Pituitary growth hormone release and gene expression in cafeteria-diet-induced obese rats

PURPOSE: To determine prospectively the feasibility and accuracy of combined gadolinium-enhanced magnetic resonance (MR) angiography, MR urography, and MR nephrography in the presurgical evaluation of potential renal transplant donors. MATERIALS AND METHODS: Twenty-two potential donors for renal transplantation were evaluated with 1.5-T MR imaging. MR angiograms were evaluated for the number of renal arteries, presence of early arterial branches, and renal artery stenoses. The renal collecting system and ureters were evaluated on the MR urograms. Renal parenchyma was assessed on the MR nephrogram. Prospective interpretation of MR images was compared with that of conventional angiograms and excretory urograms and with surgical findings. RESULTS: Gadolinium-enhanced MR angiography enabled correct identification of the arterial supply to all 44 native kidneys (44 single or dominant renal arteries and nine accessory renal arteries), four of five early arterial branches arising in the proximal 2 cm of the renal artery, a mild truncal stenosis in one renal artery, and two anomalies of the draining renal veins. The MR urogram accurately depicted a duplicated collecting system and mild unilateral pelvicalicectasis. The MR nephrogram showed renal size and a solitary cyst in one kidney, confirmed with sonography. CONCLUSION: Combined gadolinium-enhanced MR angiography, MR urography, and MR nephrography can accurately depict the arterial supply, collecting system, and renal parenchyma of donor kidneys.     

Automatic registration of pelvic computed tomography data and magnetic resonance scans including a full circle method for quantitative accuracy evaluation

The purpose of this study is to develop a method for registration of CT and MR scans of the pelvis with minimal user interaction and to obtain a means for objective quantification of the registration accuracy of clinical data without markers. CT scans were registered with proton density MR scans using chamfer matching on automatically segmented bone. A fixed threshold was used to segment CT, while morphological filters were used to segment MR. The method was tested with transverse and coronal MR scans of 18 patients and sagittal MR scans of 8 patients. The registration accuracy was estimated by comparing (triangulating) registrations of a single CT scan with MR in different orientations in a "full circle." For example, CT is first matched on transverse MR, next transverse MR is matched independently on coronal MR, and finally coronal MR is matched independently on CT. The product of the three transformations is the identity if all matching steps are perfect. Deviations from identity occur both due to random errors and due to some types of systematic errors. MR was registered on MR (to close the "circle") by minimization of rms voxel value differences. CT-MR registration takes about 1 min, including user interaction. The random error for CT-MR registration with transverse or coronal MR was 0.5 mm in translation and 0.4 degree in rotation (standard deviation) for each axis. A systematic registration error of about 1 mm was demonstrated along the MR frequency encoding direction, which is attributed to the chemical shift. In conclusion, the presented algorithm efficiently and accurately registers pelvic CT and MR scans on bone. The "full circle" method provides an estimate of the registration accuracy on clinical data.     

Radiosurgery and microsurgery for AVMs

We developed a method of velocity-coded color MR angiography using a color code from the data obtained from velocity-phase images of phase-contrast MR angiography in order to add flow direction information to MR angiograms. Phase-contrast MR angiography with reconstruction of velocity-phase images was performed in 30 patients. Two projection images from velocity-phase images of each phase-contrast MR angiogram were obtained and assigned color according to flow direction. We then superimposed the two color images onto the maximum intensity projection image of the MR angiogram. The velocity-coded color MR angiogram clearly showed flow direction from the data on the phase-contrast MR angiogram of the neck. Veins were readily distinguishable from arteries, and flow changes, such as a subclavian steal, were also identified.     

Multivoxel proton MR spectroscopy and hemodynamic MR imaging of childhood brain tumors: preliminary observations

PURPOSE: To assess multivoxel proton MR spectroscopy combined with MR imaging and hemodynamic MR imaging in the evaluation of brain tumors in children and young adults. METHODS: Fifteen patients with brain tumors and 10 healthy children underwent MR imaging and MR spectroscopy on a 1.5-T system. Ten patients with tumors had both MR spectroscopy and hemodynamic MR imaging. MR spectroscopy data sets with 1 cm3 to 3.4 cm3 resolution were acquired within 8.5 minutes by using a point-resolved spectroscopic, chemical-shift imaging technique in two dimensions with volume preselection. MR imaging was performed using fast spin-echo techniques. Hemodynamic MR imaging data were acquired every 2.5 seconds at one anatomic level using a spoiled gradient-echo sequence during intravenous bolus administration of contrast material. RESULTS: Assessment with multivoxel MR spectroscopy and hemodynamic MR imaging added about 30 minutes to the total MR examination time. Normal tissue exhibited spectral peaks from biologically significant compounds such as N-acetylaspartate (NAA), choline-containing compounds (Cho), and total creatine (tCr). Twelve biopsy-proved tumors exhibited prominent Cho, reduced NAA, variable tCr, and/or lactate or lipids, and two showed increased hemodynamic parameters. Three of the tumors treated with radiation did not reveal prominent levels of Cho. Tissue necrosis had no Cho, NAA, or tCr, and reduced hemodynamics. CONCLUSIONS: Preliminary findings by MR spectroscopy combined with MR imaging and hemodynamic MR imaging suggest that regions of active tumor may be differentiated from areas of normal tissue and areas of necrosis. These findings may enable metabolic and hemodynamic characterization of childhood brain tumors as well as suggest their response to therapy.     

Global phylogeography of the ridley sea turtles (Lepidochelys spp.) as inferred from mitochondrial DNA sequences

BACKGROUND: The cardiovascular applications of magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. These characteristics allow the accurate assessment of left ventricular mass and volume, the differentiation of infarcted from normal tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. METHODS: In addition to the conventionally used spin-echo and cine-echo techniques, newer techniques such as myocardial tagging, ultrafast MR imaging and MR coronary angiography have been developed. These newer techniques allow a more accurate assessment of ventricular function (tagging), myocardial perfusion (ultrafast imaging), and evaluation of stenosis severity (MR coronary angiography). Particularly early detection and flow assessment of stenosed coronary arteries and bypasses by MR angiography would constitute a major breakthrough in cardiovascular MR imaging. Apart from the MR imaging techniques, cardiac metabolism may be well assessed using MR spectroscopy. This provides unique information on the metabolic behaviour of the myocardium under conditions stress-induced ischemia. However, the definite niche of cardiac MR spectroscopy has still to be settled. CONCLUSION: Currently, MR techniques allow the evaluation of anatomy and function (accepted use), perfusion and viability (development phase), and coronary angiography (experimental phase). A particular strength of MR imaging is that one single MR test may encompass cardiac anatomy, perfusion, function, metabolism and coronary angiography. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics and would outweight the cost inherent to the MR angiography procedure.     

Delineation of calf deep veins using 2D-TOF MR venography without contrast media: efficacy of tourniquet and leg-warming]

We evaluated the imaging quality of 2D-TOF MR venography of the lower part of the leg and the efficacy of a tourniquet around the knee and leg-warming. In 8 healthy volunteers, MR venography was carried out under the following four conditions: (a) usual MR venography, (b) MR venography with tourniquet around the knee, (c) MR venography after leg-warming and (d) MR venography with tourniquet after leg-warming. Our results suggested that MR venography with tourniquet after leg-warming is best suited for imaging the veins of the leg. We also compared the diagnostic image quality of MR venography and conventional contrast venography in 7 patients with varices. The results showed no significant differences between the two methods. We conclude that MR venography with tourniquet after leg-warming is a technique that provides reliable information about the veins of the leg.     

Synovial fibroblasts and the sphingomyelinase pathway: sphingomyelin turnover and ceramide generation are not signaling mechanisms for the actions of tumor necrosis factor-alpha

PURPOSE: To test the hypothesis that magnetic resonance (MR) digital subtraction angiography is superior to two-dimensional time-of-flight (TOF) MR angiography for demonstration of patent arteries in the distal lower extremity. MATERIALS AND METHODS: Thirty-seven lower extremities in 23 consecutive patients were imaged with two-dimensional TOF MR angiography and two-dimensional MR digital subtraction angiography. Images were interpreted in a randomized and blinded manner. Each lower extremity was subdivided into seven potential arterial segments. The number of digital arteries visualized was also determined. Overall image quality of MR digital subtraction and TOF angiograms was compared. The relative ability of MR digital subtraction angiography and TOF MR angiography to demonstrate patent arterial segments was assessed. RESULTS: MR digital subtraction angiography was significantly superior to TOF MR angiography for demonstration of patent arterial segments and digital arteries (P < .001). MR digital subtraction angiographic images were qualitatively superior to TOF images (P < .001). CONCLUSION: Two-dimensional MR digital subtraction angiography is superior to two-dimensional TOF MR angiography for help in identifying patent segments in the distal lower extremity.     

Real-time reconstruction and high-speed processing in functional MR imaging

Access to fully processed activation maps in near real time during a functional MR examination enables run-to-run assessment of results. This is particularly useful in clinical studies, since the results of the functional MR examination can be ascertained before the patient leaves the MR suite, permitting interactive tailoring of the functional MR study. We describe how a real-time MR system can be customized to complete the following tasks in less than 3 minutes: obtain an 81-second acquisition of a multisection functional MR imaging time series using single-shot echo-planar imaging, perform image reconstruction, extract functional MR activation maps using cross-correlation and thresholding, and superimpose activation maps on previously acquired T1-weighted anatomic images.     

Nitric oxide superoxide and peroxynitrite modulate osteoclast activity

PURPOSE: To assess whether magnetic resonance (MR) spectroscopic imaging with MR imaging can improve prostate cancer localization in postbiopsy hemorrhage cases. MATERIALS AND METHODS: Records of 175 patients with prostate cancer were retrospectively reviewed; 42 patients (135 hemorrhagic sites) had spatially correlated biopsy data. Patients underwent both phased-array coil-endorectal coil MR imaging and three-dimensional MR spectroscopic imaging within 180 days after transrectal ultrasound (US)-guided biopsy. High-signal-intensity hemorrhage on T1-weighted images and corresponding high- or low-signal-intensity areas on T2-weighted images and the metabolic ratio (choline + creatine)/citrate were recorded. Cancer was identified as a low-signal-intensity area at T2-weighted MR imaging or a metabolite ratio greater than 3 standard deviations above normal at MR spectroscopic imaging. MR imaging, spectroscopic, and biopsy findings were compared. RESULTS: Forty-nine patients had postbiopsy hemorrhage. On T2-weighted images, a higher (P < .01) percentage of hemorrhagic sites demonstrated low signal intensity (80% [108 of 135 sites]), which is similar to the signal intensity seen with cancer. The addition of MR spectroscopic imaging to MR imaging resulted in a significant increase (P < .01) in the accuracy (52% to 75%) and specificity (26% to 66%) of tumor detection. CONCLUSION: The addition of MR spectroscopic imaging to MR imaging significantly improves the ability to determine the presence of prostate cancer and spatial extent when postbiopsy changes hinder interpretation with MR imaging alone.     

Fex-C1-x/Si颗粒膜的巨磁电阻效应

利用激光脉冲沉积（PLD）方法制备了沉积于硅基片上的掺杂过渡金属的非晶碳膜结构Fex-C1-x/Si。Fex-C1-x/Si的磁电阻（MR）可正可负，随温度而变化。当温度T〈258K时，Fe0．011-C0.989／Si的MR为负值；当258K〈T〈340K时，该材料的MR为正值，在室温磁场为1T时，该材料的正MR可以大于20％。且在不同的温度范围中，该材料的MR和外加磁场的依存关系呈现出不同的特点：在T=280和300K时，当磁场小于1T时，MR随磁场的增加而快速增加，之后随磁场的继续增加MR增加开始变得缓慢；在T=350K时，MR近似以磁场的B^1.5。的规律变化；而在T=30K时，MR为负值且其大小随磁场的增加而减小。利用双通道模型对该MR效应进行了初步解释。     

Stromal invasion by carcinoma of the cervix: assessment with dynamic MR imaging

OBJECTIVE: The purpose of this study was to evaluate dynamic MR imaging in assessing the depth of stromal invasion by carcinoma of the cervix and to compare dynamic MR imaging with T2-weighted and contrast-enhanced T1-weighted MR imaging. SUBJECTS AND METHODS: Forty-one patients with carcinoma that was clinically considered to be confined to the cervix were examined with T2-weighted, dynamic, and contrast-enhanced T1-weighted MR imaging before surgery. We evaluated enhancement patterns of the cervix and tumor and assessed the degree of stromal invasion with MR imaging. The degree of stromal invasion was divided into two groups: superficial disease (no stromal invasion or invasion of < or = 3 mm) and deep invasion (> 3 mm of stromal invasion). Then we compared these MR findings with histologic results for the depth of stromal invasion. RESULTS: With dynamic MR imaging, cervical carcinoma with deep invasion was seen as a focal enhanced area in the early dynamic phase. The cervical epithelium and stroma enhanced less vividly. In distinguishing deep invasion from superficial disease, we found the accuracy of T2-weighted MR images, dynamic MR images, and contrast-enhanced T1-weighted MR images to be 76%, 98%, and 63%, respectively. In particular, the detectability of 3.1-5.0 mm of stromal invasion with dynamic MR images was significantly higher than that with the other techniques: with T2-weighted MR images, we saw 3.1-5.0 mm of stromal invasion in 23% of patients; with dynamic MR images, in 92%; and with contrast-enhanced T1-weighted MR images, in none. Superficial disease was not revealed with any of the three MR techniques. CONCLUSION: We believe that dynamic MR imaging is superior to T2-weighted MR imaging and contrast-enhanced T1-weighted MR imaging when assessing the depth of invasion of cervical carcinoma.     

Evaluation of tibial plateau fractures: efficacy of MR imaging compared with CT

OBJECTIVE: CT is often used after plain films to evaluate fractures of the tibial plateau. Because MR imaging can show associated soft-tissue injuries as well as fractures, we hypothesize that MR is superior to CT for imaging these injuries. Accordingly, we compared the efficacy of MR imaging and CT in 22 patients with tibial plateau fractures. SUBJECTS AND METHODS: CT with two-dimensional reconstruction and MR examinations were performed in 22 patients with tibial plateau fractures. The images were interpreted by four radiologists and two orthopedic surgeons. Findings on CT scans and plain films were used to determine the configuration of the fractures and to classify them according to the Schatzker system. This was done with findings on MR images and plain films at a separate session. The MR images were also evaluated for ligamentous and meniscal injuries. A qualitative side-by-side comparison of two-dimensional CT scans and MR images for depiction of fracture configuration was done. Imaging results were correlated with observations from physical examinations in all patients and with surgical findings in 12 patients. RESULTS: All of the six types of fractures of the Schatzker classification were observed in this series. Comparison of two-dimensional CT reconstructions and MR images for depiction of fracture configuration revealed that the two techniques were equal in 14 patients, MR imaging was superior to CT in five patients, and CT was superior to MR imaging in three patients (who had very complex and comminuted fractures). In addition, MR imaging showed 12 complete ligamentous tears and 15 partial ligamentous tears in 15 (68%) of the 22 patients. MR showed meniscal injuries in 12 (55%) of the 22 patients. CONCLUSION: MR imaging was equivalent or superior to two-dimensional CT reconstruction for depiction of fracture configuration in most patients. In addition, MR showed significant soft-tissue injuries. We believe that MR imaging is the preferable imaging technique for most patients with fractures of the tibial plateau.     

MR tomography and MR angiography of an extensive glomus jugulare tumor

The diagnosis of a glomus jugulare tumour was established by MR tomography and MR angiography. MR tomography demarcated the tumour from the surrounding tissue and MR angiography showed the vascularity of the glomus tumour.     

Gadolinium-enhanced three-dimensional MR angiography of the aorta and peripheral arteries: evaluation of a multistation examination using two gadopentetate dimeglumine infusions

OBJECTIVE: Three-dimensional gadolinium-enhanced MR angiography is a rapid and accurate method that can at times image only a limited amount of anatomy during an examination. We evaluated a technique that doubled the anatomy imaged by obtaining two separate gadolinium-enhanced MR angiograms during a single examination. MATERIALS AND METHODS: Twenty-three patients referred for MR evaluation of aortic or peripheral vascular disease underwent two successive gadolinium-enhanced three-dimensional MR angiographic examinations during a single MR examination. An injection of 15 ml of gadopentetate dimeglumine was used for the first MR angiogram, and 25 ml was used for the second MR angiogram. The angiograms were quantitatively and qualitatively evaluated to determine the effect of residual gadolinium from the initial MR angiogram on the second angiogram. RESULTS: The two studies depicted either the entire aorta to the femoral arteries (n = 10) or the distal aorta to the popliteal arteries (n = 13). The total mean gadolinium dose was 0.245 mmol/kg per patient. An average of 15 min elapsed between injections. The value of arterial signal-to-noise ratio (mean, 48.8 versus 56.4) and artery-to-vein contrast-to-noise ratio (mean, 45.5 versus 49.0) increased between the first and second angiograms, respectively. Residual gadolinium elevated the values for venous signal-to-noise ratio (mean, 2.3 versus 7.2) and background-to-muscle signal-to-noise ratio (mean, 5.5 versus 10.1) on the second MR angiogram. Qualitative evaluation by three observers showed no significant differences in diagnostic usefulness or overall image quality between the first and second MR angiograms. CONCLUSION: The use of two low-dose gadolinium-enhanced three-dimensional MR angiograms during a single examination is a feasible approach to increase anatomic coverage when performing gadolinium-enhanced three-dimensional MR angiography of the aorta and peripheral vessels. Although background enhancement is slightly elevated on the second angiogram, such enhancement does not significantly change diagnostic usefulness or overall image quality.     

Improvement in mitral regurgitation after aortic valve replacement

This study sought to determine whether there is a quantitative improvement in mitral regurgitation (MR) after aortic valve replacement (AVR) for aortic stenosis (AS) and, if so, the mechanisms for this change. MR frequently accompanies AS. The addition of mitral valve replacement to AVR significantly increases the risk of surgery. Although previous studies have suggested a qualitative improvement in MR severity after AVR, semiquantitative analysis of this improvement has not been documented nor have the underlying mechanisms been examined. We evaluated 28 patients who had undergone 2-dimensional echo and color flow Doppler imaging an average of 1.5 +/- 2.5 months before and 2.5 +/- 4.2 months after AVR. Maximum MR area, MR percentage (MR area/left atrial area), mitral annular area, left atrial area, aortic gradient, and parameters of left ventricular geometry were measured to evaluate MR severity and to assess functional mechanisms for improvement in MR. There was a significant decrease in MR area (5.5 +/- 2.8 cm2 vs 2.5 +/- 1.9 cm2, p < or =0.0001) and MR percentage (25 +/- 11% vs 12 +/- 10% after operation, p < or =0.0001) between preoperative and postoperative studies. There was a significant reduction in aortic gradient, mitral annular area, left atrial area, and left ventricular length postoperatively. In univariate analysis, MR improvement was related to the lower preoperative left ventricular fractional area change (p = 0.027) and to the changes in fractional area change (p = 0.001) and left ventricular systolic area (p = 0.001). Thus, improvement in MR after AVR is related to changes in left ventricular function postoperatively. These data suggest that reduction in MR is due not only to decreased intraventricular pressure, but also to changes in ventricular morphology.     

A highly conserved major histocompatibility complex class I-related gene in mammals

We report here a cDNA sequence of a murine homolog of the human major histocompatibility complex (MHC) class I-related gene, MR1. The analyses revealed unprecedentedly high conservation of MR1 in the alpha1 and alpha2 domains (corresponding to the peptide-binding domains in the classical MHC class I molecules) between human and mouse (predicted amino acid identity: 90 and 89% for the alpha1 and alpha2 domain, respectively), compared to MHC class I and other class I molecules. On the other hand, conservation in the alpha3 domain (73%) is comparable to those of others, suggesting domain-specific conservation of MR1. The localization of the mouse MR1 gene was determined to be chromosome 1H1, which corresponds to the human chromosomal region where the human MR1 gene is located (chromosome 1q25). High conservation of MR1 among mammals suggests that MR1 may be involved in critical conserved biological function(s).     

Enhanced expression of hepatic acyl-coenzyme A synthetase and microsomal triglyceride transfer protein messenger RNAs in the obese and hypertriglyceridemic rat with visceral fat accumulation

PURPOSE: To assess the diagnostic yield of magnetic resonance (MR) imaging in patients with symptoms and signs related to the trigeminal nerve. MATERIALS AND METHODS: Medical records and MR imaging studies in 112 consecutive patients referred for MR imaging over 5 years were evaluated. MR images were independently reviewed by two neuroradiologists unaware of the clinical findings. Signs and symptoms at presentation were associated with either a positive or negative MR imaging outcome. Logistic regression analysis was performed to identify clinical variables related to imaging results. RESULTS: Sixty-eight (61%) patients had positive MR imaging findings related to symptoms and signs. Trigeminal neuralgia was correlated with a negative MR imaging outcome (P < .001). Numbness (P < .01), impaired sensation (P < .001), other neurologic symptoms and signs (P < .01), progression of symptoms and signs (P < .001), and duration of symptoms of less than 1 year (P < .001) corresponded to a positive MR imaging outcome. Two regression models, each with three clinical parameters (progression, duration < 1 year, and trigeminal neuralgia or impaired sensation), had comparable accuracy for prediction of the MR imaging outcome. CONCLUSION: Clinical findings can be used to identify groups in which a high or a low yield of MR imaging is correlated with symptoms and signs related to the trigeminal nerve.     

MR of hypoxic encephalopathy in children after near drowning: correlation with quantitative proton MR spectroscopy and clinical outcome

BACKGROUND AND PURPOSE: Quantitative MR spectroscopy has a proved role in the investigation of hypoxia caused by near drowning. To date, no studies have addressed the MR imaging changes that may also accompany this condition. The purpose of this study was to describe the MR imaging findings in children with hypoxic encephalopathy caused by near drowning and to compare these findings with the results of qualitative and quantitative proton MR spectroscopy and clinical outcome. METHODS: Twenty-two children (6 months to 11 years old) admitted to the pediatric intensive care unit after near drowning incidents underwent cerebral MR imaging and quantitative proton MR spectroscopy. Clinical and imaging studies were reviewed retrospectively, and subjects were grouped according to outcome: good result, persistent vegetative state, and death. Images were scored for edema, basal ganglia changes, and cortical changes, and were compared with MR spectra and outcome at days 1 to 2, 3 to 4, and 5 or more. RESULTS: Six patients had a good outcome, four remained in a persistent vegetative state, and 12 died. Generalized/occipital edema correlated with poor outcome. Indistinct lentiform nuclei margins on T1-weighted images were a frequent finding (78%). Basal ganglia T2 hyperintensity correlated with poor outcome, progressing from a patchy/peripheral distribution to diffuse high intensity. Patchy high T2 signal in the cortex or subcortical lines were specific but insensitive for poor outcome, as were brain stem infarcts. CONCLUSION: MR images in children with hypoxic encephalopathy after near drowning show a spectrum of changes. The most sensitive prognostic result may be achieved by combining MR imaging with qualitative and quantitative MR spectroscopic data.