[Comparison of dual-phase helical CT with native and ferum oxide-enhanced magnetic resonance imaging in detection and characterization of focal liver lesions]

PURPOSE

Evaluation of the diagnostic efficacy of contrast-enhanced, dual-phase spiral CT and MRI before and after administration of SPIO particles in focal hepatic disease with previously uncertain diagnosis.

MATERIAL AND METHODS

In 46 patients in whom primary or secondary hepatic malignancy was suspected, dual-phase spiral CECT and breath-held T1-weighted gradient-echo and T2-weighted fast spin-echo MRI (1.5 T, body-phased-array coil) before and after SPIO administration were compared. The indications for the subsequent MRI studies were based on ambiguous findings on CECT. The number of hepatic lesions, the overall lesion detection and characterization was evaluated by consensus and compared to the gold standard (histological proof in 30/46 of the cases, long-term follow-up in 16/46 of the cases).

RESULTS

In 34 of 46 cases the correct diagnoses were established by CECT (sensitivity 96%, specificity 48%) revealing significantly less lesions than MRI. Unenhanced MRI had sensitivity of 93% and specificity of 71%, whereas SPIO-enhanced MRI had sensitivity of 97% and specificity of 88%. The differences between the modalities were even more pronounced in the detection of lesions smaller than 10 mm with SPIO-MRI as the most sensitive method.

CONCLUSIONS

In this problem-oriented scenario, SPIO-enhanced MRI was superior to spiral CT and unenhanced MRI regarding the diagnostic efficacy in the pre-operative work-up of focal liver lesions. SPIO-enhanced MRI can be recommended as a problem-solving tool for the clinical routine.

Fluoroscopic MR of the pharynx in patients with obstructive sleep apnea

PURPOSE

The purpose of our study was to introduce an ultrafast MR imaging technique of the pharynx as a diagnostic tool for viewing the mechanism of obstruction in patients with obstructive sleep apnea.

METHODS

Six healthy volunteers and 16 patients with obstructive sleep apnea were examined on a 1.5-T whole-body imager using a circular polarized head coil. Ultrafast two-dimensional fast low-angle shot sequences were obtained in midsagittal and axial projections during transnasal shallow respiration at rest, during simulation of snoring, and during performance of the Müller maneuver. All patients underwent physical examination, transnasal fiberoptic endoscopy, and polysomnography.

RESULTS

Five to six images were obtained per second with an in-plane resolution of 2.67 x 1.8 mm and 2.68 x 2.34 mm, allowing visualization of motion of the tongue, soft palate, uvula, and posterior pharyngeal surface. MR findings correlated well with results of clinical examination. The length of obstruction in the oropharynx, which cannot be ascertained by transnasal endoscopy of the pharynx, was clearly visible MR images. Differences between patients with obstructive sleep apnea and healthy subjects in terms of the degree of obstruction in the velopharynx and oropharynx depicted on MR images during the Müller maneuver were highly significant.

CONCLUSION

We believe that ultrafast MR imaging is a reliable noninvasive method for use in the evaluation of obstructive sleep apnea.

Breathhold MR urography: comparison between HASTE and RARE in healthy volunteers

The purpose of our study was to determine relative values of rapid acquisition relaxation enhancement (RARE) and half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences in breathhold magnetic resonance (MR) urography in healthy volunteers under nonobstructive conditions of the urinary tract. A total of 20 healthy volunteers underwent MR urography with breathhold RARE and HASTE sequences at 1.5 T. For evaluation, the urinary tract was divided into nine segments on each side. Visualization of segments and artifacts was scored and the intensity ratios (InR) were determined. The upper five urinary segments were sufficiently visualized with RARE and significantly better with HASTE (renal calices, p = 0.002-0.037). The middle and lower ureter was sufficiently delineated both with RARE and HASTE, but HASTE images were statistically superior (p = 0.009-0.041). Both in RARE and HASTE images, the lower ureter was frequently superimposed by bowel contents and bowel motion. Superimposition of genital organs degraded image quality in eight of ten female volunteers. InRs were superior with HASTE in the kidney and ureter (p = 0.0003-0.0125). RARE InRs were higher in the bladder (p = 0.0008-0.014). We concluded that neither the RARE nor the HASTE sequences allowed the evaluation of the entire urinary tract under nonobstructive conditions. Although it cannot entirely replace intravenous urography, MR urography seems to lend itself to combination with other MR techniques, particularly in the investigation of pelvic or retroperitoneal disease.

[Focal liver diseases]

INTRODUCTION

Advanced therapies are improving significantly the survival of patients with malignant focal liver disease. For efficient implementation of these surgical and interventional techniques a clear concept of the diagnostic procedure is mandatory.

METHODS

Based on a review of the current literature, the different imaging modalities, including ultrasound, computed tomography, magnetic resonance tomography, nuclear medicine and angiography, are discussed and evaluated for their diagnostic efficacy in focal hepatic disease.

RESULTS

Considering clinical, diagnostic, and economical appropriateness, recommendations for diagnostic strategies in different clinical scenarios regarding focal heptic disease are presented.

CONCLUSION

If the power of specific imaging methods are relevant clinical information is known, problem-based diagnostic strategies help to avoid unnecessary, expensive and time-consuming studies in the work-up of focal liver lesions.

Breath-hold MR cholangiography with snapshot techniques: prospective comparison with endoscopic retrograde cholangiography

PURPOSE

To compare findings with magnetic resonance (MR) cholangiography with rapid acquisition with relaxation enhancement (RARE) and half-Fourier acquisition with single-shot turbo spin-echo (hereafter, half Fourier RARE) snapshot imaging techniques to those with endoscopic retrograde cholangiography (ERC).

MATERIALS AND METHODS

Heavily T2-weighted thick-section (RARE) and thin-section (half-Fourier RARE) MR cholangiography were performed prospectively, on a 1.5-T imager, in the biliary tree of 61 consecutive patients before ERC. Findings at ERC were considered the standard of reference. The radiologist and endoscopist were blinded to each other's report. On- and off-site MR cholangiographic readings were performed to detect stones (n = 24), biliary dilatation (n = 34), or stenosis (n = 36).

RESULTS

The sensitivity and specificity of MR cholangiography, respectively, calculated on a lesion-by-lesion basis, were 92.3% and 95.8% for cholangiolithiasis, 94.1% and 92.6% for duct dilatation, and 88.8% and 84.0% for stenosis. With snapshot MR cholangiography, on a patient-by-patient basis, differentiation between normal (n = 15) and abnormal (n = 46) results yielded a sensitivity of 92.4%, a specificity of 83.4%, and a positive predictive value of 95.6%. Pitfalls were caused by flow artifacts, compression by vessels, and low contrast between calculi and surrounding parenchyma.

CONCLUSION

Snapshot MR cholangiography allowed noninvasive, accurate detection of biliary stones, strictures, and dilatation similar to that with ERC. Discrepancies regarding low-grade dilatation and strictures had no clinical relevance at retrospective review.

[MRI of the small intestine with rapid MRI sequences in Crohn disease after enteroclysis with oral iron particles]

PURPOSE

To evaluate the efficacy of breathhold MRI following enteroclysis with addition of oral magnetic particles to study the extension, detection of stenoses and extraluminal manifestations in Crohn's disease.

MATERIAL AND METHODS

18 patients with Crohn's disease and potential of surgical intervention were studied with enteroclysis with addition of oral magnetic particles. T1-/T2-weighted breathhold MRI w/o spectral fat suppression w/o i.v. Gd-DTPA was applied.

RESULTS

Typical findings were marked bowel wall thickening with strong contrast enhancement. 95.8% of affected small bowel segments and 94.7% of stenoses were correctly detected by MRI. All four fistulas were detected and important extraluminal findings were seen in 6/18 patients. Additionally, one ileoileal and two ileosigmoidal adhesions, two extraluminal abscesses and affection of the right ureter were delineated.

CONCLUSION

MRI in Crohn's disease offers the potential to avoid radiation exposure in this relatively young patient group. Important additional findings relevant to indication of surgery are seen in approximately one third of cases. The replacement of transduodenal intubation by oral contrast application remains to be further studied.

Pathologic conditions in the small bowel: findings at fat-suppressed gadolinium-enhanced MR imaging with an optimized suspension of oral magnetic particles

Depiction of small-bowel pathologic conditions was optimized with use of a negative luminal contrast agent, spectral fat suppression, and gadolinium enhancement in an excised gut phantom. The method was applied in nine patients in conjunction with standard enteroclysis examinations. Bulk susceptibility effects of oral magnetic particles were canceled with use of a diamagnetic methylcellulose suspension. In the ileum, fat suppression and contrast between bowel wall and lumen was judged good or excellent in eight and nine patients, respectively. In eight of nine patients, additional mesenteric findings were depicted.

Choledocholithiasis after Billroth II surgery: MR cholangiographic diagnosis

In this case of choledocholithiasis in a patient with previous Billroth-II surgery and cholecystectomy we demonstrate the advantages of a heavily T2-weighted half-Fourier turbo-spin-echo (HASTE) sequence. This technique allows thin-slice snapshot imaging with 1.4 s per slice eliminating motion artifacts and still has the necessary heavy T2-weighting to depict biliary fluid with high contrast. In the presented case endoscopic retrograde cholangiography (ERCP) could not be performed prior to MRI due to technical problems. In a second attempt, ERCP was successful and a common bile duct stone as diagnosed by MRI before could be removed. We conclude that HASTE snapshot MR cholangiography can be used as a clinically valuable tool when other noninvasive methods are not diagnostic.

In vivo animal tests of an artifact-free contrast agent for gastrointestinal MRI

A variety of shortcomings are associated with most currently used gastrointestinal contrast agents for magnetic resonance imaging (MRI). Artifacts resulting from peristalsis and other motions in the abdominal region are produced by many positive contrast agents (which increase signal intensity). Although this is not a problem for negative contrast agents (which decrease signal intensity), some negative contrast agents produce magnetic susceptibility artifacts that are especially pronounced at high field strength and with gradient echo pulse sequences. These susceptibility artifacts are produced by both paramagnetic and diamagnetic agents. It has been demonstrated in phantoms, however, that susceptibility matching can be used to produce contrast agents with desirable relaxation and contrast properties but without deleterious susceptibility artifacts. We now report results of animal tests of such an oral contrast agent, consisting of a suspension of superparamagnetic iron oxide particles and diamagnetic barium sulfate particles, compared to individual suspensions of the iron oxide and of the barium sulfate. Iron oxide was the least effective and the matched susceptibility mixture was the most effective for the intestine, which has traditionally been the most difficult region of the GI tract to visualize clearly. Matched susceptibility mixtures, which are inherently able to yield images free of susceptibility artifacts without compromising contrast, show promise of being improved oral negative contrast agents for use in gastrointestinal MRI.

Dynamic magnetic resonance imaging in the study of vocal tract configuration

Studies of vocal tract configuration using magnetic resonance imaging (MRI) techniques have relied on static images. These images fail to identify transient movements and are subject to distortion from motion artifact limiting research application to stable motor events. This paper describes a dynamic MRI technique that permits study of transient movements within the vocal tract during speech and nonspeech tasks. Following description of the technique, results of two preliminary studies are presented. The initial study evaluated issues of measurement error and reliability. Results indicated that distance and area measurements obtained from this technique are accurate in reference to a calibration referent and reliable both within and among judges. The second study compared two aspects of vocal tract configuration in patients with adductor spasmodic dysphonia before and following treatment with Botox injection. Changes in vocal tract configuration are discussed in reference to prior observations of patients with spasmodic dysphonia. These preliminary investigations suggest that dynamic MRI has promise as a useful technique in the study of vocal tract configuration.

[Gadolinium-enhanced magnetic resonance angiography with ultra-short echo times. Initial experiences]

Magnetic resonance angiography (MRA) using three-dimensional (3D) gradient-echo sequences with ultra-short echotimes (USTE; 2 ms) and luminal enhancement of vessels with a gadolinium bolus affords the depiction of extended vascular territories with high spatial resolution within 20-60 s. Because of the ultra-short echo and repetition times, filling of the vascular lumen with gadolinium is depicted; the latter is relatively independent of the complex flow effects on which conventional MRA is based. MRA typical flow voids caused by turbulence or slow flow are thus significantly reduced and allow more reliable depiction of stenoses. After implementing the sequences on our scanner, we evaluated the potential of USTE-MRA for the delineation of various vascular territories in 56 patients. A total of 70 vascular territories were depicted and evaluated by two independent radiologists for image quality and obscuring the arteries because of the contrast of veins. Out of the 56 (4%) diagnostic angiographic quality could not be obtained in only 2 cases. In 13 patients (23%) the studies were judged suboptimal, but diagnostic. In only 3 cases (5%) was venous filling judged to obscure the arteries completely on MIPs (maximum intensity reconstructions), although the studies were diagnostic when evaluated with MRPs (multiplanar reconstructions). Venous superimposition occurred significantly more frequently in the neck than else-where. The greatest improvement over conventional MRA was obtained in the abdomen and thorax where USTE-MRAs can be obtained within a breath-hold without motional artifact.

Breathhold imaging of the upper abdomen using a circular polarized-array coil: comparison with standard body coil imaging

Current studies emphasize the use of array coils to decrease noise and increase the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We applied T1-weighted and T2-weighted standard nonbreathhold spin echo (SE) sequences and T1-weighted FLASH, TurboFLASH, T2-weighted spin-echo time (TSE), and heavily T2-weighted half Fourier acquisition single-shot TSE (HASTE) sequences during breathhold for abdominal imaging in 15 normal volunteers. The breathhold scans were performed using both a standard coil and a circular polarized array coil. We analyzed the signal intensity (SI), SNR, and CNR of abdominal organs in all sequences. SNRs increased in all cases by an overall factor of approximately 3 due to an 8% increase in overall SIs and a 50% decrease in noise when applying the array coil. Although the array-coil FLASH sequence performed at least as well as the respective SE sequence, the SNRs of the array-coil TurboFLASH, TSE breathhold, and HASTE sequences were generally lower. We conclude that array-coil imaging significantly improves fast imaging of the abdomen.

[Techniques and applications of MR pancreatography in comparison with endoscopic retrograde pancreatography]

Using heavily T2 weighted sequences, magnetic resonance tomography allows the delineation of the pancreatic duct system with high contrast. The development of fast and ultrafast imaging sequences results in a variety of different technical approaches already published. Aim of this article is the review of the different approaches and results published. In addition, we compare MRP in 34 patients with results of ERP using a snap-shot sequence approach. In this study, MRP has a sensitivity of 83.3% a specifity of 90.9% and accuracy of 83.3% regarding detection of duct changes like stenosis, occlusion and duct dilatation. Our results indicate, that MR-pancreaticography can be a valuable adjunct to MR-imaging of the pancreas.

[MRI of the pancreas: value, technique and applications]

MR imaging of the pancreas is compromised by several problems: motion artifacts from breathing, cardiac and vascular pulsation, and bowel peristalsis. These limitations can be overcome by modern scanner- and software technology. In the meantime, MRI of the pancreas can compete with well established methods as ultrasound and computed tomography (CT). In addition, new sequences provide imaging modalities comparable to angiography and ERCP. In the future, the value and the efficacy of MRI in comparison to CT, and its clinical impact has to be evaluated in clinical studies. In this article, we review the technical development of MRI of the pancreas, and discuss its clinical use.

[MRI of the pancreas: radiologic-pathologic correlation]

The typical MRI features of the most common pancreatic diseases, such as pancreatitis and adenocarcinoma of the pancreas, have been established. However, even in these common pancreatic disorders, MRI correlation with the underlying pathology is limited for clinical reasons. We emphasize MR-pathological correlation of inflammatory and neoplastic pancreatic changes, including pancreatitis, adenocarcinoma, acinar cell carcinoma, rare cystic and solid pancreatic neoplasms, and islet cell tumors. By highlighting the correlation of key pathological features with MR findings, a better understanding of the MR appearance of pancreatic pathology can be provided. In addition, MRI may prove a powerful tool in detection and characterization of pancreatic tumors.

[Functional MRI of the pharynx in obstructive sleep apnea using rapid 2D FLASH sequences]

Functional imaging of the pharynx used to be the domain of cineradiography, CT and ultrafast CT. The development of modern MRI techniques led to new access to functional disorders of the pharynx. The aim of this study was to implement a new MRI technique to examine oropharyngeal obstructive mechanisms in patients with obstructive sleep apnea (OSA). Sixteen patients suffering from OSA and 6 healthy volunteers were examined on a 1.5 T whole-body imager ("Vision", Siemens, Erlangen Medical Engineering, Germany) using a circular polarized head coil. Imaging was performed with 2D flash sequences in midsagittal and axial planes. Patients and volunteers were asked to breathe normally through the nose and to simulate snoring and the Mueller maneuver during magnetic resonance imaging (MRI). Prior to MRI, all patients underwent an ear, nose and throat (ENT) examination, functional fiberoptic nasopharyngoscopy and polysomnography. A temporal resolution of 6 images/s and an in-plane resolution of 2.67 x 1.8 mm were achieved. The mobility of the tongue, soft palate and pharyngeal surface could be clearly delineated. The MRI findings correlated well with the clinical examinations. We propose ultrafast MRI as a reliable and non-invasive method of evaluating pharyngeal obstruction and their levels.

[Phased-array superficial coil and breath holding technique in MRI of the liver. Comparison of conventional spin echo sequences with rapid fat suppressing gradient echo and turbo-spin sequences]

PURPOSE

To determine the efficacy of fast MRI techniques using a tailored imaging design (breathhold and array-surface coil), conventional T1-, T2-weighted spin-echo (SE) sequences and breathhold gradient-echo (GRE) T1- and breathhold fast SE T2-weighted images were compared.

METHODS

20 patients with proven focal liver lesions were studied on a 1.5 Tesla system. Conventional SE T1- and T2-weighted imaging, as well as GRE T1- and fast SE T2-weighted imaging was performed. Fast imaging was done during breathhold using an array-surface coil. For all sequences signal-to-noise ratios (S/N) and liver-to-lesion-contrast ratios (L/L) were measured and statistically compared. In addition, two blinded readers qualitatively evaluated all images, using a score system regarding artifacts (breathing, pulsation), number of lesions, and over-all image quality.

RESULTS

Regarding image quality parameters, S/N and L/L, there was no significant (p > 0.05) difference between the conventional and fast imaging techniques. However, GRE imaging was superior (84.8%) to conventional imaging for breathing and pulsation artifacts, while fast SE T2 imaging was equal regarding breathing artifacts, but superior (51.5%) regarding pulsation artifacts. The number of detected hepatic lesions was identical in all sequences.

CONCLUSION

The fast MRI techniques demonstrated a superiority to conventional imaging regarding image quality and presence of artifacts. Therefore, fast imaging techniques can replace conventional techniques, at least in patients that can sufficiently sustain breathing.

Diagnosis of renal artery stenosis: feasibility of combining MR angiography, MR renography, and gadopentetate-based measurements of glomerular filtration rate

OBJECTIVE

Our aim was to evaluate the feasibility of combining in a single test (1) structural evaluation of renal arteries with MR angiography, (2) functional evaluation of global glomerular filtration rates calculated on the basis of plasma disappearance of gadopentetate dimeglumine, and (3) renographic analysis of individual kidneys based on the dynamic changes in signal intensity that occur after administration of gadopentetate dimeglumine.

SUBJECTS AND METHODS

We used unenhanced MR angiography to measure patency of the renal arteries in 10 healthy volunteers and in 10 patients with renal artery stenosis. Calculations of global glomerular filtration rate were based on measurements of plasma disappearance of gadopentetate dimeglumine as shown by MR relaxometry. For renography with gadopentetate dimeglumine, we generated curves that showed changes in signal intensity in both kidneys over time; intrarenal kinetics were studied by measuring the time of arrival of gadopentetate dimeglumine in the cortex and outer medulla of the kidney. Conventional angiograms, measurements of global glomerular filtration rate based on plasma disappearance of 99mTc-DTPA, and 99mTc-DTPA renograms were used as reference standards. We compared the two different methods of determining global glomerular filtration rates by computing the correlation coefficient of the linear regression of rates derived from studies with gadopentetate dimeglumine versus rates derived from studies with 99mTc-DTPA.

RESULTS

In all volunteers, renal arteries were well visualized, and global glomerular filtration rates based on plasma clearance of gadopentetate dimeglumine were normal. In nine of 10 patients, correlation was good between findings on MR angiograms and findings on conventional arteriograms. Finding were discordant in one patient because the patient moved during the MR angiography. For all six patients studied, correlation was good between measurements of global glomerular filtration rates based on plasma clearance of gadopentetate dimeglumine and those based on clearance of 99mTc-DTPA (r = 98%).

CONCLUSION

Our results suggest the potential of magnetic resonance for a comprehensive approach for detection of renal artery stenosis. This novel approach provides structural evaluation of renal arteries with unenhanced MR angiography. MR renography is done and global glomerular filtration rates are determined by using MR relaxometry after injection of contrast material. Corticomedullary transit times can be determined on the basis of the dynamic changes in signal intensity that occur after administration of gadopentetate dimeglumine.

[Fast and ultra-fast sequences in MRI of the pelvis and retroperitoneum]

Fast and ultrafast sequences are crucial prerequisite for optimum diagnostic impact in magnetic resonance (MR) imaging of the pelvis and retroperitoneum. In MR imaging of the pelvis, heavily T2-weighted fast turbo spin echo (TSE) sequences with acquisition times of 2-4 min have widely replaced time-consuming conventional T2-weighted SE sequences due to substantial time savings and better image quality. Fast and ultrafast gradient recalled echo (GRE) sequences are the basis of dynamic contrast-enhanced studies. In MR imaging of the retroperitoneum, fast and ultrafast sequences currently play the most important role as they allow for breath-hold acquisition of a sufficient number of images free of motion artifacts. The current roles of TSE, tubo gradient spin echo (TGSE), GRE and echoplanar imaging (EPI) sequences in MR imaging of the pelvis and retroperitoneum is discussed.

Bubbles in the belly: imaging of cystic mesenteric or omental masses

The purpose of this article is to familiarize radiologists with the spectrum of "bubbles in the belly," including the current histologic classification of mesenteric or omental cysts. Although mesenteric and omental cystic masses are uncommon lesions, radiologists should be familiar with them as well as with other anomalies that can manifest as these cysts. The first step in diagnosing a cystic abdominal mass is to determine the organ from which the mass originates. The most common type of mesenteric or omental cyst is lymphangioma, but other types encountered include the enteric duplication cyst, the enteric cyst, the mesothelial cyst, and the nonpancreatic pseudocyst. Other cystic lesions that may be located in the mesentery or omentum include cystic mesothelioma, cystic spindle cell tumor, and cystic teratoma. Because of the overlap in imaging features of mesenteric or omental cysts and other cystic masses, histologic analysis is usually necessary to establish a diagnosis. The major role of the radiologist is to document the cystic nature of these abdominal masses and their mesenteric or omental origin.

Changes of soft-tissue water examined with magnetic resonance and electrical impedance tomography: an in vivo experiment

The purpose of this study was the examination of short-term changes in soft-tissue water under in vivo conditions. In 12 healthy volunteers the water distribution of a selected slice of the lower limb was examined after change of position and rapid infusion of 0.9% saline solution. Two methods were used for data acquisition: magnetic resonance imaging (MRI) (Repetition Time (TR) = 1600 msec, Inversion Time (TI) = 300 msec, Echo Time (TE) = 22 msec) and electrical impedance tomography (EIT). In orthostatic equilibrium all 12 volunteers demonstrated changes of MR signal intensity and resistivity in the range of 12% and 7%, respectively. After infusion, mean changes of signal intensity and resistivity were 7% and 4%, respectively. The overall correlation of MRI and EIT was -0.96 (p < 0.001). Results indicate that inversion recovery sequences are a sensitive method of detecting in vivo changes of water distribution in selected areas of the body.

Classification of the free fluid reservoir in the calf by electrical impedance tomography

The Electrical impedance tomography computes images of resistivity distribution which allow to analyse the body fluid content. The Sheffield system, Applied Potential Tomography (APT) was chosen to examine fluid shifts in the calf following body postural change, saline infusion (FL), and lower body negative pressure stress (LBNP). The APT allows the detection of differently reacting regions in the tomogram. The overall images of APT showed an exponential resistivity increase after the body position change from upright to 6 degrees head down tilt (HDT). During LBNP the pattern of the APT images looked the same as during FL. Both showed a resistivity decrease in the overall images. The outer surface showed a different magnitude of resistivities compared to the inner region in all experiments. A comparison of the overall APT images with the tomograms simultaneously obtained by NMR in one test subject showed the same tendency. This leads to the conclusion that the changes in the fluid reservoir of the calf may be classified by electrical impedance tomography.

[Molecular biological properties of the AIDS virus]

Genetic information on the AIDS virus, which belongs to the family of retroviruses, is encoded in a single-strand RNA. After infection of the target cell, its genomic RNA is transcribed into DNA by the reverse transcriptase. Subsequently, the DNA can be integrated into the host genome. This viral genome encodes the envelope proteins, the core proteins and the viral enzymes. There are additional genes coding for products which have regulatory functions and determine the interaction between virus and host cell. The replication cycle of the AIDS virus begins with infection of the target cell. After transcription by the reverse transcriptase, the genetic viral information may remain latent or may, under certain circumstances, lead to the expression of viral components which can be assembled at the cell membrane. New viruses are then formed by budding. Theoretically, each step in the viral replication cycle could serve as a target of therapeutic intervention. Up to now, only a few compounds have been investigated in clinical studies.

Sensory dysfunction in children who toe walk

In order to formulate a hypothesis regarding the etiology of toe walking, the sensory processing abilities of 17 mentally retarded children who toe walk were examined. A galvanic skin response was used to compare reactions of the mentally retarded children and a group of normal children to a variety of sensory stimuli. Galvanic skin response testing did not reveal significant differences between the two groups in processing sensory input. Scores of the mentally retarded children from a postrotary nystagmus test were compared to values for normal children of the same age, and the results indicated that vestibular dysfunction was present in all of the subjects. We hypothesize that children may toe walk to increase somatosensory input to the lateral vestibular nucleus (Deiter's) and the lateral vestibulospinal tract to facilitate support tone in the lower extremities during walking.