Biomedical subjects
Publications and source records attributed to A G Collins.
A 3-4% change in signal intensity correlated with visual stimulation was observed in the occipital lobes of three normal volunteers examined with MRI at 0.15 T using fluid attenuated inversion recovery pulse sequences. Similar results were observed at 1.0 T. A double difference technique in which difference images are themselves opposed provided an increase in sensitivity.
OBJECTIVE: To determine whether electric current can be induced in intracardiac catheters, thermistor wires and pacing electrodes in patients during magnetic resonance imaging (MRI). DESIGN: Prospective laboratory study. SETTING: Postgraduate medical school hospital. SUBJECTS: A sheep heart model. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Voltage generated by saline 0.9% flowing through a magnetic field and distribution of current from a catheter tip within a sheep heart model were measured in a 0.15 Tesla MRI system. Resistance of loops formed by pacing wires, a pacing electrode, and a thermistor wire were measured in saline 0.9%. Effects of rapidly changing magnetic fields and the movement of the beating heart on epicardial pacing wires were calculated theoretically. A flow of 200 mL/min of saline 0.9% induced a current of 0.1 microampere (microA) (at 0.15 Tesla). From magnetic resonance images we derived a current density of approximately 0.004 microA/mm2 (at 0.15 Tesla). Internal resistance of pacing catheters and thermistor wires was > 1 megaohm (M omega). The maximum currents calculated (for a higher field strength of 1.5 Tesla) in a circuit formed by epicardial pacing wires were 80 microA, induced by the beating heart moving the wires through the magnetic field and 46 microA, induced by the rapidly changing magnetic fields. CONCLUSIONS: Current generated by flow of conducting fluid should be safe. Pacing catheters and thermistor wires should be safe if well insulated and disconnected from external electric connections. However, current induced in epicardial pacing wires may be a hazard, and precautions should be taken. External wire tips must be separated, insulated, and coiled to lie along the axis of the magnetic field. Electrocardiography is required, and defibrillation equipment should be available.
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Phosphorus-31 magnetic resonance spectroscopy of the human liver was undertaken in 28 healthy adult individuals and in 49 patients with liver disease of varying aetiology. Data localised to the liver were obtained using chemical shift imaging techniques. The mean (+/- 1 S.D.) of the peak area ratio phosphomonoesters (PME)/phosphodiesters (PDE) in healthy adult individuals, from spectra obtained with pulse angle 45 degrees and repetition time 1 s, was 0.24 +/- 0.07. The intra-examination variability of this ratio was 20%, the intra-subject variability 27% and the inter-subject variability 32%. An increase in the PME/PDE was observed in the 31P hepatic MR spectrum from primary or secondary tumours in all 17 patients studied, which invariably represented an increase in PME/ATP and, in some cases, a reduction in PDE/ATP. The spectra did not show aetiological characteristics. A non-specific elevation in PME/PDE was also observed in the 31P hepatic MR spectra of 10 (40%) of 25 patients studied who had diffuse liver diseases, such as cirrhosis and infiltrating malignancies. The spectral pattern did not distinguish between diseases of varying aetiologies, but there was a linear correlation between increasing PME/PDE and a reduction in plasma albumin concentrations (p = 0.03). In three patients with hepatic malignancy and abnormal hepatic 31P-MRS, marked spectral changes were observed after successful treatment to debulk the tumour. Only minor changes were observed in the abnormal spectrum of a fourth patient in whom treatment was unsuccessful. Hepatic 31P-MR spectroscopy may prove useful for monitoring disease processes and treatment effects in well characterised patient populations.
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Three young men developed multiple firm asymptomatic nodules confined to the shaft of the penis. Skin biopsies from all 3 cases showed prominent necrobiotic granulomas indistinguishable from granuloma annulare. One of the patients had repeated recurrent nodules confined to the penis which were removed surgically over a period of 20 months. This unusual, but benign, presentation of granuloma annulare has to be distinguished from other granulomatous and malignant processes which may present as penile nodules.
This communication describes the use of a binomial pulse sequence designed from solvent suppression in proton spectroscopy to convert the small frequency changes associated with field variations into significant amplitude changes in magnetic resonance images. This technique can be used to demonstrate tissue susceptibility change.
The use of four-dimensional chemical shift imaging to monitor phosphorus metabolites within the human brain is illustrated. Saturation effects are described, and acquisition conditions are discussed in relation to quantification and sensitivity. The effects of magnetic field variations on spectral parameters are assessed and the use of a field mapping technique is illustrated.
The soft tissue contrast obtained in fast imaging using rapidly repeated partial saturation sequences is usually based on differences in T1. We describe here an extension of the method which results in the development of clinically useful T2-based contrast.
The results of nuclear magnetic resonance (NMR) examinations in 26 patients with histologic (15 cases) or clinical (11 cases) diagnoses of tumors within the posterior fossa were reviewed and compared with x-ray computed tomography (CT). Most tumors displayed an increase in T1 and T2 relative to brain. All seven benign tumors were seen with both CT and NMR, although one of these cases initially was misdiagnosed on the basis of the CT findings. The extent of these tumors was equally well shown with CT and NMR in three cases but was demonstrated better by NMR in four. Calcification was seen with CT but not with NMR in two of these patients. All 19 malignant tumors were demonstrated with NMR. Two of these were not seen with CT. In 12 patients minimal changes consisting of a poorly defined low-attenuation are or minor displacement of the fourth ventricle were noted with CT, although much more extensive changes were seen with NMR. In three patients the changes were equally well shown with both techniques. In the remaining two cases, the extent of the tumor was defined more accurately with contrast-enhanced CT, where the margin between tumor and surrounding edema was better seen than with NMR. Mass effects were better demonstrated with NMR in 13 patients and equally well shown in six. Bony erosion was better demonstrated with CT in two cases. Hydrocephalus with periventricular edema was seen in five patients; in each it was more clearly demonstrated with NMR. The NMR diagnosis of tumors is discussed and relevant new developments are summarized.
A nuclear magnetic resonance (NMR) imaging system is described, and preliminary results from its clinical use are presented. The properties and detection of the magnetisation due to hydrogen protons are outlined, and a rotating frame is introduced to describe the motion of the magnetisation. Radiofrequency (RF) pulses are used to rotate the magnetisation, and slice selection is achieved using a 90 degree RF pulse and a magnetic field gradient. Data acquisition and image reconstruction are explained. Three scanning sequences are described: repeated free induction decay (FID), inversion - recovery, and spin-echo. These sequences produce images whose pixel values have different dependencies on hydrogen proton density, T1 and T2. Inversion-recovery images show striking differentiation between grey and white matter in the brain. The absence of bone artifact is a significant advantage over X-ray computed tomography in the posterior fossa, where rapid repeated FID sequences can also be used to demonstrate flow effects. The considerable soft tissue contrast available with NMR is of value in demonstrating disease within the liver where T1 appears to be sensitive but relatively nonspecific diagnostic parameter. High resolution scans are of value in demonstrating the adrenal gland and spinal cord.
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Posterior fossa scans were performed on five healthy volunteers using a nuclear magnetic resonance (NMR) machine constructed by Thorn-EMI Ltd. Three different NMR scanning sequences were used. In the first, a type of saturation-recovery technique was used to produce images strongly dependent on the density of hydrogen nuclei, but with some dependence on the spin-lattice relaxation time (T1). In the second, an inversion-recovery technique was used to produce images with a stronger dependence on the spin-lattice relaxation time. In the third, a spin-echo technique was used to obtain images with a dependence on the spin-spin relaxation time (T2). All three types of NMR image were unaffected by bone artifact. Visualization of brain adjacent to the skull base was obtained without loss of detail due to partial-volume effect from bone. The saturation-recovery images highlighted arteries and veins that were clearly visible without the use of contrast agents. The inversion-recovery images showed remarkable gray-white matter differentiation enabling internal structure to be seen within the brainstem and cerebellum. The trigeminal nerve and ganglion were also seen outside the brain. Experience with the spin-echo technique is limited, but the images at the base of the brain show considerable soft-tissue detail. The NMR images of the posterior fossa in this study were comparable in quality to those obtained from a new rotate-rotate x-ray computed tomography machine and were superior in several respects.
Cutaneous application of diazinon to rats over a period of 12 weeks gives rise to a condition biochemically indistinguishable from porphyria cutanea tarda. Faecal porphyrin levels are elevated with the appearance of isocoproporphyrin in the faeces. Oral administration of diazinon does not appear to cause any disturbance of porphyrin metabolism.
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Rapid T2 dependent field echo [partial saturation (PS)] sequences were used in 38 patients with brain tumors, intracerebral hematomas, and cerebral infarction as well as other neurological and abdominal disease. Reduction in the radiofrequency excitation angle (alpha) from 90 to 30 degrees produced an increase in lesion contrast as did change of echo time (TE) from 33 to 59 or 120 ms using repetition time (TR) values in the range of 120-500 ms. The PS sequence showing most lesion contrast was compared with conventional spin echo (SE 1,500/80 and SE 1,500/120) and inversion recovery (IR 1,500/500/44 and IR 1,500/100/44) sequences. Although PS sequences with TE = 39 ms were usually inferior to conventional SE sequences, those with TE = 59 or 120 ms were comparable and in some cases (particularly hematomas) superior. The PS sequences with alpha of approximately 30 degrees, TR of 80-250 ms, and TE of 60-120 ms offer considerable savings in time compared with conventional sequences although more work will be required to explore the limits of this approach and to optimize sequences at different field strengths.
Four dimensional chemical shift imaging was used to map the relative peak heights of phosphorus metabolites of the liver and overlying skeletal muscle of a normal subject and two patients. The technique provides 31P spectra localised on a voxel-by-voxel basis and may be valuable in mapping heterogeneous structural and metabolic changes in disease.