The combination of positron emission tomography (PET) and MRI is highly desirable since the two techniques produce complementary data; PET allows the distribution of minute concentrations of positron-emitting radionuclide tracers to be mapped, while MRI can provide anatomical data with myriad soft tissue contrasts. MRI and PET data can be coregistered to provide valuable diagnostic information. A hybrid PET-MRI system would make the coregistration process more simple, and simultaneous acquisition of the PET and MRI data decreases the duration of scanning.Both PET and MRI require detectors to be placed optimally around the region of interest to maximize performance. MRI needs uniform excitation over the whole sample, and hence larger transmitter coils, but close coupling of the receiver to maximize signal to noise. The PET detector measures γ rays emanating from the sample and requires minimum attenuating or scattering material in the line of sight. The detector ring aperture is a compromise between close coupling to maximize sensitivity and a larger
The magnetic resonance imaging (MRI) features of a rheumatoid arthritic geode are presented. Development of such a cyst from before x ray diagnosis to its coalescence with the wrist joint is described. The evidence suggests that these juxta-articular cysts are not merely an intrusion of the synovial cavity into the bone marrow but start as isolated structures beneath the subchondral bone.A number of authors have reported arthritic changes in bones and joints using magnetic resonance imaging (MRI) techniques.' 2 The exciting potential of MRI is its ability to disclose both bone surface and intra-articular material, such as cartilage, synovial membrane, and synovial fluid. As part of an extended MRI study to characterise the disease both qualitatively and quantitatively, through spin-lattice (T1) and spin-spin (T2) relaxation time measurements, we describe the findings for one patient with rheumatoid arthritis whose MRI scans showed a cyst or geode in the right wrist. In addition, we have made quantitative measurements of T1 from the geode and surrounding tissues over a period of two years. The left wrist developed a similar cyst during the study and was also scanned with MRI. The investigation of this patient, we believe, sheds some light on the development of geodes in general. The MRI system was built in-house3 4 and is based on a 180 mm bore 0 5 T superconducting magnet, which enables images of the hand and wrist to be generated. Patients are able to sit comfortably with their hands in the magnet at the centre of the field. It is necessary to enclose the patient in an electrically screened room to eliminate extraneous radiofrequency signals from the system. All the images generated are from sections of the wrist about 3-5 mm thick. The images displayed here are obtained using saturation recovery sequences (TR=800 ms). Quantitative measurements were obtained by calculating T1 values of specific areas using both saturation and inversion recovery sequences.5Case report A 41 year old white woman with a six year history of classical seropositive rheumatoid arthritis,6 responding to penicillamine 375 mg a day, had pain and swelling in the wrists. At the onset of her arthritis she had been treated with azathioprine 50 mg twice daily and corticotrophin (ACTH) 20 units daily. The ACTH was reduced to 20 units on alternate days after six months and ultimately withdrawn after four years. The azathioprine was withdrawn after three years and treatment with penicillamine started because of reactivation of synovitis in her wrists and hands. The symptoms and signs regressed until she relapsed again with painful wrists in March 1987.Physical examination at that time showed synovial thickening of both wrists with pain and limitation of movement. The right wrist flexed to 200, the left to 55°. Extension was equal in both at 50°. Radial and ulnar deviation in the right wrist was 200 and in the left wrist it was 30°.Investigations at that time showed haemoglobin 132 g/l, white blood cell count 9*1 x 109/1, erythrocyte se...
The magnetic resonance imaging features of the wrist of a patient suffering from the arthropathy of haemochromatosis are presented. It is apparent that the deposition of iron within the bone marrow is focal in origin and may be associated with cyst formation. In addition, changes in serum ferritin levels with treatment suggest that the deposition is irreversible. Studies of two other patients with haemochromatosis without cyst formation in the wrists did not yield similar artefacts, in spite of having high ferritin levels and arthritis.
High-resolution magnetic resonance imaging (MRI) of the interphalangeal joints of the fingers is being employed to study arthritis. To facilitate this research, a clear understanding of the structures visualisable by MRI is necessary. A gradient echo (GE) sequence was developed that produced good contrast between cartilage and other joint structures. These detailed images, with an in-plane resolution of 200 x 100 microns, enable resolution of three cartilage zones which can be interpreted as a superficial layer at the cartilage/cartilage interface, an intermediate layer and calcified cartilage in contact with bone; these correlate well with known anatomy. Further analysis of the images indicates that although a chemical shift artifact causes changes in the images at the field strength used (0.5 T), it does not cause enough distortion to necessitate suppression of the effect. Furthermore, the only detectable susceptibility artifact at these low field strengths was a loss of signal in bone trabeculae at the bone/cartilage interface. There is clearly potential in the study of the articular structures, in particular cartilage, in detail, using high-resolution MRI.
A programmable preemphasis system has been developed for eddy-current compensation in gradient sets with or without active screening. Preemphasis parameters are nonvolatile but can be changed rapidly when working with interchangeable gradient sets. The design allows easy retrofit to existing systems. A method for setting the preemphasis is presented, together with specimen results.
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