Jörg Laubenberger

Proton magnetic resonance spectroscopy studies on human brain Myo-inositol in hypo-osmolarity and hepatic encephalopathy

BACKGROUND/AIMS Recent in vivo studies using proton magnetic resonance (1H-MR) spectroscopy showed low levels of myo-inositol in the brain in hepatic encephalopathy; the pathogenetic relevance of this observation is unclear. METHODS Myo-inositol and glutamine levels in the brain were studied in vivo by 1H-MR spectroscopy in patients with hypo-osmolarity and hepatic encephalopathy. RESULTS A patient with severe plasma hypo-osmolarity (222 mOsm/L) had almost undetectable signals for myo-inositol and glutamine/glutamate in the brain. Both signals reappeared after normalization of plasma osmolarity, suggesting that both myo-inositol and glutamine were released as organic osmolytes from the brain. A decreased cerebral myo-inositol signal is also found in low-grade hepatic encephalopathy but is accompanied by an increased glutamine signal. Cirrhotics without hepatic encephalopathy have near-normal inositol signals, and patients with acquired immunodeficiency syndrome encephalopathy have increased inositol signals. CONCLUSIONS The 1H-MR spectroscopic myo-inositol signal in the human brain predominantly reflects an osmosensitive inositol pool. It is hypothesized that its depletion in latent hepatic encephalopathy points to a disturbance of cell volume homeostasis in the brain as an early pathogenetic event. This may partly be caused by a hyperammonemia-induced glutamine accumulation in the brain.

Proton magnetic resonance spectroscopy of the brain in symptomatic and asymptomatic patients with liver cirrhosis

BACKGROUND & AIMS Hepatic encephalopathy (HE) is associated with typical changes of cerebral metabolite pattern observed by proton magnetic resonance (MR) spectroscopy consisting of a depletion of myo-inositol and an increase of glutamine. The aim of this study was to determine whether abnormalities in brain metabolism in neurologically asymptomatic patients with liver cirrhosis can be detected by spectroscopy. METHODS In a prospective study, 39 patients with liver cirrhosis were examined clinically according to standardized neuropsychological tests to define whether overt, subclinical, or no hepatic encephalopathy was present. All patients underwent proton MR spectroscopy at short echo times. RESULTS Spectroscopy allowed for the diagnosis of subclinical HE in 4 of 4 cases and of overt HE in 10 of 11 cases. In 24 cases of mere liver cirrhosis and normal neuropsychological testing, a typical metabolic pattern with a depletion of myo-inositol and an increased glutamine peak were found. A good correlation between the glutamine signal and the clinical grading was found. CONCLUSIONS Proton MR spectroscopy allows for the diagnosis of HE and subclinical HE, also shows the typical pathological metabolite pattern in patients with cirrhotic livers without subclinical HE, and might be more sensitive than neuropsychological testing. Glutamine could serve as a spectroscopic marker for the clinical state of the patients.

Median nerve compression can be detected by magnetic resonance imaging of the carpal tunnel

OBJECTIVE Clinically symptomatic carpal tunnel syndrome is not necessarily accompanied by impaired nerve conduction values. Surgical decompression, however, may immediately lead to complete and lasting relief of symptoms in these patients. Because minimally invasive techniques have reduced perioperative morbidity and vocational impairment related to operative decompression, the decision to decompress symptomatic patients (despite still unimpaired nerve conduction values) might be subject to discussion in the future. New diagnostic tools may be helpful in deciding which therapeutical options to choose. When the wrist is held either in flexion or in extension, the carpal tunnel pressure increases. To investigate the dynamic changes of the carpal tunnel shape during wrist motion, as well as the variations of space for the median nerve and its signal intensity in T2-weighting, magnetic resonance imaging (MRI) was performed on patients and healthy volunteers alike. Restitution and the persistence of pathological findings were assessed pre- and postoperatively. METHODS MRI (1.0 T) was performed on 20 wrists of patients with clinical symptoms of carpal tunnel syndrome (CTS) and pathological nerve conduction values. Healthy volunteers (20 wrists) were matched according to sex and age. MRI was performed in neutral, 45-degree extension, and 45-degree wrist flexion positions. T2-weighted signal intensity of the median nerve was measured in 18 patients pre- and postoperatively. RESULTS The cross-sectional area of the carpal tunnel in patients with CTS tends to be smaller than that found in nonsymptomatic volunteers. The cross-sectional area of the carpal tunnel decreases during wrist flexion at the pisiform and hamate level. During wrist extension, the cross-sectional area of the carpal tunnel decreases at the level of the pisiform. During extension, it increases at the level of the hamate. The cross-sectional area of the median nerve showed an increase at the pisiform level (P < 0.05), a flattening of the median nerve at the hamate hook level (P < 0.05), and palmar deviation of the flexor retinaculum at the pisiform and hamate hook level (P < 0.001). This was significantly greater in CTS patients than in individuals with normal wrists. Postoperatively, the distal flattening of the median nerve recovered in 94% of the cases reviewed. Although the signal intensity of the median nerve on T2-weighted images decreased by 67%, the motor latency recovered in only 39% of the cases. CONCLUSION The carpal tunnel was smaller in CTS patients than in healthy volunteers. During flexion and extension, the space available for the median nerve narrows. This may lead to potential median nerve compression. MRI is accurate and reliable for diagnosis and postoperative follow-up of carpal tunnel syndrome. In cases with obvious clinical symptoms and yet not measurably impaired median nerve conduction values, it may be helpful in making a decision for surgical decompression.

Pelvic floor descent: Dynamic MR imaging using a half-fourier RARE sequence

Dynamic magnetic resonance imaging (MRI) using a single shot fast spin‐echo technique was evaluated as a noninvasive alternative to cystourethography or colpocystorectography in patients with pelvic organ prolapse and/or urinary incontinence. Thirty‐two patients were included in this prospective study. Colpocystorectography was performed in 10 patients who previously had undergone hysterectomy and in 2 patients without history of hysterectomy with clinical suspicion of rectoceles. Bead‐chain cystourethrography was performed in 20 patients without hysterectomy. For dynamic MRI, a single‐slice half‐Fourier RARE sequence (imaging time 2 seconds) was used to depict the pelvic organs at different levels of pelvic strain. The results obtained with dynamic MRI were correlated with the x‐ray findings. All 17 cystoceles, 10 rectoceles, 2 enteroceles, and 7 vaginal prolapses could be demonstrated on MRI. Diagnostic information gained from these images was equivalent to that obtained with colpocystorectography and superior to that obtained with cystourethrography; with the latter, important findings were missed (four rectoceles). We conclude that dynamic MRI of the pelvic floor with a half‐Fourier RARE sequence can reliably detect descents of all three pelvic compartments, that it requires no contrast agent, and that no radiation exposure is involved.J. Magn. Reson. Imaging 1999;9:378–383.

Magnetic resonance imaging for supraspinatus muscle atrophy after cuff repair.

Between 1998 to 2000, the shoulders of 17 patients with rotator cuff tears were examined using magnetic resonance imaging preoperatively, and 6 and 12 months after open surgical repair. To assess the course of the supraspinatus muscle atrophy, the easily reproducible magnetic resonance imaging parameters occupation ratio and tangent sign in the Y-shaped view of the supraspinous fossa were evaluated and compared with the clinical examination. Occupation ratio is a quantitative parameter that reflects the area ratio, expressed as a percentage of the supraspinatus muscle belly to the supraspinous fossa. The tangent sign is a qualitative parameter that represents a line connecting the coracoid process and the apex of the scapular spine. Occupation ratio and tangent sign are reliable diagnostic tools in magnetic resonance imaging assessment of supraspinatus muscle atrophy. The sensitivity of the magnetic resonance imaging parameter occupation ratio is 75% and the specificity is 85%. The imaging parameter tangent sign has a sensitivity of 100% and a specificity of 85%. There is a significant relationship between occupation ratio, tangent sign, and improvement of strength and mobility registered in the score of Constant and Murley 12 months after surgery.

Human articular cartilage: in vitro correlation of MRI and histologic findings

Abstract. The aim of our study was to correlate MRI with histologic findings in normal and degenerative cartilage. Twenty-two human knees derived from patients undergoing amputation were examined with 1.0- and 1.5-T MR imaging units. Firstly, we optimized two fat-suppressed 3D gradient-echo sequences. In this pilot study two knees were examined with fast imaging with steady precession (FISP) sequences and fast low-angle shot (FLASH, SPGR) sequence by varying the flip angles (40, 60, 90 °) and combining each flip angle with different echo time (7, 10 or 11, 20 ms). We chose the sequences with the best visual contrast between the cartilage layers and the best measured contrast-to-noise ratio between cartilage and bone marrow. Therefore, we used a 3D FLASH fat-saturated sequence (TR/TE/flip angle = 50/11 ms/40 °) and a 3D FISP fat-saturated sequence (TR/TE/flip angle = 40/10 ms/40 °) for cartilage imaging in 22 human knees. The images were obtained at various angles of the patellar cartilage in relation to the main magnetic field (0, 55, 90 °). The MR appearances were classified into five categories: normal, intracartilaginous signal changes, diffuse thinning (cartilage thickness < 3 mm), superficial erosions, and cartilage ulcers. After imaging, the knees were examined macroscopically and photographed. In addition, we performed histologic studies using light microscopy with several different stainings, polarization, and dark field microscopy as well as electron microscopy. The structural characteristics with the cartilage lesions were correlated with the MR findings. We identified a hyperintense superficial zone in the MR image which did not correlate to the histologically identifiable superficial zone. The second lamina was hypointense on MRI and correlated to the bulk of the radial zone. The third (or deep) cartilage lamina in the MR image seemed to represent the combination of the lowest portion of the radial zone and the calcified cartilage. The width of the hypointense second zone correlated weakly to the accumulation of proteoglycans in the radial zone. The trilaminar MRI appearance of the cartilage was only visible when the cartilage was thicker than 2 mm. In cartilage degeneration, we found either a diffuse thinning of all layers or circumscribed lesions (“cartilage ulcer”) of these cartilage layers in the MR images. Early cartilage degeneration was indicated by a signal loss in the superficial zone, correlating to the histologically proven damage of proteoglycans in the transitional and radial zone along with destruction of the superficial zone. We found a strong effect of cartilage rotation in the main magnetic field, too. A rotation of the cartilage structures caused considerable variation in the signal intensity of the second lamina. Cartilage segments in a 55 °angle to the magnetic main field had a homogeneous appearance, not a trilaminar appearance. The signal behavior of hyaline articular cartilage does not reflect the laminar histologic structure. Osteoarthrosis and cartilage degeneration are visible on MR images as intracartilaginous signal changes, superficial erosions, diffuse cartilage thinning, and cartilage ulceration.

Diagnosis of the hypothenar hammer syndrome by high-resolution contrast-enhanced MR angiography

Abstract. Our objective was to describe the imaging features of hypothenar hammer syndrome using minimally invasive contrast-enhanced MR angiography in comparison with oscillography study. In five patients with hypothenar hammer syndrome Gd-BOPTA-enhanced elliptically reordered 3D pulse sequence MR was compared with oscillography findings and clinical symptoms focusing on angiographic appearance of vessel injury, distribution pattern of hand vasculature and joining branches between the radial and ulnar artery supply. All patients showed segmental occlusion at the site of trauma impact with varying involvement of the superficial palmar arch, common volar digital arteries. Embolic disease was present in 50% of patients and could be clearly identified with MRA. Good correspondence was found between angiographic appearance including the presence of collaterals, clinical symptoms and oscillography. Bilateral comparison was helpful in distinguishing between vessel variants and pathology. Bilateral Gd-BOPTA-enhanced MR angiography is a minimally invasive method to depict clearly the localization and extent of vessel injury in hypothenar hammer syndrome providing valuable information about distribution pattern of hand vasculature and presence of collaterals; however, no flow data can be obtained.

Fast functional MRA using time-resolved projection MR angiography with correlation analysis

Most recently, time‐resolved 2D MRA after injection of a contrast agent bolus for various applications has been proposed. Similar to conventional digital subtraction angiography (DSA), 2D MR DSA offers the ability to observe the dilution of the bolus in the vascular system during the passage with a temporal resolution considerably below 1 sec. The purpose of this paper is to present strategies to improve the inherent low signal‐to‐noise ratio of 2D angiograms while retaining some temporal resolution. This can be achieved by applying algorithms for time series analysis as used in functional MRI. The significantly improved image quality is demonstrated on examples from clinical studies from bronchial MRA as well as cardiovascular MRA. In addition to the increased signal‐to‐noise ratio, correlation analysis leads to suppression of background signals and to a better discrimination of overlapping vessels. Further improvements in the temporal discrimination of vessels is afforded by the use of consecutive multiple contrast agent boli as demonstrated by numerical simulations and experiments. Magn Reson Med 43:303–309, 2000.

Retrobulbar irradiation for thyroid-associated orbitopathy: double-blind comparison between 2.4 and 16 Gy

PURPOSE Retrobulbar irradiation is used as a standard therapy for thyroid-associated orbitopathy. The evidence of its effectiveness is, however, scarce. Doses from 2.5 to 20 Gy have been recommended. METHODS Forty-three patients with active thyroid-associated orbitopathy were irradiated with 2.4 Gy and 43 with 16 Gy. Five measures of outcome were used: (1) appearance of the eye region, documented with photographs; (2) Hertel exophthalmometry; (3) range of vertical eye movements; (4) eye muscle thickness (sum of three MRI sections across the eight rectus eye muscles); and (5) complaints, indicated on a visual analog scale. RESULTS At 3 and 6 months after irradiation, no difference between 2.4 and 16 Gy was found in any of the five outcome measures (p between 0.099 and 0.993; Kruskal-Wallis test, Holm correction). Most outcome measures were slightly, but not significantly, improved in both the 2.4 and the 16 Gy groups. Patient complaints had improved significantly in both groups and the eye muscle thickness was significantly reduced in the 2.4 Gy group after 6 months. CONCLUSION The lack of a difference between 2.4 and 16 Gy is compatible with four different interpretations: (1) the irradiation could be ineffective; (2) the maximal effect could be already reached at 2.4 Gy; (3) the maximal effect could lie between 2.4 and 16 Gy; and (4) the effect could increase beyond a threshold of >or=16 Gy. From general experience with inflammatory disease, the last two possibilities are unlikely; only the first two interpretations carry some probability. Although the design of the study did not allow a distinction between these two possibilities, we conclude that retrobulbar irradiation for thyroid-associated orbitopathy should not exceed 2.4 Gy.

Cardiac phase contrast gradient echo MRI: measurement of myocardial wall motion in healthy volunteers and patients

A number of methods have been proposed for the noninvasive measurement of myocardial wall motion. The paper describes a strategy for assessing myocardial motion based on the sensitivity of the phase of the MR-signal to motion using a breath-hold phase contrast technique. A motion-sensitized and a motion-compensated MR-signal are measured during successive scans. The difference between the two MR-signals is used to calculate myocardial velocity in all three spatial dimensions. Postprocessing includes the transformation of the measured velocities into an internal coordinate system of the left ventricle. Also various presentation modes and further processing of the received velocity information are provided including calculation of global motion parameters. We examined 20 patients suffering from myocardial infarction. The overall left ventricular motion can be characterized by appropriate parameters describing the rotation and contraction or expansion, respectively. Regional motional disturbances are visualized using parametric images. Contrary to the highly consistent interindividual data in normal volunteers, patients showed significant localized motion deficits.