Stefan G. Ruehm

Rapid magnetic resonance angiography for detection of atherosclerosis

BACKGROUND Choice of treatment for atherosclerosis depends on various clinical factors and radiological techniques. We aimed to assess the diagnostic accuracy of a new three-dimensional magnetic resonance angiography (3D MRA) strategy for the display of arterial vasculature from supra-aortic arteries to distal runoff vessels in 72 s. METHODS We examined five healthy volunteers and six patients over 6 weeks. Conventional digital subtraction angiography (DSA) was available as reference standard in all six patients. Magnetic resonance imaging was done on a commercially available 1.5 Tesla scanner. The imaging technique was based on the acquisition of five 3D data sets in rapid succession with an optimum single injection protocol. FINDINGS Compared with conventional catheter angiography, according to the findings of two independent and masked readers, whole-body MRA had overall sensitivities of 91% (95% CI 0.76-0.98) and 94% (0.8-0.99), and specificities of 93% (0.85-0.97) and 90% (0.82-0.96) for the detection of substantial vascular disease (luminal narrowing >50%), interobserver agreement for assessment of whole-body magnetic angiograms was very good (kappa=0.94; 95% CI 0.9-0.98). INTERPRETATION The technique provides a comprehensive non-invasive approach for morphological screening assessment of the arterial vasculature from supra-aortic arteries to the distal runoff arteries.

Dark lumen magnetic resonance colonography: comparison with conventional colonoscopy for the detection of colorectal pathology

Background: The purpose of this study was to assess the feasibility and usefulness of a new magnetic resonance (MR) colonography technique for the detection of colorectal pathology in comparison with conventional colonoscopy as the standard of reference. Patients and methods: A total of 122 subjects with suspected colorectal disease underwent “dark lumen” MR colonography. A contrast enhanced T1w three dimensional VIBE sequence was collected after rectal administration of water. The presence of colorectal masses and inflammatory lesions were documented. Results were compared with those of a subsequently performed colonoscopy. Results: MR colonography was found to be accurate regarding detection of clinically relevant colonic lesions exceeding 5 mm in size, with sensitivity and specificity values of 93%/100%. Conclusion: Dark lumen MR colonography can be considered as a promising alternative method for the detection of colorectal disease. In addition, it allows assessment of extraluminal organs.

Magnetic resonance colonography for the detection of inflammatory diseases of the large bowel: quantifying the inflammatory activity.

Introduction: The purpose of this study was to assess the diagnostic accuracy of magnetic resonance colonography (MRC) for its ability to detect and quantify inflammatory bowel disease (IBD) affecting the colon. Endoscopically obtained histopathology specimens were used as the standard of reference. Materials and methods: Fifteen normal subjects and 23 patients with suspected IBD of the large bowel underwent MRC. Three dimensional T1 weighted data sets were collected following rectal administration of water prior to and 75 seconds after intravenous administration of paramagnetic contrast (gadolinium-BOPTA). The presence of inflammatory changes in patients was documented based on bowel wall contrast enhancement, bowel wall thickness, presence of perifocal lymph nodes, and loss of haustral folds. All four criteria were quantified relative to data obtained from normal subjects and summarised in a single score. This MRC based score was compared with histopathological data based on conventional endoscopic findings. Results: MRC correctly identified 68 of 73 segments found to reveal IBD changes by histopathology. All severely inflamed segments were correctly identified as such and there were no false positive findings. Based on the proposed composite score, MRC detected and characterised clinically relevant IBD of the large bowel with sensitivity and specificity values of 87% and 100%, respectively, for all investigated colonic segments. Conclusion: MRC may be considered a promising alternative to endoscopic biopsy in monitoring IBD activity or assessing therapeutic effectiveness.

Experience after the evaluation of 700 potential donors for living donor liver transplantation in a single center

Adequate selection of donors is a major prerequisite for living donor liver transplantation (LDLT). Few centers report on the entire number of potential donors considered or rejected for living donation. From April 1998 to July 2003, a total of 111 living donor liver transplantations were performed at our institution, with 622 potential donors for 297 adult recipients and 78 potential donors for 52 pediatric recipients evaluated. In the adult group, only 89 (14%) potential donors were considered suitable, with a total of 533 (86%) potential donors rejected. Of these, 67% were excluded either at initial screening or during the first and second steps of the evaluation procedure. In 31% of all cases, the evaluation of donors was canceled because of recipient issues. In the pediatric group, 22 (28%) donors were selected, with the other 56 (72%) rejected. Costs of the complete evaluation process accounted for 4,589 Euro (€) per donor. The evaluation of a potential living donor is a complex and expensive process. We present the results on the evaluation of the largest group of potential donors for adults reported in the literature. Only 14% of potential donors in our series were considered suitable candidates. It has not yet been established who should cover the expenses of the evaluation of all rejected donors. In conclusion, all efforts should be made in order to develop an effective screening protocol for the evaluation of donors with the aim of saving time and resources for a liver transplantation program. (Liver Transpl 2004;10:1087–1096.)

Dynamic 3D MR angiography of the pulmonary arteries in under four seconds.

Although 3D MRA has been shown to provide excellent depiction of the pulmonary arterial tree, its clinical use has been limited due to lengthy breath‐holding requirements. Employing the newest gradient generation (1.5 T MR system, amplitude of 40 mT/m and a slew rate of 200 mT/m/msec), we evaluated a technique permitting the dynamic acquisition of 3D data sets of the entire pulmonary tree in under 4 seconds. Coronal image sets were collected using a repetition time of 1.64 msec and an echo time of 0.6 msec, resulting in an acquisition time of 3.74 seconds. Three volunteers and eight dyspneic patients with known or suspected pulmonary embolism underwent MRI of the pulmonary arteries. The pulmonary arterial tree was visible to a subsegmental level in all examined subjects. Regarding the presence of pulmonary emboli in four patients, there was complete concordance between MR angiographic findings and those of corroborative studies. We conclude that diagnostic MRA of the pulmonary vasculature can be obtained even in patients with severe respiratory distress. J. Magn. Reson. Imaging 2001;13:372–377.

Detection of pulmonary nodules using a 2D HASTE MR sequence: comparison with MDCT

OBJECTIVE The objective of our study was to determine the diagnostic performance of MRI based on a HASTE sequence for the detection of pulmonary nodules in comparison with MDCT. MATERIALS AND METHODS Thirty patients with known pulmonary nodules underwent both MRI and CT. CT of the lung served as the standard of reference and was performed on a 4-MDCT scanner using a routine protocol. MRI was performed with axial and coronal HASTE sequences using a high-performance 1.5-T MR scanner. Image data were analyzed in three steps after completion of all data acquisition. Step 1 was the analysis of all the CT image data. Step 2 was the analysis of all the MR image data while blinded to the results of the CT findings. Step 3 closed with a simultaneous review of all corresponding CT and MRI data, including a one-to-one correlation of the size and location of all the nodules that were detected. RESULTS Compared with the sensitivity of CT, the sensitivity values for the HASTE MR sequence were as follows: 73% for lesions less than 3 mm, 86.3% for lesions between 3 and 5 mm, 95.7% for lesions between 6 and 10 mm, and 100% for lesions larger than 10 mm. The overall sensitivity of the HASTE sequence for the detection of all pulmonary lesions was 85.4%. CONCLUSION An MRI examination that consists of a HASTE sequence allows one to detect, exclude, or monitor pulmonary lesions that are 5 mm and bigger. Suspicious lesions smaller than 5 mm still need to be validated using CT.

0.5 M Gd chelate (Magnevist®) versus 1.0 M Gd chelate (Gadovist®): Dose-independent effect on image quality of pelvic three-dimensional MR-angiography

To compare the effect on image quality of a 1.0 M gadolinium (Gd) chelate to that of a conventional 0.5 M Gd chelate, five healthy volunteers and seven patients with angiographically documented aorto‐iliac disease underwent a mono‐station three‐dimensional magnetic resonance angiography (MRA) exam (Siemens SONATA®, Erlangen, Germany) twice, once using Gadovist® 1.0 and the other time using Magnevist® as the contrast agent. All subjects received a fixed volume of Gadovist® 1.0, corresponding to a dose between 0.1 and 0.15 mmol/kg body weight followed by a saline flush. For the Magnevist® exam, the contrast agent volumes and flow rates were doubled. For both quantitative and qualitative analysis of the angiographic data sets, the arterial tree was divided into nine segments. 1 M Gadovist® 1.0‐enhanced three‐dimensional MRA data sets were characterized by significantly higher signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) values compared to 0.5 M Magnevist®‐enhanced images. The data revealed mean SNR/CNR increases exceeding 70% (P < 0.01). Although there was no statistically significant difference in the rating of image quality (P > 0.05), the Gadovist® 1.0 exam led to better delineation of the arterial morphology, especially of small vessels. J. Magn. Reson. Imaging 2001;14:602–607.

Real time high resolution magnetic resonance imaging for the assessment of gastric motility disorders

Background: The aim of this study was to evaluate whether patients with increased or decreased gastric motility can be differentiated from healthy volunteers by means of real time magnetic resonance imaging (MRI). Patients and methods: Ten healthy volunteers, 10 patients with gastroparesis, and 10 patients with functional pylorospasm/peptic pyloric stenosis underwent real time MRI. All patients were examined on two separate days; once prior to therapy and once after adequate therapy. Antral motility was quantified by calculating the gastric motility index. Results: Patients with gastroparesis showed a lower motility index compared with the reference volunteer group while the mean motility index of the patient group with pylorospasm was more than three times higher than that of the reference value of the volunteer group. However, the gastric motility index in the patient group with gastroparesis increased, and in the group with functional pylorospasm/peptic pyloric stenosis it decreased significantly after therapy. Conclusion: Real time MRI is a reliable tool for assessment of gastric motion. Furthermore, differences in gastric motility index in patients with increased or decreased gastric motility could be evaluated and quantified. Due to the non-invasive character of MRI, this imaging modality may be an attractive alternative to conventional invasive diagnostic tools for gastric motility disorders and therapeutic monitoring.

Newly Developed Techniques to Study and Diagnose Acute Renal Failure

Progress in treating human acute renal failure (ARF) is dependent on developing techniques that allow for the rapid diagnosis, quantification of injury, further understanding of the pathophysiology, and the effects of therapy. Therefore, four techniques that will facilitate this progress are described and illustrated by four different investigative teams. Techniques to measure rapid changes in GFR are available for rapid diagnosis and quantification of ARF in humans. State-of-the-art magnetic resonance imaging (MRI) presently allows for enhanced resolution of regional renal blood flow and functional evaluations in patients. Furthermore, new probes and techniques for MRI that allow for identification and quantitation of inflammation, applicable to human ARF, are being developed and tested in animal models. Finally, two-photon microscopy will allow for four-dimensional cellular and subcellular studies in animal models of ARF providing rapid insights into pathophysiology and the therapeutic effects of a variety of promising agents. Further development and utilization of these techniques, especially in concert with genetic, proteomic, and molecular approaches, will allow for needed insights into the pathophysiology and therapy in human ARF.

Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases

ObjectivesThe purpose of this study was to determine the image quality and diagnostic accuracy of three-dimensional (3D) unenhanced steady state free precession (SSFP) magnetic resonance angiography (MRA) for the evaluation of thoracic aortic diseases.MethodsFifty consecutive patients with known or suspected thoracic aortic disease underwent free-breathing ECG-gated unenhanced SSFP MRA with non-selective radiofrequency excitation and contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers independently evaluated the two datasets for image quality in the aortic root, ascending aorta, aortic arch, descending aorta, and origins of supra-aortic arteries, and for abnormal findings. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were determined for both datasets. Sensitivity, specificity, and diagnostic accuracy of unenhanced SSFP MRA for the diagnosis of aortic abnormalities were determined.ResultsAbnormal aortic findings, including aneurysm (n = 47), coarctation (n = 14), dissection (n = 12), aortic graft (n = 6), intramural hematoma (n = 11), mural thrombus in the aortic arch (n = 1), and penetrating aortic ulcer (n = 9), were confidently detected on both datasets. Sensitivity, specificity, and diagnostic accuracy of SSFP MRA for the detection of aortic disease were 100% with CE-MRA serving as a reference standard. Image quality of the aortic root was significantly higher on SSFP MRA (P < 0.001) with no significant difference for other aortic segments (P > 0.05). SNR and CNR values were higher for all segments on SSFP MRA (P < 0.01).ConclusionOur results suggest that free-breathing navigator-gated 3D SSFP MRA with non-selective radiofrequency excitation is a promising technique that provides high image quality and diagnostic accuracy for the assessment of thoracic aortic disease without the need for intravenous contrast material.