Three-dimensional computed tomographic scans in the planning of procedures for reconstructive craniofacial surgery.

Three-dimensional computed tomographic (3D CT) scans were used in the assessment of three cases being considered for craniofacial reconstructive surgery; the first patient had a frontal encephalocele, the second an orbital encephalocele and the third an apparent asymmetry of the face due to cervical scoliosis caused by developmental defects of the upper two cervical vertebrae. The 3D CT scans provided information which was of great help in deciding how best to manage each case.

Quantitative magnetic resonance imaging of vertebral bodies: a T1 and T2 study.

Multiple point T1 and T2 values of 424 vertebral bodies were measured and analysed. The influence of several factors including age, sex, location in the spine and status of neighbouring discs on the measured relaxation times were evaluated. The results indicate limitations in the region of interest approach. Vertebral bodies of different age, sex and location in the spine could not be distinguished. For heterogeneous tissues a more advanced form of image analysis appears to be essential. Diurnal factors resulting from the stress of normal ambulatory activity caused increased variation in vertebral body relaxation time values.

Does degenerative disease of the lumbar spine cause arachnoiditis? A magnetic resonance study and review of the literature.

The magnetic resonance appearances in 165 patients with symptoms suggestive of degenerative lumbar spine disease were reviewed. The aim of the study was to evaluate the relationship between abnormalities of nerve root distribution and degenerative disease of the lumbar spine in the absence of other known risk factors for arachnoiditis. Central clumping of nerve roots was present in 16 patients (9.7%) and was associated with spinal stenosis at one of the affected levels in all (p < 0.001). Spinal stenosis was present in 44 patients giving an incidence of abnormal nerve root distribution of 36% in this group. Nerve root clumping occurred in association with pure spinal stenosis (10 cases), stenosis secondary to disc prolapse (four cases) and degenerative spondylolisthesis (two cases). Nerve root clumping was confined to one vertebral level in nine cases and extended over two to four levels in seven. In five of the latter spinal stenosis was present at multiple levels. The appearance of nerve root clumping described here may result entirely from mechanical apposition of nerve roots but is indistinguishable from the central pattern of nerve root adhesions which occurs in adhesive lumbar arachnoiditis. No abnormalities of nerve root distribution were seen in association with any indicator of degenerative disk disease in the absence of stenosis. We have been unable to demonstrate the previously reported relationship between lumbar disk degeneration and arachnoiditis and discuss this with a critical review of the literature. Abnormal central clumping of nerve roots as described in arachnoiditis may occur in association with spinal stenosis in the absence of other risk factors although the cause for this appearance remains unexplained. Arachnoiditis-like changes extending over more than one vertebral level are rare (7%) except in the presence of spinal stenosis at multiple levels (29%). Awareness of this appearance may avoid a possibly incorrect diagnosis of arachnoiditis in the presence of a treatable stenosis.

How frequent is chronic lumbar arachnoiditis following intrathecal Myodil?

Chronic lumbar arachnoiditis has numerous causes, including the introduction of contrast media into the lumbar subarachnoid space. The oily contrast medium Myodil (iophendylate) is often cited but the true incidence of symptomatic lumbar arachnoiditis due solely to the presence of Myodil is unknown. A retrospective review of 98 patients in whom Myodil was introduced by ventriculography or cisternography, i.e. remote from the lumbar spine, revealed no cases of chronic lumbar arachnoiditis. All patients were monitored closely for periods ranging from 1 to 28 years. We conclude that, in these circumstances, it is rare for Myodil to produce symptomatic arachnoiditis.

Patterns of chronic adhesive arachnoiditis following Myodil myelography: the significance of spinal canal stenosis and previous surgery.

109 patients who had undergone Myodil myelography on at least one occasion were identified. The patterns of lumbar nerve root distribution in this group were examined using magnetic resonance imaging. The relationship between these patterns and the presence of spinal stenosis or previous surgery was investigated. Chronic adhesive arachnoiditic nerve root patterns were seen in 68 patients and were classified into three groups according to Delemarter et al. Central clumping of nerve roots (type 1) and complete opacification of the thecal sac (type 3), extending over at least one vertebral level, were significantly related to spinal stenosis at an adjacent level (p < 0.0001). Peripheral adhesion of nerve roots to the theca (type 2) was significantly related to previous surgery at the level of abnormality (p < 0.00005). Only a single case of arachnoiditic nerve root patterns was seen in the absence of stenosis or previous surgery. We conclude that chronic adhesive arachnoiditis is significantly related to previous Myodil myelography in the presence of spinal stenosis or previous surgery but that Myodil alone rarely produces these changes.

The effects of sodium nitroprusside on Doppler signals from a soft tissue tumour.

In a previous study, we described the effects of systemic vasoconstriction on the Doppler signals from a soft tissue tumour (Taylor et al, 1989). Our conclusions were that vasoconstriction produced significant changes in the signals from normal vessels and enhanced the differences between normal and neoplastic vessel signals. The aim of this study was to determine whether converse changes were produced by vasodilatation.

Magnetization transfer contrast (MTC) imaging of skeletal muscle at 0.26 Tesla--changes in signal intensity following exercise.

Magnetization transfer contrast (MTC) imaging of skeletal muscle before and after exercise has been studied in normal volunteers at 0.26 Tesla. A saturation pulse was applied over a range of offset frequencies immediately before a gradient recall echo sequence. Substantial signal loss was observed in all muscles. After exercise, selective saturation resulted in a significant increase of contrast between active and less active muscle, a phenomenon attributable to an increase in extracellular water content. MTC imaging provides a more sensitive method to detect changes in water distribution in human skeletal muscle.

Clinical evaluation of fast spin echo sequences for cranial magnetic resonance imaging at 0.5 tesla.

Fast spin echo (FSE) sequences enable T2-weighted MR scans to be obtained in a fraction of the time necessary for conventional SE sequences with long TR and long TE. Comparison has been made of a FSE sequence (TR = 4000 ms, effective TE = 100 ms, 2 NEX) with the T2-weighted SE sequence (TR = 2000 ms, TE = 90 ms, 1-2 NEX) normally used in 35 patients referred for cranial MRI. Contrast-to-noise ratios (CNR) for grey:white matter and brain:CSF on the FSE sequence compared favourably with variable echo (VE) sequences which take up to three times as long to acquire. Although the conspicuity of some pathological lesions such as multiple sclerosis plaques was inferior to that of conventional T2-weighted SE scans, no lesions were missed on FSE scans. The FSE sequence was more prone to movement artefacts. The benefit of the markedly increased patient throughput made possible by using the FSE sequence outweighs the slight reduction in sensitivity for small lesions.

In vivo evaluation of myocardial infarction by computed tomography: an experiment with electrocardiographic gating.

Retrospectively gated and ungated images of normal and 24 h post-infarction mini-pig hearts were obtained. The 11 imaged infarcts were transcatheter embolisation of the branches of the left anterior descending coronary artery. Using a contrast infusion technique and scanning during infusion, four infarcts were clearly detected as low-attenuation areas in the myocardium, one of these showing adjacent contrast enhancement. Two other infarcts showed as enhancing regions. Two small infarcts (0.8-1.0 cm3) were not detected and three others were in doubt. Streaking and other artefacts presented difficulties in image interpretation, which were sometimes resolved by gating. A comparison is made of these findings with those obtained from experiments with dogs, of comparable methodology. Differences are considered to result from anatomical differences between the two species, more particularly in the collateral blood supply to the myocardium.

The effects of angiotensin II on Doppler signals from a soft-tissue tumour.

A 10 mHz continuous-wave Doppler system has been used to detect blood flow within a sarcoma implanted in a rabbit's ear. The effects of vasoconstriction produced by intravenous angiotensin II were studied. Criteria are described that enabled differentiation of the Doppler signals from the tumour from those of the adjacent central artery. The effect of vasoconstriction upon these criteria is also described.

Electron density and atomic number determination by computed tomography. Part I: Methods and limitations. Part II: A study of colloid cysts.

The feasibility of extracting electron density and effective atomic number from measurements of tissue in vitro and in vivo has previously been reported. The method requires scans to be obtained at two different beam energies. Optimization of these energies at 40 keV and 80 keV could enable a variation of 1 part in 400 of effective atomic number to be detected. The method is subject to certain limitations related to accuracy and sensitivity. The effect of varying the concentrations of certain atoms has been modelled demonstrating the limits below which variation in effective atomic number is unlikely to be detectable at acceptable radiation doses. A series of 12 patients with colloid cysts has been considered. All were treated by bilateral ventriculo-cisternostomy from one to 23 years ago. Nine of these patients, and the colloid cyst of one patient who died before treatment could be instituted, have been subjected to double energy scanning. The results suggest that the high attenuation values observed in colloid cysts are due to increased electron density and not to any increase in high atomic number elements. The cysts do not appear to change in size or content over long periods.

The role of abdominal computed tomography in lymphoma following treatment.

Two hundred and six patients with biopsy-proven lymphoma, 74 with Hodgkin's disease and 132 with non-Hodgkin's lymphoma had abdominal computed tomography for assessment of remission status (108 patients) or for investigation of relapse (98 patients). In 43 patients with diffuse large cell lymphomas scanned at a time of apparent complete remission CT was abnormal in 21. Sixteen of these patients have relapsed and died. Only one patient has relapsed in the group who have normal CT scans. This difference was significant (p=0.00001). This difference was not seen in nodular lymphomas. There were very few patients with Hodgkin's disease in whom the CT scan was abnormal and there is a suggestion that many abnormalities following treatment may represent inactive Hodgkin's disease or fibrosis only. CT played a major role in diagnosing the full extent of relapse in both non-Hodgkin's lymphoma and Hodgkin's disease. Over 50% of the abnormal sites detected by CT would not have been shown by any other non-invasive investigation. Five patients with treated Hodgkin's disease who had "B" symptoms only suggesting relapse were all shown by CT to have extensive intra-abdominal disease.

MR imaging of the intervertebral disc: a quantitative study.

The T1 and T2 relaxation times and the proton density of the nucleus pulposus have been measured in 107 normal and 18 surgically proven degenerate intervertebral discs. Data from total saturation recovery and spin echo sequences have been utilised in a robust multi-point method and relaxation times and proton density calculated. The results show that both the T1 and T2 values of the normal nucleus pulposus decrease with age. There was no significant correlation between proton density and age in normal discs. At all ages there was a highly significant difference between the T1 values of normal and degenerate discs. With T2 a highly significant difference in the younger age groups reduced to no distinction in the seventh decade. The observed change in the T1 and T2 values of the nucleus is in agreement with the reduction of water content known to occur with age. Our results indicate that quantitative MR imaging may assist in the diagnosis of intervertebral disc degeneration.

A comparison of angiographic and electrocardiographically gated computed tomographic measurements of left-ventricular function.

Fifty patients with ischaemic heart disease have been studied by electrocardiographically gated computed tomography (CT) and left-ventricular angiography to assess the accuracy of the former in the measurement of left-ventricular volumes and ejection fraction. There was no significant difference in the measurements of end-diastolic volume (p = 0.9, r = 0.81). Computed tomography significantly overestimated end-systolic volume (p less than 0.001, r = 0.89) and significantly underestimated ejection fraction (p less than 0.001, r = 0.74). Although there is some variation between the two sets of measurements, the correlation between the two techniques is good, indicating that electrocardiographically gated CT could be a useful noninvasive technique for assessing left-ventricular function.

Quantitative magnetic resonance imaging in rectal carcinoma.

T1 and T2 relaxation times have been calculated in 30 patients with rectal carcinoma and seven patients with a fibrotic pelvic mass. The relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin-echo sequences. The results show that the calculated T1 relaxation value is a useful discriminant between carcinoma and pelvic fibrosis and should improve the detection of early tumour recurrence.

Identification of intracardiac thrombus: comparison of computed tomography and cross-sectional echocardiography.

Thirty-eight patients with conditions predisposing to intracardiac thrombus have been studied by computed tomography and cross-sectional echocardiography. Computed tomography identified 22 cases of intracardiac thrombus (13 left ventricular, eight left atrial and one right atrial). Cross-sectional echocardiography identified five of these left ventricular thrombi and the right atrial thrombus, but none of the left atrial thrombi. In addition, measurements of thrombus density on computed tomography identified a significant difference (p less than 0.02) between the density of a new compared with an organized thrombus.

Quantitative tissue characterisation in pancreatic disease using magnetic resonance imaging.

Twenty-nine patients, 27 of whom had either inflammatory disease of the pancreas or pancreatic tumour, were studied by magnetic resonance imaging (MRI) and computed tomography (CT). Six healthy volunteers were studied by MRI alone. The pancreatic T1 and T2 relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin echo sequences. Magnetic resonance imaging can demonstrate the normal pancreas and a variety of pathological processes greater than 1-2 cm in size, but with less spatial resolution than CT. The relaxation-time results indicated no significant discrimination between chronic pancreatitis and pancreatic tumour. A significant elevation in the relaxation times was observed, however, in those patients with calcific chronic pancreatitis compared with the non-calcific chronic pancreatitic group and normal controls, suggesting a different pathophysiology for the two subgroups of chronic pancreatitis. The active phase of acute pancreatitis was associated with significantly elevated relaxation times, which returned to normal levels during the resolved phase of the disease. Associated extrapancreatic fluid collections were characterised by their very long relaxation times. The problems associated with spatial resolution, respiratory motion and lack of quantitative tissue characterisation suggest that MRI of the pancreas, using present methods, is unlikely to contribute to the overall management of patients with exocrine pancreatic disease.

Detection of coronary artery bypass graft patency as assessed by magnetic resonance imaging.

In a study of 22 patients with 60 coronary artery bypass grafts, magnetic resonance imaging (MRI) correctly assessed graft patency or occlusion in 90% of cases when compared with selective coronary graft angiography and computed tomography. It is concluded that MRI can detect a normally functioning coronary artery bypass graft and could be used as a non-invasive technique to assess graft patency in patients presenting with post-operative angina.

Magnetic resonance imaging of the mini-pig heart: the effect of gadolinium-DTPA on normal myocardium.

The effect of gadolinium-diethylene-triamine-penta-acetic acid (Gd-DTPA) on normal, mini-pig myocardium was investigated with magnetic resonance imaging. Results indicate that intravenous administration of Gd-DTPA produces a significant enhancement of mini-pig myocardial signal intensity, which in all cases was maintained in excess of 50 min. No significant enhancement was demonstrated in skeletal muscle.

A method for the clinical measurement of relaxation times in magnetic resonance imaging.

A method for the determination of relaxation times in clinical magnetic resonance images is described. Three components are measured: the spin-lattice (T1) and spin-spin (T2) relaxation times and the proton density (M infinity). These components are separated in the algorithm to give increased tissue discrimination. Multiple data points are used to minimise error and increase reproducibility. Errors that arise in imaging data because of the short sequence repetition periods are considered and a technique for their reduction described. Clinical results obtained using the method are reviewed. These results demonstrate the clinical utility of the technique.