Magnetic resonance imaging of the thorax

Magnetic resonance imaging (MRI) is a new technique in chest radiology. It appears to be particularly useful in examining the hila. Other regions of the mediastinum can also be successfully imaged, and vessels are well seen. MRI has become the procedure of choice for evaluating dissecting aortic aneurysms, especially in stable patients. Imaging of other conditions and diseases has yielded information comparable to that obtained with CT.     

Magnetic resonance imaging of renal transplants: initial experience

Magnetic resonance imaging (MRI) was used in 45 renal transplant investigations (38 patients) using a Picker 0.15 T resistive system and a localized surface coil. An attempt was made to define optimal sequences in the evaluation of both normal and pathological transplants. Three sequences were found to be of value; a T1 weighted sequence (IR2180/700/40) to assess corticomedullary differentiation and its loss in acute rejection and acute tubular necrosis, a T2 weighted sequence (SE2000/80) for assessment of renal vessels and disturbances in blood supply, and a STIR (short tau inversion recovery) sequence (IR800/100/40) to define further the distended collecting system in obstruction and the presence of any perirenal collection. Encouraging results have been obtained, particularly in cases of acute rejection. It is suggested that the MRI scan is a useful screening test in cases of clinical doubt and may even obviate biopsy in some cases.     

Magnetic resonance imaging of laser phototherapy: initial experience

Interventional magnetic resonance imaging (MRI) is a newly established field, made possible by improvements in imaging times and the development of nonferromagnetic materials. Interstitial laser therapy (ILT) is a promising new technology in which laser energy is adininistered percutaneously via optical fibers. In this study, MRI was used to image acute experimental lesions induced nv ILT. Nine experimental lesions were induced in the musculature of an adult swine using an argon laser,' with output power of 1–4 watts, and exposure times of 10–40 s. T2-weighted images were obtained immediately after laser energy administration. The animal was then sacrificed and lesions were dissected and examined histologically. On MRI, target like lesions were seen with a high intensity center surrounded by two alternating concentric rings of low and high intensity. Histologically, concentric zones of tissue disruption were present. A center cavity was surrounded by a zone of coagulative necrosis, followed by a zone of vascuolated tissue abutting normal muscle. We conclude that MRI is capable of imaging acute histological changes. Appropriate development of a scale relating MR changes to acute and long-term histologic changes will allow us to optimize 3 D control and monitoring of ILT.     

Magnetic resonance imaging of the pediatric spine

The authors conclude that MRI is the imaging mode of choice for the evaluation of extradural and intramedullary tumors and for the screening of all children with suspected spinal pathology.     

Magnetic resonance imaging of the pediatric pelvis.

The increased use of MR imaging in the pediatric population is due to the lack of ionizing radiation, multiplanar imaging capability, and excellent tissue contrast differentiation. MR imaging is most commonly indicated in the evaluation of tumors to provide information about resectability and extent of lesions. It is also useful in the evaluation of congenital anomalies of the pelvic organs. This is a rapidly changing field; the development of fast-scanning techniques and contrast agents for the bowel should further improve the utilization of MR imaging in pediatrics.     

Nuclear magnetic resonance imaging of the liver: initial experience

Nuclear magnetic resonance (NMR) scans of the liver were obtained in 12 normal volunteers and 32 patients using a whole-body machine developed by Thorn-EMI Ltd., and the results were compared with x-ray computed tomography (CT). Two types of NMR scan, saturation-recovery and inversion-recovery, were performed in order to obtain values for the spin-lattice relaxation time, T1. Although the saturation-recovery scans show little soft-tissue detail, the inversion-recovery scans demonstrated the interlobar fissure, hepatic veins, portal veins, bile ducts, and gallbladder. In comparison with CT (Siemens Somatom 2), both types of NMR scan showed some blurring due to respiratory movement but much less linear artifact across the liver from the air-fluid interface in the stomach. Focal disease within the liver was demonstrated by both CT and NMR, although an area of focal atrophy and another of hepatic infarction were only recognized with NMR. In diffuse disease the pattern varied. In steatosis CT was virtually diagnostic, while NMR showed no specific features. In hemochromatosis, hepatitis, eight cases of cirrhosis, and one of Wilson disease, both techniques showed abnormalities of varying specificity. In two cases of cirrhosis and one of primary biliary cirrhosis, only the NMR scan was abnormal. Nuclear magnetic resonance images are now sufficiently anatomically detailed to permit serious comparisons with technically advanced computed tomography. The information revealed is fundamentally different and can be expected to have some diagnostic utility.     

Magnetic resonance imaging in pediatric vascular disease

Magnetic resonance imaging (MRI) was used to study eight children with known vascular disease proved by angiography. Congenital and acquired large vessel disease was equally well demonstrated noninvasively by both MRI and angiography, and in one patient MRI provided superior information about pulmonary artery patency.     

Magnetic resonance imaging in pediatric elbow fractures

Purpose: Magnetic resonance imaging (MRI) evaluation of pediatric elbow trauma with or without a visible fracture on radiography.

Material and Methods: MRI was performed in the acute phase in 25 children with an elbow injury. Nine patients with an elbow effusion only on radiographs and 16 with a fracture or luxation seen on radiographs underwent subsequent MRI. No sedation was used.

Results: MRI revealed eight occult fractures (89%) in seven out of nine patients who had only an effusion on radiographs. Based on MRI findings, septic arthritis was suspected in one patient. Two patients out of five with a supracondylar fracture on the radiograph had a cartilage lesion in the humerus. MRI depicted a 3-mm gap on the articular surface in two patients with a lateral condyle fracture, a more accurate fracture location in two patients than the radiographs, and an additional occult fracture in two patients. MRI showed a fracture not seen on radiographs in two of three patients with prior luxation.

Conclusion: MRI is a sensitive and accurate method in the diagnosis of pediatric elbow injuries, especially when only an effusion is present on radiographs. Occult fractures are more common in pediatric patients with elbow injury than reported earlier.     

Magnetic resonance urography: initial experience of a low-dose Gd-DTPA-enhanced technique

Contrast-enhanced magnetic resonance urography (MRU) is a promising tool in the evaluation of the renal collecting system, but it can be limited by T2^* effects resulting from hyperconcentrated gadolinium chelates. The aim of this study was to evaluate a low-dose dimeglumine gadopentetate (Gd-DTPA) MRU technique consisting of a dynamic fast low-angle-shot (FLASH) 2D sequence and a static fast imaging in steady state precession (FISP) 3D sequence for depicting the kidneys and urinary tract. The Gd-DTPA dose (0.01 mmol/kg) was established experimentally in a healthy volunteer study. Ninety-one patients presenting with various renal disorders were examined with a low-dose Gd-DTPA MRU and a T2-weighted turbo spin echo (TSE) MRU technique on a 1.5-T system. Image quality and diagnostic value were considered at least satisfactory in 98.9 % of the FLASH 2D studies, 83.5 % of the FISP 3D studies and 78.5 % of the TSE T2-weighted studies. Typical enhancement patterns were established for the renal cell carcinoma and transitional cell carcinoma. The major limitations were motion artefacts and insufficient hydration of the patients. Low-dose Gd-DTPA MRU appears to be a useful technique in the evaluation of the kidneys and urinary tract, especially in cases of renal tumours. Received: 26 February 1998; Revised: 25 January 1999; Accepted: 14 June 1999     

Magnetic resonance imaging of the thorax. Past, present, and future

Magnetic resonance imaging is a valuable modality of extreme flexibility for specific problem-solving capability in the thorax. This article reviews MR applications in the imaging of great vessels, which are currently the most important applications in the thorax; other established applications in the thorax; and pulmonary functional MR imaging.     

Nuclear magnetic resonance imaging of the thorax

Nuclear magnetic resonance (NMR) images of the thorax were obtained in ten normal volunteers, nine patients with advanced bronchogenic carcinoma, and three patients with benign thoracic abnormalities. In normal volunteers, mediastinal and hilar structures were seen with equal frequency on NMR images and computed tomographic scans. The hila were especially well displayed on spin-echo images. Spin-echo images showed mediastinal invasion by tumor, vascular and bronchial compression and invasion, and hilar and mediastinal adenopathy. Tumor and benign abnormalities could be separated from mediastinal and hilar fat because of their longer T1 times. Lung masses and nodules as small as 1.5 cm could be seen on the spin-echo images. NMR imaging shows promise for assessment of benign and malignant mediastinal, hilar, and lung abnormalities.     

Magnetic resonance imaging of the mediastinal vessels in pediatric patients

The appearance of new and better magnetic resonance imaging (MRI) techniques have made the MRI a very important imaging method for the evaluation of thoracic vessels in pediatrics. The 3D angio-MRI using GD is capable of clearly demonstrating the morphology of the aorta and pulmonary vessels. The MRI may significantly reduce the number of angiographies needed and, in some patients, may even provide additional information to the angiography.     

Magnetic resonance imaging of fetal anomalies in utero: early experience

Five cases of fetal dysmorphology were examined with high-resolution sonography and magnetic resonance imaging (MRI). Postpartum confirmation was available in all cases. The high contrast resolution of MRI resulted in clear depiction of the abnormalities, particularly dilated fluid-filled structures, whereas the real-time capability and spatial resolution of sonography permitted better appreciation of anatomic detail. While sonography will remain the primary imaging method for pregnancy, MRI appears to be a promising complementary technique in difficult cases.     

Magnetic resonance imaging of congenital heart disease in the pediatric patient

Current state-of-the-art MR imaging offers a high resolution evaluation of cardiac anatomy in the child with congenital heart disease. Although echocardiography remains the standard initial evaluation modality, MR imaging plays a key role in supplementing this information in the pediatric thorax. Although applications for this modality continue to be defined, some indications have become clear. The future of MR imaging promises better spatial resolution, faster image acquisition times, and in vivo spectroscopic capabilities.     

Driven equilibrium magnetic resonance imaging of articular cartilage: initial clinical experience

PURPOSE: To evaluate three-dimensional driven equilibrium Fourier transform (3D-DEFT) for image quality and detection of articular cartilage lesions in the knee. MATERIALS AND METHODS: We imaged 104 consecutive patients with knee pain with 3D-DEFT and proton density (PD-FSE) and T2-weighted (T2-FSE) fast spin echo. Twenty-four went on to arthroscopy. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) efficiency were measured. Subjective image quality, fat suppression, and cartilage thickness visibility were assessed. Cartilage lesions on 3D-DEFT and T2-FSE were compared with findings outlined in operative reports. RESULTS: SNR efficiency was higher for 3D-DEFT and PD-FSE than for T2-FSE (P < 0.02). 3D-DEFT and PD-FSE showed superior cartilage thickness visibility compared with T2-FSE (P < 0.02). T2-FSE showed better fat suppression and fewer image artifacts than 3D-DEFT (P < 0.04). 3D-DEFT had similar sensitivity and similar specificity for cartilage lesions compared with PD-FSE and T2-FSE. CONCLUSION: 3D-DEFT provides excellent synovial fluid-to-cartilage contrast while preserving signal from cartilage, giving this method a high cartilage SNR. 3D-DEFT shows the full cartilage thickness better than T2-FSE. T2-FSE had superior fat saturation and fewer artifacts than 3D-DEFT. Overall, 3D-DEFT requires further technical development, but is a promising method for imaging articular cartilage.     

Magnetic resonance microscopy of the rat thorax and abdomen

With magnetic resonance (MR) microscopy, high-resolution volumetric imaging (3DFT) of small animals is possible. Although these techniques are suitable for imaging the head and other small stationary objects, breathing and cardiac motion degrade the quality of body images. Scan synchronous ventilation and cardiac gating methods have been developed that permit acquisition of high-resolution images from anywhere in the body of small animals (150 to 400 g). Anesthetized rats were ventilated in synchrony with three-dimensional Fourier spin warp (3DFT) sequence (TR = 400 to 1000 ms, TE = 20 ms). Eight or 16 slices (1.2 or 2.5 mm thick) were acquired simultaneously. Effective pixel size was 200 X 200 mu. Imaging was performed in a 1.5 T, 1-m bore research system using a 28-cm diameter high field gradient coil and a 6-cm diameter radio frequency coil. For thoracic imaging, acquisitions were gated to the QRS of the ECG. Scan synchronous ventilation eliminated breathing motion artifacts and permitted visualization of peripheral vascular structures in the lung and liver. In images that were also cardiac gated, cardiac chambers and major thoracic vessels, including the coronary arteries, were well demonstrated. Thus, thoroughly characterized rodent models can now be studied with MR not only to explore noninvasively the intricacies of mammalian pathomorphology, but also to test the capabilities of MR and aid in interpreting MR data.