Supra- and juxtarenal aneurysms of the abdominal aorta: preoperative assessment with thin-section spiral CT

PURPOSE

To assess the contribution of thin-section spiral computed tomography (CT) to the preoperative radiologic evaluation of juxta- and suprarenal abdominal aortic aneurysms.

MATERIALS AND METHODS

Thirty-eight patients (26 men, 12 women; age range, 60-81 years) with infrarenal (n = 23), juxtarenal (n = 8), and suprarenal (n = 7) aneurysms underwent digital subtraction angiography (DSA) and 2-mm-collimation spiral CT. Cine-interactive display of overlapping axial, reformatted, and maximum intensity projection images were used for CT image analysis. CT findings were compared with angiographic and surgical findings.

RESULTS

The proximal extent of the juxta- and suprarenal aneurysms (n = 15) could be correctly predicted in 12 cases (80%) with DSA and was exactly determined in 14 (93%) with CT. All renal arteries except three accessory renal arteries were correctly depicted with spiral CT (83 of 86 [96%]). With DSA as the standard of reference, renal artery stenoses of at least 70% were accurately assessed in 95% of cases.

CONCLUSION

Thin-section spiral CT can provide additional information in the preoperative diagnosis of juxta- and suprarenal aneurysms.

Contrast-enhanced MR angiography

Despite many optimizations, the current limitations of plain MR angiography include: saturation that impairs the visualization of veins and arteries with slow flow and spin-dephasing signal voids in locations with turbulent flow. Recently, the use of contrast agents has been proposed to cope with these remaining problems. Because of induced shortening of the T1 of the blood, saturation in the blood vessels is overcome. As a result, arteries and veins are visualized with the same signal intensity, which makes the technique less flow-dependent. In combination with short T1-weighted acquisitions, today CE MRA can be obtained while the patient is holding his breath. This last approach is most promising for abdominal applications since the respiratory motion can be frozen. As these acquisitions also use very short echo times, spin dephasing can be reduced. In conclusion, the use of contrast agents has greatly increased the clinical usefulness of MR angiography.

Identification of the surface-exposed lipids on the cell envelopes of Mycobacterium tuberculosis and other mycobacterial species

The surface-exposed lipids of Mycobacterium tuberculosis, Mycobacterium avium, Mycobacterium kansasii, Mycobacterium gastri, Mycobacterium smegmatis, and Mycobacterium aurum were isolated by gentle mechanical treatment of cells with glass beads. Analysis of the exposed lipids demonstrated a selective location of classes of ubiquitous lipids on the surfaces of mycobacteria. While phosphatidylethanolamine and phosphatidylinositol mannosides were exposed in all the species examined, dimycoloyl trehalose ("cord factor") was identified in the surface components of M. aurum only. Furthermore, monomycoloyl trehaloses and triacylglycerides were identified in the surface-exposed lipids of M. avium and M. smegmatis but not in those of the other mycobacterial species examined. The species- and type-species specific lipids were present on the mycobacterial cell surface: phenolic glycolipids, dimycocerosates of phthiocerols, and lipooligosaccharides were identified in the surface-exposed materials of M. tuberculosis (Canetti), M. kansasii, and M. gastri, whereas glycopeptidolipids were identified in the outermost lipid constituents of M. avium and M. smegmatis. This difference in the surface exposure of lipids of various mycobacterial species may reflect differences in their cell envelope organizations. Brief treatments of M. tuberculosis with Tween 80 prior to the use of glass beads led to erosion of regions of the capsule to expose gradually both cord factor and other lipids on the cell surface of the tubercle bacillus, demonstrating that the latter lipids are buried more deeply in the cell envelope and leading to the proposal of a scheme for the location of the capsular lipids of the tubercle bacillus.

Paramagnetic metalloporphyrins: infarct avid contrast agents for diagnosis of acute myocardial infarction by MRI

In previous experiments in tumors we demonstrated that metalloporphyrins are particularly avid for nonviable tumor components. This study was performed to find out whether these agents can be used as MRI contrast agents for the visualization of acute myocardial infarction (MI). A total of 44 rats, 6 normal controls and 38 with occlusive MI (2-24 h old), were used. Gadolinium mesoporphyrin (Gd-MP) or manganese tetraphenylporphyrin (Mn-TPP) was intravenously injected at doses of 0.1, 0.05, and 0.01 mmol/kg. Three to 24 h after injection, axial and coronal T1-weighted (TR/TE 300/15 ms) spin-echo MR images were obtained before and after killing the animals and correlated with triphenyl tetrazolium chloride (TTC) histochemical preparations. The Gd-MP content in infarcted and noninfarcted myocardium was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES). MRI without contrast media could not discern the MI. However, 3-24 h after injection of either Gd-MP or Mn-TPP, the infarcted area was positively stained on MR images. This area matched well with the negatively TTC-stained area on the heart slices (r = 0.97). The contrast ratios between the infarcted necrotic myocardium and the noninfarcted regions varied from 150 to 300% depending on the type of agents and doses used. Neither false-positive nor false-negative findings were encountered. The metalloporphyrin concentration was more than 10 times higher in the infarcted than in the noninfarcted heart. Metalloporphyrins appear to be promising MRI contrast agents for detection and quantification of necrosis in MI. These preclinical results may open new perspectives in cardiac imaging.

Computer-assisted planning of oral implant surgery. An approach using virtual reality

A planning system for oral implant surgery is described. This system allows the interactive placement and adjustment of models representing oral implants on CT volume data. These CT data can be shown as two-dimensional (2D) slices, or as a three-dimensional (3D) surface-rendered model. The viewpoint is fully adaptable, and stereoscopy results in an enhanced insight in the interrelation between implants and structures. This approach offers many advantages when compared with the traditional manual planning or with a 2D computer based planning. Clinical trials are being performed.

Helical CT for the preoperative localization of islet cell tumors of the pancreas: value of arterial and parenchymal phase images

OBJECTIVE

In two-phase helical CT, organs are scanned in both the arterial and the parenchymal phase after IV injection of contrast material. The purpose of our study was to evaluate the usefulness of two-phase helical CT for the preoperative localization of pancreatic islet cell tumors.

MATERIALS AND METHODS

Ten patients with 11 surgically proven islet cell tumors were included in the study. Helical CT scans of the pancreas were obtained with 5-mm collimation and overlapping image reconstruction. Images were obtained in the arterial and parenchymal phases after contrast material injection. A test bolus was used for tailored bolus timing. Images were analyzed by two observers. If a tumor was detected, its density relative to the surrounding parenchyma was scored by consensus, using a five-point scale.

RESULTS

Nine of 11 tumors could be located using two-phase helical CT (sensitivity, 82%), including one 4-mm gastrinoma. Two lesions smaller than 5 mm could not be visualized. Two tumors were easier to detect (n = 1) or could only be detected on parenchymal-phase images (n = 1). Tumor conspicuity was better on arterial-phase images in two patients.

CONCLUSION

Our results show that obtaining CT scans in both the arterial and the parenchymal phase leads to improved detection of pancreatic islet cell tumors.

A semiautomatic three-dimensional segmentation method for disarticulation of bone structures on spiral computed tomography images

The use of binary thresholding for segmenting bone structures on spiral computed tomography images is negatively influenced by partial volume effects (PVEs) induced by the image acquisition. PVE leads to mixed voxels, making the binary decision "bone" or "nonbone" a difficult one to take. As a result, two distinct bone structures that are close to each other will often appear to be connected by this method. A typical example consists of "acetabulum/femural head" pairs in the pelvic region. To separate them, a clinical user must interactively draw a disarticulation line. This procedure is time consuming (often interaction in 50 slices is needed) and leads to unsmooth visualization of the disarticulated areas (by three-dimensional [3D] rendering techniques). We developed a semiautomatic cutting algorithm that leads to smooth disarticulated surfaces and considerably decreases the amount of user interaction. A sheet detection operator is applied to automatically separate bone structures. Detected sheets are used as disarticulation lines. Postprocessing ensures that sheets not relevant for the application do not influence the resulting image. Our approach is encapsulated in an interactive segmentation environment based on thresholding and 3D connected-component labeling. Results are shown for pelvic region, wrist, and foot bone disarticulations.

Sequential studies of severely hypometabolic tissue volumes after permanent middle cerebral artery occlusion. A positron emission tomographic investigation in anesthetized baboons

BACKGROUND AND PURPOSE

In the positron emission tomography literature, markedly hypometabolic brain tissue (oxygen metabolism < 1.3 to 1.7 mL.100 g-1.min-1) has often been equated with irreversible damage in the human brain. By serial positron emission tomography measurements, we investigated the temporal evolution of the volume of severely hypometabolic brain tissue after permanent middle cerebral artery occlusion in anesthetized baboons with, as a perspective, the development of rational therapeutic strategies.

METHODS

Seven anesthetized and ventilated baboons underwent sequential positron emission tomography examinations with the 15O steady-state technique before and 1, 4, 7, and 24 hours and 14 to 29 days after occlusion. In each baboon the infarct volume was calculated by quantitative histological procedures after 19 to 41 days of occlusion.

RESULTS

The sequential measurement of regional oxygen metabolism demonstrated an extension (for > or = 24 hours) of the volume of severely hypometabolic tissue as defined by both absolute and relative metabolic thresholds, and this profile of evolutivity is observed no matter the threshold used. Mean (+/- SEM) infarction volume of 2.4 +/- 0.6 cm3 was comparable to a tissue volume with oxygen consumption < 40% of contralateral metabolism. The volume of hypometabolic tissue was essentially stable at the 1-, 4-, and 7-hour postocclusion studies, increased markedly at the 24-hour study point, and increased even further in the chronic-stage study (on average, 17 days after occlusion). The tissue that eventually displayed a severely hypometabolic state at the final measurement showed a significant decrease of oxygen metabolism and cerebral blood flow at each time analyzed. In that tissue, the oxygen extraction fraction increased significantly at 1 hour (although not thereafter).

CONCLUSIONS

The extension of severely hypometabolic volume after middle cerebral artery occlusion reinforces the concept of a dynamic penumbra and suggests the existence of a relatively large window of therapeutic opportunity in which it may be possible to develop neuroprotective strategies. Our study suggests that maximum infarct volume is determined at some time between 24 hours and 17 days after permanent middle cerebral artery occlusion in anesthetized baboons.

Three-dimensional CT-imaging of the ossicular chain

In eight patients, with a known air-conduction hearing loss, three-dimensional images of the ossicular chain were constructed based on heavily overlapping high resolution CT-slices, obtained from a spiral CT data set. High quality three-dimensional images could be obtained in all eight patients. Supplementary information was derived from these three-dimensional images in three patients; in one, this supplementary information had therapeutic importance. The slight image quality loss in spiral-CT of the temporal bone, compared with conventional CT, is in some cases largely compensated by the possibility of rendering high quality secondary reconstructions.

Contribution of PET in the diagnosis of recurrent colorectal cancer: comparison with conventional imaging

The clinical value of total body PET with FDG was evaluated in 76 patients presenting with or suspected of recurrent local or distant colorectal cancer. PET results were compared to those of routine imaging (CT pelvis, CT/US liver and CXR). The accuracy of PET for local disease was 95% which was superior to CT-pelvis (accuracy 65%). PET accuracy for liver metastases (98%) compared favourably to CT/US-liver accuracy (93%). Unexpected extra-hepatic mestastases were detected by PET in 14 locations in 10 patients. Also, a primary breast cancer was found in one patient. The main value of PET appeared an improved staging of apparently resectable, local or distant recurrent disease. Thereby, a more adequate indication of major secondary surgery could be attained.

[Three-dimensional imaging of acetabular fractures using spiral CT]

Seven adult patients with acetabular fractures were investigated with conventional X-rays, axial spiral computed tomographic (CT) images and three-dimensional (3D) surface rendered reconstructions. Spiral CT has the advantage that it acquires the data much faster than incremental CT, resulting in less motion artefacts. A semi-automatic three-dimensional environment for segmentation has been developed in our institution. It created significant reduction of user interaction and improved visualization of acetabular and femoral joint surfaces. The main advantages of three-dimensional visualization of acetabular fractures included: creation of unlimited and unique views by which fracture location, fracture extension, fragment shape and fragment position became more clear, better visualization of acetabular dome and quadrilateral plate and more simple and easier interpretation of these complex fracture patterns. On the other hand, 3D surface reconstructions do not accurately demonstrate undisplaced fractures, intra-articular fragments may be obscured, congruence assessment is uneasy, and soft tissue injuries are not shown. Therefore, we consider 3D images of acetabular fractures as being complementary to and not a substitute to plain radiographs and axial CT scans.

Cloning, sequencing, and expression of the apa gene coding for the Mycobacterium tuberculosis 45/47-kilodalton secreted antigen complex

Effective protection against a virulent challenge with Mycobacterium tuberculosis is induced mainly by previous immunization with living attenuated mycobacteria, and it has been hypothesized that secreted proteins serve as major targets in the specific immune response. To identify and purify molecules present in culture medium filtrate which are dominant antigens during effective vaccination, a two-step selection procedure was used to select antigens able to interact with T lymphocytes and/or antibodies induced by immunization with living bacteria and to counterselect antigens interacting with the immune effectors induced by immunization with dead bacteria. A Mycobacterium bovis BCG 45/47-kDa antigen complex, present in BCG culture filtrate, has been previously identified and isolated (F. Romain, A. Laqueyrerie, P. Militzer, P. Pescher, P. Chavarot, M. Lagranderie, G. Auregan, M. Gheorghiu, and G. Marchal, Infect. Immun. 61:742-750, 1993). Since the cognate antibodies recognize the very same antigens present in M. tuberculosis culture medium filtrates, a project was undertaken to clone, express, and sequence the corresponding gene of M. tuberculosis. An M. tuberculosis shuttle cosmid library was transferred in Mycobacterium smegmatis and screened with a competitive enzyme-linked immunosorbent assay to detect the clones expressing the proteins. A clone containing a 40-kb DNA insert was selected, and by means of subcloning in Escherichia coli, a 2-kb fragment that coded for the molecules was identified. An open reading frame in the 2,061-nucleotide sequence codes for a secreted protein with a consensus signal peptide of 39 amino acids and a predicted molecular mass of 28,779 Da. The gene was referred to as apa because of the high percentages of proline (21.7%) and alanine (19%) in the purified protein. Southern hybridization analysis of digested total genomic DNA from M. tuberculosis (reference strains H37Rv and H37Ra) indicated that the apa gene was present as a single copy on the genome. The N-terminal identity or homology of the M. tuberculosis and M. bovis BCG purified molecules and their similar global and deduced amino acid compositions demonstrated the perfect correspondence between the molecular and chemical analyses. The presence of a high percentage of proline (21.7%) was confirmed and explained the apparent higher molecular mass (45/47 kDa) determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis resulting from the increased rigidity of molecules due to proline residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of metalloporphyrin-induced "specific" enhancement in experimental liver tumors: comparison of magnetic resonance imaging, microangiographic, and histologic findings

RATIONALE AND OBJECTIVES

We investigated the tumor specificity of gadolinium mesoporphyrin (Gd-MP) and manganese tetraphenylporphyrin (Mn-TPP) as magnetic resonance (MR) imaging contrast agents.

METHODS

Fifteen rats with multiple hepatocellular carcinomas and eight rats with implanted Novikoff hepatomas were given intravenous injections of either Gd-MP or Mn-TPP at 0.05 mmol/kg, which was compared with nonspecific gadopentetate dimeglumine (0.3 mmol/kg). T1-weighted spin-echo images were obtained before and up to 48 hr after injection and compared with corresponding microangiograms and histologic specimens. The relative enhancement of organs and tumors was plotted as a function of time.

RESULTS

Initially, both metalloporphyrins behaved as nonspecific agents, similar to gadopentetate dimeglumine, and enhanced the tumor by perfusion and diffusion. However, metalloporphyrins, but not gadopentetate dimeglumine, caused a delayed (> or = 3 hr) enhancement in some compartments of certain lesions. The MR imaging-microangiography-histology matching technique revealed that those compartments were actually nonviable components, including necrosis (n = 10), thrombosis (n = 7), and cystic secretion (n = 3), but not viable tumor tissue.

CONCLUSION

Metalloporphyrins did not prove to be tumor specific. However, the observed affinity for nonviable tissue has elicited other potential applications for these agents.

Healthy aging, memory subsystems and regional cerebral oxygen consumption

The present study was designed to search for concomitant age-related changes in memory subsystems, defined according to current structural theories, and resting oxygen consumption in selected brain regions. We have investigated a sample of subjects between 20 and 68 years of age and strictly screened for their good health. We applied in the same subjects a battery of neuropsychological tests selected to investigate several memory subsystems, and high-resolution positron imaging with stereotaxic localization to study a purposely limited number of cerebral structures, selected on a priori hypotheses to match the different memory subsystems. Our results showed significant age-related changes in performance on some tests, consistent with the literature, including an increase in semantic memory and a decrease in both working memory (central executive system) and verbal episodic and explicit memory. There was also an age-related linear decrease in global brain oxygen consumption which regionally reached statistical significance for the neocortical areas and the left thalamus. There was a limited number of significant, age-independent correlations between the raw psychometric test scores and resting regional oxidative metabolism. Consistent with our present understanding of the functional anatomy of memory, the Associate Learning scores (verbal episodic and explicit memory) were positively correlated with left hippocampal and thalamic metabolism. The positive relationships found between right hippocampal metabolism and performance in the Associate Learning and the Brown-Peterson tests were less expected but would be consistent with findings from recent PET activation studies. The results from this investigation are discussed in the light of current knowledge concerning the neuropsychology and the neurobiology of both aging and memory.

Abdominal pain in the postpartum: role of imaging

The post-delivery evaluation of the obstetric patient presenting with severe abdominal pain can be a challenge to the obstetrician, the internist, and the radiologist. Besides non-pregnancy-related causes of abdominal pain, several pregnancy-related complications should be included in the list of differential diagnoses. Based on pathogenesis, these conditions can be divided in four categories: thromboembolic disease, infectious complications, mechanical complications, and complications of preeclampsia. Most disease processes can be adequately visualized with sonography. CT can be indicated for the evaluation of the extent of ovarian vein thrombosis and for depiction of deep abdominal collections in obese patients or in cases of abundant overlying abdominal gas. MRI can be useful to provide the specific diagnosis of hemorrhagic liver infarction in the clinical setting of a HELLP syndrome.

The use of magnetic resonance angiography in stereotactic neurosurgery

The authors discuss the advantages and disadvantages of the use of magnetic resonance (MR) angiography images in stereotactic neurosurgery. Current computer programs designed to assist the neurosurgeon in the planning of stereotactic neurosurgical interventions use intraarterial digital subtraction angiography images to visualize the blood vessels. Magnetic resonance angiography is a recent technique with a number of advantages over the digital subtraction method: it is less invasive and less prone to complications; it provides truly three-dimensional data sets that can be viewed from any direction; and it can visualize both stationary and flowing tissues with the same imaging device and localizer frame. Although digital subtraction images are still superior in contrast and vascular detail, state-of-the-art high-resolution MR angiography sequences provide sufficient vascular detail for planning surgery. Contrast-enhanced MR angiography images were acquired using adapted gradient-echo sequences to compensate for flow-induced distortions; postacquisition distortion correction was not necessary. Five methods to integrate and inspect a possible trajectory in the MR angiography data are discussed. Initial clinical experience with eight patients led to the conclusion that MR angiography is a valuable imaging modality that can be integrated reliably into a stereotactic neurosurgery planning procedure.

Characterisation of intracranial aneurysms with MR angiography

The purpose of this study was to compare the accuracy of 3D time-of-flight (TOF) acquisitions in the characterisation of intracranial aneurysms. Fourteen patients with aneurysms proven on intra-arterial angiography were first studied with a 3D TOF acquisition. When the aneurysms were incompletely demonstrated, additional MR angiography (MRA) acquisitions were performed, including black-blood MRA, 2D TOF, phase-contrast and contrast-enhanced TOF.3D TOF MRA was sufficient for detection of the aneurysm in 13 of 14 cases and characterisation of the aneurysm was possible in 6. All the initial shortcomings of the TOF technique could be analysed and explained by means of additional MRA techniques. This study suggests that the combination of different MRA techniques offers new possibilities for noninvasive investigation of intracranial aneurysms.

Effect of manganese dipyridoxal diphosphate on liver magnetic resonance imaging and serum bilirubin in rats with removable biliary obstruction

RATIONALE AND OBJECTIVES

It is known that manganese dipyridoxal diphosphate (Mn-DPDP) causes persisting liver enhancement in cholestatic rats, that free Mn++ plus bilirubin induces intrahepatic cholestasis, and that free Mn++ is released in vivo after Mn-DPDP injection. Hence, there is a concern about potential secondary intrahepatic cholestasis in patients who have biliary obstruction. In this study, we further investigated this issue.

METHODS

Removable total biliary obstruction (RTBO) was induced in 12 rats. Six of them (group A) received Mn-DPDP (25 mumol/kg). The others (group B) served as control animals. The data from serial magnetic resonance imaging and serum bilirubin tests were compared.

RESULTS

Without Mn-DPDP, a minimal increase of the liver intensity was observed in both groups because of cholestasis. In group A, the intensity of the liver was strongly enhanced with Mn-DPDP but normalized within 48 hr after removal of the obstruction. In both groups, total bilirubin levels increased up to 131.67 mumol/l 2 days after RTBO but rapidly decreased within 4 hr and almost normalized within 24 hr after removal of the obstruction, suggesting a lack of Mn-DPDP influence on the bilirubin level.

CONCLUSION

We found that Mn-DPDP did not cause secondary intrahepatic cholestasis. Retained Mn++ is likely eliminated after restoration of bile flow. These results indicate that Mn-DPDP can be used in patients who have obstructive jaundice as long as it is followed by successful bile drainage.

[Application of spiral CT in the head and neck region]

In comparison with other regions of the body, spiral CT has only been recently applied in the radiological evaluation of the head and neck region. Some interesting applications seem to emerge. The fast data acquisition allows to examine children (e.g. temporal bone examinations) without sedation, to reduce patient moving artefacts in adults, and to limit the dose of injected contrast material in enhanced studies. Furthermore, without additional irradiation, images with a very small table increment can be calculated out of the volumetric data set, allowing generation of high quality secondary reconstructions.

[Clinical application of three-dimensional spiral CT in skeletal disorders]

Three-dimensional (3D) computed tomographic reformations are used as an adjunct to standard axial computed tomography (CT) in the evaluation of disorders affecting areas of complex anatomy such as the skull, the spine, the pelvis, hands and feet. 3D-CT can provide a clear impression of lesion extent, pattern, shape and proximity to adjacent structures. This unique spatial information potentially has a significant impact on decisions regarding resectability, surgical approach and repair. The basic requirements for high-quality 3D-reformations are an absence of patient movement and narrow-width transaxial sections. Spiral CT significantly contributes to fulfilling these requirements. In addition, spiral CT scan data can be used to produce the ultimate representation of the third dimension: a life-size palpable medical model. In this review we describe the process of three-dimensional reconstruction and highlight potential problems arising during 3D-imaging processing. Useful clinical applications of spiral CT for 3D-visualization of skeletal pathology are discussed.

[Spiral CT of the pancreas]

Spiral CT allows rapid acquisition of axial images during a single breath-hold. This results in optimal vascular and parenchymal opacification and eliminates respiratory misregistration. These factors also contribute to high quality multiplanar displays. Double phase spiral CT allows repeated scanning in the vascular (arterial) phase and in the parenchymal phase after contrast injection, resulting in optimal detection of parenchymal as well as vascular lesions. The advantages and applications of spiral scanning for imaging the pancreas are discussed.

[Spiral CT angiography]

Spiral CT angiography (CTA) is a promising technique for the evaluation of vascular lesions. We review some important technical aspects in CTA such as longitudinal resolution, determination of injection scan interval and limitations of three-dimensional rendering techniques. Several current and potential applications are discussed.

[Spiral CT of cerebral aneurysms]

Spiral CT was performed in 9 patients with 13 cerebral aneurysms known from angiography. All lesions were detected by spiral CT, the smallest lesion measuring 3 mm in diameter. The neck of the aneurysm and the anatomical relations could be determined very accurately in all cases. Advantages of spiral CT over magnetic resonance angiography include: the short examination time, the independence of flow rate and cardiac output, and the excellent visualisation of calcification, thrombus and the bony landmarks. Disadvantages are the necessity of iodinated contrast media, the long postprocessing and reconstruction time and the possibility of overlap from bone and venous blood.

[Spiral CT of the renal blood vessels]

Spiral CT angiography has been successfully applied to the detection and grading of renal artery stenoses. In this manuscript the technique, the diagnostic accuracy and the advantages and limitations of this new method are discussed.

[Spiral CT of the liver: detection of focal liver lesions]

The advantages of spiral CT mainly reside in the possibility to scan the entire liver volume in a single period of about 20 to 30 seconds, while the patient holds his breath. This high acquisition speed allows to selectively evaluate the entire liver during the arterial and/or portal venous phase. In addition, spiral CT is a true volumetric technique that allows a posteriori calculation of perfectly contiguous or even overlapping slices. These two specifications, high acquisition speed and the absence of data gaps improves the detection of focal liver lesions.

Determination of scan delay time in spiral CT-angiography: utility of a test bolus injection

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.

Novel mutation in 16S rRNA associated with streptomycin dependence in Mycobacterium tuberculosis

Molecular characterization of a streptomycin-dependent mutant of Mycobacterium tuberculosis revealed the presence of a novel mutation in the rrs gene encoding 16S rRNA. Insertion of an additional cytosine in the 530 loop of 16S rRNA, a region known to be involved in streptomycin susceptibility and resistance, was associated with streptomycin dependence.

Spiral CT of the temporal bone: value of image reconstruction at submillimetric table increments

Axial spiral CT of the temporal bones with a nominal slice thickness of 1 mm and 180 degrees linear interpolation was performed in 13 patients. In 18 temporal bones, the spiral data set was used to reconstruct overlapping axial images with a table increment of 0.1 mm. These images gave additional information in four cases: in two by examining the heavily overlapping axial images themselves, and in two by obtaining supplementary information from secondary image reconstructions. In two cases less information was obtained than by using the conventional incremental images. This study shows that reconstructing overlapping slices can be useful, even if the temporal bone is scanned at 1 mm nominal slice thickness.

Magnetic resonance angiography of supratentorial tumours: comparison with selective digital subtraction angiography

We compared magnetic resonance angiography (MRA) and intra-arterial digital subtraction angiography (IADSA) in the study of brain tumours and assessed the utility of gadolinium-enhanced MRA. We studied 17 patients with supratentorial brain tumors. The entire brain was imaged with multiple overlapping thin volume acquisitions. After IV injection of gadolinium-DTPA, a single thick-slab MRA acquisition was performed. Standard three-dimensional (3D-TOF) acquisitions (in six patients) and 3D-TOF with magnetization transfer prepulse and tilted optimisation nonsaturing radiofrequency excitation pulses (in 11 patients) were used. Displacement of the anterior cerebral artery, main stem and insular branches of the middle cerebral artery was seen well on unenhanced and contrast-enhanced MRA. Displacement of the lenticulostriate and anterior choroidal arteries was seen only once, after Gadolinium. Tumour encasement of the middle cerebral artery was demonstrated in one patient. Tumour vessels were seen in 2 of 8 cases before and 3 of 8 after gadolinium; Tumour hypervascularity was seen only after gadolinium, in 3 of 8 cases. Study of the veins was possible only on gadolinium-enhanced MRA. Displacement of the venous angle was seen in 4 of 7 patients in the frontal, and in all of 8 patients on the lateral projections. Early venous drainage was not seen. Patency of the dural venous sinuses was demonstrated in all patients, but in one neoplastic occlusion of a cortical vein was recognized.

Magnetic resonance imaging of the masseter muscle: a preliminary genetic study in monozygotic and dizygotic twins

Magnetic resonance images of the head were taken in five monozygotic and seven dizygotic twins in order to calculate bilaterally masseter muscle cross-sectional areas and total volume. Comparing correlation coefficients between cotwins, genetic influences could be expected for maximal cross-sectional area but not for volume measurements. Model fitting revealed that additive genetic factors explained 93.9% of the variance for the left and 82.4% for the right maximal masseter muscle cross-sections. It is anticipated that while the number of masseter muscle fibers is under strong genetic control, the length of individual fibers can be influenced by specific environmental factors. In the second part of the investigation, cephalometric measurements from lateral headplates were compared with these masseter muscle values in 10 twin pairs. Only three of the 15 angular and five (three vertical, one transversal, and one sagittal measurement) of the 20 linear measurements were significantly correlated with masseter muscle values.

Protocol for the clinical functionality assessment of a workstation for stereotactic neurosurgery

The objective of this study is to establish a protocol for the technical and clinical evaluation of a workstation for the planning of stereotactic neurosurgical interventions that has been developed in the framework of a joint European research project. Although several such workstations have been proposed before, they lacked the final and most important step, that of clinical validation. They failed to rigorously prove that their product was useful. The authors present a new method that is applicable to the evaluation of a wide range of medical technologies. Their protocol basically assesses the clinical relevance of the user requirements that are at the root of the development of the new technology. The evaluation consists of two stages. During functional specification, iterative prototyping is used to establish the clinical requirements and to assure the quality of the final product. A case study design is used in a second stage that assesses the clinical usability. A before-after study gives a first indication of cost effectiveness and improvement of health care quality.

Time-of-flight MR angiography of the brain: comparison of acquisition techniques in healthy volunteers

OBJECTIVE

The saturation phenomenon that limits vessel visibility in unenhanced time-of-flight MR angiograms can be overcome by the injection of MR contrast agents that shorten the T1 of the blood. Unlike the situation with unenhanced MR angiographic acquisitions, in which the MR parameters must be carefully adjusted to reduce saturation effects, optimization procedures for contrast-enhanced MR angiography focus on the acquired shortening of the T1 of the blood and the time evolution of the T1 over the entire measurement. To improve the quality of contrast-enhanced time-of-flight MR angiographic acquisitions in the brain, we compared different acquisition techniques that exploit shortening of the T1 of the blood.

SUBJECTS AND METHODS

High-resolution MR angiographic examinations were done with a 1-T MR system for 12 healthy volunteers. Doses of 0.1 and 0.2 mmol of gadopentetate dimeglumine per kilogram of body weight were injected on two separate days to allow for identical timing of the comparative studies after contrast material injection. The effects of dose of contrast material, MR parameters (TR and flip angle), method of injecting the contrast material (monophasic, biphasic, or continuous slow injection), and K-space acquisition schemes (regular schemes versus collecting the central K-space lines near the beginning or the end of the acquisition) were studied.

RESULTS

Higher doses provided better MR angiograms. The flip angle and the TR had to be adjusted on the basis of the Ernst equation and therefore depended on an estimation of the averaged T1 value over the entire measurement. Comparison of the different K-space acquisition schemes confirmed that the evolution of the T1 of the blood over the entire measurement time is important, especially for longer measurements. There was no noticeable difference between the MR angiograms acquired with monophasic or biphasic injections. These injection schemes provided more detailed MR angiograms than did continuous slow injection over the entire measurement.

CONCLUSION

Our results show that the quality of contrast-enhanced MR angiograms can be remarkably increased when acquisition techniques that exploit the short T1 of the blood are used.

Potential role of bile duct collaterals in the recovery of the biliary obstruction: experimental study in rats using microcholangiography, histology, serology and magnetic resonance imaging

Obstructive cholestasis induced in animals at the level of the lobar and common bile ducts is known to be reversible with time. This study was conducted not only to test the hypothesis that formation of bile duct collaterals is responsible for the recovery of biliary obstruction but also to assess the potential of hepatobiliary agent-enhanced magnetic resonance imaging for visualizing cholestasis. A total of 52 rats were divided into three groups with selective biliary obstruction, total biliary obstruction and sham surgery. We studied the evolution of cholestasis by correlating microcholangiographic, histological findings with the results of liver tests and hepatobiliary agent-enhanced magnetic resonance imaging. Lobar cholestasis undetected by liver tests but seen on magnetic resonance imaging as a difference between ligated and unligated lobes, occurred in 15 out of 20 rats subjected to selective biliary obstruction within 48 hr after ligation, and recovered later on as a result of the development of bile duct collaterals. Five rats failed to show local cholestasis as a result of the existence of interlobar accessory bile channels. All 18 total biliary obstruction-treated rats were cholestatic soon after ligation, as confirmed by high serum bilirubin and alkaline phosphatase levels and as documented by poor liver enhancement on magnetic resonance imaging. Cholestasis recovered within 4 wk with normalization of liver enhancement on magnetic resonance imaging as a result of the formation of bile duct collaterals (as demonstrated by microcholangiographic and histological study). Bile duct collateral formation is responsible for the recovery from obstructive cholestasis in rats. A similar mechanism might be present in conditions of bile duct obstruction without cholestasis. Hepatobiliary agent-enhanced magnetic resonance imaging is more sensitive than blood tests in detecting local cholestasis and can be used to monitor noninvasively the evolution of biliary obstruction.

Three cases of non-tumoural tight stenosis of the bifurcation of the hilar bile ducts

Stenosis of the bifurcation of the hepatic bile duct is usually caused by malignant lesion. We report on three different causes of benign stenosis of the hepatic confluence with a similar radiological pattern on direct cholangiography. The first case is considered a spontaneous neuroma, the second a periductal abscess, and the third case a postoperative stricture Bismuth type 4.

Transient inducible events in different tissues: in situ studies in the context of the development and expression of the immune responses to intracellular pathogens

Intracellular pathogens whether facultative like Mycobacterium sp., e.g. Bacillus Calmette Guérin, Listeria monocytogenes or strictly intracellular like Leishmania sp. initiate either asymptomatic infectious processes or disease depending both on factors of the host (genetic as well as environmental ones) and the infectious/pathogenic agents. In this contribution, we first summarized informations which justify to develop in situ analysis to decipher the sequential events that result in different modes/classes of immune responses. How the mode of the immune response is determined remains a main question to address. Although it has recently become clear, in vitro, that immunocompetent cells and their cytokines are critical to set on a stable mode of immune response, acting on naive T cells, this area deserves more in vivo studies. Indeed, peripheral T cells, at different stages of differentiation, may exist in vivo (a) naive/virgin, (b) experienced, (c) effector T cells, depending on the level of stimulation of the immune system by either endogenous or exogenous (e.g. gut flora) signals. The three chosen examples illustrate our contributions in this field focusing on three different non-lymphoid tissues which may become infected: bone marrow (Bacille de Calmette Guérin), liver (Listeria monocytogenes), skin (Leishmania major). These three illustrations also allow to attract attention on the interest of using mice of genetically different strains the immune response of which is set up under different modes.

Imaging of polypoid endoluminal growing bile duct tumors

We reviewed the radiological documents and protocols of 196 cases of bile duct tumors examined over a period of 12 years: 20 of them (10.2%) presented with a polypoid endoluminal growth. The aim of this study was to provide a better knowledge about the radiological features of this less frequent kind of tumor. In these 20 cases, the correct diagnosis of bile duct lesion was provided in 100% by E.R.C.P., P.T.C., U.S. as well as C.T., and in 42% by arteriography. The correct diagnosis of tumor was made by E.R.C.P. in 86%, by P.T.C. in 88%, by U.S. in 61%, by C.T. in 63%, and by arteriography in 25%. A correct diagnosis of tumor could be reached in all cases by combination of several examination techniques. The anatomopathological diagnosis was: bile duct adenocarcinoma (7 cases), adenocarcinoma of the ampulla of Vater (4), villous adenoma of Vater's ampulla (2), cystadenoma (1), cystadenocarcinoma (1), hepatocellular carcinoma (1), apudoma (1), and metastases (3).

Simultaneous occurrence of developmental venous anomalies and cavernous angiomas

PURPOSE

To study the clinical and radiologic findings in 15 patients presenting with both developmental venous anomalies and cavernous angiomas and to determine which lesions caused the acute clinical symptoms.

METHODS

Lesions were infratentorial in 7 patients and supratentorial in 7 other patients. In one patient the developmental venous anomaly was infratentorial and the cavernous angioma supratentorial. In all 15 patients clinical examination and CT were performed. In 10 patients MR was performed at the time of the initial CT scan. In 5 patients only late MR is available.

RESULTS

Acute clinical signs were present in 9 patients (epilepsy, hemiplegia, meningeal signs, cranial nerve deficit). On CT the cavernous angioma was missed in 9 patients, in 6 patients because of acute hemorrhage. On MR the cavernous angioma was missed in 1 of 2 cases with acute hemorrhage but seen in all other patients. On repeat MR all cavernous angiomas were correctly identified. On CT, 11 developmental venous anomalies were seen. On MR all developmental venous anomalies were seen.

CONCLUSIONS

The frequent association of developmental venous anomalies and cavernous angiomas is confirmed. MR is superior to CT in the detection of both cavernous angiomas and developmental venous anomalies. Furthermore our data support the hypothesis that cavernous angiomas and not the developmental venous anomalies cause the acute clinical symptoms because of hemorrhage.

Sonographic diagnosis of ischemic colitis

An abdominal ultrasound examination performed on two patients with abdominal pain showed segmental wall thickening of the colon that proved to be due to ischemic colitis. In one case, the typical "target lesion" was recognized. These findings could be confirmed with computed tomography, whereas a single contrast enema was unable to demonstrate the ischemic disease. In the second case, a typical five-layered structure of the bowel wall could be demonstrated. It is concluded that US can be useful in the early diagnosis of colonic ischemia.

Gadodiamide injection at 0.1 and 0.3 mmol/kg body weight: a phase III double-blind, parallel, randomised clinical investigation of known or suspected central nervous system lesions at 1.5 T

We studied 78 patients with clinically suspected central nervous system abnormalities (66 intracranial, 12 spinal) by MRI before and after administration of the nonionic contrast medium gadodiamide injection. A parallel, double-blind, randomised design was followed. Two dosages were used: 38 patients underwent studies with 0.1 mmol/kg body weight (b.w.) and 40 with 0.3 mmol/kg b.w. MRI showed abnormalities in 36 of the 38 patients receiving the lower dose and 39 of the 40 patients receiving the higher dose. In 3 patients from each group more lesions were seen following injection than before. The contrast medium improved the delineation of abnormal structures and assessment of tumour size and increased their signal intensity indices in both groups, but especially at the higher dose. Administration of gadodiamide injection provided more diagnostic information in about 75% of the patients, independently of the dose. There were no reports of discomfort, but 7 patients reported adverse events considered unrelated to the gadodiamide injection. The two doses were found to be equally safe and efficient for diagnosis.