Dynamic changes of ADC, perfusion, and NMR relaxation parameters in transient focal ischemia of rat brain.

The potential of multiparametric MRI parameters for differentiating between reversibly and irreversibly damaged brain tissue was investigated in an experimental model of focal brain ischemia in the rat. The middle cerebral artery (MCA) was occluded by intraluminal suture insertion for 60 or 90 min, followed by 4.5 h of reperfusion. The apparent diffusion coefficient (ADC) of brain water, T(1) and T(2) relaxation times, and CBF(i), an MR-derived index of cerebral perfusion, were repeatedly measured and correlated with the outcome from the ischemic impact. A novel user-independent approach for segmentation of ADC maps into classes of increasing injury was introduced to define regions of interest (ROIs) in which these parameters were evaluated. MCA occlusion led to a graded decline of ADC, which corresponded with both the severity of flow reduction and an increase in T(1) and T(2) relaxation times. Removal of the suture led to a triphasic restitution of blood flow consisting of a fast initial rise, a secondary decline, and final normalization. Postischemic reperfusion led to a rise of ADC irrespective of the duration of ischemia. However, the quality of recovery declined with increasing severity of the ischemic impact. Throughout the observation time, T(1) and T(2) showed a continuous increase, the intensity of which correlated with the severity of ADC decline during ischemia. Particularly with longer ischemia time, elevated T(2) in combination with reduced ADC yielded a lower probability of recovery during recirculation, while intraischemic perfusion information contributed less to the prediction of outcome. In conclusion, the combination of MR parameters at the end of ischemia correlated with the probability of tissue recovery but did not permit reliable differentiation between reversibly and irreversibly damaged tissue.

Temperature and viscosity dependence in the stereoselective formation of the inverted housane for the photochemical nitrogen loss from the deuterium-stereolabeled parent diazabicyclo[2.2.1]hept-2-ene.

For the liquid-phase photolytic denitrogenation of the stereolabeled DBH derivative exo-d2-diazabicyclo[2.2.1]heptene (exo-d2-1), the k(inv)/k(ret) ratio of the inverted [2(inv)] and retained [2(ret)] housanes (bicyclo[2.1.0]pentanes) depends on the viscosity of the medium. For this purpose, the viscosity was varied by changing the solvent (various alcohols and diols, n-hexane, and acetonitrile) at constant temperature and by changing the temperature (-50 to +100 degrees C) in one single solvent, namely n-butanol. This viscosity effect is consistent with a stepwise denitrogenation mechanism in the liquid-phase photolysis of DBH, which proceeds through an unsymmetrical, nitrogen-containing transient, namely the singlet diazenyl diradical. The simple free-volume model adequately accounts for the observed viscosity behavior of the k(inv)/k(ret) ratio in terms of frictional effects. The temperature dependence discloses a small but measurable difference in the internal activation energies for the inversion and retention processes of the proposed diazenyl diradical.

1H- and (31)P-MR spectroscopy of primary and recurrent human brain tumors in vitro: malignancy-characteristic profiles of water soluble and lipophilic spectral components.

In vitro NMR spectroscopy was performed on specimen of human brain tumors. From all patients, tissue samples of primary tumors and their first recurrences were examined. (31)P- and (1)H-spectra were recorded from samples of meningioma, astrocytoma and glioblastoma. A double extraction procedure of the tissue samples permitted acquisition of information from the membrane fraction and from the cytosolic fraction. (31)P-spectra were used to analyze the lipophilic fraction (phospholipids of the membrane) of the tissue extracts, while the (1)H-spectra reflected information on the metabolic alterations of the hydrophilic, cytosolic fraction of the tissue. The tumor types showed distinctive spectral patterns in both the (31)P- and the (1)H-spectra. Based on the total detectable (31)P signal, the level of phosphatidylcholine was about 34% lower in primary astrocytomas than in primary glioblastomas (p = 0.0003), whereas the level of sphingomyelin was about 45% lower in primary glioblastomas than in primary astrocytomas (p = 0.0061). A similar tendency of these phospholipids was observed when comparing primary and recurrent astrocytoma samples from the same individuals [+15% (p = 0.0103) and -23% (p = 0.0314) change, respectively]. (1)H-spectra of gliomas were characterized by an increase of the ratios of alanine, glycine and choline over creatine as a function of the degree of malignancy. In agreement with findings in the (31)P-spectra, the (1)H-spectra of recurrent astrocytomas showed metabolic profiles of increased malignancy in comparison to their primary occurrence. Since gliomas tend to increase in malignancy upon recurrence, this may reflect evolving tumor metabolism. (1)H-spectra of meningiomas showed the highest ratio of alanine over creatine accompanied by a near absence of myo-inositol. Phospholipid profiles of meningiomas showed higher fractional contents of phosphatidylcholine along with lower phosphatidylserine compared to astrocytomas, while higher phosphatidylethanolamine and sphingomyelin fractional contents distinguished meningiomas from glioblastomas. The extraction method being used in this study combined with high-resolution (1)H- and (31)P-MRS provides a wide range of biochemical information, which enables differentiation not only between tumor types but also between primary and recurrent gliomas, reflecting an evolving tumor metabolism.

Magnetic resonance prediction of outcome after thrombolytic treatment.

Treatment of clinical stroke with recombinant tissue plasminogen activator (rt-PA) carries the risk of hemorrhagic complications. Hence, predictors of therapeutic outcome with respect to (a) reperfusion and (b) tissue recovery would be very useful to identify potentially salvageable brain tissue. Magnetic resonance (MR) parameters, especially the apparent diffusion coefficient of water (ADC), perfusion-weighted imaging (PWI) and T(2) relaxometry are thought to provide this information. We evaluated the prognostic implications of ADC, PWI and T(2) relaxometry immediately before initiation of thrombolytic treatment in a model of clot embolism in rats. Animals (n = 14) were treated with intraarterial rt-PA (10 mg/kg) at 90 min after embolism. MR imaging was repeatedly performed at 4.7 T before and up to 5.5 h after embolism. ADC was calculated from diffusion-weighted images (b-values: 30, 765, 1500 s/mm(2)), arterial spin tagging was used for PWI, and quantitative T(2) relaxometry was performed with a Carr-Purcell-Meiboom-Gill (CPMG) sequence. A reperfusion index was calculated to assess the quality of thrombolytic recanalization. The decline of ADC at the end of the experiment to below 80% of control was defined as unfavorable outcome. The probability of tissue injury at the end of the experiments increased with the severity of ADC changes before the initiation of treatment (probability of unfavorable outcome: 21%, 44%, 65% for ADC values of 80-90%, 70-80% and <70% of control, respectively). Pretreatment PWI or T(2) relaxometry also correlated with outcome but-alone or in combination with pretreatment ADC maps-did not improve injury prediction over that obtained by ADC alone. Outcome was influenced positively by successful reperfusion the quality of which, however, could not be predicted by pre-treatment MR characteristics. The data demonstrate that ADC mapping performed before the initiation of thrombolytic treatment provides reliable risk assessment of impeding brain injury but due to uncertainties of postischemic reperfusion does not allow precise outcome prediction in individual experiments.

Laparoscopic and percutaneous radiofrequency ablation of the kidney: acute and chronic porcine study.

OBJECTIVES: The chronic effects of renal radiofrequency ablation are unknown. Herein, we investigate the anatomic and physiologic sequelae of laparoscopic and percutaneous renal radiofrequency ablation in acute and chronic porcine models. METHODS: Our study comprised two phases-an acute phase and a chronic phase. In the acute phase, bilateral laparoscopic renal radiofrequency ablation was performed in 6 animals (12 renal units), which were euthanized immediately after surgery. In the chronic study, bilateral percutaneous renal radiofrequency ablation was performed in 5 animals (10 renal units). One animal each was euthanized at postoperative day 3, 7, 14, 30, and 90. RESULTS: Ultrasound-monitored laparoscopic (n = 12) and percutaneous (n = 10) radiofrequency ablations of the lower pole of the kidney were technically successful in each instance. No intraoperative complications occurred. In the survival experiments, the radiolesions showed gradual spontaneous resorption and ultimate renal autoamputation, while maintaining pelvocalyceal integrity as confirmed by ex vivo retrograde ureteropyelogram. Serum creatinine and hematocrit remained stable in all survival animals. Postoperative complication occurred in 1 chronic animal with nonobstructive small bowel dilation at autopsy. CONCLUSIONS: Laparoscopic and percutaneous renal radiofrequency ablation are technically feasible. The anatomic and physiologic sequelae of renal radiosurgery are favorable. Improved techniques of real-time monitoring of the evolving renal radiolesion are necessary.

Laparoscopic lymphocelectomy: a multi-institutional analysis.

PURPOSE: Because symptomatic lymphoceles are infrequent, single center studies generally report small numbers of patients. We report a multi-institutional experience with and long-term outcome following laparoscopic lymphocelectomy in 81 patients. MATERIALS AND METHODS: Data were obtained from 9 institutions at which at least 5 cases of laparoscopic lymphocelectomy had been performed. Baseline patient demographics, operative time and blood loss, special operative adjunct techniques, postoperative course, convalescence, complications and lymphocele recurrence data were collected and analyzed. RESULTS: A total of 56 men and 25 women with a mean age of 41 years were included in the study. Lymphocele formed after renal transplantation in 78 patients (96%) and after pelvic lymph node dissection in 3 (4%). Average operating time was 123 minutes with a mean blood loss of 43 ml. Omentopexy was performed in 11 cases (13.6%). No intraoperative stenting of the transplant ureter was performed. Intraoperative complications consisted of laryngospasm, bladder injury, inferior epigastric artery injury and mild renal capsule hematoma in 1 patient each. Conversion to open surgery was required for repair of bladder injury in 1, repair of preexisting hernia in 1, unusually thickened lymphocele wall in 1 and inaccessible lymphocele location in 4 cases. Mean time to ambulation and resumption of regular diet was 1 day, and mean hospital stay was 1.5 days. Postoperative complications included trocar site hernia in 1 and urinary retention in 2. Convalescence averaged 2.5 weeks. During a mean followup of 27 months 5 patients (6%) had lymphocele recurrence. CONCLUSIONS: Laparoscopic lymphocelectomy is safe, minimally invasive and effective. It is an excellent alternative to the conventional open surgical approach.

Quantitative T*(2) and T'(2) maps during reversible focal cerebral ischemia in rats: separation of blood oxygenation from nonsusceptibility-based contributions.

Quantitative imaging contrast is evaluated which allows the selective measurement of the blood oxygenation state during cerebral ischemia within a multiparametric imaging study on rats. In a first step, the ambiguities arising in T*(2)-weighted images due to T*(2) heterogeneity are eliminated by calculating T*(2) maps. Then, 1/T'(2) maps are calculated according to 1/T'(2) = 1/T*(2) - 1/T(2) to eliminate nonsusceptibility-induced changes of 1/T*(2) after the induction of stroke. This is of particular importance in the presence of vasogenic edema. The changes Delta(1/T'(2)) after the onset of ischemia selectively quantify the variations of the deoxyhemoglobin content during the development of the infarct. The presented results are not available from conventionally recorded parameters of a stroke study and, together with perfusion-weighted images, form a powerful combination to analyze the oxygen consumption and the metabolism of the tissue. Magn Reson Med 42:1027-1032, 1999.

Gradient echo time dependence and quantitative parameter maps for somatosensory activation in rats at 7 T.

The dependence of functional magnetic resonance imaging (MRI) contrast on the gradient echo time TE in T2*-weighted blood oxygenation level-dependent (BOLD) fast low-angle shot (FLASH) imaging has been studied at 7 T for electrical forepaw stimulation in alpha-chloralose anesthetized rats. The observed variation of both the activation signal intensity and spatial pattern with echo time TE, resulting from the regional heterogeneity of T2*, was assessed by the calculation of quantitative T2* and quantitative STE = 0 maps, the latter representing the back-extrapolated signal intensity for TE = 0. The subsequently determined T2* and STE = 0 activation maps allowed a pixelwise separation of true BOLD from inflow contributions to forepaw stimulation-induced signal change in the somatosensory cortex of rat brain. For functional activation experiments performed with one single echo time the prior measurement of a quantitative T2* map is recommended as minimum further information to judge the intensity and the regional pattern of the resulting activation maps.

Structure analysis of a fusogenic peptide sequence from the sea urchin fertilization protein bindin.

The structure of "B18", an 18-residue fusogenic peptide from the sea urchin fertilization protein bindin, was investigated in several membrane-mimicking environments with circular dichroism and nuclear magnetic resonance spectroscopy. The fully conserved peptide sequence represents the minimal functional part of the 24 kDa protein, which can bind to membranes and induce fusion of lipid vesicles. The B18 peptide undergoes a coil-helix transition in the presence of TFE, showing a transient tendency to self-associate. Its NMR structure in 30% TFE exhibits two helical regions at either side, connected by a flexible loop. In DPC and SDS detergent micelles, this loop becomes distinctly bent, presumably due to the high degree of curvature of the micelles. The loop contains a histidine-rich motif for binding zinc, which is required for the fusogenic function of the peptide. Therefore, we monitored the structural response of B18 and of recombinant bindin toward this ion. Like TFE, and in a mutually cooperative manner, zinc induces a partially helical structure in both the peptide and the protein. Complex formation via the histidine residues rigidifies the flexible loop and is accompanied by self-association of the molecules. The data suggest that the zinc-bound functional state is a continuous amphipathic alpha-helix, bearing some resemblance to a leucine zipper. Two hydrophobic patches on one face could favorably penetrate into a membrane, while two arginines on the other face could interact with lipid phosphate groups. The three-dimensional model of the B18 sequence thus contributes to a better understanding of peptide-induced vesicle fusion in general, and of the lipid-protein interactions of sperm bindin in particular.

Retroperitoneal and pelvic extraperitoneal laparoscopy: an international perspective.

OBJECTIVES: To assess technical preferences and current practice trends of retroperitoneal and pelvic extraperitoneal laparoscopy. METHODS: A questionnaire survey of 36 selected urologic laparoscopic centers worldwide was performed. RESULTS: Twenty-four centers (67%) responded. Overall, 3988 laparoscopic procedures were reported: transperitoneal approach (n = 2945) and retroperitoneal/extraperitoneal approach (n = 1043). Retroperitoneoscopic/extraperitoneoscopic procedures included adrenalectomy (n = 74), nephrectomy (n = 299), ureteral procedures (n = 166), pelvic lymph node dissection (n = 197), bladder neck suspension (n = 210), varix ligation (n = 91), and lumbar sympathectomy (n = 6). Mean number of total laparoscopic procedures performed in 1995 per center was 41 (range 5 to 86). Major complications occurred in 49 (4.7%) patients and included visceral complications in 26 (2.5%) patients and vascular complications in 23 (2.2%). Open conversion was performed in 69 (6.6%) patients, electively in 41 and emergently in 28 (visceral injuries, n = 16; vascular injuries, n = 1 2). Retroperitoneoscopy/extraperitoneoscopy is gaining in acceptance worldwide: in 1993, the mean estimated ratio of transperitoneal laparoscopic cases versus retroperitoneoscopic/ extraperitoneoscopic cases per center was 74:26; however, in 1996 the ratio was 49:51. CONCLUSIONS: Retroperitoneoscopy and pelvic extraperitoneoscopy are important adjuncts to the laparoscopic armamentarium in urologic surgery. The overall major complication rate associated with retroperitoneoscopy/extraperitoneoscopy was 4.7%.

Staple occlusion of the infrarenal aorta: a videoscopic retroperitoneal approach.

PURPOSE: The purposes of this study were to determine whether available laparoscopic stapling devices could be used to interrupt the diseased human aorta, and to develop a videoscopic technique for retroperitoneal exposure and control of the infrarenal aorta in pigs. Our long-term goal is to develop a minimally invasive approach to the treatment of abdominal aortic aneurysms by exclusion and extraanatomic bypass. METHODS: Ten diseased, formalin-preserved human cadaver aortas underwent stapling using a laparoscopic stapling device. The aortas were then pressurized to superphysiologic levels to assess the integrity of the staple line. Ten swine underwent retroperitoneal video-assisted exploration with control and staple occlusion of the aorta and iliac artery. RESULTS: The staple line was complete and remained intact after pressurization in nine of 10 cadaver aortas, despite the presence of complex calcified disease. One aorta had a 2-mm opening through the staple line. Through the left retroperitoneal approach, the infrarenal aorta and left iliac artery could be dissected and controlled. A modified pledgeted technique used for stapling resulted in hemostasis of the staple line and exclusion of flow without injury to adjacent structures. CONCLUSIONS: The diseased human aorta can be occluded using available laparoscopic staplers. These swine experiments demonstrate the feasibility of the retroperitoneal approach for exclusion of infrarenal aortic aneurysms.

Solitary pancreas transplantation. Experience with 62 consecutive cases.

OBJECTIVE: To determine the safety and efficacy of solitary pancreas transplantation in the treatment of IDDM. RESEARCH DESIGN AND METHODS: A single-center retrospective case series of 62 consecutive solitary pancreas transplants (20 sequential pancreas after kidney, 42 pancreas transplants alone) performed in 57 adult IDDM patients was studied. Indications for solitary pancreas transplantation were 1) the presence of two or more overt diabetic complications and/or 2) glucose hyperlability with hypoglycemic unawareness and impaired quality of life. The recipient group consisted of 31 men and 26 women with a mean age of 38 years (range 25-62) and a mean duration of diabetes of 26 years (range 14-52). Mean pretransplant glycohemoglobin level was 9.9 +/- 2.6%. Organ acceptance was restricted to ideal donors and man-dated a minimum of a two-antigen match (mean human leukocyte antigen ABDR match 2.7). The mean cold ischemia time was 16.6 h. Whole-organ pancreas transplantation was performed with bladder drainage by the duodenal segment technique. All patients were managed with either triple or quadruple immunosuppression. Monitoring included prospective urine cytology as well as cystoscopic transduodenal needle biopsies. RESULTS: The mean length of initial hospital stay was 18 days, and mean hospital charges were $106,341. The incidences of rejection, infection, and surgical complications were 70, 55, and 47%, respectively. Overall patient and graft survival rates were 86 and 52%, respectively, with a mean follow-up of 28 months. All patients with functioning grafts had excellent metabolic control (mean glycohemoglobin level 5.1%) and achieved good rehabilitation. CONCLUSIONS: Despite morbidity, solitary pancreas transplantation can be performed with improving success, can enhance quality of life, and can offer an opportunity to arrest secondary diabetic complications.

Video-assisted, retroperitoneal approach for abdominal aortic aneurysm exclusion.

Abdominal aortic aneurysm (AAA) repair is a common procedure associated with significant morbidity and mortality. Although attempts have been made to reduce operative risk in patients with significant comorbid disease by combining aneurysm exclusion with axillofemoral bypass, the morbidity is not greatly reduced when the standard operative approach is required for exclusion. The authors describe a technique for staple exclusion of AAA using a minimally invasive, video-assisted retroperitoneal approach.

Access technique for retroperitoneoscopy.

PURPOSE: The access technique for retroperitoneoscopy is not well established, and differs from transperitoneal laparoscopic access in 3 key aspects: 1) location and technique of primary trocar placement, 2) optimal positioning of the balloon dilator and 3) technique for safe placement of secondary ports. Our method of obtaining retroperitoneoscopic access addresses these issues. MATERIALS AND METHODS: A total of 37 patients underwent retroperitoneoscopic surgery of the kidney and upper ureter. RESULTS: Our technique facilitates balloon placement within Gerota's fascia, minimizes peritoneal injury and optimizes port placement during retroperitoneoscopic surgery. CONCLUSIONS: Although our success rate for placing the balloon within Gerota's fascia has improved, additional experience is required to achieve subfascial balloon placement more consistently.

Pancreas allograft rejection: correlation of transduodenal core biopsy with Doppler resistive index.

PURPOSE: To determine the usefulness of sonographically obtained resistive indexes (RIs) in the diagnosis of pancreas allograft rejection. MATERIALS AND METHODS: Findings were studied from 78 transduodenal pancreas allograft biopsies that were ultrasound-guided and cystoscopically directed. The 78 biopsies included 40 that were compared directly with baseline RI data. Biopsies were categorized by result and correlated with concurrent RIs (including 26 RIs obtained within 24 hours of biopsy) with the chi2 test for categoric variables and the Student t test for continuous variables. Sensitivity, specificity, and positive and negative predictive values were calculated with standardized formulas. RESULTS: The mean RIs between the no rejection, mild acute rejection, and moderate acute rejection groups were not statistically significantly different; however, the mean RI associated with chronic rejection was statistically significantly higher (P < .05) than that in the other groups. The sensitivity, specificity, and positive and negative predictive values of either an elevated RI (> 0.70) or greater than 10% increase in the RI above the baseline value in the diagnosis of acute rejection were approximately 50%. CONCLUSION: Neither the absolute level of the RI nor the relative increase was correlated with acute rejection proved at biopsy. Changes in RIs after pancreas transplantation were a poor indicator of acute rejection, but the absolute value of the RI was elevated in cases of chronic rejection.

Detection of multiple conformations of the E-domain of 5S rRNA from Escherichia coli in solution and in crystals by NMR spectroscopy.

NMR spectroscopy of the E-domain fragment of Escherichia coli 5S rRNA indicates that this molecule exists in solution as either a stem-loop or as a duplex with two U-U base pairs in the bulge region. At temperatures below 27 degrees C, interconversion between the monomeric and dimeric forms in solution occurs on a time scale of weeks and allows the preparation of samples on which NMR structure determinations can be carried out on predominantly monomeric or dimeric species. The NMR results obtained provide comparison data for the distinction between A- and B-form E.coli 5S rRNA and for the possible kinetics of conversion between these forms. NMR evidence is presented that the duplex form also exists in crystals and suggestions are made for means to obtain stem-loop conformations of E-domain and other small RNA stem-loop sequences in crystals.

Sequential assignments in uniformly 13C- and 15N-labelled RNAs: the HC(N,P) and HC(N,P)-CCH-TOCSY experiments.

An approach for the simultaneous acquisition of HCN and HCP as well as HCN-CCH-TOCSY and HCP-CCH-TOCSY triple resonance data sets for 13C-/15N-labelled RNAs is presented. The new HCN-CCH-TOCSY scheme unambiguously links all sugar resonances to the base nitrogen. In addition, simultaneous acquisition of HCN-CCH-TOCSY and HCP-CCH-TOCSY data sets provides sequential and base-type information in a single experiment, thereby saving data acquisition time as well as providing complementary data sets that are useful in clarifying ambiguous assignments. Virtually complete sequence-specific phosphate-ribose 1H, 31P, and base 15N1,9, assignments as well as partial 13C assignments could be obtained in a single experiment for a 0.5-mM sample of a 19-mer ribonucleotide.

Initial analysis of 750 MHz NMR spectra of selective 15N-G,U labelled E. coli 5S rRNA.

The overall folding of an RNA molecule is reflected in its base pairing pattern. The identification of that pattern provides a first step towards the determination of the structure of an RNA molecule. We show that the application of heteronuclear NMR methods at 750 MHz to E. coli 5S rRNA (120 nucleotides) selectively labelled with 15N in guanine and uridine allows observation of base pairing patterns for a larger RNA molecule. We also present evidence that the fold of the E-domain of the 5S rRNA (nt 79-97) as a contiguous part of the 5S rRNA and as an isolated molecule is virtually the same.