A. Hemmingsson

Magnetic Resonance Imaging in Diffuse Malignant Bone Marrow Diseases

Twenty-four patients with malignant bone marrow involvement or polycythemia vera, 8 patients with reactive bone marrow and 7 healthy individuals were examined with spin-echo magnetic resonance imaging at 0.35 T and 0.5 T. Signs of an increased longitudinal relaxation time, T1, were found when normal bone marrow was replaced by malignant cells, polycythemia vera or reactive marrow. A shortened T1 was indicated in 4 patients in bone marrow regions treated by radiation therapy; the marrow was most likely hypocellular in these cases. The estimated T1 relaxation times were highly correlated to the cellularity of the bone marrow as assessed by histology. Among patients with close to 100 per cent cellularity neither T1 nor T2 discriminated between the various malignancies or between malignant and reactive, non-malignant bone marrow. Characterization of tissues in terms of normalized image intensities was also attempted, the motive being to avoid approximations and uncertainties in the assessment of T1 and T2. The normalization was carried out with respect to the image of highest intensity, i.e. the proton density weighted image. The results were in agreement with those for T1 and T2. It was concluded that MRI is valuable for assesssing bone marrow cellularity, but not for differentiating between various bone marrow disorders having a similar degree of cellularity.

Magnetic Resonance Imaging in Primary Amyloidosis

Twelve patients with primary amyloidosis (AL) were investigated with magnetic resonance imaging (MRI). In 9 patients an abnormal thickening of the heart walls was present and in 2 macroglossia was found at MRI. T1 was significantly increased in liver (p<0.05) and subcutaneous fat (p<0.01) while it was decreased in the spleen (p<0.05). T2 was significantly decreased (p<0.01) in the spleen in patients with amyloidosis, while it was not significantly altered in the liver or subcutaneous fat. After therapy T1 of the liver was reduced towards normal values in 4 patients. It is concluded that MRI might be a method to quantitate the amount of amyloid deposits in the tissue, and that the effect of therapy may be monitored with this technique.

Calculation of MRI artifacts caused by static field disturbances

Theory indicates that in magnetic resonance imagining, according to the spin-wrap method, the distortions in the image caused by a locally disturbed static magnetic field should show up as displacements in the slice-selection and read-out directions, proportional to the magnitude of the field disturbance and inversely proportional to the strengths of the imagining gradients. In phase-contrast images, phase effects may be described by the product of field disturbance, gyromagnetic ratio and data collection delay. To test this theory spheres with aberrant permeability (steel, air) were imaged immersed in water. The resulting images showed good agreement with simulated images calculated under the above assumptions. The implications of the above assumptions. The implications of these results concerning contrast media consisting of magnetic particles are discussed.

Magnetic Resonance Imaging for Assessment of Treatment Effects in Mediastinal Hodgkin's Disease

Six patients with mediastinal involvement of Hodgkins disease were examined with magnetic resonance imaging (MRI) at 0.35 T before and/or at various stages of therapy, with the sequences TR/TE: 500/35, 500/70, 1600/35 and 1600/70. Before therapy the image intensity of tumour involved lymph nodes deviated considerably from fat and muscle, but no clear difference was discerned between histopathologic subtypes or tumour localizations. After efficient therapy, the tumour image intensities and relaxation rates approached those of muscle and fibrous tissue, but remained at pre-therapy values when the patient was not in full remission. A similar pattern was found in a ‘normal-tissue’—‘tumour’ plot, based on vector analysis of the original sets of 4 images. It is concluded that persistent tumour involvement in the mediastinum may be distinguished from fibrosis and that MRI may thus be of value in the follow-up of patients with Hodgkins disease.

Angiography, Computed Tomography, Magnetic Resonance Imaging and Ultrasonography in Detection of Liver Metastases from Endocrine Gastrointestinal Tumours

Twenty-five patients with endocrine tumours (13 with endocrine pancreatic tumours and 12 with carcinoids) were examined with angiography, computed tomography, magnetic resonance imaging and ultrasonography. Seventeen patients had liver metastases and were followed between 3 and 66 months with serial examinations during treatment with chemotherapeutic agents and interferon. The efficiency of the various techniques to detect metastases was investigated. Analysis of changes in tumour size during treatment was made to see if treatment effects could be monitored with radiologic examinations. Ultrasonography was the best non-invasive method for detection of metastases and is recommended as standard method for imaging in this group of patients. Angiography was even better showing extremely small metastases, less than 5 mm, and is recommended in selected cases. With one exception, no significant change in tumour size was noted in spite of clear laboratory and clinical signs of therapy effect indicating that tumour size determination is not useful for therapy monitoring in this type of disease.

An Attempt to Characterize Malignant Lymphoma in Spleen, Liver and Lymph Nodes with Magnetic Resonance Imaging

An attempt was made to explore whether relaxation times and/or normalized image intensities obtained from magnetic resonance imaging (MRI) can separate malignant and non-malignant lymphomatous tissue. Spin-echo (SE) techniques with repetition times of 500 and 1500 ms and echo times of 35 and 70 ms were used for estimating T1 and T2. Estimation of T1 and T2 with such a low number of spin-echo sequences resulted in considerable variation in the data especially when T1 was long. Similar information was also extracted by normalizing the image intensities to the ‘proton density’ image (1500/35), and the spread of the data was then markedly reduced. Therefore, the method of normalizing was considered a more appropriate way of handling the image data when only a few sequences were available. No significant difference could be discerned in the MRI parameters between normal spleens and spleens infiltrated with malignant lymphoma, between normal livers and livers in patients with malignant lymphoma and between lymph nodes with low or high grade non-Hodgkin lymphoma. Lymphomatous tissue had similar MRI characteristics irrespectively of whether the cells were malignant or not, or located in spleens or in lymph nodes. The main biologic explanation for variation in data seems to be mostly the variable amounts of fibrosis, necrosis, oedema and/or iron content.

Magnetic Resonance Imaging, Chest Radiography, Computed Tomography and Ultrasonography in Malignant Lymphoma

Magnetic resonance imaging (MRI) was compared with chest radiography, computed tomography (CT) and ultrasonography (US) for demonstration of spleen and liver engagement and enlarged lymph nodes in patients with malignant lymphoma. The investigation comprised 24 patients with Hodgkins disease (HD) and 39 with non-Hodgkin lymphoma (NHL). MRI demonstrated enlarged lymph nodes, distinctly separated from vessels, fat, muscle, liver and occasionally also pancreas without any contrast medium. The distinction between lymph nodes and spleen was, however, poor in the images. In the mediastinum, MRI was superior to chest radiography and had an accuracy similar to that of CT. In the abdomen and the pelvis MRI had slight advantages over CT in detection of enlarged lymph nodes. Compared with US the MRI results were similar in the abdomen and somewhat better in the pelvis. MRI and US were better than CT in revealing HD infiltrates in the spleen. Infiltration of NHL in the spleen was slightly better disclosed at US than at CT and MRI; most of the NHL infiltration, confirmed at histopathology, could, however, not be revealed with any of the modalities, except when the size of the spleen was considered. Regions in the spleen, displayed with low image intensity in the T2 weighted image, were most likely due to increased amount of fibrotic tissue in the lymphomatous lesions. Good demonstration of lymph nodes and lymphomatous lesions in the spleen with MRI required two sequences; one with short TR and TE (T1 weighted image) and one with long TR and TE (T2 weighted image).

Double-Contrast MR Imaging of Reperfused Porcine Myocardial Infarction An Experimental Study Using Gd-DTPA-BMA and Dy-DTPA-BMA

Purpose: Myocardial infarctions were induced in 12 pigs to investigate whether a double-contrast method, combining a positive and a negative MR contrast agent, could improve the visualization of reperfused myocardial infarctions. Material and Methods: All 12 pigs were subjected to 80 min of occlusion followed by reperfusion. In the double-contrast group (6 pigs), Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1.0 mmol/kg b.w.) were administered i.v. after 30 min of reperfusion. In the remaining 6 pigs, a single injection of Gd-DTPA-BMA (0.3 mmol/kg b.w.) was given after 30 min of reperfusion. All pigs were sacrificed 10 min postcontrast injection, corresponding to a reperfusion time of 40 min. The hearts were excised and imaged with MR. The concentrations of Gd and Dy were measured in infarcted and nonischaemic myocardium using ICP-AES. Results and Conclusion: Contrast media concentrations were more than 4-fold higher in infarcted compared with nonischaemic myocardium. The infarctions were best shown on T1-weighted images, and there were no differences between the double and single contrast groups. In the T2-weighted images, the infarctions were significantly better visualized in the double-contrast group, due to a Dy-induced signal intensity loss in nonischaemic myocardium.

Mr Imaging of Acute Myocardial Infarction in Pigs Using Gd-DTPA-Labeled Dextran

Myocardial infarctions were induced in 12 pigs. In 6 pigs, dextran-(Gd-DTPA)15 (≈0.1 mmol Gd/kg b.w.) was injected i.v. 4 to 4.5 hours after coronary artery occlusion. ECG gated MR images were obtained repeatedly before (n = 4) and after (n = 6) contrast medium injection. Relaxation times in blood samples were measured repeatedly. The animals were sacrificed 2 hours after contrast medium administration. The hearts were excised, reexamined in the MR equipment and stained with triphenyltetrazolium chloride (TTC) in order to define areas of infarction. The remaining 6 pigs were sacrificed 6 hours after occlusion without administration of contrast medium. These hearts were only imaged ex vivo. In vivo, the infarctions could not be identified with or without dextran-(Gd-DTPA)15. Ex vivo, without contrast medium, the infarctions had an increased signal intensity, most pronounced in the T2-weighted images. Dextran-(Gd-DTPA)15 caused a prolonged, pronounced shortening of T1 and T2 in blood samples. The infarct demarcation improved in the T1-weighted images after injection of dextran-(Gd-DTPA)15, due to a moderate enhancement in normal myocardium and a stronger enhancement at the periphery of the infarctions, while the central parts of the infarctions were only weakly enhanced.

Oral Superparamagnetic Particles for Magnetic Resonance Imaging Effect in Plain and Viscous Aqueous Suspensions

As a potential gastrointestinal MR contrast medium magnetic particles have been evaluated in preclinical studies as well as in healthy volunteers. The main problem was to achieve an even distribution of the aqueous suspension of magnetic particles in the entire intestine. To improve the distribution of the contrast medium, a viscosity-increasing agent was added to the preparation. In the plain aqueous suspension the magnetic particles sedimented rapidly and caused artifacts, whereas no such sedimentation occurred in the viscous preparation. The contrast effect, as well as the presence of artifacts, increased with particle concentration. The general contrast effect was good in all 5 volunteers, and the contrast medium was well distributed in the small intestine, including the duodenum. There were no artifacts observed, and the contrast medium was well tolerated. The viscosity-increasing agent will thus be introduced in further clinical studies.