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Biomedical subjects

R C Mehta

Publications and source records attributed to R C Mehta.

17 recordsLinked to original sources
PubMed1995

Adsorption of salmon calcitonin to PLGA microspheres.

PURPOSE: The interaction of salmon calcitonin (sCT) and poly (d,l-lactide-co-glycolide) was detected during preparation and evaluation of microspheres. The purpose of this study was to quantitate the extent and nature of the interaction. METHODS: Blank microspheres were prepared by an aqueous emulsification solvent extraction technique. Adsorption studies were carried out at six concentrations of sCT and three concentrations of microspheres. Adsorption isotherms were constructed using the Langmuir and Freundlich treatments. RESULTS: Adsorption at 1 mg/ml sCT concentration resulted in almost complete depletion of the peptide from the adsorption medium with the time to reach maximum adsorption decreasing with increasing microsphere concentration. At sCT concentrations below 100 micrograms/ml, a true equilibrium occurred in 1 hour or less while at higher concentrations (up to 350 micrograms/ml), a transient equilibrium was reached in 1 to 2 hours, followed by further adsorption of the peptide. The adsorption followed the Langmuir isotherm at concentrations below 200 micrograms/ml, indicating formation of a monolayer. Multilayer interaction, described by the Freundlich isotherm, occurred at higher concentrations and resulted in complete depletion of sCT from the adsorption medium. The affinity constant during monolayer formation was 0.09 and the plateau surface concentration was 5.1 micrograms/mg. The multilayer peptide-peptide adsorption showed a lower affinity (0.025) but higher capacity (24 micrograms/mg) than the monolayer peptide-polymer adsorption. CONCLUSIONS: The results show that poly (d,l-lactide-co-glycolide) microspheres have a high adsorption capacity for sCT which must be considered in formulating a controlled delivery product of this peptide.

Adsorption↗
PubMed1995

Central nervous system tumor, infection, and infarction: detection with gadolinium-enhanced magnetization transfer MR imaging.

PURPOSE: To quantitatively measure the degree of contrast enhancement of central nervous system (CNS) tumor, infection, and infarction by means of magnetization transfer (MT) magnetic resonance (MR) imaging. MATERIALS AND METHODS: T1-weighted MR images obtained before and after administration of contrast material with and without MT in 14 patients with CNS tumors were evaluated by means of a contrast-to-noise ratio (C/N). Another 72 patients with a variety of lesions underwent contrast material-enhanced T1-weighted MR imaging prospectively with and without MT; C/N was also evaluated. RESULTS: All lesions had a higher C/N on T1-weighted postcontrast MT images than on conventional images. C/N was 65 +/- 5 (mean +/- standard error) for MT and 42 +/- 4 for conventional images. C/N improved by a factor of 1.6-2.1 in the three disease categories. In intracranial tumors, the MT technique itself did not contribute significantly (P < .001) to the increase in C/N in the absence of gadopentetate dimeglumine. In fact, the C/N was lower for nonenhanced T1-weighted MT images. CONCLUSION: Concurrent use of gadopentetate dimeglumine and MT results in a statistically significant (P < .001) increase in C/N in CNS tumor, infection, and infarction.

Adult↗
PubMed1995

MR evaluation of vertebral metastases: T1-weighted, short-inversion-time inversion recovery, fast spin-echo, and inversion-recovery fast spin-echo sequences.

PURPOSE: To compare the detectability of vertebral metastatic disease on T1-weighted, short-inversion-time inversion recovery (STIR), fast spin-echo (FSE), fat-saturated FSE, and inversion recovery FSE (IRFSE) MR sequences using percent contrast and contrast-to-noise ratios. METHODS: Patients with proved metastatic disease underwent imaging on a 1.5-T MR system with sagittal T1-weighted (800/20/2 [repetition time/echo time/excitations]) (91 patients), STIR (1400/43/2; inversion time, 140) (91 patients), FSE (4000/180/2) (46 patients), fat-saturated FSE (4000/180/2) (16 patients), and IRFSE (29 patients) sequences. Percent contrast and contrast-to-noise ratio were calculated for the lesions. The number of metastatic lesions detected with each of the pulse sequences was also calculated. RESULTS: Mean percent contrast was, for T1-weighted sequence, -42.2 +/- 1%; STIR, 262 +/- 34%; FSE, 121 +/- 21%; fat-saturated FSE, 182 +/- 6%; and IRFSE, 272 +/- 47%. The mean contrast-to-noise ratio for T1-weighted was -4.63 +/- 1.7; STIR, 10.8 +/- .98; FSE, 4.16 +/- .76; fat-saturated FSE, 4.87 +/- .19; and IRFSE, 5.2 +/- .87. STIR and IRFSE showed the highest number of lesions, followed by T1-weighted, fat-saturated FSE, and FSE sequences. T1-weighted sequences showed 94%, FSE 55%, and fat-saturated FSE 78% of the lesions detected. Epidural metastatic lesions were better depicted on T1-weighted, FSE, and fat-saturated FSE sequences. CONCLUSION: STIR was superior to both T1-weighted and FSE (with and without fat saturation) for detection of metastatic lesions, in terms of both percent contrast and contrast-to-noise ratio and visibility. IRFSE was equal to STIR for the detection of metastasis by both subjective and objective criteria. T1-weighted, FSE, and fat-saturated FSE sequences were superior to STIR and IRFSE in the detection of epidural metastatic disease. IRFSE provided faster scanning time, which could be translated into greater resolution.

Adolescent↗
PubMed1992

Fat emulsion particle-size distribution in total nutrient admixtures.

The fat particle-size distribution in and physical stability of two commercially available lipid emulsions before and after their use in total nutrient admixtures (TNAs) are reported. Four TNAs without electrolytes and four TNAs with electrolytes were prepared; each type of TNA was prepared with Liposyn II and with Intralipid. Particle size was measured in the < 1-micron range by using photon correlation spectroscopy and in the 2-60-microns range by using light blockage. Admixtures with or without electrolytes were stored for two or nine days at 4 degrees C followed by one day at 25 degrees C. For the fraction of fat particles of < 1 micron in diameter, Intralipid and Liposyn II had a mean particle size of 374 and 313 nm, respectively. The admixtures containing electrolytes showed a decrease in mean particle size of about 7%. Admixtures with Intralipid contained 2 x 10(7) particles larger than 2 microns per milliliter (1.7% of total fat), compared with 1 x 10(6) particles per milliliter (0.05-0.15% of total fat) for admixtures with Liposyn II. The addition of electrolytes increased the particle counts for Liposyn II-containing admixtures. Upon storage, Intralipid-containing admixtures with electrolytes showed an initial increase followed by a decrease in the mean diameter of particles of < 1 micron. All the admixtures were stable in terms of pH and visual appearance. Intralipid-containing admixtures with electrolytes showed a decrease in the number of particles in the 2-60-microns size range, while Liposyn II-containing admixtures with electrolytes showed an increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Incompatibility↗
PubMed1992

Physiologic imaging of the brain.

Advances in imaging hardware for positron emission tomography and single-photon emission CT, coupled with a wide variety of radiopharmaceutical agents, have allowed these techniques to be used in the evaluation of neoplasm, stroke, epilepsy, and dementia. Cerebral perfusion agents continue to be the mainstay of single-photon emission CT imaging but, in addition to the evaluation of ischemia, it has seen an increasing role in the study of dementia, neuropsychiatric disorders, and seizures. Positron emission tomography scanning has had similar applications but it is playing a greater part in the evaluation of neoplasms, including primary gliomas and pituitary adenomas. Stable-xenon CT has shown value in the study of ischemia associated with meningitis, sickle cell disease, chronic subdural hematomas, and cerebral arteriovenous malformations. MR diffusion imaging shows promise in the evaluation of white matter pathology and some tumors.

Brain↗
PubMed1991

Skeletal effects of calcitonin in ovariectomized rats.

Although calcitonin (CT) has been shown to be effective for the prevention of bone loss in early postmenopausal women, the skeletal effects of the hormone specifically during the early stages of estrogen deficiency have not been characterized histomorphometrically to date. The current study involves use of the ovariectomized (OVX) rat as an animal model for early postmenopausal bone loss to perform such a histomorphometric analysis. One group of OVX rats was injected sc with salmon CT on alternate days for a 6-week period. Additional groups of OVX and sham-operated control rats were treated with vehicle alone. In comparison to control rats, the proximal tibia of vehicle-treated OVX rats were characterized by a 3-fold decrease in cancellous bone volume and significant increases in osteoblast surface (+200%), osteoclast surface (+143%), mineralizing surface (+111%), mineral apposition rate (+36%), bone formation rate (+181%), and longitudinal bone growth (+38%). In contrast, treatment of OVX rats with CT normalized tibial cancellous bone volume and significantly decreased all of the above cellular- and fluorochrome-based indices of bone turnover to near control levels. The results indicate that CT treatment depresses bone turnover and prevents the development of osteopenia in OVX rats. These findings are consistent with the bone protective effect of CT in early postmenopausal women and further support the OVX rat as an animal model for the preclinical evaluation of prophylactic treatments for postmenopausal bone loss.

Animals↗
PubMed1989

Frostbite injury: prediction of tissue viability with triple-phase bone scanning.

Triple-phase bone scans were obtained in seven patients within 48 hours of admission for frostbite injuries. Three patterns of perfusion imaging and delayed bone imaging were observed: hyperemic blood flow with normal early blood pool and normal delayed bone images; absent blood flow and absent early blood pool depiction, but depiction of bone in delayed images; and absent perfusion and absent blood pool depiction, with no bone uptake in the delayed images. The first pattern indicated mild ischemia that required no surgical treatment, the second indicated ischemia with occasional superficial tissue infarction that required minor debridement, and the third pattern indicated deep-tissue and bone infarction that required amputation. The triple-phase bone scan is a useful indicator of tissue viability as early as 2 days after cold injury and appears to have a clinical role in the evaluation of frostbite injuries. The perfusion and blood pool images demonstrate the ischemic tissue at risk, while the delayed bone scan images demonstrate the extent of deep-tissue and bone infarction.

Adolescent↗
PubMed1988

Chromatographic studies of mitomycin C degradation in albumin microspheres.

Serum albumins and polylactic acid (PLA) have been used as bioerodable polymers in the preparation of drug-containing microspheres for parenteral drug delivery. The albumin microsphere may be prepared via either chemical cross-linking or heat denaturation of the protein. Heat-denatured albumin microspheres containing mitomycin C (MMC) have been used in pre-clinical and clinical investigations. Due to the high reactivity of MMC as a bifunctional alkylating agent, a study on the stability of MMC in the albumin and PLA microspheres has been carried out using a high-performance liquid chromatographic (HPLC) method. Human serum albumin (HSA) microspheres were prepared using an emulsion method via either heat denaturation at 120 or 170 degrees C or the use of 0.5 M biacetyl as a cross-linking agent. The PLA microspheres were prepared by an emulsion method at 55 degrees C. HPLC analysis of the HSA microspheres showed that about 37% of MMC was converted to 2,7-diaminomitosene derivatives in microspheres prepared by heat denaturation at 120 degrees C. The degradation increased to 82% when the microspheres were prepared with a denaturation temperature of 170 degrees C. The use of biacetyl as a cross-linking agent in the preparation of HSA microspheres resulted in a complete degradation of the incorporated MMC. Biacetyl was found to interact with MMC leading to the formation of 7-aminomitosene derivatives. In contrast to the albumin system, MMC may be incorporated into PLA microspheres without degradation.

Albumins↗
PubMed1988

Osteosarcoma arising in Paget's disease of the calvarium.

Paget's disease of the bone occasionally transforms into sarcomatous tumors such as osteosarcoma. While Paget's disease demonstrates markedly increased uptake of bone scanning radiopharmaceutical, osteosarcomas complicating this condition often show decreased uptake. An unusual scan appearance of the osteosarcoma is presented in which the tumor showed intense uptake of the tracer on the bone scan. The extent of the sarcoma as delineated by the bone scan corresponded closely to the size of the lesion as seen on computerized tomography and magnetic resonance imaging and was confirmed at surgery.

Aged↗
PubMedDate not supplied

MR imaging of primary trochlear nerve neoplasms.

We present the clinical, anatomic, and MR imaging findings in six patients with seven primary trochlear nerve neoplasms, as well as the MR and clinical criteria that serve to establish the diagnosis of these rare cranial nerve neoplasms. Three patients had a history of neurofibromatosis and five patients had clinical evidence of a trochlear nerve palsy. Six of seven neoplasms produced localized, fusiform enlargement of the proximal cisternal segments of the trochlear nerves. The lesions that were visible on noncontrast MR scans (T1-, T2-, and proton density-weighted) had signal intensities that were virtually identical to normal brain parenchyma. All lesions showed intense, homogeneous enhancement on contrast-enhanced scans. Contrast-enhanced imaging was necessary for the detection of five of seven lesions and greatly increased the value of the MR study in all six patients.

Adult↗