Sacral stress fractures in long-distance runners.
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Adult↗
Biomedical subjects
C F Beaulieu
Publications and source records attributed to C F Beaulieu.
Using biphasic CT to reveal gastrointestinal arteriovenous malformations.
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Aged↗
Volume rendering of CT data: applications to the genitourinary tract.
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Adult↗
Perspective volume rendering of CT and MR images: applications for endoscopic imaging.
PURPOSE: To use perspective volume rendering (PVR) of computed tomographic (CT) and magnetic resonance (MR) imaging data sets to simulate endoscopic views of human organ systems. MATERIALS AND METHODS: Perspective views of helical CT and MR images were reconstructed from the data, and tissues were classified by assigning color and opacity based on their CT attenuation or MR signal intensity. "Flight paths" were constructed through anatomic regions by defining key views along a spline path. Twelve movies of the thoracic aorta (n=3), tracheobronchial tree (n=4), colon (n=3), paranasal sinuses (n=1), and shoulder joint (n=1) were generated to display images along the flight path. All abnormal results were confirmed at surgery. RESULTS: PVR fly-through enabled evaluation of the full range of tissue densities, signal intensities, and their three-dimensional spatial relationships. CONCLUSION: PVR is a novel way to present volumetric data and may enable noninvasive diagnostic endoscopy and provide an alternate method to analyze volumetric imaging data for primary diagnosis.
Aorta, Thoracic↗
Diffusion-weighted MR microscopy with fast spin-echo.
A diffusion-weighted fast spin-echo (FSE) imaging sequence for high-field MR microscopy was developed and experimentally validated in a phantom and in a live rat. Pulsed diffusion gradients were executed before and after the initial 180 degrees pulse in the FSE pulse train. This produced diffusion-related reductions in image signal intensity corresponding to gradient ("b") factors between 1.80 and 1352 s/mm2. The degree of diffusion weighting was demonstrated to be independent of echo train length for experiments using trains up to 16 echoes long. Quantitative measurements on a phantom and on a live rat produced diffusion coefficients consistent with literature values. Importantly, the eight- to 16-fold increase in imaging efficiency with FSE was not accompanied by a significant loss of spatial resolution or contrast. This permits acquisition of in vivo three-dimensional data in time periods that are appropriate for evolving biological processes. The combination of accurate diffusion weighting and high spatial resolution provided by FSE makes the technique particularly useful for MR microscopy.
Animals↗
Oligomerization and conformation change in solutions of calf lens gamma II-crystallin. Results from 1/T1 nuclear magnetic relaxation dispersion profiles.
From analyses of the magnetic field dependence of 1/T1 (nuclear magnetic relaxation dispersion [NMRD] profiles) of water protons in solutions of highly purified calf lens gamma II-crystallin, we find that monomers form oligomers at relatively low concentrations, which increase in size with increasing concentration and decreasing temperature. At approximately 16% by volume and -4 degrees C, the mean oligomeric molecular weight is approximately 120-fold greater than the monomeric value of 20 kD. Below this concentration, there is no indication of any substantive change in conformation of the monomeric subunits. At higher concentrations, the tertiary structure of the monomer appears to reconfigure rather abruptly, but reversibly, as evidenced by the appearance of spectra-like 14N peaks in the NMRD profiles. The magnitudes of these peaks, known to arise from cross-relaxation of water protons through access to amide (NH) moieties of the protein backbone, indicate that the high concentration conformation is not compact, but open and extended in a manner that allows enhanced interaction with solvent. The data are analogous to those found for homogenates of calf and chicken lens (Beaulieu, C. F., J. I. Clark, R. D. Brown III, M. Spiller, and S. H. Koenig. 1988. Magn. Reson. Med. 8:47-57; Beaulieu, C. F., R. D. Brown III, J. I. Clark, M. Spiller, and S. H. Koenig. 1989. Magn. Reson. Med. 10:62-72). This unusually large dependence of oligomeric size and conformation on concentration in the physiological range is suggested as the mechanism by which osmotic equilibrium is maintained, at minimal metabolic expense, in the presence of large gradients of protein concentration in the lens in vivo (cf Vérétout and Tardieu, 1989. Eur. Biophys. J. 17:61-68). Finally, the results of the NMRD data provide a ready explanation of the low temperature phase transition, and "cold-cataract" separation of phases, observed in gamma II-crystallin solutions; we suggest that the phases that separate are the two major conformers detected by NMRD.
Animals↗
31P nuclear magnetic resonance and laser spectroscopic analyses of lens transparency during calcium-induced opacification.
The authors studied the relationships between lens phosphate metabolites and transparency in (1) normal intact calf lenses, (2) whole-lens homogenates, (3) cortical homogenates, and (4) cortical homogenates that were opacified by the addition of calcium. Transparency was measured with the use of laser spectroscopy. Phosphate metabolites and pH were measured with the use of phosphorus nuclear magnetic resonance (31P NMR) spectroscopy. 31P NMR spectra of fresh whole-lens homogenates and fresh intact lenses were nearly identical. In fresh tissue, adenosine triphosphate (ATP) accounted for 59%, 55%, and 61% of the total phosphorus detected in intact lenses, whole-lens homogenates, and cortical homogenates, respectively. As ATP decreased over time to undetectable levels, no loss of transparency was measured, indicating no relationship between ATP levels and lens opacification. In contrast, the authors found that the loss of transparency in cortical homogenates produced by additions of 5, 10, and 20 mM calcium chloride was associated with increased levels of sugar phosphates and glycerol phosphorylcholine and with decreased levels of inorganic phosphate. Loss of cortical transparency was associated with both increases or decreases in pH from the normal value.
Adenosine Triphosphate↗
Relaxometry of lens homogenates. II. Temperature dependence and comparison with other proteins.
We have extended our earlier work (C.F. Beaulieu, J.I. Clark, R.D. Brown III, M. Spiller, and S.H. Koenig, Magn. Reson. Med. 8, 45 (1988] on the magnetic field dependence of 1/T1 (NMRD profiles) of calf lens nuclear homogenates, at 25 degrees C, to 5 degrees C, and to other protein systems as well. These include concentrated solutions of myoglobin and bovine serum albumin, both globular proteins, the first compact and roughly spherical, the other extended, flexible, and with weak internal bonding; chicken lens homogenate, for which the dominant crystallins (lens proteins) are approximately 70% alpha-helical compared with calf crystallins, which are essentially all beta-sheet; and hen egg white, both native and heat-denatured. Our earlier conjectures regarding a reversible change in protein organization of the calf lens crystallins as a function of solute protein concentration is given added support. Our findings suggest that cytoplasmic homogenate can be characterized as a heterogeneous and polymorphic solution of crystallins. At high concentrations the NH moieties of the protein backbone become accessible to solvent with water (not NH proton) exchange rates greater than 10(4) s-1. This conclusion is based on two aspects of the observed NMRD profiles. At low crystallin concentration, the profiles of calf and chicken lens homogenates are similar in form to those of myoglobin and native hen egg white, a form that has been studied previously for a range of diamagnetic globular proteins and has been demonstrated to arise from the rotational thermal motion of the solute molecules. At high crystallin concentrations, the NMRD profiles of the lens homogenates develop a monotonic background (high rates at low fields), much like that of the heat-denatured egg-white sample and those of most tissues. In addition, there is a set of peaks in the central part of the profiles of the concentrated crystallins, seen also in the denatured egg white and some tissues but not in the myoglobin sample, which is known to arise from cross-relaxation interactions between the water protons and (through the intermediary of the NH proton) the 14N quadrupolar levels. The magnitude of these peaks, which is larger by an order of magnitude for native calf lens homogenates than for any tissue, requires that the majority of the NH moieties be accessible to water. Finally, going to 5 degrees C for the native calf lens homogenate takes the sample below the temperature of reversible phase separation, and it becomes opaque.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
From E.M. microprobe analysis to NMRD studies of the lens.
We describe how electron microscope X-ray emission spectroscopy (XES) was the basis for recent studies of lens cytoplasm using proton nuclear magnetic resonance, NMR, relaxation methods. Although electron microscopy and NMR are very different techniques, the phosphorus distributions that were observed in whole lens using XES led to studies of proton relaxation rates in lens cytoplasm. Proton NMR is sensitive to water-protein interactions that exist in transparent lens cytoplasm. The cytoplasm is transparent because the interactions produce Fourier components in the density fluctuations of lens cytoplasm that remain small relative to the wavelength of light (1). New information on the interactions that are involved in the development and maintenance of transparent cytoplasm may be obtained using methods of proton NMRD (2).
Animals↗
Relaxometry of calf lens homogenates, including cross-relaxation by crystallin NH groups.
We studied the magnetic field dependence of the longitudinal relaxation rates of water protons (1/T1 nuclear magnetic relaxation dispersion (NMRD) profiles) in transparent homogenates of calf lens. The samples included nuclear homogenates with total (heterogeneous) crystallin contents between 34% (v/v) (native) and 14% (diluted) as well as cortical homogenate, 21% (native) and 34% (concentrated). The NMRD profiles had two components: a monotonic dispersive component (analogous to that of both globular protein solutions and diamagnetic tissue) and "14N quadrupolar peaks." 14N peaks have never been reported for protein solutions, only for tissues and dehydrated proteins. These peaks occur between 0.5 and 5 MHz proton Larmor frequency and arise from interactions of solvent water protons with NH moieties of proteins. The 14N peaks in lens cytoplasm are very large and may correlate with the crystallin structure and interactions required to maintain short-range order and lens transparency. The monotonic and 14N quadrupolar components were largest in concentrated samples, but with different concentration dependencies. The dispersive components of samples above approximately 19% protein concentration had a fixed functional form, the amplitude of which varied with protein volume fraction, f, by the multiplicative factor f/(1 - f), suggesting spatial organization and dynamics of the solute proteins that are relatively independent of water content. In contrast, at concentrations less than 19%, the NMRD profiles are concentration dependent, indicating a dependence of the orientational relaxation time of the proteins on protein-protein interactions seen previously in other globular proteins at these concentrations. The 14N peaks are not resolved below approximately 19% protein and increase linearly with incremental volume fraction at protein concentrations above 19%. In addition, the 14N peaks in nuclear homogenates are 50-100% larger than those of cortical homogenates at the same concentrations. Partial substitution of solvent D2O for H2O decreases the peak heights, indicating that an exchangeable proton mediates the interaction between solvent protons and protein 14N nuclei.
Animals↗
Reduction of ringing and blurring artifacts in fast spin-echo imaging.
A simple method was devised to reduce ringing and blurring artifacts caused by discontinuous T2 weighting of k-space data in fast spin-echo magnetic resonance (MR) imaging. The method demodulates the weighting function along the phase-encoding direction by using multiple T2 values derived from a set of non-phase-encoded echoes obtained from an extra excitation. The performance of this method was evaluated by computer simulations and experiments, which confirmed its capability of effectively reducing or, in some cases, even completely removing the ringing and blurring artifacts. The results also show that the proposed method produces better results than other artifact reduction methods. The method is particularly useful at high magnetic field strengths (7.1-9.4 T) and with strong gradients (> 20 G/cm) used in MR microscopy, in which the apparent T2 values are short for most tissues. The authors expect that the proposed method will find useful applications in various fast spin-echo pulse sequences.
Artifacts↗
Clinical image. Lipoblastoma of the thigh: MR appearance.
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Biopsy↗
The infraconal compartment: a multidirectional pathway for spread of disease between the extraperitoneal abdomen and pelvis.
PURPOSE: The space below the kidneys where the anterior and posterior pararenal spaces converge has been defined only vaguley in the past. We describe observations on clinical CT cases and studies on cadavers that lead to a refinement in the terminology for this extraperitoneal compartment. METHOD: Abdominal/pelvic CT scans from 18 patients and the scans of 2 cadavers injected in the femoral region with iodinated contrast material were reviewed concerning the location and distribution of fluid or gas collections relative to the renal fascial enclosure. RESULTS: Pathologic processes involving the anterior or posterior pararenal spaces in addition to the pelvic extraperitoneal spaces were always accompanied by collections in the space below the cone of renal fascia. CONCLUSION: The term infraconal compartment is a suggested term for the caudal continuation of the anterior and posterior pararenal spaces. This compartment serves as an important multidirectional pathway for the spread of disease between the extraperitoneal abdomen and the pelvis. Fluid collections within this compartment have a characteristic CT appearance.
Body Fluids↗
Do arterial phase helical CT images improve detection or characterization of colorectal liver metastases?
Our goal was to determine if arterial phase images from dual phase helical CT improve either the detection or the characterization of hepatic metastases in patients with colorectal carcinoma. Sixty-two patients with known colorectal cancer underwent 65 dual phase helical CT examinations to evaluate for possible liver metastases. Three blinded reviewers independently evaluated the portal venous phase images alone to determine if hepatic metastases were present or absent. Arterial phase images were then analyzed to determine if they identified additional lesions or aided in characterizing small hepatic lesions. Scores of the two methods for diagnosing metastases were compared with the "gold standard" established by a consensus panel of three other radiologists who reviewed all images together with clinical, pathologic, and other imaging data. The addition of arterial phase imaging did not detect any new metastases. However, in 6 of the 64 technically adequate examinations, hepatic arterial phase images increased lesion conspicuity and significantly increased diagnostic confidence when compared with portal vein phase scans alone. In patients with colorectal cancer, the addition of arterial phase imaging does not increase sensitivity, but improves the specificity in diagnosing liver metastases in a small number of cases. Dual phase helical CT does not appear to be indicated in the evaluation of liver metastases from colorectal cancer.
Adult↗
Detection of colonic polyps in a phantom model: implications for virtual colonoscopy data acquisition.
PURPOSE: Virtual colonoscopy is a new method of colon examination in which computer-aided 3D visualization of spiral CT simulates fiberoptic colonoscopy. We used a colon phantom containing various-sized spheres to determine the influence of CT acquisition parameters on lesion detectability and sizing. METHOD: Spherical plastic beads with diameters of 2.5, 4, 6, 8 and 10 mm were randomly attached to the inner wall of segments of plastic tubing. Groups of three sealed tubes were scanned at 3/1, 3/2, 5/1 collimation (mm)/pitch settings in orientations perpendicular and parallel to the scanner gantry. For each acquisition, image sets were reconstructed at intervals from 0.5 to 5.0 mm. Two blinded reviewers assessed transverse cross-sections of the phantoms for bead detection, using source CT images for images for acquisitions obtained with the tubes oriented perpendicular to the gantry and using orthogonal reformatted images for scans oriented parallel to the gantry. RESULTS: Detection of beads of > or = 4 mm was 100% for both tube orientations and for all collimator/pitch settings and reconstruction intervals. For the 2.5 mm beads, detection decreased to 78-94% for 5 mm collimation/pitch 2 scans when the phantom sections were oriented parallel to the gantry (p = 0.01). Apparent elongation of beads in the slice direction occurred as the collimation and pitch increased. The majority of the elongation (approximately 75%) was attributable to changing the collimator from 3 to 5 mm, with the remainder of the elongation due to doubling the pitch from 1 to 2. CONCLUSION: CT scanning at 5 mm collimation and up to pitch 2 is adequate for detection of high contrast lesions as small as 4 mm in this model. However, lesion size and geometry are less accurately depicted than at narrower collimation and lower pitch settings.
Colon↗
Visualization modes for CT colonography using cylindrical and planar map projections.
PURPOSE: The purpose of this study was to demonstrate the limitations to the effectiveness of CT colonography, colloquially called virtual colonoscopy (VC), for detecting polyps in the colon and to describe a new technique, map projection CT colonography using Mercator projection and stereographic projection, that overcomes these limitations. METHOD: In one experiment, data sets from nine patients undergoing CT colonography were analyzed to determine the percentage of the mucosal surface visible in various visualization modes as a function of field of view (FOV). In another experiment, 40 digitally synthesized polyps of various sizes (10, 7, 5, and 3.5 mm) were randomly inserted into four copies of one patient data set. Both Mercator and stereographic projections were used to visualize the surface of the colon of each data set. The sensitivity and positive predictive value (PPV) were calculated and compared with the results of an earlier study of visualization modes using the same CT colonography data. RESULTS: The percentage of mucosal surface visualized by VC increases with greater FOV but only approaches that of map projection VC (98.8%) at a distorting, very high FOV. For both readers and polyp sizes of > or =7 mm, sensitivity for Mercator projection (87.5%) and stereographic projection (82.5%) was significantly greater (p < 0.05) than for viewing axial slices (62.5%), and Mercator projection was significantly more sensitive than VC (67.5%). Mercator and stereographic projection had PPVs of 75.4 and 78.9%, respectively. CONCLUSION: The sensitivity of conventional CT colonography is limited by the percentage of the mucosal surface seen. Map projection CT colonography overcomes this problem and provides a more sensitive method with a high PPV for detecting polyps than other methods currently being investigated.
Adult↗