis. Few studies have demonstrated risk factors that overlap with hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), though not all appear to arise in the background of cirrhosis. The imaging appearances of these tumors may overlap with those of HCC and CC and discriminating features such as classic enhancement patterns and biliary ductal dilation are not universally present. Serum tumor markers, such as alpha-fetoprotein and carbohydrate antigen 19-9, may be helpful when they are discordant with imaging or if both are elevated to a significant degree. In regards to management and prognosis, most studies demonstrate worse outcomes compared with HCC or CC. In the United States, the diagnosis of HCC is frequently made with imaging alone, and subsequent management decisions, including organ allocation for transplantation, rely upon the radiological diagnosis. Given the importance of radiological diagnosis, awareness of this tumor type is essential for appropriate management.

Magnetic resonance imaging of iatrogeny: understanding imaging artifacts related to medical devices.

Medical devices are frequently encountered in patients presenting for imaging studies. Knowledge of the device composition, dwell time, and location is essential for determining the safety and potential impact on the quality of magnetic resonance imaging (MRI) examinations. Anticipation of MRI artifacts associated with implanted devices allows the radiologist to adjust parameters to mitigate their effect on the anatomy of interest and to avoid pitfalls in interpretation. The purpose of this article is to present a pictorial review of the MRI appearance of commonly encountered implanted devices and foreign objects in order to help the radiologist anticipate their impact on final image quality.

PACS administrators' and radiologists' perspective on the importance of features for PACS selection.

Picture archiving and communication systems (PACS) play a critical role in radiology. This paper presents the criteria important to PACS administrators for selecting a PACS. A set of criteria are identified and organized into an integrative hierarchical framework. Survey responses from 48 administrators are used to identify the relative weights of these criteria through an analytical hierarchy process. The five main dimensions for PACS selection in order of importance are system continuity and functionality, system performance and architecture, user interface for workflow management, user interface for image manipulation, and display quality. Among the subdimensions, the highest weights were assessed for security, backup, and continuity; tools for continuous performance monitoring; support for multispecialty images; and voice recognition/transcription. PACS administrators' preferences were generally in line with that of previously reported results for radiologists. Both groups assigned the highest priority to ensuring business continuity and preventing loss of data through features such as security, backup, downtime prevention, and tools for continuous PACS performance monitoring. PACS administrators' next high priorities were support for multispecialty images, image retrieval speeds from short-term and long-term storage, real-time monitoring, and architectural issues of compatibility and integration with other products. Thus, next to ensuring business continuity, administrators' focus was on issues that impact their ability to deliver services and support. On the other hand, radiologists gave high priorities to voice recognition, transcription, and reporting; structured reporting; and convenience and responsiveness in manipulation of images. Thus, radiologists' focus appears to be on issues that may impact their productivity, effort, and accuracy.

Communication of Incidental Imaging Findings on Inpatient Discharge Summaries After Implementation of Electronic Health Record Notification System.

OBJECTIVES: Inadequate follow-up of incidental imaging findings (IIFs) can result in poor patient outcomes, patient dissatisfaction, and provider malpractice. At our institution, radiologists flag IIFs during report dictation to trigger electronic health record (EHR) notifications to providers and patients. Nurse coordinators directly contact patients or their primary care physicians (PCPs) regarding IIFs if follow-up is not completed within the recommended time frame. Despite these interventions, many patients and their PCPs remain unaware of IIFs. In an effort to improve awareness of IIFs, we aim to investigate communication of IIFs on inpatient discharge summaries after implementation of our EHR notification system. METHODS: Inpatient records with IIFs from 2018 to 2021 were retrospectively reviewed to determine type of IIFs, follow-up recommendations, and mention of IIFs on discharge summaries. Nurse coordinators spoke to patients and providers to determine their awareness of IIFs. RESULTS: Incidental imaging findings were reported in 51% of discharge summaries (711/1383). When nurse coordinators called patients and PCPs regarding IIFs at the time follow-up was due, the patients and PCPs were aware of 79% of IIFs (1096/1383). CONCLUSIONS: With implementation of EHR notifications to providers regarding IIFs, IIFs were included in 51% of discharge summaries. Lack of inclusion of IIFs on discharge summaries could be related to transitions of care within hospitalization, provider alert fatigue, and many diagnostic testing results to distill. These findings demonstrate the need to improve communication of IIFs, possibly via automating mention of IIFs on discharge summaries, and the need for care coordinators to follow up on IIFs.

Tumor volume and subvolume concordance between FDG-PET/CT and diffusion-weighted MRI for squamous cell carcinoma of the cervix.

PURPOSE: To compare [(18)F]fluorodeoxyglucose (FDG)/positron emission tomography (PET)/computed tomography (CT) and magnetic resonance imaging (MRI) for evaluating patients with cervical cancer. We compared tumor characteristics on FDG-PET and apparent diffusion coefficient (ADC) maps on diffusion-weighted MRI (DWI) to evaluate concordance of two functional imaging techniques. MATERIALS AND METHODS: Twenty women with cervical cancer underwent pretreatment FDG-PET/CT and pelvic MRI. Images were rigidly fused by pelvic anatomy using coregistration software. Tumor contours on PET images were generated by autosegmentation of the region containing at least 40% of the maximum standardized uptake value (SUV). DWI contours were generated by manual segmentation. Tumor volume similarity was evaluated using the [PET]/[ADC] volume proportion, Dice's coefficient, and the mean SUV isothreshold at the surface of each ADC contour. Tumor subvolume similarity was evaluated with analysis of variance (ANOVA). RESULTS: The [PET]/[ADC] volume proportion was 0.88 ± 0.14. Dice's coefficient between PET and ADC tumor contours was 0.76 ± 0.06. The mean SUV isothreshold at the ADC-delineated tumor surface was 34 ± 4%. Subvolumes with increased metabolic activity on FDG-PET also had more restricted diffusion on DWI (P < 0.0001, ANOVA). CONCLUSION: Concordance of functional imaging was observed between FDG-PET and DWI for cervical cancer. Tumor subvolumes with increased metabolic activity on FDG-PET also have greater cell density by DWI.

Impact of Predictive Text Clinical Decision Support on Imaging Order Entry in the Emergency Department.

PURPOSE: Imaging clinical decision support (CDS) is designed to assist providers in selecting appropriate imaging studies and is now federally required. The aim of this study was to understand the effect of CDS on decisions and workflows in the emergency department (ED). METHODS: The authors' institution's order entry platform serves up structured indications for imaging orders. Imaging orders are scored by CDS on the basis of appropriate use criteria (AUC). CDS triggers alerts for imaging orders with low AUC scores. Because free text alone cannot be scored by CDS, an artificial intelligence predictive text (AIPT) module was implemented to guide the selection of structured indications when free-text indications are entered. A total of 17,355 imaging orders in the ED over 6 months were retrospectively analyzed. RESULTS: CDS alerts for low AUC scores were triggered for 3% of all imaging study orders (522 of 17,355). Providers spent an average of 24 seconds interacting with alerts. In 18 of 522 imaging orders with alerts, alternative studies were ordered. After AIPT implementation, the percentage of unscored studies significantly decreased from 81% to 45% (P < .001). CONCLUSIONS: In a quaternary academic ED, CDS alerts triggered by low AUC scores caused minimal increase in time spent on imaging order entry but had a relatively marginal impact on imaging study selection. AIPT implementation increased the number of scored studies and could potentially enhance CDS effects. CDS implementation enables the collection of novel data regarding which imaging studies receive low AUC scores. Future work could include exploring alternative models of CDS implementation to maximize its impact.

Potentiation of novel porphyrin based photodynamic therapy against colon cancer with low dose doxorubicin and elucidating the molecular signalling pathways responsible for relapse.

Photodynamic therapy (PDT) is a promising non-invasive treatment modality for cancer and can be potentiated by combination with chemotherapy. Here, we combined PDT of novel porphyrin-based photosensitizers with low dose doxorubicin (Dox) to get maximum outcome. Dox potentiated and showed synergism with PDT under in vitro conditions on CT26.WT cells. The current colon cancer treatment strategies assure partial or even complete tumour regression but loco-regional relapse or distant metastasis is the major cause of death despite combination therapy. The spared cells after the treatment contribute to relapse and it is important to study their behaviour in host environment. Hence, we developed relapse models for PDT, Dox and combination treatments by transplanting respectively treated equal number of live cells to mice (n = 5) for tumour formation. Most of the treated cells lost tumour forming ability, but some treatment resistant cells developed tumours in few mice. These tumours served as relapse models and Western blot analysis of tumour samples provided clinically relevant information to delineate resistance strategies of individual as well as combination therapies at molecular level. Our results showed that low dose Dox helped in increasing the tumour inhibiting effect of PDT in combination therapy, but still there are indeed possibilities of relapse at later stages due to chemoresistance and immune suppression that may occur post-treatment. We observed that the combination therapy may also lead to the development of multidrug resistant (MDR) phenotype during relapse. Thus, this study provided clinically relevant information to further strengthen and improve PDT-drug combination therapy in order to avoid relapse and to treat cancer more effectively.

Investigation of Hole-Transfer Dynamics through Simple EL De-Convolution in Non-Fullerene Organic Solar Cells.

In conventional fullerene-based organic photovoltaics (OPVs), in which the excited electrons from the donor are transferred to the acceptor, the electron charge transfer state (eECT) that electrons pass through has a great influence on the device's performance. In a bulk-heterojunction (BHJ) system based on a low bandgap non-fullerene acceptor (NFA), however, a hole charge transfer state (hECT) from the acceptor to the donor has a greater influence on the device's performance. The accurate determination of hECT is essential for achieving further enhancement in the performance of non-fullerene organic solar cells. However, the discovery of a method to determine the exact hECT remains an open challenge. Here, we suggest a simple method to determine the exact hECT level via deconvolution of the EL spectrum of the BHJ blend (ELB). To generalize, we have applied our ELB deconvolution method to nine different BHJ systems consisting of the combination of three donor polymers (PM6, PBDTTPD-HT, PTB7-Th) and three NFAs (Y6, IDIC, IEICO-4F). Under the conditions that (i) absorption of the donor and acceptor are separated sufficiently, and (ii) the onset part of the external quantum efficiency (EQE) is formed solely by the contribution of the acceptor only, ELB can be deconvoluted into the contribution of the singlet recombination of the acceptor and the radiative recombination via hECT. Through the deconvolution of ELB, we have clearly decided which part of the broad ELB spectrum should be used to apply the Marcus theory. Accurate determination of hECT is expected to be of great help in fine-tuning the energy level of donor polymers and NFAs by understanding the charge transfer mechanism clearly.

Renal measurements on CT angiograms: correlation with graft function at living donor renal transplantation.

PURPOSE: To determine which measurement of donor renal size on computed tomographic (CT) angiograms has the greatest correlation with renal function preoperatively in the donor and postoperatively in the transplant recipient. MATERIALS AND METHODS: Informed consent was waived for this retrospective HIPAA-compliant study approved by the institutional review board. Renal length, total volume, and cortical volume were measured on renal donor CT angiograms in 111 patients. Preoperative serum creatinine values for donors and postoperative creatinine values for recipients at hospital discharge and 6, 12, 24, and 36 months after transplant were collected, and estimated glomerular filtration rate (eGFR) was calculated. Correlation coefficients with 95% confidence intervals (CIs) were obtained for renal measures and donor eGFR and for renal measures adjusted to recipient body habitus and posttransplant creatinine level in the recipient. Thresholds were set for adjusted length and volumes, and the odds ratio (OR) for creatinine level less than 1.5 mg/dL at 36 months was calculated. RESULTS: Renal volumes and length were correlated with donor eGFR (r=0.58 [95% CI: 0.44, 0.69] for cortical volume, 0.56 [95% CI: 0.42, 0.68] for total volume, and 0.43 [95% CI: 0.27, 0.57] for renal length). All three measures, adjusted to recipient body habitus, were correlated with recipient renal function from discharge (r=-0.41 to -0.43) up to 36 months after transplantation (r=-0.33 to -0.41). By using a threshold of 1.5 for cortical volume to recipient weight, 2.25 for total volume to recipient weight, and 0.175 for renal length to recipient weight, the odds of creatinine level greater than 1.5 mg/dL were four times as great for smaller kidney-to-recipient weight ratios, a statistically significant pattern for cortical volume (OR, 4.07; 95% CI: 1.10, 15.09) but not total volume (OR, 4.24; 95% CI: 0.90, 20.01) or renal length (OR, 4.08; 95% CI: 0.48-34.29). CONCLUSION: Renal length and volumes correlated with recipient renal function up to 36 months after transplant. A low ratio of cortical volume to recipient weight was associated with diminished renal function at 36 months after transplant.

Magnetic resonance imaging of focal liver lesions: approach to imaging diagnosis.

This article is a review of magnetic resonance imaging (MRI) of incidental focal liver lesions. This review provides an overview of liver MRI protocol, diffusion-weighted imaging, and contrast agents. Additionally, the most commonly encountered benign and malignant lesions are discussed with emphasis on imaging appearance and the diagnostic performance of MRI based on a review of the literature.

MR imaging findings of ectopic pregnancy: a pictorial review.

Because of its lack of ionizing radiation and excellent soft-tissue contrast, magnetic resonance (MR) imaging is being increasingly used in the evaluation of acute abdominal pain in the pregnant patient. Roughly 2% of all pregnancies are ectopic. Although ectopic pregnancy is usually diagnosed on the basis of a combination of clinical, laboratory, and ultrasonographic findings, it occasionally is initially identified at MR imaging. Thus, it is imperative that the radiologist should be familiar with the variable appearance of ectopic pregnancy at MR imaging and should evaluate for ectopic pregnancy at any time when (a) a patient has positive results of a pregnancy test and (b) an intrauterine pregnancy is not definitively seen. Because of potential issues of fetal safety, a conservative approach should be used for MR imaging in pregnancy. An MR imaging protocol for the evaluation of possible appendicitis in pregnant women is detailed. Specific findings that can aid in the diagnosis of ectopic pregnancy are the lack of an intrauterine pregnancy, isolated hemoperitoneum, tubal masses, hematosalpinx, and interstitial masses. In the differential diagnosis of acute abdominal pain in pregnancy, consideration should be given to the more unusual forms of ectopic pregnancy, such as angular pregnancy, cornual pregnancy, and abdominal pregnancy. Potential mimics of ectopic pregnancy include placental abnormalities, ovarian neoplasms, and corpus luteum cysts.