Biomedical subjects
Publications and source records attributed to G Marchal.
We present a patient with idiopathic liver hemochromatosis and mild secondary cirrhosis complicated by Yersinia sepsis and miliary liver abscesses proven by echography and CT.
Twenty patients [15 men, 5 women, 19-71 years old (mean 52 years)] highly suspected of having tumoral liver pathology were prospectively studied with motion compensated T2-weighted spin echo (SE) [repetition time (TR) 2,200 ms, echo time (TE) 90 ms] and Gd-DOTA enhanced gradient echo fast low angle shot [TR 60 ms, TE 10 ms, angle 30 degrees) sequences. The final diagnoses were hemangioma (five), hepatocellular carcinoma (four), focal nodular hyperplasia (one), adenoma (one), metastasis (two), abscess (two), echinococcal cyst (one), tumor of unknown origin (three), cirrhosis (one). Contrast enhanced images were obtained during the early vascular phases after intravenous bolus injection of Gd-DOTA at a dose of 0.1 mmol/kg (0.2 ml/kg). After Gd-DOTA, positive contrast enhancement was seen in 11 cases, negative enhancement in 4, and nonenhancement in 6. Contrast patterns were similar to contrast enhanced CT. In terms of visibility of lesions, the unenhanced motion-compensated T2 SE sequences were superior to the nonenhanced gradient echo sequences in 12 patients and equal in 8. After gadolinium enhancement, T2-weighted SE images were superior to the postcontrast gradient echo images in eight cases, equal in eight and inferior in four cases.
Magnetic resonance was performed in five patients with obstructive hydrocephalus due to surgically proven colloid cyst of the third ventricle. On T1-weighted images two lesions were homogeneously hyperintense and another homogeneously isointense with the surrounding brain parenchyma. On T2-weighted images these three lesions were strongly hypointense except for a hyperintense rim at the periphery. At surgery in these patients the cyst was thin walled and filled with viscous colloidal material. In two patients the content of the lesion was composed of two layers. The outer layer was hyperintense and the inner layer hypointense in one patient. In the other patient the periphery of the lesion was isointense with central hypointensity. On T2-weighted images the content of both lesions was hyperintense at the periphery with central hypointensity. In these last two patients at surgery the cyst was thin walled too. However, two clearly different components could be found in the cyst content: an outer component composed of amorphous material and cellular debris and an inner component consisting of viscous material.
A new method of CT is proposed: "volume scanning," produced by continuous table incrementation during continuous scanning. This approach was successfully implemented on a commercially available third generation scanner with continuous measuring system and slip ring technology (Somatom Plus; Siemens AG, Erlangen, F.R.G.). Different phantoms were scanned with volume scanning at different table incrementation speeds and with conventional scanning with standard sequential table incrementation. Comparison of the results showed that in volume scanning, a table incrementation speed equal to the slice thickness per second provides the optimal compromise between acquisition volume and level of artifact production. Different reconstruction parameters available were tested for optimal artifact reduction. A 240 degrees reconstruction angle offered the best results. Experiments on geometrical distortion and contrast resolution revealed hardly any difference between volume scans and conventional scans. Up to now volume scanning has been used in 20 patients. Images obtained in the thoracic, pelvic, and upper abdominal region show exceptionally sharp anatomical detail with minimal artifacts. Volume scanning opens new possibilities in fast sequential dynamic contrast studies in the abdomen and chest.
Fifty patients with newly diagnosed, untreated intracranial tumors were examined with 1H nuclear magnetic resonance single-volume spectroscopy (MRS) using a 1.5 T whole-body MR system. Prior to the MRS, contrast enhanced MR and/or CT imaging studies were carried out. Histological verification was obtained in all patients except one. All tumor spectra revealed distinct abnormalities as compared with the normal brain spectra. Although most meningiomas showed a rather characteristic spectral pattern, generally features specific for the various tumor types were not observed. For instance, though a strong lactic acid signal was seen in most malignant tumors, this signal was also evident in five benign neoplasms.
Gadolinium-enhanced MR was performed in 28 patients with 17 supratentorial and 11 cerebellar venous angiomas. The use of gadolinium allowed detection of 9 of 28 venous angiomas (32%) that were not visible before gadolinium or which were only recognized in retrospect. Before gadolinium the peripheral medullary veins that are typical for these venous malformations were only visualized in 4 of 17 (23%) supratentorial and in 5 of 11 (45%) cerebellar lesions, for a total of 9 of 28 (32%) venous angiomas. After intravenous administration of gadolinium these veins were seen in 27 of 28 (96%) venous angiomas. Extension of the lesions to the wall of the ventricles was seen in 24 of the 28, 16 of 17 supratentorial and 8 of 11 cerebellar, lesions after gadolinium. This information was missed on plain MR in 6 of these lesions. The type of venous drainage, either superficial or deep, could be determined by gadolinium-enhanced MR in all cases where angiography was available for comparison. Before gadolinium this information was not available in eight patients. The intravenous administration of gadolinium adds significant information in the MR study of venous angioma.
Henoch-Schönlein purpura is rarely considered in the differential diagnosis of ureteral obstruction in children. Renal ultrasound and intravenous urography may reveal hydroureteronephrosis but usually fail to yield a specific diagnosis. In this child CT differentiated between an intrinsic ureteral stenosis (hemorrhagic ureteritis) and an extrinsic ureteral stenosis (retroperitoneal fibrosis), two rare complications of Henoch-Schönlein purpura. The CT findings of hemorrhagic ureteritis are described.
Axial and sagittal proton density and T2-weighted MR images (TR 2,500-3,000 ms, TE 15-22 and 85-90 ms) were performed in 50 patients with multiple sclerosis (MS) on a 1.5 T superconductive system. The number of plaques on the axial and sagittal images in the periventricular white matter, the corpus callosum, the brain stem, the cerebellum, and the basal ganglia were counted separately by two independent observers. A total of 858 lesions (mean 17.40 +/- 21.57) were seen on the axial series and 1,196 (mean 24.32 +/- 26.22) on the sagittal scans. More lesions were visualized on sagittal images in the periventricular region (mean 18.79 +/- 21.69 versus 13.34 +/- 16.45; p less than 0.001) and the corpus callosum (mean 3.00 +/- 2.72 versus 0.57 +/- 1.19; p less than 0.001). In the brain stem more lesions were visualized on the axial images (mean 1.55 +/- 2.55 versus 0.87 +/- 1.20; p less than 0.05). In the cerebellum and basal ganglia, scans in the two planes were equivalent (p greater than 0.5). In three patients lesions were seen on the sagittal series, while the axial scans were normal. Sagittal T2-weighted images appear to demonstrate significantly more MS plaques than transverse images, especially in the periventricular region and the corpus callosum. This is explained by partial volume averaging, by the orientation of some cerebral structures (e.g., corpus callosum) with regard to the section plane, and by the longer diameter of the lesions in the axial plane.
Most MR angiography (MRA) techniques use macroscopic blood motion to characterize the flowing spins. A different approach is represented by the use of contrast enhancement of blood pooling agents. The intravenous injection of one of these agents, namely Gd-DTPA polylysine, produces a shortening of the blood T1 below the T1 values of fat and soft tissues. In this study on experimental MRA in rabbits, we used an imaging sequence with a 90 degrees saturation pulse and a 180 degrees inversion recovery pulse. Both the saturation and inversion recovery times were adjusted to suppress the signals of soft tissues and fat. The remaining ultrashort T1 blood was imaged with a projective velocity refocused spin echo or gradient echo sequence. Magnetic resonance angiography provided excellent vessel detail with a 30-60 s acquisition time. In addition, there was no need for further processing after image acquisition because the projection was obtained immediately. The disadvantages of the technique are the need for contrast medium injection and the nonselectivity of MRA.
Most sequences for MR angiography (MRA) used today exploit the macroscopic motion of the blood to differentiate vessels from the stationary tissues. An alternative approach to inflow based MRA is contrast enhanced MRA, in which relaxation agents are used to selectively shorten the T1 of the blood below the T1 value of the stationary tissues. We have evaluated cerebral Gd enhanced MRA, comparing it with conventional angiography and noncontrast inflow based MRA. Contrast/enhanced MRAs were obtained at 1.0 T with a 3D FISP sequence with TR/TE/alpha: 35-40 ms, 7-11 ms/TE/25 degrees. Contrast enhancement was obtained by a biphasic injection of a double dose of Gd-DOTA (0.2 mmol/kg) during image acquisition. With the described technique the conspicuity of both cerebral arteries and veins is improved compared to nonenhanced inflow MRA.
Both perfusion and diffusion contribute to NMR signal enhancement after intravenous injection of a nonspecific contrast agent. In the present study the roles of perfusion and diffusion in the contrast enhancement of induced liver lesions in the rat and the rabbit were evaluated. This was done by comparing Gd-DOTA absolute enhancement signal-to-noise versus time plots of various lesions with the findings from microangiography and histology. Four types of enhancement could be recognized. Diffusion was the major factor in the delayed enhancement seen in lesions that had large extravascular diffusion space.
To assess both the effect of Mn-DPDP as a hepatobiliary-specific contrast agent in bile duct obstruction and the relative role of liver and kidney in the elimination of this agent from the body, an animal experiment was set up. Twelve rats were used and divided into three groups. In group 1 the common bile duct was ligated, in group 2 bile duct ligation was limited to one lobe, and group 3 served as control. Magnetic resonance T1-weighted SE images were obtained before and after the injection of 25 mumol/kg of Mn-DPDP during the first 2 h and at day 1, 2, 3, 4, and, in some animals, up to 21 days. In normal rats the absolute enhancement signal-to-noise ratio (S/N) versus time plots obtained from the liver after Mn-DPDP injection returned to precontrast values within 24 h. In the group with common bile duct ligation, important liver enhancement persisted up to 21 days. In the group with selective obstruction, liver intensity normalized after 3 days. The S/N plots from spleen, renal cortex, and obstructed liver lobe showed similarities in time course. The present data indicate that Mn elimination is strongly impaired in the presence of bile duct obstruction. Renal glomerular filtration is ineffective in eliminating Mn from the body. The persisting splenic and renal cortical enhancement suggests that free Mn or some Mn-DPDP metabolite either is strongly bound to plasma proteins and acts as a blood pooling agent and/or is uptaken by the splenic or renal parenchyma.
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OBJECTIVE: The usefulness of a test bolus of contrast medium for predicting the optimal scan delay time in spiral CT-angiography (CTA) was determined. MATERIALS AND METHODS: Two axial single level CT studies were performed at the level of the pancreas in 20 patients, first after injection of a 12 ml "test" bolus, second after administration of a 90 ml bolus. The time interval between the start of the test bolus injection and peak aortic enhancement (T-peak) was measured and compared with the time required to reach a 50, 100, and 150 HU level of aortic enhancement after 90 ml bolus injection. RESULTS: The time required to reach 50, 100, and 150 HU enhancement during the 90 ml bolus was largely variable (mean SD 4.9 s). The T-peak varied between 11 and 32 s (mean 20, SD 6.1 s). There was a strong correlation between the T-peak and the time to the different levels of enhancement during the 90 ml bolus (R2 > or = 0.83). The mean time to 50, 100, and 150 HU enhancement was T-peak -3.3 s (SD 2.5 s), T-peak -1.2 s (SD 2.4 s), and T-peak + 1.3 s (SD 2.4 s). CONCLUSION: The injection of a test bolus improves the timing of a spiral CTA acquisition.
PURPOSE: The purpose of this study was to investigate the influence of different parameters (object size, shape, orientation, contrast, observer, and window setting) on the accuracy of volume measurements in spiral CT. METHOD: The phantom study consisted of two parts. First, well-circumscribed ellipsoid objects were scanned with conventional and spiral CT. Volumes were determined by two observers using manual contour delineation and summation-of-areas. The influence of object size, CT technique, and observer was assessed. Second, irregularly shaped gingerroots were scanned and the effect of observer, contrast, and orientation was investigated. Also assessed in both parts of the study was the effect of window setting. RESULTS: Spiral CT offered higher accuracy and reproducibility than conventional CT did. The accuracy of volume measurements was mainly determined by the window setting used for image display. Using an "optimized" window center value halfway between object density and background density resulted in overestimation of true object volumes if the number of slices through the object (number of samples) was low. Other factors (contrast, observer-related errors in contour delineation) were less important. CONCLUSIONS: Volume measurements of small objects, obtained with spiral CT and using manual contour delineation, may be grossly erroneous. Major causes of inaccuracy are an inappropriate window center selection and undersampling.
Double-phase (dual-phase) spiral computed tomography (CT) represents a technologic advance that allows two evaluations of hepatic blood flow during a single 19-29-second breath hold: once during the hepatic arterial phase (HAP) and again during the portal venous phase (PVP). Perfusion disorders of the hepatic parenchyma are more readily observed at double-phase spiral CT. The various hepatic perfusion disorders are related to (a) portal venous inflow obstruction, (b) hepatic venous outflow obstruction (e.g., Budd-Chiari syndrome, cardiac failure, mediastinal fibrosis), (c) mediastinal or thoracic venous inlet obstruction, (d) focal liver lesions, (e) inflammatory processes, (f) normal anatomic variants in the hepatic blood supply, (g) altered hemodynamics after the placement of a transjugular intrahepatic portosystemic shunt, and (h) uncertain causes. In general, the area of involvement appears hyperattenuating on HAP images and of normal or near-normal attenuation on PVP images. Familiarity with the spiral CT appearances of different types of perfusion disorders allows the radiologist to separate clinically insignificant flow phenomena from perfusion disorders caused by underlying parenchymal or vascular disease.
BACKGROUND AND PURPOSE: Combined perfusion and oxygen metabolism PET imaging is highly predictive of spontaneous outcome after middle cerebral artery (MCA) stroke, independent of clinical scores, but whether the assessment of perfusion alone by SPECT provides similar information remains unclear. We have assessed the prognostic value of (99m)Tc-HMPAO-SPECT at the acute stage of stroke. METHODS: Twenty-seven first-ever nonhemorrhagic MCA territory stroke patients were prospectively studied 4-20 h (mean: 12 h) after onset with (99m)Tc-HMPAO-SPECT. None was part of a therapeutic trial or received thrombolysis. Neurological deficits were quantified at admission and 2 months later with Orgogozo's MCA scale. SPECT images were visually classified by 3 independent observers into one of three patterns, as follows: pattern I = marked and extensive tracer hypofixation; pattern II = moderate and/or focal hypofixation with or without combined hyperfixation, and pattern III = normal or increased uptake without hypofixation. In addition to this visual analysis, we also calculated a voxel-based 'hypoperfusion score', an index of severity x extent of hypofixation according to Mountz's method. RESULTS: There was a good intra- and interobserver agreement. After consensus, 9, 14 and 4 patients were classified in patterns I, II and III, respectively. These patterns had a significant predictive value for raw outcome but not for percentage recovery (p = 0.008 and p = 0.127, respectively). Thus, all patients in pattern III had a good outcome, while most (but not all) patients in pattern I had a poor or intermediate outcome; pattern II patients were more evenly distributed among outcomes. Hypoperfusion scores were highly significantly positively correlated with both 2-month outcomes and percentage recoveries, even after controlling the predictive value of day 0 MCA scores by partial correlations. COMMENTS: We found that SPECT had a significant added predictive value even when compared to admission neurological scores. Although less accurate than PET, (99m)Tc-HMPAO-SPECT may help to predict spontaneous individual neurological evolution, especially whenever perfusion images are normal or show an increased tracer uptake without associated hypofixation.
Although 'intrahemispheric diaschisis' (i.e. a hypometabolism affecting the cerebral hemisphere ipsilateral to but remote from the infarct) may classically exacerbate acute-stage neurological deficit and influence early recovery, it has been studied only rarely. Out of a series of 30 patients with first-ever middle cerebral artery (MCA) territory stroke, we analyzed the data from 19 survivors investigated by (15)O positron emission tomography (PET) both in the acute (within 5-18 h of clinical onset) and subacute (approximately 3 weeks later) stage, and for whom chronic-stage CT coregistered with PET was available to assess infarct topography and size. Orgogozo's MCA scale was used to assess neurological deficits at the time of, and recovery between, the PET studies. Oxygen consumption was obtained for both PET sessions for the whole ipsilateral hemisphere (excluding ventricles and infarct), as well as for the thalamus and the occipital and mesial-prefrontal cortex (i.e. potentially deafferented tissue outside the MCA territory). In all regions except the occipital cortex, the oxygen consumption significantly decreased between the first and the second session, without significant correlation with the concomitant changes in MCA scores. However, acute-stage mesial-prefrontal metabolism was significantly correlated with neurological recovery. Also, both the hemisphere and the mesial-prefrontal metabolism at the second session were significantly correlated with both infarct size and concomitant MCA scores, but the latter relationship became insignificant when infarct size was taken into account. This study reveals no evidence of acute intrahemispheric diaschisis after MCA territory stroke in man. However, it documents for the first time a phenomenon of delayed intrahemispheric remote hypometabolism developing while the patients clinically recover. Because the degree of this secondary phenomenon is a function of infarct size, a mechanism of degeneration of the damaged neuron terminals is likely. Finally, contrary to other reports, neurological recovery was not a function of thalamic hypometabolism, but appeared to be influenced by acute-stage mesial-frontal metabolism, perhaps because this region is part of a network that has an important compensatory role in motor recovery.