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Biomedical subjects

E R Ritenour

Publications and source records attributed to E R Ritenour.

29 records · Page 2Linked to original sources
PubMed1980

Response and recovery kinetics of a solid tumour after irradiation.

The effects of local tumour radiation over the dose range 7.5-30 Gy on the growth and cell kinetics of rat hepatoma H-4-II-E have been investigated. A plot of growth delays against log surviving fraction was linear below a fraction of 0.03, but failed to extrapolate to the origin. Following a single dose of 15 Gy to the tumour, DNA-precursor incorporation, labelling and mitotic indices were depressed for 7 days. Tumour cellularity, measured as DNA/g tumour, was reduced and the rate of increase of total clonogenic cells slower than after complete tumour recovery. From Day 7 to Day 9 all indices of proliferation recovered to about control levels, clonogenic cell numbers increased more rapidly and tumour cellularity was restored. Repopulation of the tumour therefore appeared to take place mainly after Day 7. Incorporation of [3H]-TdR into tumour DNA reached twice the control values on Day 9. The rate of tumour growth accelerated after the initial decrease, and maximum tumour growth rate was also twice the control values on Day 13. Accelerated growth rates in irradiated tumours, above those of control tumours, occurred 10-16 days after treatment. The effectiveness of sequential therapy may therefore be improved if given during this period of of accelerated tumour growth.

Animals↗
PubMed1980

Changes in growth rate of an experimental solid tumor following increasing doses of cyclophosphamide.

Well-defined times for minimum and maximum growth rates of rat hepatoma 3924A were found when cyclophosphamide doses were increased from 50 to 250 mg/kg. Minimum growth rates occurred 8 to 10 days after treatment and maximum growth rates occurred 13 to 16 days after treatment in 5 groups of 10 animals each that received 50, 100, 150, 200, and 250 mg of cyclophosphamide per kg. Tumor growth delay increased from 6 to 18 days when the dose was increased from 50 to 250 mg/kg. The accelerated growth rate of treated tumors on Day 14 after cyclophosphamide (150 mg/kg) was more than twice that of controls on the same day, 0.349 +/- 0.030 (S.E.) (day-1) and 0.156 +/- 0.011 (day-1), respectively. In addition, the accelerated growth rate of treated tumors on Day 14 was greater than that of controls at initiation of treatment, 0.298 +/- 0.026 (day-1) on Day 2. Increased DNA synthetic rate precedes increased tumor cell proliferation, which, in turn, increases tumor volume. Thus, biochemical studies demonstrating increased cellular proliferation confirm accelerated tumor growth following treatment.

Animals↗
PubMedDate not supplied

Axial and lateral resolution of rotational intravascular ultrasound: in vitro observations and diagnostic implications.

PURPOSE: To determine the axial and lateral resolution of a rotating intravascular ultrasound system and the diagnostic implications for the diagnosis of early artherosclerosis. METHODS: The resolution of a 20 MHz rotating transducer was tested in a specially designed high-resolution phantom and in five aortic autopsy specimens with varying degrees of early atherosclerosis. RESULTS: The best lateral resolution is at the minimal distance between transducer and object. Measurements in the wire phantom showed this to be better than 0.43 mm. This is less than the axial resolution which is better than 0.13 mm. Decreasing lateral resolution with increasing distance between transducer and object is manifested by arcing and overestimation of the extent of focal atherosclerotic lesions. CONCLUSION: Axial resolution is significantly better than lateral resolution. Rapid deterioration of lateral resolution affects the diagnostic ability to characterize the extent of early atherosclerosis. Eccentric positioning of the transducer tip, particularly in larger vessels, will therefore influence diagnostic accuracy in vivo.

Adolescent↗
PubMedDate not supplied

Ionization produced by electron beams beneath curved surfaces.

Ionization produced by high-energy (6-18 MeV) electrons beneath cylindrical surfaces has been measured and compared to ionization at corresponding locations under a flat surface. Results are reported as ionization ratios over a range of depths, off-axis distances, radii of curvature, and electron energies. Phantoms with cylindrical entrance surfaces (radii 6-15 cm) were utilized to simulate patient contours. Measurements reveal that ionization ratios may depart from unity by as much as 50% and that a simple shifting of isodose curves may be insufficient to compensate for perturbation in electron dose distribution introduced by curved surfaces.

Electrons↗
PubMedDate not supplied

Duplex Doppler estimation of resistive index in arcuate arteries of sedated, normal female dogs: implications for use in the diagnosis of renal failure.

The resistive index (RI), an ultrasonographic method of evaluating intrarenal resistance to blood flow, may be used to aid in diagnosis of renal failure. Values for arcuate artery RI, expressed as mean +/- two standard deviations, were obtained in clinically normal female dogs sedated with atropine, acepromazine maleate, diazepam, and ketamine hydrochloride. No statistically significant differences were noted between the values for the right kidney (0.33 to 0.57) versus the left kidney (0.32 to 0.56); however, the values were statistically significantly lower than values reported for nonsedated, normal dogs.

Acute Kidney Injury↗
PubMedDate not supplied

Magnetic resonance imaging: the basic physical and clinical concepts. Part I.

Noninvasive evaluation of the human body has become an essential tool in the diagnosis of disease processes. Recent developments in nuclear magnetic resonance imaging (MRI) have extended a powerful chemical analytic technique to the medical imaging field. This article presents the fundamental principles of MRI in terms of the concept of transmission and reception of energy. The physical principles of spin resonance are discussed in Part I. Spin relaxation and pulse sequences will be examined in Part II and III. A selected bibliography directs the reader to a more detailed discussion of the pertinent physics.

Humans↗
PubMedDate not supplied

Magnetic resonance imaging: the basic physical and clinical concepts. Part II.

Noninvasive evaluation of the human body has become an essential tool in the diagnosis of disease processes. Recent developments in nuclear magnetic resonance imaging (MRI) have extended a powerful chemical analytic technique to the medical imaging field. This article presents the fundamental principles of MRI in terms of the concept of transmission and reception of energy. The physical principles of spin resonance were discussed in Part I. Spin relaxation and pulse sequences will be examined in Part II and III. A selected bibliography directs the reader to a more detailed discussion of the pertinent physics.

Biophysical Phenomena↗
PubMedDate not supplied

Magnetic resonance imaging: the basic physical and clinical concepts. Part III.

Noninvasive evaluation of the human body has become an essential tool in the diagnosis of disease processes. Recent developments in nuclear magnetic resonance imaging (MRI) have extended a powerful chemical analytic technique to the medical imaging field. This article presents the fundamental principles of MRI in terms of the concept of transmission and reception of energy. A selected bibliography directs the reader to a more detailed discussion of the pertinent physics.

Humans↗