Electron spin echo envelope modulation studies of the semiquinone anion radical of cholesterol oxidase from Brevibacterium sterolicum

The electron spin echo envelope modulation (ESEEM) technique of pulsed EPR spectroscopy was applied to the anionic semiquinone of the cholesterol oxidase flavin cofactor, formed when the enzyme was photoreduced in the presence of 5-deazariboflavin and EDTA. Fourier transforms of the three-pulse ESEEM spectra showed the presence of 14N nuclei magnetically coupled to the paramagnet. In 2H2O buffer the surroundings of the flavin ring were shown to be accessible to solvent exchange, with a deuterium population in close proximity to the paramagnetic centre. Upon binding of the pseudosubstrate, dehydroisoandrosterone, subtle changes were observed in the coupling to nitrogen nuclei, which are interpreted as changes in the electron density distribution of the flavin ring system. The results are discussed in terms of the three-dimensional structure reported for the protein and the flavin ring architecture.     

Fast spin echo vs conventional spin echo in cervical spine imaging

The major attraction of fast-spin-echo (FSE) imaging is reduced acquisition time; however, careful review of the literature reveals many weaknesses: phase-encoded blurring, truncation artefact, bright fat signal, reduced magnetic susceptibility and increased motion artefact. Our aim was a prospective, blinded comparison of FSE and conventional spin echo (CSE) in the cervical spine. Both sequences were performed in 43 patients (19 males and 24 females; mean age 45 years, range 15-66 years). Twenty-eight patients were studied at 1.5 T and 15 at 0.5 T. Typical sequence parameters were: at 1.5 T, TR/TE 2000/90 CSE and 3000/120 FSE, and at 0.5 T, 2200/80 CSE and 2800/120 FSE. Time saved on the FSE was used to increase the matrix and the number of acquisitions. Two neuroradiologists evaluated the images for pathology, artefacts, disc signal intensity, thecal sac compression and image quality. Ten patients had cord lesions; 2 (20 %) were missed on CSE. In 4 of 10 patients with moderate/severe thecal sac compression, the degree of stenosis was apparently exaggerated on CSE. The mean degree of confidence for the CSE sequences was 1.8 and for the FSE 1.1, where 1 is optimal. For cervical spine imaging, FSE should be preferred to CSE.     

Proton dosimetry in bone using electron spin resonance

We have studied the ESR response of proton-irradiated (in vitro) bone. The ESR response as a function of proton (E = 105 MeV) dose to bone was linear from 0 to 50 Gy and similar to the photon (E = 6 MV) dose response. The ESR depth response (Bragg) curve was depressed as compared to a depth-response curve determined with a parallel plate ionization chamber (PPIC). There was a short-term ESR signal fade in the Bragg peak region, likely attributable to the organic component in bone. We are continuing to investigate these latter two effects.     

Breath hold MR cholangio-pancreatography (MRCP) using long echo train length fast spin echo sequence in combination with surface coil

To test the feasibility of MR cholangio-pancreatography (MRCP) using long echo train length (32) fast spin echo sequence in combination with shoulder surface coil, 20 patients who had had ERCP were examined. Good correlations were acquired between the findings obtained by two modalities in terms of ductal strictures, dilatations and intraductal lesions. MRCP was considered to be an examination of choice in various kinds of pathologies affecting biliary duct as well as pancreatic duct for its non-invasiveness and reasonable image quality.     

Using nitroxide spin labels. How to obtain T1e from continuous wave electron paramagnetic resonance spectra at all rotational rates

Historically, the continuous wave electron paramagnetic resonance (CW-EPR) progressive saturation method has been used to obtain information on the spin-lattice relaxation time (T1e) and those processes, such as motion and spin exchange, that occur on a competitive timescale. For example, qualitative information on local dynamics and solvent accessibility of proteins and nucleic acids has been obtained by this method. However, making quantitative estimates of T1e from CW-EPR spectra have been frustrated by a lack of understanding of the role of T1e (and T2e) in the slow-motion regime. Theoretical simulation of the CW-EPR lineshapes in the slow-motion region under increasing power levels has been used in this work to test whether the saturation technique can produce quantitative estimates of the spin-lattice relaxation rates. A method is presented by which the correct T1e may be extracted from an analysis of the power-saturation rollover curve, regardless of the amount of inhomogeneous broadening or the rates of molecular reorientation. The range of motional correlation times from 10 to 200 ns should be optimal for extracting quantitative estimates of T1e values in spin-labeled biomolecules. The progressive-saturation rollover curve method should find wide application in those areas of biophysics where information on molecular interactions and solvent exposure as well as molecular reorientation rates are desired.     

Contributions to the Gaussian line broadening of the proxyl spin probe EPR spectrum due to magnetic-field modulation and unresolved proton hyperfine structure

The data on the role of lipid peroxidation in the effects of UV irradiation of blood are reviewed. Lipid photoperoxidation in blood cells is the result of photochemical transformation of lipid hydroperoxides, both existing and newly formed ones, into free radicals and direct photolysis of photooxidants. Dark lipid autoperoxidation is also induced by UV radiation. Both peroxidation and photooxidation of lipids are inhibited by low concentrations of antiradical antioxidants. The cyclooxygenase-catalyzed peroxidation of arachidonic acid in blood cells is stimulated by UV radiation. This process is suppressed by acetylsalicylic acid and indomethacin. The therapeutic activity of the blood that was UV-irradiated and then infused into rats with peritonitis was due to the cyclooxygenase activation.     

Comparison of fat-saturation fast spin echo versus conventional spin-echo MRI in the detection of rotator cuff pathology

The purpose of this study was to compare the diagnostic performance of fat-saturation fast-spin-echo (FSE) T2-weighted (T2W) sequences with conventional spin-echo (CSE) T2W sequences in the detection of rotator cuff pathology using surgery as the reference standard. Oblique coronal dual-echo CSE and FSE T2W images with fat saturation from 50 surgically confirmed MR shoulder examinations were acquired on a 1.5-T MR scanner. Blinded MR readers retrospectively analyzed each imaging sequence separately and ultimately correlated both sequences together with findings at surgery. FSE was 100% sensitive and 94% specific in detection of full-thickness tears (n = 19) and 73% sensitive and 97% specific in the detection of partial-thickness rotator cuff tears (n = 13). There was no statistically significant difference in the performance of FSE with fat saturation compared with CSE. The two discrepancies between imaging sequences related to the extent of partial-thickness tears. Our findings suggest that fat-saturation FSE imaging can effectively replace CSE imaging in the evaluation of rotator cuff pathology.