Comprehensive Magnetic Resonance Imaging Protocol Research Articles

A Magnetic Resonance Imaging Protocol for the Evaluation of Pediatric Postappendectomy Abscess: A Quality Improvement Project

IntroductionComputed tomography (CT) scans are often used when cross-sectional imaging is required for evaluation of postappendectomy abscess, exposing children to a source of ionizing radiation. Our aim was to decrease the use of CT scans in pediatric postappendectomy patients by 50% in 12 mo and to sustain those results for 1 y. MethodsA comprehensive magnetic resonance imaging protocol was introduced in 2018 at a tertiary children's hospital within a general health system to replace CT scans in suspected pediatric postappendectomy abscess. Diagnostic and clinical outcomes were compared preprotocol (2015-2017) and postprotocol (2018-2022) implementation using standard univariate statistics. P < 0.05 was considered significant. Quality improvement methodology was used to design and implement the protocol. ResultsSixty eight pediatric postappendectomy patients received cross-sectional imaging during the study period. Overall, CT scans were used exclusively (100%, n = 27) in the preimplementation period compared to 31.7% (n = 13) of cross-sectional imaging in the postimplementation period. However, in the first year of protocol implementation, CT scan use only decreased to 78% of cross-sectional studies performed. The majority of protocol deviations (54%) also occurred in this time period. With improved education and reinforcement, CT scan utilization decreased to approximately 24% of cross-sectional studies annually. Missed abscess rate, time to diagnosis, drainage procedure type, readmission, and reoperation were similar between preimplementation and postimplementation periods. ConclusionsImplementation of a postappendectomy abscess magnetic resonance imaging protocol was associated with decreased CT utilization in the pediatric population, while maintaining comparable diagnostic evaluation and clinical outcomes. Adherence to quality improvement principles facilitated achieving goals and sustaining gains.

Can magnetic resonance imaging replace computed tomography scans in the evaluation of pediatric post-appendectomy abscess?

BackgroundComputed tomography scans have been used when cross-axial imaging is required to evaluate pediatric post-appendectomy abscesses. To reduce a source of radiation exposure, our institution converted to using contrast-enhanced magnetic resonance imaging to replace computed tomography scans in this clinical context. Our aim is to evaluate the performance of magnetic resonance imaging compared to computed tomography scans and associated clinical outcomes in this patient population. MethodsA contrast-enhanced comprehensive magnetic resonance imaging protocol was implemented to evaluate a post-appendectomy abscess in 2018. A retrospective chart review was performed from 2015 to 2022 for pediatric patients (<18 years old) with prior appendectomy and subsequent cross-sectional imaging to evaluate for an intraabdominal abscess. Patient characteristics and clinical parameters between the 2 modalities were abstracted and compared using standard univariate statistics. ResultsThere were a total of 72 post-appendectomy patients who received cross-axial imaging, which included 43 computed tomography scans and 29 magnetic resonance imaging during the study interval. Patient demographics were comparable between cohorts and rates of perforated appendicitis at the index operation (computed tomography: 79.1% vs magnetic resonance imaging: 86.2%). Missed abscess rate, abscess size, management technique, drainage culture results, readmission, and reoperation were similar between imaging modalities. Median request to scan time was longer for magnetic resonance imaging than computed tomography (191.5 vs 108 minutes, P = .04). The median duration of a comprehensive magnetic resonance imaging scan was 32 minutes (interquartile range 28–50.5 minutes). ConclusionContrast-enhanced magnetic resonance imaging provides an alternative cross-sectional imaging modality to computed tomography scans to evaluate pediatric post-appendectomy abscesses.

Characterization of Contrast-Enhancing and Non-contrast-enhancing Multiple Sclerosis Lesions Using Susceptibility-Weighted Imaging.

Susceptibility-weighted magnetic resonance imaging (MRI) (SWI) offers additional information on conventional MRI contrasts. Central veins can be identified within lesions, and recently, it has been suggested that multiple sclerosis (MS) lesions with slowly expanding demyelination, so-called smoldering lesions, can be identified by a phase rim surrounding the lesion. We analyzed post-contrast SWI in regard to intrinsic lesion characteristics in a cohort of MS patients. A total of 294 MS patients were evaluated using a 3-T MRI. A comprehensive MRI protocol was used including post-contrast SWI. Lesions of at least 5 mm in size were analyzed on conventional MRI and SWI with a structured reporting scheme with a focus on SWI lesion characteristics. A total of 1,323 lesions were analyzed: 1,246/1,323 (94%) were non-enhancing and 77/1,323 (6%) were contrast-enhancing (CE) lesions. In CE lesions, the following patterns were seen: contrast enhancement was nodular in 34/77, ring-shaped enhancement was present in 33/77, and areas of peripheral enhancement were present in 10/77. In CE lesions, an association with central veins was found in 38/77 (50%). In 75/1,246 (6%) non-enhancing lesions, a central dark dot in keeping with a central vein was seen, whereas 162/1,246 (13%) showed peripheral hypointense dots/rims, 199/1,246 (16%) showed scattered hypointense dots mainly within the lesion area, and in 374/1,246 (30%), no SWI hypointensity was detected. Furthermore, 436/1,246 (35%) lesions showed isointensity to the surrounding tissue and were not visible on SWI. SWI is able to offer additional aspects of MS pathology also when used after the application of a contrast agent. Veins connected to lesions, a potentially useful marker in the differential diagnosis of MS, were seen in about 50% of enhancing lesions. Susceptibility artifacts, suggested to mark the presence of myelin-laden macrophages and smoldering inflammation, were visible in 28% of lesions as hypointense dots in and in the periphery of the lesion. Given those results, SWI may provide practical useful additional information in the evaluation of the lesion status in MS patients.

MRI evaluation of acute appendicitis in pregnancy

In recent years, magnetic resonance imaging (MRI) has become a valuable diagnostic tool for evaluation of acute abdominal pain in pregnancy. MRI offers an opportunity to identify the normal or inflamed appendix as well as a variety of other pathologic conditions that can masquerade clinically as acute appendicitis in pregnant women. Visualization of the normal appendix by MRI virtually excludes the diagnosis of acute appendicitis and may help reduce the negative laparotomy rate in this patient population. Here we discuss a comprehensive MRI protocol for evaluation of pregnant women with abdominal pain, focusing on the appearance and location of the normal and diseased appendix, and we describe an approach to diagnosing acute appendicitis and other conditions with MRI.

Diffusion-weighted Magnetic Resonance Imaging for the Staging of Liver Fibrosis

Diffusion-weighted magnetic resonance (MR) imaging (DWI) has been suggested for staging liver fibrosis. The aim of this study was to evaluate the diagnostic accuracy of DWI for the noninvasive assessment of hepatic fibrosis. We retrospectively compared DWI from clinically acquired MR scans with histologic methods. Liver biopsy specimens were staged F0-F4 in accordance with the METAVIR score. Hepatic steatosis was classified on a 5-point scale. Hepatic iron was graded on a 3-point scale. Liver inflammation was scored according to the modified hepatic activity index. Nonparametric methods, linear regression models, and receiver operating characteristic analyses were used to determine diagnostic accuracy and apparent diffusion coefficient (ADC) cutoff values. Liver ADC values were inversely correlated with fibrosis stage: P = -0.54 (P < 0.0001). Although there was substantial overlap in the ADC distributions, the differences in ADC values by METAVIR stages F0 versus (vs.) F1-4, F0-1 versus F > 1, F0-2 versus F3-4 and F0-3 versus F4 were all significant. For prediction of fibrosis stage 1, stage 2, stage 3, and stage 4 area under the receiver operating characteristic curve of 0.79, 0.77, 0.77, and 0.79 were obtained, respectively. Inflammation also correlated significantly with ADC values (P = -0.23, P = 0.03), but iron content (P = 0.17) or steatosis (P = 0.63) did not correlate with ADC measurements. Liver ADC can be used to predict liver fibrosis with acceptable diagnostic accuracy. DWI should be included in further prospective studies to validate a comprehensive MR imaging protocol for the noninvasive assessment of hepatic fibrosis.

A standardized, comprehensive magnetic resonance imaging protocol for rapid and precise quantification of HIV‐1‐associated lipodystrophy

Although multiple methods have been proposed, there is no current gold standard for assessing HIV-1-associated lipodystrophy. HIV-1-infected participants were randomly enrolled and surveyed about changes in the abdomen, thigh, cheek and neck areas. Magnetic resonance imaging (MRI) sequences of these sites were obtained. Participants were grouped according to survey results, and the MRI measurements were compared between groups. One hundred participants were included in the study, of whom 79% reported any body fat changes. Persons reporting increased abdominal girth had higher visceral ([mean+/-standard deviation] 142+/-75 vs. 59+/-48 cm2; P<0.0001) and total abdominal adipose tissue than those reporting no change (344+/-119 vs. 201+/-95 cm2; P<0.0001). The amount of localized fat was less for persons reporting sunken cheeks and reduced diameter of the legs compared with those who noted no changes (5.9+/-3.6 vs. 9.3+/-3.8 cm2; P<0.0001, and 35+/-28 vs. 112+/-56 cm2; P<0.0001). Participants reporting increased neck girth had a thicker fat layer in the dorsocervical region compared with those reporting no change (4.0+/-1.8 vs. 2.3+/-1.4 cm; P<0.0002). MRI is a precise method for rapidly surveying body regions affected by HIV-1-associated lipodystrophy. Our proposed protocol provides a rapid, comprehensive survey of these areas, without the need to combine multiple modalities or to expose subjects to radiation.

Pulmonary Arterial Hypertension: Diagnosis with Fast Perfusion MR Imaging and High-Spatial-Resolution MR Angiography—Preliminary Experience

To determine prospectively the accuracy of a magnetic resonance (MR) perfusion imaging and MR angiography protocol for differentiation of chronic thromboembolic pulmonary arterial hypertension (CTEPH) and primary pulmonary hypertension (PPH) by using parallel acquisition techniques. The study was approved by the institution's internal review board, and all patients gave written consent prior to participation. A total of 29 patients (16 women; mean age, 54 years +/- 17 [+/- standard deviation]; 13 men; mean age, 57 years +/- 15) with known pulmonary hypertension were examined with a 1.5-T MR imager. MR perfusion imaging (temporal resolution, 1.1 seconds per phase) and MR angiography (matrix, 512; voxel size, 1.0 x 0.7 x 1.6 mm) were performed with parallel acquisition techniques. Dynamic perfusion images and reformatted three-dimensional MR angiograms were analyzed for occlusive and nonocclusive changes of the pulmonary arteries, including perfusion defects, caliber irregularities, and intravascular thrombi. MR perfusion imaging results were compared with those of radionuclide perfusion scintigraphy, and MR angiography results were compared with those of digital subtraction angiography (DSA) and/or contrast material-enhanced multi-detector row computed tomography (CT). Sensitivity, specificity, and diagnostic accuracy of MR perfusion imaging and MR angiography were calculated. Receiver operator characteristic analyses were performed to compare the diagnostic value of MR angiography, MR perfusion imaging, and both modalities combined. For MR angiography and MR perfusion imaging, kappa values were used to assess interobserver agreement. A correct diagnosis was made in 26 (90%) of 29 patients by using this comprehensive MR imaging protocol. Results of MR perfusion imaging demonstrated 79% agreement (ie, identical diagnosis on a per-patient basis) with those of perfusion scintigraphy, and results of MR angiography demonstrated 86% agreement with those of DSA and/or CT angiography. Interobserver agreement was good for both MR perfusion imaging and MR angiography (kappa = 0.63 and 0.70, respectively). The combination of fast MR perfusion imaging and high-spatial-resolution MR angiography with parallel acquisition techniques enables the differentiation of PPH from CTEPH with high accuracy.

MR imaging: a "one-stop shop" modality for preoperative evaluation of potential living kidney donors.

At many institutions, magnetic resonance (MR) angiography is the technique of choice for assessment of the renal arteries and renal parenchyma in potential living kidney donors. The renal arteries and renal veins have a varied anatomy and may consist of one or more vessels at several levels with variable calibers and levels of branching. These findings may play an important role in the surgeon's decision about which kidney to harvest, especially if laparoscopic nephrectomy is used. A comprehensive MR imaging protocol is used at one hospital to assess the arteries, veins, parenchyma, and collecting system of the kidneys. The protocol includes T2-weighted single-shot fast spin-echo imaging, fat-saturated T2-weighted fast spin-echo imaging, three-dimensional MR angiography and MR venography, and delayed fat-saturated three-dimensional T1-weighted gradient-echo imaging. Meticulous assessment of the source images as well as images produced with various postprocessing methods, such as full maximum intensity projection, targeted maximum intensity projection, and axial and oblique reformation, allows detailed description of the vascular anatomy and its relationship to the collecting system and parenchyma to facilitate the surgeon's decision making. The findings of MR imaging are comparable with those of other imaging modalities.

Coronary artery disease: assessment with a comprehensive MR imaging protocol--initial results.

A comprehensive magnetic resonance (MR) imaging protocol for assessment of coronary artery disease (CAD) is presented. The protocol includes multiphase gradient-echo cine MR imaging for assessment of cardiac function, first-pass myocardial perfusion imaging at rest and during adenosine stress, MR imaging with delayed contrast enhancement for assessment of myocardial viability, and coronary MR angiography with a three-dimensional respiratory navigator-gated technique. In 10 patients, the protocol was completed in 61.5 minutes +/- 5.5 and yielded high image quality and diagnostic accuracy. This protocol may provide an integrated noninvasive screening tool for patients with CAD.

Right-lobe living related liver transplantation: evaluation of a comprehensive magnetic resonance imaging protocol for assessing potential donors.

The purpose of this study was to determine the practicability and diagnostic accuracy of a magnetic resonance (MR) protocol capable of replacing computed tomography, catheter angiography, and endoscopic retrograde cholangiopancreatography for the presurgical evaluation of potential liver donors before right hepatectomy. MR imaging (MRI) was performed on a 1.5 T scanner using a phased-array torso surface coil for signal reception. The following image sets were collected: axial two-dimensional (2D) T1-weighted fast low angle shot (FLASH), axial 2D T2-weighted half-Fourier acquisition single-shot turbo-spin-echo (HASTE) with fat saturation, coronal MR cholangio-pancreatography (MRCP) based on 2D multisection HASTE and single-section single-shot rapid acquisition with relaxation enhancement (RARE) imaging, dynamic contrast-enhanced three-dimensional (3D) FLASH, and contrast-enhanced T1-weighted FLASH. 3D FLASH data sets were collected before and after an intravenous administration of Multihance (gadobenate dimeglumine, Gd-BOPTA; Bracco, Milano, Italy), 0.2 mmol/kg of body weight. Thirty-eight potential liver donors were assessed by means of MRI. Twenty patients also underwent digital subtraction angiography (DSA). Of these, 16 patients underwent liver harvesting. MR angiography (MRA) data sets correlated with DSA results, and MRCP results correlated with intraoperative findings. Patients were excluded as potential donors based on insufficient liver mass of the left hepatic lobe (n = 5) or presence of hepatic pathological states (n = 9) seen at MRI, such as hemangiomas, focal nodular hyperplasias, or hepatic steatosis. MRCP showed the biliary system to the level of the first hepatic side branch. Dilated ducts were present in 4 patients. MRA depiction of hepatic arterial morphological characteristics correlated with catheter angiography results in all 20 patients: Three left hepatic arteries originating from the left gastric artery, three aberrant right hepatic arteries originating from the superior mesenteric artery, and two aberrant origins of both hepatic arteries and one common hepatic artery originating from the superior mesenteric artery were correctly identified on MRA. Similarly, the portal venous system was fully assessed on MRA. A comprehensive assessment of the hepatic parenchyma, biliary and pancreatic ductal system, and hepatic arterial, portal, and venous systems can be accomplished using the outlined protocol.

MR angiography after renal revascularization: spectrum of expected anatomic results and postintervention complications.

The use of magnetic resonance (MR) angiography in screening for renal artery stenosis has been extensively evaluated. However, the MR angiographic findings after renal artery revascularization are not as well characterized. The renal artery and parenchyma can be evaluated after revascularization with a comprehensive MR imaging protocol that includes T1- and T2-weighted spin-echo sequences, three-dimensional (3D) gadolinium-enhanced MR angiography, and 3D phase-contrast MR angiography. Because surgical techniques for revascularization vary, knowledge of the surgical procedure is necessary to ensure inclusion of the pertinent anatomy at 3D gadolinium-enhanced MR angiography and to define appropriate 3D phase-contrast MR angiography volumes. The 3D gadolinium-enhanced MR angiography volume can be manipulated to view relevant vascular anatomy at the optimal obliquity and section thickness. This protocol allows robust, noninvasive evaluation of the expected arterial anatomy after revascularization, including renal artery endarterectomy, aortorenal bypass grafts, and extraanatomic reconstructions. In cases of suspected postrevascularization complications, gadolinium-enhanced MR angiography is useful because of its lack of nephrotoxicity and radiation exposure. Immediate complications of renal revascularization include renal artery thrombosis, renal infarction, and perinephric hemorrhage. Long-term complications include aneurysms of bypass grafts and recurrent stenosis of the renal artery.

Comprehensive MR imaging protocol for stroke management: tissue sodium concentration as a measure of tissue viability in nonhuman primate studies and in clinical studies.

To investigate sodium magnetic resonance (MR) imaging for monitoring tissue viability in stroke. A comprehensive MR imaging protocol used to measure apparent diffusion coefficient and perfusion parameters was extended to include sodium imaging. Tissue sodium concentration was estimated by using a two-compartment model. This protocol lasted less than 45 minutes. These parameters were followed over the first 6 hours in a nonhuman primate model (n = 2) of acute embolic stroke without or with thrombolytic therapy. This protocol was used in patients in whom acute (< 24 hours, n = 11) or nonacute (> or = 24 hours, n = 31) stroke was ultimately confirmed. The animal model showed abnormal diffusion and perfusion parameters in the lesion immediately after embolization, and these remained abnormal for over 6 hours. Tissue sodium concentration increased with time (5.7 mmol/L/h) unless halted with thrombolytic therapy. Regions with sodium concentrations over 70 mmol/L were histochemically verified as being infarcted. In patients in whom stroke older than 6 hours was clinically confirmed, sodium concentrations over 70 mmol/L were found in the appropriate brain regions. Tissue sodium concentration provides a sensitive measure of tissue viability that is complementary to the diagnostic role of diffusion and perfusion imaging for ischemic insult.