Biomedical subjects

R D Black

Publications and source records attributed to R D Black.

13 recordsLinked to original sources

PubMed1998

Measuring the progression of foreign-body reaction to silicone implants using in vivo MR microscopy.

We used in vivo magnetic resonance (MR) microscopy to follow the growth of fibrous capsule as a foreign body reaction to silicone implants in rats. Anesthetized rats were imaged 1, 7, 14, and 28 days after silicone-coated MR imaging coils were sutured to their neck muscles. On the twenty-eighth day, rats were sacrificed and coils and adjacent tissues were removed en bloc and fixed in formalin, reimaged with MR, and sectioned for conventional histology. Three-dimensional (3-D) spin-echo [3DFT] acquisition gave in-plane resolution of 32 x 32 microns in vivo and 16 x 16 microns ex vivo. All MR images showed a diffuse band of elevated signal intensity between the silicone of the coil and adjacent tissue. The border of the hyperintense band was thin and not well defined at seven days post-implantation. From 7-28 days, the band showed relatively homogeneous signal intensity and its thickness increased 44% on the rectus muscle side and 78% on the subcutaneous side. The capsule thickness determined either by MR in vivo and ex vivo microscopy or conventional histology was not significantly different, and there was a significant correlation between thickness measurements among those methods. MR in vivo microscopy provides sufficient resolution and spatial information to serially evaluate the growth of the foreign body fibrous capsule over time, thus achieving greater accuracy and consistency in measurements.

Animals↗

PubMed1996

Signal-to-noise ratio comparison between surface coils and implanted coils.

The signal-to-noise ration (SNR) from implanted coils is widely known to be superior to that from surface coils. This article addresses the quantitative aspects of this improvement by explicitly evaluating the magnetic vector potential in a conducting medium of finite extent for both implanted and surface coils. The predictions of the model are tested with actual image data from spin warp experiments on gelatin phantoms. The authors derived a simplified expression that yields the gain in SNR of an implanted coil relative to that of a surface coil and is valid in many practical situations.

Animals↗

PubMed1996

In vivo He-3 MR images of guinea pig lungs.

The authors imaged the lungs of live guinea pigs with hyperpolarized (HP) helium-3 as a magnetic resonance (MR) signal source. HP He-3 gas produced through spin exchange with rubidium metal vapor was delivered through an MR-compatible, small-animal ventilator. Two- and three-dimensional lung images acquired with ventilation-gated, radial k-space sampling showed complete ventilation of both lungs. All images were of high quality, demonstrating that HP He-3 allows high-signal-intensity MR imaging in living systems.

Animals↗

PubMed1996

Human lung air spaces: potential for MR imaging with hyperpolarized He-3.

Two healthy volunteers who had inhaled approximately 0.75 L of laser-polarized helium-3 gas underwent magnetic resonance imaging at 1.5 T with fast gradient-echo pulse sequences and small flip angles ( < 10 degrees). Thick-section (20 mm) coronal images, time-course data (30 images collected every 1.8 seconds), and thin-section (6 mm) images were acquired. Subjects were able to breathe the gas (12% polarization) without difficulty. Thick-section images were of good quality and had a signal-to-noise ratio (S/N) of 32:1 near the surface coil and 16:1 farther away. The time images showed regional differences, which indicated potential value for quantitation. High-resolution images showed greater detail and a S/N of approximately 6:1.

Adult↗

PubMed1995

MR imaging with hyperpolarized 3He gas.

Magnetic resonance images of the lungs of a guinea pig have been produced using hyperpolarized helium as the source of the MR signal. The resulting images are not yet sufficiently optimized to reveal fine structural detail within the lung, but the spectacular signal from this normally signal-deficient organ system offers great promise for eventual in vivo imaging experiments. Fast 2D and 3D GRASS sequences with very small flip angles were employed to conserve the norenewable longitudinal magnetization. We discuss various unique features associated with performing MRI with hyperpolarized gases, such as the selection of the noble gas species, polarization technique, and constraints on the MR pulse sequence.

Animals↗

PubMed1994

Electronics for a high temperature superconducting receiver system for magnetic resonance microimaging.

We describe an MRI (magnetic resonance imaging) receiver system that incorporates a high temperature superconducting (HTS) resonator as a surface coil. Techniques for measuring the Q of the HTS resonator in a 7 Tesla field are discussed. A method for coupling a room temperature copper resonant circuit to the HTS element is covered, and it is shown that such a coupling scheme preserves the signal-to-noise (SNR) gain afforded by the HTS coil. A preamplifier with a noise figure (NF) of < 0.15 dB at 300 MHz is described.

Electric Impedance↗

PubMed1993

A high-temperature superconducting receiver for nuclear magnetic resonance microscopy.

A high-temperature superconducting-receiver system for use in nuclear magnetic resonance (NMR) microscopy is described. The scaling behavior of sources of sample and receiver-coil noise is analyzed, and it is demonstrated that Johnson, or thermal, noise in the receiver coil is the factor that limits resolution. The behavior of superconductors in the environment of an NMR experiment is examined, and a prototypical system for imaging biological specimens is discussed. Preliminary spin-echo images are shown, and the ultimate limits of the signal-to-noise ratio of the probe are investigated.

Animals↗

PubMed1993

Histology by magnetic resonance microscopy.

Magnetic resonance microscopy (MRM) has advanced from a technical challenge to a practical tool in a wide range of basic sciences. This article focuses on the use of MRM as a tool for histological studies. The technical challenges of limited signal to noise have been overcome by improved radio-frequency (rf) coil design and 3DFT encoding with large arrays. Resolution limits imposed by motion in in vivo studies have been overcome by improved physiologic monitoring and control and projection encoding. Integration of technologies now permits routine studies in vivo down to 50 microns. MRM has also been applied to in vitro studies of fixed tissues where absence of motion allows studies down to 10 microns. The nondestructive nature of the technique allows repeated studies of the same sample, retrospective studies through any arbitrary plane, registered studies using different contrast mechanisms, and examination of valuable specimens. The many and unique proton contrasts provided by MRM, i.e., T1, T2, and diffusion weighting, permit direct examination of the state of water in tissues, something not possible with other microscopic techniques. Finally, the inherent three-dimensional nature of MRM allows acquisition of perfectly registered isotropic 3D arrays that, when displayed with appropriate visualization tools, provide new perspectives to histologic examination. The technology of MRM continues to develop rapidly. New pulse sequences are reducing acquisition times. New computer architectures allow larger arrays. A new class of superconducting rf probe has increased the signal to noise ratio by 10 times. These developments promise routine use of MRM in histology studies with resolution to 1 micron in the near future.

Animals↗

PubMed1992

Immunotoxicity in the bovine animal: a review.

The immune system is a complex biological system involving cellular defenses as well as endogenous and exogenous factors. The potential for immune system exposure to immunotoxins in the environment is well documented. However, caution should be exercised when extrapolating meaningful conclusions from experimental data to assess risk factors to the bovine. Mycotoxins alter immune-mediated activities in cattle and are major immunotoxic risks. Another risk to the bovine is lead. Poor disposal of pollutants in the environment enhances this risk factor. One of the most controllable risk factors is the administration of immunotoxic drugs and biologics. Most of these compounds have minimal immunotoxic activity at recommended dosages. The extra-label use of drugs resulting in super-therapeutic concentrations has increased the probability that certain drugs may act immunotoxicologically.

Adrenal Cortex Hormones↗

PubMed1988

Glutathione concentrations in rat lung bronchoalveolar lavage fluid: effects of hyperoxia.

Glutathione concentrations were measured in rat bronchoalveolar lavage fluid (BALF) obtained from normal rats and rats exposed to a fraction of inspired oxygen (FiO2) of 0.8 for up to 5 days. We also perturbed rat lung glutathione concentrations by administering the compound diisopropylidene acetone (phorone) to a separate group of animals and correlated changes in BALF glutathione with changes in lung tissue glutathione. We found that reduced glutathione is present in normal rat BALF but glutathione disulfide is extremely low. Increases in lung tissue glutathione concentration and in BALF glutathione concentration occurred after 5 days of exposure to hyperoxia. Animals treated with phorone exhibited decreases in lung glutathione concentration two hours after dosing and increases in lung glutathione concentration 24 hours after dosing. Rat BALF obtained from phorone-treated animals at 2 or 24 hours after administration revealed that changes in BALF glutathione concentrations reflected changes in lung tissue glutathione concentration. The presence of glutathione in lung lavage fluid suggests that the compound could be playing an extracellular role in the lung, either as an antioxidant or as a coenzyme for other glutathione-related enzymatic reactions.

Animals↗

PubMed1987

Chronic Acinetobacter calcoaceticus var anitratus pneumonia.

Gram-negative bacteria most often affect the lung in an acute, suppurative process; however, these organisms may also produce chronic pneumonia. Acinetobacter calcoaceticus has not been reported previously as a cause of chronic pneumonia. We present a patient with fatal, chronic community-acquired Acinetobacter pneumonia with chest wall invasion at autopsy.

Acinetobacter Infections↗

PubMed1982

Severe cytomegalovirus infection in multiply transfused, splenectomized, trauma patients.

During a 2-year period 5 previously healthy young men who had undergone splenectomy and received multiple transfusions for trauma had severe cytomegalovirus (CMV) infection. Their illness was characterised by a long period of high fever, severe interstitial pneumonitis with dyspnoea and hypoxaemia, and an unusually high lymphocytosis (12 000-26 000 cells/microliter) with numerous atypical forms. The presumptive diagnosis was based on the patients' seroconversion and viral excretion, on the clinical and haematological findings which were typical of severe CMV infection, and on the absence of other infective organisms. In 1 case widespread CMV pneumonitis was confirmed at necropsy. These observations raise the possibility that splenectomy increases the severity and modifies the pattern of CMV infection, since during the same period no other case of severe CMV infection was observed among a large number of patients who had received multiple transfusions but had not undergone splenectomy.

Abdominal Injuries↗

PubMedDate not supplied

Lyme disease complicated by the Jarisch-Herxheimer reaction.

A 31-year-old woman diagnosed with Lyme disease was treated with amoxicillin. One hour after the first antibiotic dose, the patient became acutely ill. She developed hypertension, fever, and rigors. Shortly afterward, she became hypotensive and required fluid resuscitation. This systemic illness, the Jarisch-Herxheimer reaction, was first noted in association with antibiotic therapy for neurosyphilis. Thus, the institution of antibiotic therapy may be complicated by the Jarisch-Herxheimer reaction.

Adult↗