The effect of chemical shift misrepresentation on cortical bone thickness on MR imaging.
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Bone and Bones↗
Biomedical subjects
D L Burk
Publications and source records attributed to D L Burk.
High resolution MR imaging of the knee.
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Humans↗
Magnetic resonance imaging of spinal dysraphism.
MR imaging has become the definitive diagnostic procedure for the evaluation of suspected spinal dysrhaphic processes. Techniques for spinal MR imaging are discussed and MR findings in patients with surgically verified dysrhaphic spinal lesions are reviewed.
Child↗
Pediatric musculoskeletal magnetic resonance imaging.
MRI has demonstrated clinical applicability and improved diagnostic capability in the musculoskeletal system to a degree rivaling its success in the neurologic system. For certain regions such as the joints, the superficial nature of these structures is ideal for the application of localized radiofrequency coils, enabling considerably improved signal, spatial resolution, and detectable contrast. The multiplanar capability is often invaluable in assessing such regions as the weight-bearing surfaces of the hips. It has been shown to be the most sensitive single test for diagnosing avascular necrosis, and has yielded very high resolution images of the internal architecture of the joints and soft tissues in an entirely noninvasive manner and without the need for the administration of exogenous contrast agents. Short TE images are quite useful in evaluating fatty background regions of interest, such as the bone marrow and subcutaneous tissue, whereas long TR and TE studies are frequently more suitable for soft tissue pathology. The lack of ionizing radiation and the continued failure of intensive research to disclose any deleterious effects at the levels used for clinical diagnostic imaging make this tool especially appealing for application to the pediatric population. With the continual development of new pulsing sequences, contrast agents, and further advances in imaging/spectroscopic correlation, magnetic resonance imaging of the musculoskeletal system is ensured of a solid role in the clinical diagnostic evaluation of the pediatric population.
Bone Diseases↗
Strategies for musculoskeletal magnetic resonance imaging.
There is a broad range of clinical applications for MRI in the diagnosis of musculoskeletal disease, and the emphasis in this article is on the evaluation of the joints and extremities. A discussion of basic principles, including radiofrequency coils, positioning, pulsing sequences, imaging planes, and technical parameters is followed by discussions of tailored approaches to the evaluation of mass lesions and joint pathology for specific regions of the musculoskeletal system. In the final section, consideration is given to the overall role of MRI in the diagnosis of musculoskeletal disorders with respect to other established imaging modalities.
Bone Cysts↗
The magnetic resonance imaging appearance at 1.5 tesla of cartilaginous tumors involving the epiphysis.
Three cases of lytic, calcified epiphyseal lesions with plain film and computed tomography features suggestive of chondroblastoma were imaged by magnetic resonance imaging. Histopathologic correlation was obtained in each case. Two cases of chondroblastoma showed low signal intensity on both short (TR600/TE20ms) and long (TR2500/TE80ms) spin echo (SE) images. The third case, a clear cell chondrosarcoma, demonstrated increased signal intensity on moderately T2 weighted (TR2500/TE40ms) images. These findings suggest that magnetic resonance imaging may be helpful in distinguishing these lesions.
Adolescent↗
Spinal and paraspinal neurofibromatosis: surface coil MR imaging at 1.5 T1.
Twelve patients with neurofibromatosis affecting the spine and paraspinal regions were examined with magnetic resonance (MR) imaging performed using a 1.5-T magnet, surface coils, and spin-echo pulse sequences. In all 11 patients with neurofibromas, these tumors had slightly greater signal intensity than muscle on T1-weighted images and markedly increased signal intensity on T2-weighted images. In seven patients central areas of decreased signal intensity within the neurofibromas were demonstrated on T2-weighted images. In one patient these central areas corresponded pathologically to relatively fibrous components of the tumors surrounded by myxoid matrix. Five patients had extensive plexiform neurofibromatosis, one had lateral meningoceles, one had a neurofibrosarcoma, three had extradural spinal cord compression, and two had cystic intramedullary tumors of the spinal cord. The ability to obtain high-resolution, multiplanar images in a noninvasive fashion makes surface coil MR imaging an ideal technique for evaluating neurofibromatosis involving the spinal cord, spinal canal, and paraspinal soft tissues.
Humans↗
The biophysical basis of tissue contrast in extracranial MR imaging.
So that radiologists can understand better the differences between tissues that determine MR image contrast, the biophysical basis of proton-MR tissue contrast is reviewed. Differences in the molecular sizes of water, fat, and protein macromolecules affect the rate of molecular motion, which in turn influences relaxation times. Differences in the physical state of water within tissues determine the extent to which the motion of water is restricted by binding to hydrophilic macromolecules (e.g., protein), which in turn causes variable amounts of T1 and T2 shortening. Understanding these concepts and knowing the location in the body of free water, cellular tissues, fat, collagen, bone, and tissue iron improve the radiologist's ability to extract useful information from MR images.
Adipose Tissue↗
Radiology of wrist and hand injuries in athletes.
Traumatic injuries are a major cause of hand and wrist pain in athletes. Wrist injuries include fractures, dislocations, and instability patterns. Hand injuries include tendon injuries, ligamentous injuries, and fractures. In this article we have presented the radiographic appearance of the more common of these injuries.
Athletic Injuries↗
Acetabular fractures: three-dimensional computer tomographic imaging and interactive surgical planning.
Three-dimensional imaging can provide a valuable perceptual link between conventional radiographs and axial computed tomographic scans in the evaluation of complex acetabular fractures. With the 3D83 computer program, three-dimensional images can be generated to correlate with standard radiographic views. Unique images can also be created that offer perspectives unobtainable by conventional radiography. More sophisticated interactive techniques allow computer simulation of surgical approaches.
Acetabulum↗
1.5-T surface-coil MRI of the knee.
Five normal knees and 20 knees with suspected abnormalities involving the menisci or articular surfaces were examined with high-resolution surface-coil MRI. Surgical correlation was available in 15 cases. Signal-to-noise ratios were optimized using a field strength of 1.5 T and a round 7.6-cm surface coil. Spatial resolution was maximized by using fields of view reduced to as small as 8 cm. Separate examinations of the medial and lateral joint compartments were performed with the surface coil positioned vertically adjacent to the meniscus of interest. Ten meniscal tears were identified using sagittal and coronal images. T1-weighted images were adequate to detect most meniscal tears, and T2-weighted images were useful for providing an "arthrogram effect" in the presence of a joint effusion. Extrameniscal lesions that were examined included osteonecrosis of the femoral condyle, subchondral cysts, rheumatoid arthritis, degenerative arthritis, and anterior cruciate ligament tears. MRI was useful in determining the integrity of articular cartilage overlying defects in the subchondral bone and in detecting gross cartilage lesions in arthritis, but was less sensitive than arthroscopy in evaluating moderate changes in the hyaline cartilage.
Arthritis, Rheumatoid↗
Three-dimensional computed tomography of acetabular fractures.
Computer programs that produce 3D surface reformations from sets of contiguous axial CT scans were used in evaluating a variety of acetabular fractures in 20 patients. The 3D images were easily correlated with plain radiographs, and new views were produced that provided a unique perspective not obtainable by conventional radiography. The 3D images were useful in complex displaced fractures in cases in which the interpretation of plain radiographs was difficult. Plain radiographs and conventional CT scans were more sensitive than the 3D images in detecting undisplaced fractures.
Acetabulum↗
Pelvic and acetabular fractures: examination by angled CT scanning.
A new technique of direct angled CT scanning of pelvic and acetabular fractures is presented that allows visualization of the entire ring on a single image or two adjacent images.
Acetabulum↗
Observations at sea level and altitude on basal metabolic rate and related cardio-pulmonary functions.
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Adolescent↗
MR imaging of shoulder injuries in professional baseball players.
Magnetic resonance (MR) imaging was used to evaluate the shoulders of 10 symptomatic professional baseball players and one asymptomatic player, with surgical correlation in six cases and arthrographic correlation in two cases. Seven small rotator cuff tears measuring 0.5-1 cm were identified on MR images, with arthrographic and surgical confirmation of these findings in two patients and surgical confirmation only in three patients. Cortical irregularity and/or subchondral cyst formation at the posterior aspect of the greater tuberosity near the insertion site of the infraspinatus tendon was found in five of the seven players with rotator cuff tears. Similar findings were noted in the asymptomatic volunteer and in one of the three players without cuff tear, who also had irregular thickening of the posterior capsule. These findings are believed to represent chronic avulsive changes resulting from the deceleration stresses of the follow-through motion.
Adult↗
Effect of MR imaging on the normal human pineal body: measurement of plasma melatonin levels.
Production of melatonin, a hormone synthesized and secreted by the pineal body, has been suppressed by electromagnetic fields in some but not all animal studies. Magnetic resonance (MR) imaging at 1.5 T was evaluated for its ability to modulate the level of melatonin in eight male volunteers. Subjects were exposed to three conditions, respectively, between 1:00 and 2:00 AM on different nights: (a) a series of routine MR pulse sequences for brain imaging in dark conditions, (b) dark control conditions, and (c) bright-light control conditions. Plasma was analyzed for melatonin and cortisol levels. Hormonal changes were analyzed by one-factor repeated measures within-subject analysis of variance. These conditions were associated with significant differences in melatonin levels: F(2, 6) = 7.95, and P = .021. Subjects exposed to darkness showed a typical increase in melatonin concentration. Subjects exposed to bright light showed a characteristic suppression of melatonin concentration. Those exposed to the MR imaging fields showed an increase in melatonin level similar to that seen in the dark control condition. Light and MR imaging had no significant effects on cortisol levels. Thus, MR imaging at field strengths known to modulate melatonin levels in rats did not suppress melatonin production in human subjects.
Adult↗
Femoral head avascular necrosis in sickle cell anemia: MR characteristics.
Since considerable expansion of hematopoietic marrow occurs in patients with sickle cell anemia (SCA), magnetic resonance images of 20 hips in 10 patients with known homozygous SCA were reviewed to determine a) if low signal hematopoietic marrow extended into the femoral capital epiphysis and b) if the MR characteristics of avascular necrosis (AVN) differed depending on the type of epiphyseal marrow. Our results revealed variable epiphyseal marrow type; mixed (fatty and hematopoietic) marrow (42%), fatty marrow (32%), hematopoietic marrow (16%) and hemosiderotic marrow (10%). AVN occurred irrespective of the underlying marrow. Segmental areas of low signal intensity in variable shapes (ring, band, crescent or large homogeneous area) was the most consistent MR manifestation of AVN in SCA. A low signal intensity peripheral rim surrounding a central zone, isointense with epiphyseal marrow on T1 and T2 weighted images, was most frequently observed similar to that described in patients without hemoglobinopathy. The notable difference, however, was of segmental areas within the same femoral head that demonstrated variable central zone signal on T2 weighted images. Further, while an increase in hip joint fluid is commonly seen with both early and advanced AVN in patients without hemoglobinopathy; it was increased in only one hip in patients with SCA. The observed differences in MR characteristics may be due to different pathophysiology of AVN in patients with SCA.
Adolescent↗
Multiple spin-echo MR imaging of the body: image contrast and motion-induced artifact.
For a given TR and TE, image quality changes when the number of spin echoes obtained is varied. To investigate the importance of this in clinical imaging, a total of 4 patients and 9 volunteers had MRI examinations of the abdomen (n = 7) and/or pelvis (n = 8) which included at least 2 sequences with identical TR (2000 or 2500 ms), TE (80 ms) and other parameters, but with a different series of refocusing pulses. Sequences included single-echo (S), asymmetric and symmetric double-echo (AD and SD) and quadruple-echo (Q) techniques. Image contrast and severity of motion-induced artifact was measured via blind examination by 3 independent MRI radiologists and calculation of signal-difference, signal-difference-to-noise ratios and intensity of motion-induced "ghost artifact." The order of decreasing signal differences was S, SD, AD and Q, and all of three liver lesions were better seen with S than with SD techniques. These observations are consistent with signal loss from cumulative inaccuracies from multiple 180 degrees RF pulses. The order of increasing intensity of ghost artifact was Q, SD, AD and S, consistent with the beneficial motion artifact-reducing effects of even-echo rephasing. Knowledge of these effects of multi-echo imaging allows one to make informed decisions about imaging protocols rather than to simply obtain multiple echoes "because they are free."
Abdomen↗