Atrial emptying with orthotopic heart transplantation using bicaval and pulmonary venous anastomoses: a magnetic resonance imaging study.

OBJECTIVES: We hypothesized that orthotopic heart transplantation with bicaval and pulmonary venous anastomoses preserves atrial contractility. BACKGROUND: The standard biatrial anastomotic technique of orthotopic heart transplantation causes impaired function and enlargement of the atria. Cine magnetic resonance imaging (MRI) allows assessment of atrial size and function. METHODS: We studied 16 patients who had undergone bicaval (n = 8) or biatrial (n = 8) orthotopic heart transplantation without evidence of rejection and a control group of 6 healthy volunteers. For all three groups, cine MRI was performed by combining coronal and axial gated spin echo and gradient echo cine sequences. Intracardiac volumes were calculated with the Simpson rule. Atrial emptying fraction was defined as the difference between atrial diastolic and systolic volumes, divided by atrial diastolic volume, expressed in percent. All patients had right heart catheterization. RESULTS: Right atrial emptying fraction was significantly higher in the bicaval (mean [+/- SD] 37 +/- 9%) than in the biatrial group (22 +/- 11%, p < 0.05) and similar to that in the control group (48 +/- 4%). Left atrial emptying fraction was significantly higher in the bicaval (30 +/- 5%) than in the biatrial group (15 +/- 4%, p < 0.05) and significantly lower in both transplant groups than in the control group (47 +/- 5%, p < 0.05). The left atrium was larger in the biatrial than in the control group (p < 0.05). Cardiac index, stroke index, heart rate and blood pressure were similar in the transplant groups. CONCLUSIONS: Left and right atrial emptying fractions are significantly depressed with the biatrial technique and markedly improved with the bicaval technique of orthotopic heart transplantation. The beneficial effects of the latter technique on atrial function could improve allograft exercise performance.

Temperature changes caused by MR imaging of the brain with a head coil.

Tissue heating caused by exposure to RF radiation is a primary safety concern in MR imaging. Therefore, to determine temperature changes caused by high field strength MR imaging of the brain with a head coil, we measured body and skin temperatures in 35 patients immediately before and after clinical MR imaging. MR imaging was performed with a 1.5 T MR system using a 28-cm, open-bore RF transmit/receive head coil specifically designed for examinations of the brain. The average body temperature was 36.6 +/- 0.2 degrees C before MR imaging and 36.6 +/- 0.2 degrees C immediately afterward (mean +/- SD, p = not significant). The average forehead skin temperature increased from 32.6 +/- 0.6 to 32.8 +/- 0.5 degrees C (p less than .01), and the average outer canthus skin temperature increased from 32.1 +/- 0.6 to 32.7 +/- 0.6 degrees C (p less than .01) after MR imaging. The highest skin temperature recorded was 34.2 degrees C, and the largest temperature change was +2.1 degrees There were no statistically significant changes in the average skin temperatures of the upper arm and hand. We conclude that patients undergoing MR imaging of the brain with a head coil at the RF radiation exposure we studied experience no significant changes in average body temperature and statistically significant increases in local (i.e., areas within the head coil) skin temperatures. The observed elevations in skin temperatures were physiologically inconsequential.

Development and clinical application of kinematic MRI of the patellofemoral joint using an extremity MR system.

PURPOSE: Kinematic magnetic resonance imaging (MRI) of the patellofemoral joint provides diagnostic information pertaining to patellar alignment and tracking during the earliest increments of joint flexion, when abnormalities that affect this joint are the most apparent. Recently, a low-field strength (0.2 Tesla) dedicated extremity MR system has been designed, such that only the body part that is being imaged is placed inside of the magnet bore. The purpose of this investigation was to develop a kinematic MRI technique for the patellofemoral joint using the extremity MR system and to apply this procedure in the clinical setting. METHODS: An incremental, passive positioning kinematic MRI technique was developed for the patellofemoral joint that involved obtaining three different axial section locations with the patellofemoral joint extended and then imaging these same section locations repeatedly as the patellofemoral joint was flexed in four increments up to 36 degrees of flexion. MR images were obtained using a T1-weighted spin echo sequence. Five (10 PFJ) asymptomatic volunteers and nine patients (9 PFJ) with patellofemoral joint symptoms were studied. RESULTS: Volunteers had normal kinematic MRI examinations. Seven patients had lateral subluxation, and two patients had excessive lateral pressure syndrome. Two patients with lateral subluxation seen on their kinematic MRI studies had Merchant views (x-rays obtained at 45 degrees) that showed "normal" patellar alignment, illustrating the importance of imaging the patellofemoral joint at 30 degrees or less. CONCLUSIONS: A kinematic MRI technique was successfully developed for the low-field extremity MR system and utilized for clinical applications. This procedure may be used to determine the presence and severity of patellar malalignment and abnormal tracking patterns.

Magnetic resonance imaging of shoulder impingement.

MRI is an accurate technique for diagnostic evaluation of a broad spectrum of shoulder pathology. In particular, rotator cuff injuries are a frequent cause of pain and disability. The mechanism of injury to the supraspinatus tendon usually begins with microscopic tears of fibers of the triple helix collagen molecule. This leads to increased motion of the bound water within the collagen molecule that lengthens the effective T2 of the tendon, allowing short TE imaging sequences to detect signal in abnormal tendons. Clinically significant disease probably does not occur without frank collagen rupture, and the associated collection of free water within the severely diseased tendon presents as high signal on long TE images. Thus, the clinical significance of tendon disease is best evaluated on long TR, long TE image acquisitions. Any process that accelerates microscopic tear formation or delays repair can increase a patient's risk of supraspinatus tendon tears. Impingement is the most important process accelerating microscopic tear formation. MRI's multiplanar, tomographic imaging ability markedly improves the ability to sensitively and specifically detect bony impingement. Hopefully, this will allow earlier arthroscopic decompression and improved patient prognosis with impingement.

Alterations in body and skin temperatures caused by magnetic resonance imaging: is the recommended exposure for radiofrequency radiation too conservative?

Increases in tissue temperature caused by exposure to radiofrequency (RF) radiation are a primary safety concern of magnetic resonance imaging (MRI). Therefore, body and skin temperatures were measured in six subjects before (20 min), during (30 min) and after (20 min) MRI procedures performed at specific absorption rates (SARs) six to 10 times higher than the limit recommended by the UK National Radiological Protection Board. Body temperature was unchanged throughout the experiment. Abdominal skin temperature increased significantly (p less than 0.05) during MRI, decreased significantly post-MRI, but was still significantly (p less than 0.05) higher than baseline. The highest abdominal skin temperature recorded was 36 degrees C. Upper arm, forearm and chest skin temperatures increased significantly (p less than 0.05) during MRI and remained elevated post-MRI. The highest skin temperatures recorded on the upper arm, forearm and chest were 38.1, 36.0 and 34.5 degrees C, respectively. Thigh and calf skin temperatures were not significantly changed during MRI. These alterations in tissue temperatures were physiologically trivial and easily tolerated by the subjects, suggesting that the recommended exposure to RF radiation during MRI of the body for patients with normal thermoregulatory function may be too conservative.

Pathogenesis of rotator cuff disorders. Magnetic resonance imaging characteristics.

In summary, rotator cuff pathology is a continuum that begins with degeneration of collagen fibers at a rate that exceeds that of repair. The degenerative process is accelerated with aging, chronic inflammatory diseases, impingement, and repetitive activity. A tendon weakened by disease may then be torn by routine physical activity. MR imaging can help predict which patients are at risk for rotator cuff disease because of abnormal anatomy and can detect the disease at an early stage so that the progression may be altered before a tear occurs.

Musculotendinous injury.

Over the past decade, MR imaging has become one of the most valuable imaging tools for evaluation of musculoskeletal pathology. This is due to its high sensitivity to the vast majority of acute and chronic musculoskeletal injuries and the starting anatomic clarity provided. The latter feature allows definition of characteristic injury patterns, which is the key to most diagnoses and also usually allows accurate grading of the severity of injuries. Careful attention to imaging technique and the specific architectural patterns of musculotendinous disruption by the imaging specialist will result in accurate diagnoses for the patient and referring physician.

Magnetic resonance arthrography of the shoulder.

Recently, there have been attempts to improve the accuracy of MR imaging by distending the glenohumeral joint with fluid prior to imaging. This article reviews the techniques employed in performing MR arthrography, imaging characteristics of MR arthrography, and diagnostic use of the procedure.

MRI of the knee in diffuse pigmented villonodular synovitis.

Magnetic resonance imaging (MRI) was performed on 11 patients with surgically proven pigmented villonodular synovitis (PVNS) of the knee. PVNS was diagnosed on the basis of presence of hemosiderin, joint effusion, and hyperplastic synovium without significant joint destruction. MRI provided a detailed map of the distribution of the disease within the joint, emphasizing the common occurrence of the disease behind the cruciate ligaments and in synovial cysts in the popliteal fossa. MRI aided in preoperative planning and postoperative follow-up for residual and recurrent disease. Nine additional cases of joint hemorrhage, hemophilia, desmoplastic tumors, and synovial chondromatosis were included to delineate differential diagnostic criteria.

The painful shoulder: diagnosis and treatment.

The shoulder is one of the most complex joints in the body requiring coordinated, functioning muscles and joints to have a fluid, rhythmic motion. The shoulder consists of the glenohumeral (GH) joint, the acromioclavicular (AC) joint, the scapulothoracic (ST) joint, and the sternoclavicular (SC) joint. This article will examine the shoulder anatomy, clinical syndromes, and treatment for common shoulder disorders.

Comparison of magnetic resonance imaging and radionuclide imaging in the evaluation of renal transplant failure.

Magnetic resonance imaging (MRI) was compared with radionuclide scintigraphy (RNS) in 16 patients with renal transplants undergoing renal failure to determine which modality could best discriminate between rejection, acute tubular necrosis (ATN), and cyclosporin nephrotoxicity (CN). Although all rejecting transplants had reduced corticomedullary differentiation (CMD) on T1-weighted MR images, four of five cases of ATN had appearances that could not be distinguished from rejection. A normal CMD suggests nonrejection, but diminished CMD is nonspecific. Tc-99m DTPA/I-131 hippuran RNS was superior to MRI in differentiating rejection from ATN. Although ATN and CN have similar RNS patterns, this distinction can usually be made based on the clinical time course. Other potential uses of MRI in the evaluation of the renal transplants are discussed.

The impact of MRI on our understanding of the pathology of sports injuries.

NMR imaging has become an important diagnostic tool in the evaluation of musculoskeletal disease. However, its ability to evaluate pathogenic mechanisms of disease may eventually have even a greater impact on patient care. NMR imaging has significantly affected our understanding of the clinical significance of meniscal tears and appropriate patient management. It has also extended our understanding of the prevalence and importance of x-ray and arthroscopically occult bone, tendon and ligament injuries. By knowing the pathogenic mechanisms of disease, we can more reliably diagnose and treat pathology. In particular, many horizontal degenerative tears in older patients may be asymptomatic and are best left in place. Many acute tears may be best treated with immediate meniscal repair. MR imaging can reliably different these tear types with non-invasive imaging. MR's ability to detect bone injuries may lead to aggressive early non-weightbearing on injured bone, thereby preserving the subchondral bone from collapse and the joint from secondary osteoarthrosis. MRI's ability to detect and stage degenerative tendonosis of tendons and ligaments, such as the rotator cuff, may lead to arthroscopic decompression or debridement which provides symptomatic relief and may preserve and protect the intact cuff.

Magnetic resonance imaging of the knee: evaluation of meniscal disease.

The advent of MR imaging in musculoskeletal radiology, coupled with advances in the past decade in the treatment of knee disorders, has fueled an explosion of interest in MR imaging of the knee. Evaluation of meniscal pathology has been central to this development. The accuracy of MR imaging in the diagnosis of meniscal tears is now well established; attention has more recently been focused on the prevalence, natural history, and clinical significance of other intrameniscal signal abnormalities, as well as on the postoperative meniscus. Nonmeniscal knee disorders that may clinically mimic meniscal lesions are also reliably diagnosed with MR imaging. Technical advances in pulse sequences allow knee imaging with enhanced accuracy and efficiency.

Corneal temperature changes induced by high-field-strength MR imaging with a head coil.

High-field-strength/high-frequency magnetic resonance (MR) imaging systems can cause tissue heating. Since the eye is particularly susceptible to temperature elevations because of its relatively poor blood supply, the authors measured corneal temperatures in 33 patients immediately before and after MR imaging performed with a 1.5-T (64-MHz) imager and a transmit/receive head coil at estimated peak specific absorption rates (SAR) ranging from 2.54 to 3.05 W/kg. There was a statistically (P less than .001) significant increase in the average corneal temperature (32.7 degrees C +/- 0.7 before imaging, 33.2 degrees C +/- 0.5 after). The changes in corneal temperature ranged from 0.0 degrees C to 1.8 degrees C (mean, 0.5 degrees C), and the highest corneal temperature measured after imaging was 34.4 degrees C. In animal models, the eye temperature threshold for radio frequency-induced cataractogenesis is between 41 degrees C and 55 degrees C. The authors conclude that clinical MR imaging with use of a head coil at the SARs studied causes relatively minor increases in corneal temperature that do not appear to pose any thermal hazard to ocular tissue.

High-field-strength MR imaging and metallic biomedical implants: an ex vivo evaluation of deflection forces.

Ferromagnetic biomedical implants are considered a contraindication for MR imaging primarily because of the potential hazards associated with their movement or dislodgment. Many metallic biomedical implants are composed of nonferromagnetic materials and do not present a danger to patients during MR imaging. Therefore, to evaluate the ferromagnetic qualities of 36 different metallic biomedical implants (four aneurysm clips, six hemostatic clips, four dental implants, seven prosthetic heart valves, eight orthopedic prostheses, one artificial urinary sphincter, three contraceptive diaphragms, and three cerebral ventricular shunt tube connectors) not previously evaluated with a high-field-strength MR system, we measured deflection forces at the portal of the magnet of a 1.5-T MR system. Fourteen of the 36 metallic biomedical implants were determined to be ferromagnetic as indicated by their deflection in the static magnetic field. However, only the four aneurysm clips (Drake, Mayfield, McFadden, and Sundt-Kees) had sufficient ferromagnetism to warrant exclusion of patients with these implants from imaging with a 1.5-T MR system because of the possibility of movement or displacement. The calculated deflection forces for these aneurysm clips were comparable with previously reported values of certain aneurysm clips that have been designated to present a risk for patients undergoing MR imaging. Patients with 32 of 36 metallic biomedical implants tested can be safely imaged with high-field-strength MR systems.

Temperature, heart rate, and blood pressure changes associated with clinical MR imaging at 1.5 T.

Temperature, heart rate, and blood pressure responses to high-field-strength magnetic resonance (MR) imaging were studied in 50 patients who underwent procedures at exposures to radiofrequency radiation above the present recommended whole-body average specific absorption rate (SAR) of 0.4 W/kg. Body temperature significantly increased an average of 0.2 degrees C. The highest body temperature recorded after MR imaging was 37.5 degrees C. There was no significant correlation between the change (before and after imaging) in body temperature and whole-body average SARs. Changes in skin temperatures were variable, depending on anatomic site. The largest change was 3.5 degrees C, and the highest skin temperature recorded after imaging was 35.1 degrees C. There was a modest correlation between the change in skin temperatures and whole-body average SARs. Average heart rate and average mean blood pressure measured immediately before imaging were not significantly different afterward. High-field-strength MR imaging at the whole-body average SARs of 0.42-1.2 W/kg studied was not associated with any temperature- or hemodynamic-related deleterious effects.

Magnetic resonance imaging of hereditary hernias of the peroneus longus muscle.

Herniation of the left peroneus longus muscle was present in three male members of the same family, being the first reported case of this condition in a familial setting. The hernias were differentiated from other mass lesions and varices by magnetic resonance imaging. The images demonstrated a fascial defect originating in the area where vessels and nerves penetrate the fascia, suggesting that the three men had a congenital weakness in the fascia.

Aneurysm clips: assessment of magnetic field interaction associated with a 0.2-T extremity MR system.

Twenty-two different aneurysm clips were tested by means of the deflection angle test for magnetic field interaction associated with a 0.2-T extremity magnetic resonance (MR) system. At the opening of the magnet bore and 5 inches (13 cm) and 10 inches (25 cm) away from the magnet bore, respectively, deflection angles were 14 degrees, 2 degrees, and 0 degree for one clip and were 17 degrees, 4 degrees, and 0 degree for another, and were 0 degree for the remaining 20 clips. Because the patient's head does not enter the magnet bore, extremity MR imaging of patients with the aneurysm clips evaluated in this study should be safe.