Computed Tomography in Early Diagnosis of Local Recurrence of Rectal Carcinoma

Local recurrence is a common problem among patients treated surgically for adenocarcinoma of the rectum and rectosigmoid. When a local recurrence has become clinically manifest, curative therapy is virtually impossible. Asymptomatic local recurrences are difficult to find clinically, especially in patients treated with an abdominoperineal resection. In 177 patients who had undergone locally curative surgery and had had an uneventful recovery, a postoperative follow-up program, including computed tomography (CT), was carried out. In 77 per cent (137/177) a mass was observed in the pelvis at the first postoperative CT. This mass partly represents fibrosis due to radiation therapy. The risk of developing local recurrence cannot be foreseen from a CT image. CT should not be performed by routine but only in patients with symptoms in whom local recurrence cannot be verified by clinical examination, and always with CT-guided needle biopsy of the detected mass.

Effect of Interferon on T1 Relaxation Times of Liver Metastases from Endocrine Gastrointestinal Tumours

Eight patients with liver metastases from endocrine gastrointestinal tumours were examined with magnetic resonance imaging of the liver before and during treatment with interferon. T1, T2 and tumour size were measured and compared with tumour marker levels and symptomatic improvement or deterioration. Before therapy all tumours showed a long T1 and T2, in comparison to normal liver and fat, and during therapy they all showed a decrease in T1. As no change in liver T1 and fat T1 occurred, the decreased tumour T1 is considered to be a therapy effect. This cannot be fully explained but is possibly due to a reduction in tumour growth rate during interferon treatment. There was no certain correlation between tumour T1 and tumour marker levels or symptomatic changes.

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.

Combination of Gadolinium and Dysprosium Chelates as a Cellular Integrity Marker in MR Imaging

A combination of gadolinium (Gd) and dysprosium (Dy) chelates was investigated as a potential marker of cell-membrane integrity by means of a double-contrast effect in MR imaging. Blood samples with varying hematocrit (Hct) levels containing intact or lysed cells were used as model systems. With intact cells, the agents were assumed to be distributed solely extracellularly and the highest Hct studied (69%) was assumed to mimic the ratio of extracellular to intracellular water in tissue. The combined effect on image intensity of Gd (in a concentration corresponding to 0.2 mmol/kg b.w. in humans) and Dy (0.6 mmol/kg b.w.) applied simultaneously was a marked difference in signal intensity between samples with intact and lysed cells in both the T1- and T2-weighted spin-echo images with a corresponding increase in the contrast-to-noise ratio. This was the result of a T1 reduction caused by Gd with a negligible Dy susceptibility effect in areas with lysed cells. On the other hand, the Dy susceptibility effect (i.e. reduced apparent T2) dominated in areas with intact cells. Thus, the combination of Gd and Dy may serve as a marker of cell-membrane integrity in MR examinations.

Superparamagnetic Particles as an Mri Contrast Agent for the Gastrointestinal Tract

Non-biodegradable superparamagnetic particles containing magnetite were evaluated as a potential contrast agent for the gastrointestinal tract. The particles were administered to pigs perorally either suspended in water or mixed with food. The gastrointestinal tract structures were excellently depicted through a lowered signal intensity of their content in both T1 and T2 weighted images. Relatively large volumes with low particle concentration seemed to give a good contrast agent distribution, especially when the administration was extended over a period of time. Problems with artefacts and blurring in the images caused by a too high local concentration of the contrast agent should also be minimized by using low particle concentrations.

Nonresectable Adenocarcinoma of the Rectum Assessed by Mr Imaging before and after Chemotherapy and Irradiation

Thirty-four patients with nonresectable adenocarcinoma of the rectum, defined as tumor fixation at digital examination, were examined with MR. All 34 patients had, according to MR imaging, perirectal tumor growth. In 23 (68%) of the patients, the tumor has reached an adjacent organ. Eight of these patients had disturbances of the MR characteristics in the adjacent organ which proved to be due to overgrowth, i.e., to tumor invasion into these structures. In the remaining 15 patients, without disturbed MR characteristics, 7 had tumor overgrowth at laparotomy. When there was a visible space between the tumor and adjacent organs, there was no sign of tumor overgrowth at laparotomy, except in one case. In 24 patients, examined both before and after combined irradiation and drug therapy, tumor regression was registered after treatment. MR imaging seems to be useful in the assessment of resectability and to evaluate preoperative anticancer treatment in patients with nonresectable rectal carcinoma.

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

Six patients with mediastinal involvement of Hodgkin's 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 Hodgkin's disease.

Effect of Superparamagnetic Particles as Oral Contrast Medium at Magnetic Resonance Imaging

Non-biodegradable superparamagnetic particles were used as an oral contrast medium in different concentrations, and evaluated in 25 human volunteers. The aim of the study was to determine the most appropriate concentration of the contrast medium, and to evaluate the effect, distribution, safety and tolerance. With the concentration of 1.0 g/l a substantial reduction of the signal intensity in the bowel was achieved in both T1 and T2 weighted images. The intraabdominal structures were well differentiated from the bowels containing contrast medium. ‘Metal’ artifacts and blurring of adjacent structures, probably due to an increased local concentration, were observed at higher dosages. The distribution of the preparation in the gastrointestinal tract varied between individuals. As a rule a good contrast effect was achieved in the small bowel with the exception of the duodenum. The contrast medium was well accepted and did not cause any side effects of clinical importance. The results suggest that the preparation is well tolerated by humans and may be a useful contrast medium for abdominal MR imaging.

Mr Imaging with Histopathological Correlation in Vertebral Metastases of Breast Cancer

In 5 patients with advanced breast cancer and spinal metastases MR imaging of the spine was performed before and/or after death. T1-, proton density-, and T2-weighted and “phase contrast” images were obtained in the sagittal plane. Autopsies included histopathologic examination of whole sagittal sections of the vertebral body. The relative signal intensities on the different MR sequences of various tissues identified histologically were evaluated. “Phase contrast” images combined with T1-weighted images were highly sensitive in detecting metastases. All metastatic tumours over 3 mm in size were found with MR imaging. Vertebrae containing connective tissue and reactive bone marrow had an MR appearance similar to that of metastases even though no metastases were found histopathologically.

Oral Superparamagnetic Particles for Magnetic Resonance Imaging

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.

Detection of Breast Cancer Metastases in the Cervical Spine

Thirty women with breast cancer and indications of possible cervical spine metastases underwent skeletal scintigraphy, conventional radiography, MR imaging and CT. By combining all examinations a diagnosis was settled in each patient and the different imaging techniques were compared. For all of the 26 patients with metastases in the cervical spine the correct diagnosis was found with MR imaging and CT. Both modalities also revealed paravertebral tumour growth, MR (n = 8) more than CT (n = 3). The sensitivity of skeletal scintigraphy in detecting metastases in the cervical spine was rather low, but as these examinations cover the whole body they are still convenient screening procedures, and combined with conventional radiography of selected areas are probably sufficient in many cases. Supplementary examinations with CT or MR would be valuable in patients with equivocal findings at screening for metastases or with clinical indications of metastases that remain unexplained after scintigraphy and radiography.

Quantitation of Atherosclerosis in Femoral Arteriography with Ecg Gated Exposures

Using a densitometric method introduced in 1977 by Crawford et coll. (6) the volumes of segments of the femoral artery were calculated from two angiographic series in each of 13 patients. ECG gated exposures were used to minimise the error of the method. The reproducibility of the method was found to be better than in a previous study in which ECG gating was not used. The method may therefore be of use in long term angiographic follow-up studies of atherosclerotic lesions, although the impact of different investigation parameters on methodologic precision is still not fully known.

MR imaging properties and pharmacokinetics of MnDPDP in healthy volunteers

Purpose: Thirteen male volunteers were studied to evaluate the MR imaging properties and pharmacokinetics of 10 mM mangafodipir trisodium infusion (MnDPDP, Teslascan).

Material and Methods: Doses of 5 and 10 μmol/kg b.w. were administered by bolus injection (<1 min) to 5 subjects, and by infusion (20 min) to 8 subjects, with a 3-week wash-out between doses. Infusion subjects underwent MR imaging.

Results: At 1 h after infusion, the plasma concentration of Mn was reduced to ∼15% of the maximum value. Fifteen to 20% of Mn was recovered in the urine, and 50–60% was recovered in the faeces. The rapid initial plasma clearance of Mn is consistent with both rapid tissue uptake and rapid renal elimination. Increases in signal intensity were apparent on T1-weighted images of the liver, pancreas, spleen, renal cortex and the renal medulla, but not in regions of the brain protected by an intact blood-brain barrier. Increases were seen in the choroid plexus and pituitary. Contrast-related adverse events, only flushing of moderate intensity, occurred in bolus injection subjects.

Conclusion: At 5 and 10 μmol/kg, mangafodipir produces relatively long-lasting enhancement of several abdominal organs, including the liver, pancreas and kidney.

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.

MR Imaging of Gadolinium-DTPA-BMA-Enhanced Reperfused and Nonreperfused Porcine Myocardial Infarction

To investigate whether Gd-DTPA-BMA-enhanced MR imaging permits differentiation between reperfused and nonreperfused myocardial infarction, myocardial infarction was induced in 12 domestic pigs. In 6 pigs, Gd-DTPA-BMA, 0.3 mmol/kg b.w. was administered i.v. 60 min after the occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Gd-DTPA-BMA after 20 min of reperfusion. Radiolabeled microspheres were used to confirm zero-flow during the occlusion period and reperfusion in the infarcted myocardium. All pigs were killed 20 min after injection of contrast medium, and the hearts were excised and imaged with MR. The Gd concentration was measured in infarcted and nonischemic myocardium by ICPAES. In the reperfused hearts, the infarctions were strongly highlighted, corresponding to a 5-fold higher Gd concentration in infarcted vis-à-vis nonischemic myocardium. In the hearts subjected to occlusion without reperfusion, there was only a rim of enhancement in the peripheral part of the infarctions.

Magnetic Resonance Imaging with Maximum Contrast between Two Selected Tissues Composed of Recordings with Three Repetition Times

A method is presented which in a composed image maximizes the image intensity difference between two selected tissues. The composition is made from several magnetic resonance (MR) images from the same slice but with different MR imaging parameters. The method is illustrated with a patient with liver metastases for whom the technique was used to emphasize metastases above normal liver parenchyma.

Diagnostic efficacy of MnDPDP in MR imaging of the liver

Purpose: To assess the diagnostic efficacy, safety and tolerability of mangafodipir trisodium (MnDPDP, Teslascan) in MR imaging of the liver.

Material and Methods: Eighty-two patients from 4 centres underwent MR imaging with pre-contrast sequences including T1-weighted SE and GRE, and T2-weighted turbo SE sequences. MnDPDP at a dose of 5 μmol/kg b.w. was administered by slow i.v. infusion, and 20–60 min after infusion the T1-weighted SE and GRE sequences were repeated. Diagnostic efficacy was evaluated by counting the number of lesions and by evaluating whether more information for lesion characterisation was available in post-contrast images. Safety and tolerability were assessed by recording adverse events and infusion-related discomfort.

Results: Significantly more lesions were found in MnDPDP-enhanced T1-weighted SE and GRE images than in unenhanced images of the same sequences. More lesions were also found in these images compared with T2-weighted images at a level of marginal significance. More information was obtained from MnDPDP-enhanced images in 40 cases. Mild to moderate adverse events were experienced by 17% of the patients.

Conclusion: MnDPDP-enhanced images can improve lesion detection in the liver and are helpful for lesion characterisation. To obtain optimal diagnostic information of liver lesions T2-weighted images are also valuable. MnDPDP is a safe contrast agent for MR imaging of liver lesions.

Effect of Superparamagnetic Particles in Agarose Gels

The effect of different preparations of superparamagnetic particles, designed as potential MR contrast media for the gastrointestinal tract (oral magnetic particles, OMP, diameter of 3.5 μm, iron content 20% by weight) and for the reticuloendothelial system (intravenous magnetic particles, IMP, mean diameter of 0.3 μm, iron content 30% by weight), were evaluated in agarose gels in vitro, using a 0.5 T whole body MR system. The iron content ranged from 2.1 × 10−4 to 2.1 × 10−1 mg Fe/ml in both preparations. Both preparations reduced the signal intensities substantially over a range of concentrations in spin echo sequences. Generally, the signal intensity decreased monotonously with concentration, except for IMP at low concentrations, at which a minor signal intensity increase was observed on T1 and proton density weighted images. The reduction of the signal intensity was stronger in gradient echo and phase contrast sequences, as compared to corresponding spin echo sequences with similar timing. Both IMP and OMP had a pronounced T2 effect, the effect of IMP being stronger than that of OMP. IMP had a relatively smaller T1 effect, whereas T1 was almost unaffected by OMP. Susceptibility artifacts occurred at higher concentrations of both OMP and IMP, in all sequences used. Thus, OMP reduced the signal intensity, without causing significant artifacts, on both T1 and T2 weighted images over a relatively wide range of concentrations.

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.

Field-Echo Pulse Sequences Used under Suspended Respiration for Detection of Liver Metastases

To obtain a fast MRI sequence for detection of liver metastases under suspended respiration, two healthy volunteers were examined with the field echo sequence FLASH, using a large number of repetition times, echo times, flip angles and matrix sizes. The spleen was used to simulate liver metastases and contrast-to-noise ratios between liver and spleen were calculated and the sequence with the highest ratio was considered optimal. The different FLASH sequences were also compared with spin echo sequences using short repetition and echo times. A FLASH sequence with a repetition time of 140 ms, an echo time of 14 ms, a flip angle of 80 to 100 degrees and a matrix size of 128×256 was considered the most suitable for detecting liver metastases. This sequence, together with other FLASH and spin echo sequences, were used for examination of five patients with liver metastases from endocrine gastrointestinal tumours.

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 Hodgkin's 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).

Repeat Femoral Arteriography in Hyperlipidemic Patients

Femoral arteriography was performed in 62 patients with significant hyperlipidemia. Sixty were asymptomatic and two had intermittent claudication. The patients participated in a study aiming to demonstrate whether serum lipid lowering by drugs could influence the development of femoral artery atheromatous disease. Half of the patients were treated with fenofibrate and nicotinic acid and the other half served as a control group. At the first arteriography atherosclerotic lesions were found in 46 of the 62 patients (74%). Arteriography was repeated up to three times without complications. Visual analysis of angiograms revealed considerable inter-observer variation. An attempt was made to assess the angiograms by a computerized method which, however, still needs improvement and a computer designed for image analysis. Most patients had small or moderate atheromatous deposits in the femoral artery at the initial examination, in most cases showing no change during the study period of 18 months. Regression was found in five patients of the treated group, but in none of the control patients as judged by visual gradation (p<0.001).

Superparamagnetic Particles as Oral Contrast Medium in MR Imaging of Malignant Lymphoma

Non-biodegradable superparamagnetic particles, in plain and viscous aqueous suspensions, were used as an oral contrast medium in 34 patients with known or suspected malignant lymphoma. The contrast effect, the occurrence of artifacts, and the distribution were evaluated in the plain and the viscous aqueous suspensions, and the diagnostic information received from abdominal MR examinations performed without bowel contrast medium was compared with that of post-contrast examinations. Magnetic particles in the concentration of 0.5 g/l displayed a good contrast effect at 0.5 T, and helped in differentiating the intestine from adjacent tissues, resulting in increased diagnostic information in abdominal MR imaging. In the patients given the viscous aqueous suspension the occurrence of artifacts caused by the magnetic particles decreased considerably, and the distribution was homogeneous and improved compared with that in patients given the plain aqueous suspension.

Relaxation Enhancement of the Dog Liver and Spleen by Biodegradable Superparamagnetic Particles in Proton Magnetic Resonance Imaging

Bio-degradable superparamagnetic particles of about 0.5 μm diameter were investigated in 2 dogs as potential intravenous contrast enhancing agents for the reticuloendothelial system. The particles lowered the MRI signal of the liver for all investigated sequences, while the signal of the spleen was lowered only in T2 weighted sequences. No clear effect was seen on signals of fat and muscle. There was a pronounced effect on T 2 in both liver and spleen but relatively little effect on T1. Diminishing contrast effect with time indicates that the particles degrade. The particles did not have any adverse effects on the general state of the dogs or on routine liver and kidney function tests.

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.

Magnetic Resonance Imaging of the Transplanted Kidney

Interstitial fibrosis is a frequent finding in biopsies from long-term renal allografts, and may be due to chronic cyclosporine nephrotoxicity or chronic rejection. In this study, long-term renal transplants were investigated with magnetic resonance (MR) imaging, and the results were correlated to histopathology and graft function. Seventeen patients were investigated with MR one to 10 years after transplantation and with simultaneous ultrasonographically guided cortical needle biopsy and function tests. Histopathology included semiquantitative grading of degree of fibrosis and quantitation of ratios of tubular structures to interstitial tissue. The correlation between the histopathological assessment of interstitial fibrosis and graft function was good. Poor differentiation between the renal cortex and the renal medulla at MR imaging was correlated to high degree of interstitial fibrosis in the kidney transplants as well as to reduced graft function. MR examination may thus be of value in the evaluation of long-term renal transplants with chronic functional changes.

Magnetic Resonance Imaging of Acute Myocardial Infarction in Pigs Using Gd-Dtpa

Six pigs with coronary artery occlusion were investigated with MR imaging before and subsequently for about 2.5 hours at repeated intervals after the intravenous administration of Gd-DTPA (0.4 mmol/kg). The animals were sacrificed after a total occlusion time of 6 hours and the hearts were excised. The excised hearts were then reexamined in the MR equipment and stained with TTC (triphenyl tetrazolium) in order to define areas of infarction. Four control hearts with 6-hour-old infarctions were only imaged ex vivo without any previous administration of contrast media. In vivo, there was no clear demarcation of infarction with or without Gd-DTPA. Ex vivo, without any contrast media, the infarctions were poorly discriminated with a discretely increased signal intensity relative to normal myocardium in the T2 weighted images. Gd-DTPA was found to accumulate in the infarctions, which caused an elevated signal intensity most pronounced in the T1 weighted images. This considerably improved the delineation of the infarcted area.

Gd-DTPA-Enhanced MR Imaging in Mediastinal Hodgkin's Disease

Gd-DTPA-enhanced MR imaging of 15 patients with primary mediastinal Hodgkin's disease was done before, during and after treatment. A total of 43 MR examinations were performed. After successful treatment, 13 patients had residual masses with reduced signal intensity (SI) ratio in the T2-weighted images. The majority of these also had decreased contrast enhancement as compared with the corresponding primary tumour. There was a significant positive correlation between the contrast enhancement and the SI ratios in the T2-weighted images of the primary tumours and/or the residual masses. Necrosis was seen in 3 of the primary tumours and one patient had a cystic residual mass. These necrotic/cystic lesions were easier to detect with the use of Gd-DTPA. Low SI ratio in the T2-weighted image and low contrast enhancement of the residual mass seem to indicate residual inactivity. Gd-DTPA facilitates the differentiation between cystic/necrotic and solid lesions.

Motion Associated Susceptibility Artifacts

A bowel labeling agent is important for improving abdominal MR. Besides providing contrast between the bowel and other organs, the contrast agent itself is a potential source of artifacts. The artifacts created by superparamagnetic particles (SPP) subjected to motion have been studied in vitro at 0.5 T, and compared to artifacts created by a paramagnetic compound. Apart from the expected static effects of the SPP, movement induced additional artifacts were seen as signal displacements in the phase-encoding direction. The artifacts were obvious at an iron concentration of 1 mg Fe/ml, barely visible at 0.2 mg Fe/ml, and completely absent at 0.1 mg Fe/ml. Artifacts were also evident with the SPP outside the imaging slice. This further emphasizes the importance of choosing the lowest effective dose when using SPP contrast agents. For the paramagnetic agent, motion propagated artifacts consisted of high and low signal regions in a mosaic pattern.

Double-Contrast Enhanced Mr Imaging of Myocardial Infarction in the Pig

Myocardial infarction was induced by ligating a diagonal branch of the left anterior descending artery in 18 pigs. All pigs were sacrificed 6 h after the occlusion. Dysprosium diethylenetriaminepentaacetic acid bismethylamide (Dy-DTPA-BMA, 1.0 mmol/kg) was administered i.v. to 6 pigs, starting 3 min before sacrifice (injection time approximately 1 min). In a second group of 6 pigs, a double-contrast technique was used, consisting of an i.v. injection of gadolinium-DTPA-BMA (0.4 mmol/kg) 2 h before sacrifice, followed by an i.v. injection of Dy-DTPA-BMA (1.0 mmol/kg) 3 min before sacrifice. Six additional pigs, subjected to 6 h of coronary artery occlusion without administration of contrast medium, served as controls. The hearts were excised and imaged with MR. In the control animals, the infarctions demonstrated an increased signal intensity in the proton density- and T2-weighted images. Administration of Dy-DTPA-BMA primarily improved infarct visualization in the proton density- and T2-weighted images, due to reduction of signal intensity in nonischemic myocardium. The double-contrast technique further improved infarct visualization in all sequences.

MR-Cholangiography with a Double Contrast Technique

The combination of superparamagnetic particles (SPP) as a ‘negative’ contrast agent for the liver parenchyma and Cr-HIDA as a ‘positive’ one for the bile ducts was tested in dogs. The maximum effect of SPP was present about 30 minutes after injection with a reduction of the image intensity of the liver close to the background noise level at the highest dosages. This effect lasted for about 4 to 5 hours and it had disappeared after 24 hours. Before any contrast administration or after Cr-HIDA the bile ducts were not discernible, but a high signal in the gallbladder was present 15 to 30 minutes after injection of Cr-HIDA. After SPP the wider bile ducts were discernible because of the lowering of the signal intensity in the liver. When SPP were followed by Cr-HIDA, the bile had a higher signal intensity, and even tiny bile ducts were visible. After cholecystokinin visualization of the choledochus duct was achieved as well as contrast filling of the duodenum. The blood, urine and liver function tests were found normal during the experiments. The combination of superparamagnetic particles and Cr-HIDA seems to be a promising method for MR-cholangiography. An evaluation of the anatomic structures of the liver should be possible with this method in different pathologies.

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.

First-pass myocardial perfusion MR imaging with outer-volume suppression and the intravascular contrast agent NC100150 injection: preliminary results in eight patients

The authors evaluated the feasibility of combining single-shot T2-weighted turbo spin-echo magnetic resonance (MR) imaging and first-pass myocardial perfusion MR imaging with an intravascular ultrasmall superparamagnetic iron oxide (USPIO) contrast agent, NC100150 Injection (3 mg of iron per kilogram of body weight). Eight patients with coronary vessel disease underwent T2-weighted turbo spin-echo MR imaging (in-plane resolution, 1-2 mm) during the first pass of the USPIO contrast agent. The mean decrease in signal intensity in myocardium perfused by a nonstenotic coronary artery was 59% +/- 13 (SD) (P < .012) This method is feasible for imaging of myocardial perfusion.

Spectroscopy of large volumes: spectroscopic imaging of total body fat

An extremely large volume of interest (VOI) approximately 60 dm(3) was used for the measurement of the proton ((1)H) spectrum of the human body. The measurements were performed at 1.5 T with a high-speed spectroscopic imaging technique that uses read gradient during acquisition. The spectrum was computed from coronal 30 mm thick slices of a normal male and female volunteer. The fat/water ratio of the body was used to quantify the fat depots. The results were corrected for relaxation effects and were in good agreement with published values of subjects with comparable body mass index (BMI).

Spectroscopic imaging of bone marrow composition in vertebral bodies

The proton spectroscopic imaging technique that uses read gradient during acquisition was used for the measurement of the proton spectra in the lumbar and thoracic part of the spine of a patient with breast cancer without known skeletal metastases. The bone marrow fat/water ratios were evaluated in the same location before and after chemotherapy treatment. The results were corrected for relaxation effects. The fat/water ratios showed a significant increase as a consequence of the bone marrow degradation process due to chemotherapy. The proposed spectroscopic imaging technique offers rapid acquisition of proton spectra from large volumes of the vertebral bodies.

Contrast agents in acute myocardial infarction

The experimental design in examination of acute myocardial infarctions should be valid in terms of flow, perfusion and re-flow after intervention. The contrast agents concentration in experimental studies can be measured by microdialysis. We have assessed the usefulness of different extracellular and blood pool contrast agents for visualization of the area at risk in coronary artery occlusions. The double contrast technique, where Dy-DTPA-BMA was combined with Gd-DTPA-BMA yielded a superior infarct visualization. Blood pool agents for example NC100/150 injection is also promising in first path myocardial perfusion imaging.

High-resolution spectroscopic imaging of the human skin

High-resolution water, fat and chemical shift artefact-free images of different areas of the skin were obtained on a whole-body MR unit (1.5 T) with commercial receiver surface coil with a diameter of 25 mm and high-power gradients (23 mT/m). Sufficient signal-to-noise ratio was achieved by lowering receiver bandwidth to +/-10 kHz or lower and shortening the echo time to 11 (13) ms. Spectroscopic image data sets were acquired with resolution 0.102 x 0.133 mm in plane and slice thickness 0.5 mm. The results demonstrate that it is possible to produce high-quality water and fat micro-images of the skin layers using only a few chemical shift encoding steps in a clinically reasonable time (approximately 2 minutes per slice).

Evaluation of nonperfused myocardial ischemia with MRI and an intravascular USPIO contrast agent in an ex vivo pig model

The ultrasmall superparamagnetic iron oxide (USPIO) preparation NC100150 Injection (Clariscan; Nycomed Imaging, Oslo, Norway) was tested for its ability to delineate nonperfused myocardium under steady-state conditions. An experimental animal model of focal myocardial ischemia induced by ligation of the distal part of the left anterior descending artery was used. The contrast agent was administered in four doses: 0, 4, 8, and 12 mg Fe/kg body weight. Magnetic resonance examination ex vivo, including T1-, T2-, and T2*-weighted sequences, was performed. Nonperfused myocardium was determined by fluorescein. The best delineation of nonperfused myocardium was found with a T1-weighted inversion recovery/turbo spin-echo sequence and doses of 4 and 8 mg Fe/kg body weight, where 95% of the volume was discernible at the dose of 4 mg Fe/kg body weight. The results suggest that steady-state imaging by T1-weighted sequence with the use of NC100150 Injection to delineate nonperfused myocardium is feasible. J. Magn. Reson. Imaging 2000;12:866-872.

Chemical shift artifact-free microscopy: spectroscopic microimaging of the human skin

A spectroscopic imaging technique with high spatial resolution was used for the study of human skin in vivo. The measurements were performed using a whole-body magnetic resonance system (1.5 T) with standard gradients and a standard 8-cm diameter circular surface coil. A decisive gain in signal-to-noise ratio was achieved by reducing the receiver bandwidth of the imaging system to values less than +/-5 kHz. The chemical shift misregistration was eliminated by post-detection data processing. The method was tested on different kinds of skin, on the foot sole and head. Water, fat, and chemical shift artifact-free images were obtained with resolution 0.107 x 0.143 mm in plane and slice thickness 1 mm. A major advantage of the spectroscopic imaging procedure is that the pulse sequence can be optimized for the maximum signal-to-noise ratio. There is no need for special modification of the sequence to circumvent the chemical shift artifacts (water, fat suppression, etc.).

Characterization of human head vasculature by percolation parameters

A data reduction procedure, originally proposed for characterization of fractals and random percolation clusters, has been used to evaluate the vascular system of the human head. The motivation behind this study arose from the wish to study empirically transport properties of vascular systems and to find a suitable formalism for their description. MR angiographic data acquired by a standard 3D inflow method were used. The evaluated parameters refer to the backbone fractal dimensionality and the correlation length. The fractal dimensionality of the backbone was found to be 1.71 for the human head vasculature. This value fits the theoretical range of random percolation networks. It is concluded that concepts of percolation theory might have some value for characterizing the structure and transport properties of the vascular system.

Magnetic resonance spectroscopic imaging for visualization and correction of distortions in MRI: high precision applications in neurosurgery

We present a method for the quantification and correction of geometrical/intensity distortions of magnetic resonance images predominantly caused by bulk magnetic susceptibility shifts due to susceptibility heterogeneities of measured biologic tissues and shape of the object under investigation. The method includes precise and fast measurements of the static magnetic-field distribution inside the measured object and automated data processing. Magnetic-field deviations in the range (-2.4; 2.6) ppm were found in the human brain at B0 = 1.5 T. For routinely used imaging parameters, with a read gradient strength of about approximately 1 mT/m, the magnetic-field perturbations in the human brain can cause geometrical distortions up to +/-4 mm and intensity changes up to +/-50%. MR images corrected by the described method are suitable for planning high precision applications in neurosurgery.

Chemical shift artifact-free imaging: a new option in MRI?

A high-speed proton spectroscopic imaging method with high spatial resolution was used for obtaining water, fat, and chemical shift artifact-free images on a 1.5 T MR scanner. The technique is based on a fast radiofrequency (RF) spoiled gradient-echo sequence. The chemical shift information is encoded by incrementing the echo time in a series of image records. Suppression of water or fat signals is not used. The technique does not require a highly homogeneous magnetic field. Spectroscopic images of a human volunteer were compared with corresponding conventional images obtained using the short inversion time inversion recovery (STIR) and the selective partial inversion recovery (SPIR) methods. The results demonstrate that it is possible to produce images entirely free from chemical shift artifacts using only a few chemical shift encoding steps. The technique also produces pure water and fat images which are significantly better than those produced by using the conventional methods STIR and selective partial inversion recovery. The described method appears to be promising for routine clinical applications because it can be fully automated.

Uptake of mangafodipir trisodium in liver metastases from endocrine tumors

The purpose of the study was to investigate retrospectively whether mangafodipir trisodium (MnDPDP) can enhance the liver metastases from endocrine tumors. Thirteen patients with endocrine tumors and liver metastases underwent T1-weighted spin-echo (SE) and turbo gradient-echo (GRE) MRI conducted before and 20 to 60 minutes after i.v. infusion of MnDPDP. Additional 24-hour-delay scans were performed in 8 of 13 patients. MR signal intensity (SI) was measured in liver parenchyma and metastases, which was then related to that of paraspinal muscle. A total of 30 lesions on precontrast and postcontrast images and 18 lesions on 24-hour-delay images were measured. An enhancement by 49% in SE and 40% in GRE images (P = .0001) was observed in tumor tissues after MnDPDP infusion. In 24-hour-delay images, the SI of the lesions remained relatively high, but in liver parenchyma, it decreased significantly, and the tumor-liver tissue contrast was reduced.

1H-spectroscopic imaging with read gradient during acquisition in inhomogeneous fields: analysis, measurement strategy, and data processing

The proton magnetic resonance spectroscopic imaging techniques that use read gradient during acquisition produce proton spectra with high spatial and moderately high spectroscopic resolution in a reasonable time for in vivo applications. These techniques suffer mainly from the spatial and spectral distortions caused by the convolution of spectral/spatial information (chemical-shift artifacts) and from the spectral shifts caused by static magnetic field inhomogeneities. The investigators analyze the chemical-shift artifacts in the presence of nonnegligible static magnetic field inhomogeneities and propose a postdetection processing scheme to correct for such effects. Spectral artifacts caused by chemical shifts, spectral line overlapping, streak broadening, and magnetic field inhomogeneities are discussed. The postdetection data processing scheme is demonstrated on measurements of a phantom as well as a human leg.