Prepolarized fast spin-echo pulse sequence for low-field MRI.

Clinical MRI systems use magnetic fields of at least 0.5T to take advantage of the increase in signal-to-noise ratio (SNR) with B(0). Low-field MRI apparatus is less expensive and offers the potential benefit of improved T(1) contrast between tissues. The poor inherent SNR at low field can be offset by incorporating prepolarizing field pulses with the MRI pulse sequence. The prepolarizing field does not need to be as homogeneous as the detection field, so it can be generated by a relatively inexpensive electromagnet. Prepolarizing hardware for a 0.01T MRI system was developed together with a prepolarized MRI pulse sequence that incorporates fast imaging techniques to reduce acquisition times by a factor of 5 relative to standard methods. Comparison images of test objects show that most of the enhanced SNR is retained with the fast method. Low-field images of a human wrist acquired using the fast prepolarized method are also shown.

T*1e and T*2e maps derived in vivo from the rat using longitudinally detected electron spin resonance phase imaging: application to abdominal oxygen mapping.

A novel imaging modality is introduced which uses radiofrequency longitudinally detected electron spin resonance (RF-LODESR). It is capable of providing qualitative and semiquantitative information on a variety of parameters reflecting physiological function, the most significant being tissue oxygenation. Effective spin-lattice (T*1e) and spin-spin (T*2e) electronic relaxation time maps of the abdomen of living 200-g rats were generated after intravenous administration of a triarylmethyl free radical (TAM). These maps were used to evaluate oxygen distribution. Differences between the liver, kidneys, and bladder were noted. Conclusions were made regarding the distribution, perfusion, and excretion rate of the contrast medium. Ligature-induced anoxia in the kidney was also visualized. LODESR involves transverse ESR irradiation with a modulated excitation, and observing oscillations in the spin magnetization parallel to the main magnetic field. The T*1e and T*2e maps were calculated from a set of LODESR signal phase images collected at different detection frequencies. Each phase image also provides qualitative information on tissue oxygen levels without any further processing. This method presents an alternative to the conventional transverse ESR linewidth-based oximetry methods, particularly for animal whole-body imaging applications.

Electron spin relaxation time measurements using radiofrequency longitudinally detected ESR and application in oximetry.

Longitudinally detected ESR (LODESR) involves transverse ESR irradiation with a modulated source and observing oscillations in the spin magnetization parallel to the main magnetic field. In this study, radiofrequency-LODESR was used for oximetry by measuring the relaxation times of the electron. T1e and T2e were measured by investigating LODESR signal magnitude as a function of detection frequency. We have also predicted theoretically and verified experimentally the LODESR signal phase dependence on detection frequency and relaxation times. These methods are valid even for inhomogeneous lines provided that T1e>>T2e. We have also developed a new method for measuring T1e, valid for inhomogeneous spectra, for all values of T1e and T2e, based on measuring the spectral area as a function of detection frequency. We have measured T1e and T2e for lithium phthalocyanine crystals, for the nitroxide TEMPOL, and for the single line agent Triarylmethyl (TAM). Furthermore, we have collected spectra from aqueous solutions of TEMPOL and TAM at different oxygen concentrations and confirmed that T1e values are reduced with increased oxygen concentration. We have also measured the spin-lattice electronic relaxation time for degassed aqueous solutions of the same agents at different agent concentrations. T1e decreases as a function of concentration for TAM while it remains independent of free radical concentration for TEMPOL, a major advantage for oxygen mapping. This method, combined with the ability of LODESR to provide images of exogenous free radicals in vivo, presents an attractive alternative to the conventional transverse ESR linewidth based oximetry methods.

Continuous-wave magnetic resonance imaging of short T(2) materials.

There is growing interest in the use of magnetic resonance imaging (MRI) to examine solid materials where the restricted motion of the probed spins leads to broad lines and short T(2) values, rendering many interesting systems invisible to conventional 2DFT pulsed imaging methods. In EPR T(2) seldom exceeds 0.1 mus and continuous-wave methods are adopted for spectroscopy and imaging. In this paper we demonstrate the use of continuous-wave MRI to obtain 2-dimensional images of short T(2) samples. The prototype system can image samples up to 50 mm in diameter by 60 mm long and has been used to image polymers and water penetration in porous media. Typical acquisition times range between 10 and 40 min. Resolution of 1 to 2 mm has been achieved for samples with T(2) values ranging from 38 to 750 mus. There is the possibility of producing image contrast that is determined by the material properties of the sample.

Effects of a controlled-release cisplatin delivery system used after resection of mammary carcinoma in mice.

OBJECTIVE: To evaluate efficacy of a controlled-release cisplatin delivery system, used after marginal resection of mammary carcinoma (ie, resection of grossly evident tumor) in mice, to prevent tumor regrowth and metastasis. ANIMALS: 42 female C3H-HeJ mice. PROCEDURE: Mice were inoculated with mammary carcinoma cells. Between 2 and 6 days later, tumors were marginally resected and mice were assigned to 1 of 3 groups: no treatment (control; n = 14), cisplatin administered intraperitoneally (i.p. cisplatin; 14), and cisplatin delivered by use of an open-cell polylactic acid system placed within the tumor bed (slow-release cisplatin; 14). Tumor regrowth was measured daily. Mice were euthanatized 14 days after surgery, and complete necropsies were performed. RESULTS: Tumor regrowth was not detected in the slow-release cisplatin group; however, tumor regrowth was detected in 7 of 14 mice in the i.p. cisplatin group and 14 of 14 mice in the control group. Median (+/-SD) number of days to tumor regrowth was 13.5+/-0.64 and 7.79+/-0.87 in the i.p. cisplatin and control groups, respectively. Mice in the i.p. cisplatin group had significantly delayed tumor regrowth, compared with control mice. Metastases to lungs were detected in 8 of 14 control mice but were not detected in mice in either cisplatin treatment group. CONCLUSIONS AND CLINICAL RELEVANCE: The open-cell polylactic acid with cisplatin delivery system was successful in delaying local tumor regrowth and metastasis in mice with marginally resected mammary carcinoma. Use of a controlled-release cisplatin delivery system may be an effective adjunct treatment following excision of mammary carcinoma in humans and other animals.

Gradiometer pick-up coil design for a low field SQUID-MRI system.

We describe the use of liquid helium-cooled (4.2 K) gradiometer coils and a DC superconducting quantum interference device (SQUID) preamplifier to improve the SNR of magnetic resonance imaging (MRI) at 0.01 T. Gradiometer windings are used both to reduce lossy interactions with the MRI system's room temperature magnet and gradient coils and also to reject interference from more distant sources, which reduces the need for RF shielding. We have tested both axial and planar (figure-of-eight) gradiometer configurations. The figure-of-eight gradiometer has a more rapid fall-off in sensitivity with increasing distance from its windings than the axial gradiometer, but this is compensated for by reduced lossy interactions and improved interference rejection. We have used the system to image the human arm.

Assessment of dorsal nerve root and spinal cord dorsal horn function in clinically normal dogs by determination of cord dorsum potentials.

OBJECTIVE: To establish normal predictive values for cord dorsum potential (CDP) onset latency after thoracic and pelvic limb sensory or mixed nerve stimulation in adult dogs. ANIMALS: 26 clinically normal adult dogs. PROCEDURE: Sensory nerve action potentials (SNAP) were recorded proximally from tibial and lateral superficial radial nerves after distal stimulation. The CDP were recorded from the L4-L5 interarcuate ligament for the tibial nerve and from the C7-T1 interarcuate ligament for the radial nerve. Linear regression analyses were performed for CDP onset latency, and mean +/- SD was calculated for CDP onset to peak latency differences and sensory nerve conduction velocities (SNCV). RESULTS: For the tibial nerve, expected CDP onset latency (CDPOL) = -1.194 + 0.014 X pelvic limb length (mm; R2 = 0.912); CDPOL = -2.156 + 0.011 X pelvic limb/spinal length (mm; R2 = 0.911); and CDPOL = 0.941 + 2.197 X tibial nerve SNAP latency (milliseconds; R2 = 0.903). For the radial nerve, CDPOL = -0.9 + 0.014 x thoracic limb length (mm; R2 = 0.873); and CDPOL = 1.454 + 1.874 X radial nerve SNAP latency (milliseconds; R2 = 0.903). Mean +/- SD for CDP onset to peak latency difference for tibial and radial nerves was 3.1+/-0.3 and 3.0+/-0.4 milliseconds, respectively. CONCLUSIONS: Strong linear associations exist between CDPOL and a number of easily measured peripheral independent variables in dogs. There is also a narrow range of normal values for CDP onset to peak latency differences that is independent of limb length. CLINICAL RELEVANCE: CDP evaluation can be used to accurately assess functional severity and distribution of abnormalities in proximal sensory nerves, dorsal nerve roots, and spinal cord dorsal horns in dogs with suspected neuropathy, radiculopathy, or myelopathy involving the brachial or lumbosacral intumescences.

Chemically induced analgesic nephropathy in the rat monitored by proton-electron double-resonance imaging (PEDRI).

Proton-electron double-resonance imaging (PEDRI) was used to assess renal function by monitoring the flow of the exogenous nitroxide free radical proxyl carboxylic acid (PCA) through normal and injured kidneys in the living rat. Kidney damage was induced by treatment with 2-bromoethylamine (BEA), which provides a well established model for human analgesic nephropathy. PCA clearance rates for liver, abdominal blood vessels, and renal tissues were determined from serial PEDRI images of normal rats (n = 6) and rats treated with BEA (n = 21). Different groups of BEA-treated animals were imaged on day 4 (n = 6), day 6 (n = 6), and day 9 (n = 9) after treatment. In BEA-treated rats, there was an increase in PCA half-life in all tissues studied. This increase was greatest in the kidney tissues and the effect progressed with time after treatment. The effect is probably due to BEA-induced damage to the tubules in the renal cortex and may not be related to the primary lesions in the renal medulla.

Design, construction and use of a large-sample field-cycled PEDRI imager.

The design, construction and use of a large-scale field-cycled proton-electron double-resonance imaging (FC-PEDRI) imager is described. The imager is based on a whole-body sized, vertical field, 59 mT permanent magnet. Field cycling is accomplished by the field compensation method, and uses a secondary, resistive magnet with an internal diameter of 52 cm. The magnetic field can be switched from zero to 59 mT or vice versa in 40 ms. It is used with a double-resonance coil assembly (NMR/EPR) comprising a solenoidal NMR transmit/receive coil and a coaxial, external birdcage resonator for EPR irradiation. Experiments to image the distribution of an exogenous nitroxide free radical in anaesthetized rabbits are described.

Characterization of plasma immunoglobulin G concentrations of llamas.

OBJECTIVE: To develop appropriate reference ranges for plasma IgG concentrations of llamas. ANIMALS: 643 llamas on 5 farms. PROCEDURE: Plasma IgG concentration was measured by using a single radial immunodiffusion assay kit. Farm of origin, age, body condition score, and sex were recorded for each llama. The effect of each factor on plasma IgG concentration was evaluated separately, using ANOVA; the association between age and IgG concentration was evaluated, using linear regression. Multivariable regression models were developed to examine concurrent effects of age, sex, body condition score, farm, and various interactions on IgG concentration. RESULTS: The IgG concentrations were between 127 and 3,969 mg/dl. In llamas < 12 months old, farm of origin accounted for 29% of variability for IgG concentration. Reference range for plasma IgG concentrations in llamas < 12 months old was 391 to 2,357 mg/dl; for llamas > 12 but < 28 months old was 771 to 2,796 mg/dl; and for llamas > 28 months old was 570 to 3,264 mg/dl. These ranges were applicable only for the kit used in this study. CONCLUSIONS: Healthy llamas have a wide range of IgG concentrations. Determinants of IgG concentration are multifactorial, and their importance varies with age of the llamas. CLINICAL IMPLICATIONS: The wide range of IgG concentrations observed in healthy llamas and the influence that age and farm may have on IgG concentrations indicate that a result for one specific llama should be interpreted in relation to those of its herdmates.

Evaluation of prognostic factors for dogs with primary lung tumors: 67 cases (1985-1992).

OBJECTIVE: To determine associations between clinical and histologic factors in dogs with primary lung tumors and outcome and to develop a histologic grading method for primary lung tumors. DESIGN: Retrospective study. ANIMALS: 67 dogs undergoing thoracotomy and lobectomy for primary lung tumors. PROCEDURE: Medical records and histologic sections were reviewed to evaluate factors of prognostic importance. Association of these factors with disease-free interval (DFI) and survival time was evaluated, using the Cox proportional hazards model. Median DFI and survival time were determined, using the Kaplan-Meier product-limit method. RESULTS: Clinical and histologic factors significantly associated with prognosis were histologic score, detection of clinical signs, and metastasis to regional lymph nodes. On the basis of histologic score, a histologic grading method was developed. Dogs with well-differentiated tumors had significantly longer survival time and DFI (median DFI, 493 days) than dogs with moderately (median DFI, 191 days) or poorly (median DFI, 0 days) differentiated tumors. Dogs with clinical signs or metastasis to regional lymph nodes had shorter survival times and DFI than dogs in which lung masses were discovered as an incidental finding. CLINICAL IMPLICATIONS: Dogs with well-differentiated, nonmetastasized, primary lung tumors that do not have clinical signs associated with the tumor have a favorable prognosis. Dogs with more advanced disease or aggressive tumors histologically may require treatment, such as chemotherapy in combination with surgery. The grading method proposed here for primary lung tumors may be useful in other dogs with primary lung tumors.

Survey of diplomates of the American College of Veterinary Surgeons regarding postoperative intra-abdominal adhesion formation in horses undergoing abdominal surgery.

OBJECTIVE: To obtain information from specialists in equine surgery as to prevalence of, predisposing factors for, and methods to prevent postoperative adhesion formation in horses undergoing abdominal surgery. DESIGN: Survey. PROCEDURE: Surveys were mailed to 196 diplomates of the American College of Veterinary Surgeons involved in equine practice. RESULTS: 60 (31%) surveys were returned. Most respondents (55/60) routinely informed clients of the risk of postoperative adhesion formation in horses with small intestinal lesions. When asked after which procedures they routinely used measures to prevent adhesions, 56 of 60 (93%) indicated that they did after small intestinal resection and anastomosis and 56 of 60 (93%) indicated that they did after any abdominal surgery in foals. The 4 methods most frequently listed when respondents were asked which methods were effective at preventing adhesion formation were meticulous surgical technique, administration of antibiotics and nonsteroidal anti-inflammatory drugs, intraoperative peritoneal lavage, and methods that prevent abdominal contamination. Most respondents (50/60) thought that at least some horses with colic secondary to adhesion formation could be managed medically. Fifty-four (90%) respondents indicated that they were successful less than half of the time when treating horses with adhesions severe enough to require additional surgery. CONCLUSION: In general, respondents thought that less than 15% of horses undergoing abdominal surgery would develop adhesions, but that horses with small intestinal disease and foals were most prone to develop adhesions. Meticulous surgical technique was thought to be the most important factor in preventing adhesions, and many prevention regimens reported to be effective in the literature were not commonly used in practice.

The excretion mechanism of the spin label proxyl carboxylic acid (PCA) from the rat monitored by X-band ESR and PEDRI.

Proton electron double resonance imaging (PEDRI) was used for monitoring in vivo the distribution, metabolism and, in particular, the excretion mechanism of the exogenous nitroxide free radical proxyl carboxylic acid (PCA) in the rat. PCA clearance half-lives through liver, abdominal vessels, and renal tissues were determined from a series of PEDRI images for normal rats (n = 5) and rats treated with probenecid (n = 5), a competitive inhibitor of the tubular secretion process. The approximately doubled renal half-lives of the treated animals suggest that tubular secretion accounts for about 50% of PCA renal loss in the normal rat and reabsorption is insignificant. PCA binding to bovine serum albumin was investigated by X-band ESR and the bound fraction was found to be less than 10% of the total PCA. Most probably, PCA binds to hydrophilic sites. Blood PCA concentration investigated by X-band ESR exhibited biphasic behavior and PEDRI results confirmed the in vivo metabolic reduction of PCA by rat liver cells.

Adenomatous polyps and carcinoma in situ of the canine colon and rectum: 34 cases (1982-1994).

The medical records of 34 dogs (median age, eight years) with colorectal mucosal lesions were reviewed. Hematochezia was the most common (82%) presenting sign. Most dogs (79%) presented with solitary masses located in the rectum. After histological review, 12 masses were classified as adenomatous polyps and 22 as carcinoma in situ. Recurrence of clinical signs were common (41%), and malignant transformation of the tumor was documented in 18% of the cases. A higher recurrence rate and malignant transformation occurred in dogs presented with multiple masses or diffuse disease and in dogs initially diagnosed with carcinoma in situ.

A mechanical evaluation of the resistance of various interfragmentary wire configurations to torsion.

Fourteen interfragmentary orthopedic wire configurations were tested in torsion using a transverse fracture polyvinylchloride pipe model. These models included single and double Kirschner pins with and without orthopedic wire added to the configuration. The orthopedic wire was applied in either an encircling, figure-of-eight (skewer pin), or cruciate pattern. Double Kirschner pins were applied in a mono- or biplanar fashion. An external fixator model was also tested. Stiffness, yield load, safe load, and energy of absorption were measured and calculated for each model. Orthopedic wire added to any configuration increased stiffness. All single pin configurations with orthopedic wire and the external fixator had the highest stiffness. Two Kirschner pins had a higher torsional yield load and safe load than single pin configurations with or without orthopedic wire. The external fixator model had the highest torsional yield load, safe load and energy of absorption of all configurations tested. However, the external fixator was only significantly different in safe load from the 900 biplanar configurations with wire and the cross pin configuration with encircling wire. The 900 biplanar configurations with wire and the cross pin configuration with encircling wire were equally as effective as the external fixator model in yield load and energy of absorption.

Continuous-wave NMR imaging of solids.

Current pulsed nuclear magnetic resonance methods of imaging samples such as solids with short spin-spin relaxation times are restricted to use with T2 values longer than approximately 10 microseconds. In the present study a method of imaging ultra-short T2 samples using continuous- wave, swept-field NMR is presented that, in principle, will be able to overcome this restriction. The technique is identical to that used in continuous-wave electron paramagnetic resonance imaging of paramagnetic species and involves irradiating the sample continuously with a radiofrequency excitation in the presence of a strong stationary magnetic field gradient. When the main magnetic field is swept over a suitable range, the variation of the NMR absorption signal with applied magnetic field yields a one-dimensional projection of the object under study along the gradient direction. Two- or three-dimensional image data sets may be reconstructed from projections that are obtained by applying the gradient in different directions. Signal-to-noise ratio can be improved by modulating the magnetic field and employing a lock-in amplifier to recover signal variations at the audio modulation frequency. Preliminary experiments were performed using a 7 Tesla magnet and a 300 MHz continuous-wave radiofrequency bridge with lock-in detection. The apparatus is described and the results of pilot experiments that employed vulcanized rubber samples are presented. The ability of the technique to detect short T2 samples was demonstrated by the presence of a background signal from the Perspex former of the birdcage resonator used for signal reception.

Prospective characterization of the clinicopathologic and immunologic features of an immunodeficiency syndrome affecting juvenile llamas.

The clinicopathologic and immunologic features of 15 llamas affected with juvenile llama immunodeficiency syndrome (JLIDS) are described. Healthy adult (n = 10) and juvenile (n = 10) llamas served as controls. JLIDS llamas were characterized by wasting, and clinically apparent, repeated infections were frequently observed. The median age at which a health problem was first perceived was 11.6 months. All 15 affected llamas died or were killed, and JLIDS was confirmed at necropsy. The median duration of illness was 3.5 months. Lymphocyte blastogenesis assays showed suppressed responses (particularly to Staphylococcus sp. Protein A) in JLIDS llamas. No evidence of retroviral infection was detected. Mild, normocytic, normochromic, non-regenerative anemia, low serum albumin concentration and low to low-normal globulin concentrations were typically found on initial clinical evaluation. Lymph node biopsies showed areas of paracortical depletion. All llamas affected with JLIDS had low serum IgG concentrations, pre-vaccination titers against Clostridium perfringens C and D toxoids of < or = 1:100, and no titer increase following vaccination.

Measurement of field distributions in ultrasonic cleaning baths: implications for cleaning efficiency.

The information available on ultrasound field distributions in cleaning baths is limited. Two techniques capable of providing this information have been investigated. The first employs a thermistor probe coated with ultrasound absorbing material and uses the rate of temperature rise when the ultrasound is switched on as a measure of local energy density. A motorized scanning frame has been used to map field distributions in three dimensions using the technique. The second technique, the Sarvazyan (dye/paper) method, uses Astralux paper placed in a bath containing an aqueous solution of methylene blue dye. More dye is transferred to the paper in areas where the ultrasound field is most intense. Pockets of gas are trapped in pores in the paper which provide additional nuclei for initiation of cavitation events and these produce small areas of intense staining about 1 mm in diameter, which are related to cavitational activity. The techniques reveal non-uniformities both in the field distribution and in the pattern of cavitational activity in ultrasound cleaning baths. Methods for assessing ultrasound field distributions are required in order to ensure that energy densities are sufficient to initiate cleaning action throughout ultrasonic cleaning baths.