Denis H. Carr

Contrast agents in magnetic resonance imaging

With the advent of magnetic resonance imaging (MRI) it has become apparent that paramagnetic contrast agents may have a place in clinical practice. The mechanism of action, development, techniques of use and initial animal and clinical results are reviewed. Gadolinium diethylene triamine penta acetic acid (Gd3+-DTPA) has proved an effective paramagnetic contrast agent in experimental animals and clinical trials with this agent commenced in November-December 1983. Gd3+-DTPA will cross a damaged blood-brain barrier, is excreted mainly by glomerular filtration and is distributed mainly in the extracellular space. No short-term toxicity has been detected. Long-term toxicity is, as yet, unknown. Optimum dose, pulse sequences and timing of imaging remain to be determined by further studies but Gd3+-DTPA shows promise as a useful addition to MRI.

A comparison of bone scanning and radiology in the evaluation of patients with metabolic bone disease

Bone scans and radiographs were evaluated in 80 patients with metabolic bone disease (27 with osteoporosis, 14 with primary hyperparathyroidism, 24 with renal osteodystrophy and 15 with osteomalacia). The bone scan did not suggest a metabolic bone disorder in any of 27 patients with histologically proven osteoporosis. In 22 (81%) patients radiographs were reported as showing osteoporosis. In 10 (70%) vertebral fractures were seen on X-ray while these were noted in 11 (41%) patients on the bone scan. Vertebral fractures were usually visualised on the bone scan when these had occurred less than one year previously. In primary hyperparathyroidism the bone scan was suggestive of a metabolic bone disorder in 7 of 14 (50%) patients, while radiographs were reported as showing evidence of hyperparathyroidism in three (21%) cases. The bone scan suggested the presence of a metabolic bone disorder in all 24 patients with renal osteodystrophy and 15 patients with osteomalacia while the correct diagnosis was obtained in 14 (58%) and nine (60%) of these patients on X-ray. It is concluded that the bone scan is the more sensitive investigation in patients with osteomalacia, primary hyperparathyroidism and renal osteodystrophy. For osteoporosis radiology is the investigation of choice but the bone scan may be of value in assessing the duration of vertebral collapse.

Gadolinium-DTPA in the assessment of liver tumours by magnetic resonance imaging.

The effect of gadolinium-DTPA (Gd-DTPA, Schering AG) as a magnetic resonance imaging (MRI) contrast agent was studied in 15 patients with liver tumours. A dose of 0.1 mmol/kg was used. An analysis of the time-course of enhancement, a comparison of four different pulse sequences, and a dose-comparison study were carried out with monitoring of haematological and biochemical parameters before and after injection of Gd-DTPA. Maximum enhancement, that is, increase in signal intensity, was noted on IR1400/400/13 between 10 and 20 min after injection while on SE580/40 and SE580/80 maximum enhancement was noted 30 min after injection. In some cases enhancement was noted up to 120 minutes after injection. SR1000/13f sequences showed very little enhancement. On comparison with contrast-enhanced X-ray computed tomography (CT), enhancement was greater on MRI in seven cases, equal in six and less in two, as assessed subjectively. Additional lesions were shown in one case using Gd-DTPA compared to precontrast enhanced MRI scans. However, no additional lesions were seen on contrast-enhanced MRI scans compared to contrast-enhanced CT scans. Gd-DTPA is capable of enhancing liver tumours on MRI and may have a place in the assessment of the operability of such lesions.

Computed tomography in pre-operative assessment of bullous emphysema

Nine patients with bullous emphysema for which surgery was being considered have been investigated with computed tomography (CT). In six out of nine patients (67%) CT showed more extensive disease or bilateral disease where only unilateral was suspected from postero-anterior and lateral chest radiographs. Only one patient proceeded to surgery and post-operative CT showed satisfactory re-expansion of the compressed lung. Surgery was abandoned in one patient as a result of the CT findings. Computed tomography is of value in patients with bullous emphysema in assessing the extent of disease and may assist the surgeon in operative planning.

The radiology of fibrolamellar hepatoma

Seven patients with fibrolamellar hepatoma were examined with computed tomography (CT), ultrasonography and angiography. On CT the tumours were large, of low attenuation, had a well-defined edge and some contained areas of calcification or necrosis. Ultrasonography revealed well-defined masses of mixed echogenicity, occasionally involving the portal vein. In one patient there was dilatation of the intrahepatic biliary tree. Arteriography showed vascular tumours with involvement of the portal vein in five cases and compression of the inferior vena cava in five cases. CT and ultrasonography are the most useful radiological investigations for suggesting the diagnosis of fibrolamellar hepatoma which should be considered in the case of any large solitary well-defined hepatic tumour in the noncirrhotic liver of a young person.

Abnormal regional distribution of ventilation in middle-aged smokers: Comparison of changes in 81Krm ventilation scans and computed tomography of the lung

In 1980 we found that abnormalities in regional distribution of ventilation, as assessed by 81Krm lung scans, were common in middle-aged smokers with normal chest radiographs and mild impairment of overall lung function. In 1984 we repeated 81Krm scans in 16 continuing smokers then aged 50-64 years and with mean forced expiratory volume in one second 93% (20 SD) of predicted values who had previous 81Krm scans performed in 1980. To assess the role of disease of the peripheral airspaces in causing abnormal regional ventilation, we also obtained computed tomograms (CT) of the lungs and measured carbon monoxide transfer of the lungs in these men. Krypton scans in seven men who had normal or minor focal defects of ventilation in 1980 were unchanged in 1984. Scans in seven of the nine men who had abnormal scans in 1980 remained abnormal in 1984 but there was no overall deterioration in the abnormality of ventilation in these men; in men with similar grading in 1980 and 1984 some of the peripheral defects present in 1980 had resolved and some new abnormal areas had appeared. Minor localised abnormalities of CT scans, as assessed visually, were present in eight of the 16 men and were associated with lower values of carbon monoxide transfer coefficient (mean 78% vs 98% predicted in men with normal scans, P less than 0.01) and lung density (mean -894 vs -869 HU in men with normal scans, P less than 0.054) suggesting the CT changes were due to alveolar destruction. Abnormality of the krypton scan was not significantly associated with abnormality of the CT scan or with a reduction in carbon monoxide transfer. The results of the krypton lung scans confirm that non-uniformity of regional ventilation is often present in asymptomatic middle-aged smokers and suggest that this non-uniformity is in part due to temporary occlusion of airways. Abnormality in regional ventilation was not associated with the anatomical changes shown by the CT scan, suggesting that airway narrowing was more important than alveolar destruction in causing regional abnormalities of ventilation in these men.

Visibility of the renal fascia at intravenous urography

Contrary to the accepted understanding that visibility of the perirenal fascia at urography is a rare finding and when seen is usually associated with renal pathology, a recent report has suggested that it is a fairly common, normal finding. In a retrospective study, 261 unselected intravenous urograms performed over a 3-month period were analysed. The findings indicate a low incidence of perirenal fascia visualisation and, when present, an association with renal pathology.