Biomedical subjects

R D Peters

Publications and source records attributed to R D Peters.

17 recordsLinked to original sources

PubMed1999

Quantifying tissue damage due to focused ultrasound heating observed by MRI.

Focused ultrasound heating of ex vivo bovine kidney and liver was monitored using magnetic resonance imaging (MRI) to investigate the quantitative relationship between time-dependent temperature elevations and altered contrast in MR images due to thermal coagulation. Proton resonance frequency shift MR thermometry was performed during heating at 10 sec intervals (single-slice fast spoiled GRASS [FSPGR], theta/TE/TR 30 degrees/11/39 msec, field of view 8 cm, 256 x 256, 3 mm slice thickness, 1 NEX); post-heating MR images were T1-weighted (3D-FSPGR, theta/TE/TR 60 degrees/25/200 msec, 1 mm slice thickness, 3 NEX). Analysis of the resulting temperature versus time data using the Arrhenius relationship and a simple binary discrimination model showed that thermal coagulation occurred with heating at approximately 54 degrees C for 10 sec in both tissues and could be predicted with approximately 625 microm spatial resolution. These results suggest that quantitative MR guidance of thermal coagulation therapy is feasible, and they provide information useful for designing future investigations in vivo.

Animals↗

PubMed1999

Heat-source orientation and geometry dependence in proton-resonance frequency shift magnetic resonance thermometry.

The proton-resonance frequency (PRF) shift method of thermometry has become a promising tool for magnetic resonance image-guided thermal therapies. Although the PRF thermal coefficient has recently been shown to be independent of tissue type when measured ex vivo, significant discrepancy remains on its value for tissues measured in vivo under a variety of experimental conditions. The authors identify a potential source of variation in the PRF thermal coefficient that arises from temperature-induced changes in the volume magnetic susceptibility of tissue and is dependent on the orientation and geometry of the heat-delivery device and its associated heat pattern. This study demonstrates that spatial variations in the apparent PRF thermal coefficient could lead to errors of up to +/-30% in the magnetic resonance estimated temperature change if this effect is ignored.

Algorithms↗

PubMed1998

Ex vivo tissue-type independence in proton-resonance frequency shift MR thermometry.

The temperature sensitivity of the proton-resonance frequency (PRF) has proven valuable for the monitoring of MR image-guided thermal coagulation therapy. However, there is significant inconsistency in reported values of the PRF-thermal coefficient, as measured from experiments encompassing a range of in vivo and ex vivo tissue types and experimental conditions. A method of calibrating the temperature dependence of the PRF is described and results are presented that indicate a tissue-type independence. To this end, other possible mechanisms for variations in the PRF-thermal coefficient are suggested, including physiological perturbations and volume magnetic susceptibility effects from geometry and orientation.

Animals↗

PubMed1997

Magnetic resonance imaging of temperature changes during interstitial microwave heating: a phantom study.

Changes in magnetic resonance (MR) signals during interstitial microwave heating are reported, and correlated with simultaneously acquired temperature readings from three fiber-optic probes implanted in a polyacrylamide gel phantom. The heating by a MR-compatible microwave antenna did not interfere with simultaneous MR image data acquisition. MR phase-difference images were obtained using a fast two-dimensional-gradient echo sequence. From these images the temperature-sensitive resonant frequency of the 1H nuclei was found to decrease approximately by 0.008 ppm/ degree C. The method and results presented here demonstrate that noninvasive MR-temperature imaging can be performed simultaneously with interstitial microwave thermal treatment.

Biophysical Phenomena↗

PubMed1994

Better Beginnings, Better Futures: a community-based approach to primary prevention.

Better Beginnings, Better Futures is a 25-year primary prevention policy research demonstration project. Its major purpose is to assess the extent to which community-based primary prevention programs can be effective in preventing emotional, behavioural, physical and cognitive problems in children from economically disadvantaged communities. The project grew out of a number of primary prevention initiatives introduced by the Ontario Ministry of Community and Social Services (MCSS) since the late 1970s. Eleven sites, four of them located on native reserves, received funding in January, 1991 to establish programs in their communities. From the beginning, a qualitative, naturalistic research approach has been utilized to document and understand the ways in which the programs have developed in the various Better Beginnings communities.

Affective Symptoms↗

PubMed1992

Association of intrauterine fetal growth retardation and learning deficits at age 9 to 11 years.

OBJECTIVE: We examined the association of fetal and newborn complications, socioeconomic status, and home environment with learning deficits as assessed between 9 and 11 years of age. STUDY DESIGN: A total of 218 high-risk newborns have been assessed at 1, 4, and 9 to 11 years of age. Fetal and newborn complications included 77 newborns with growth retardation. Socioeconomic variables included parental occupation and education. Outcome measures at 9 to 11 years included the Woodcock Reading Mastery Test and the Wide Range Achievement Test. Motor and cognitive development was assessed by a neurologic examination, the Bruininks-Oseretsky Test of Motor Proficiency, and the Wechsler Intelligence Scale for Children. Behavior was assessed with the Achenbach Child Behavior Check List and Connor's Teacher Rating Scale. RESULTS: Learning deficits were identified in 77 of the 218 children (35%). Children with learning deficits had lower full-scale IQ scores and behavioral problems of inattention and anxiety. Both fetal growth retardation and the father's occupation score were independently associated with these learning deficits. CONCLUSION: Fetal growth retardation, socioeconomic status, and behavioral characteristics of inattention and anxiety are associated with less favourable academic achievement at 9 to 11 years of age.

Child↗

PubMed1991

Physically abusive and nonabusive mothers' perceptions of parenting and child behavior.

Physically abusive and nonabusive mothers were studied for differences in perceptions of the parenting role and of child behavior problems. Findings suggested systematic differences in attributional style of the abusive mothers, supporting the hypothesis that such mothers are hyperreactive to their children's misbehavior. These mothers also tended to minimize both their own contribution to negative parent-child interactions and their children's role in positive ones.

Adult↗

PubMed1981

Effects of self-instructional training on cognitive impulsivity of mentally retarded adolescents.

The cognitive style dimension of reflection-impulsivity was assessed for 27 retarded adolescents using the Matching Familiar Figures Test. The most impulsive adolescents subsequently received training in self-instruction while observing a reflective model or observed the model without specific training in self-instruction. Posttraining measures indicated that the self-instruction procedure produced significantly more reflective responding than did the model-alone procedure. The results also suggested the presence of a developmental lag in cognitive style among the retarded children compared to recent norms for nonretarded children. The finding that the retarded youth were responsive to self-instructional training appears to be inconsistent with Luria's (1961) contention that retarded individuals are incapable of using the language-based second signaling system to influence and control their own behavior.

Adolescent↗

PubMed1975

Factors in the modification by isolation of electroconvulsive shock-produced retrograde amnesia in the rat.

It has been demonstrated that placing rats in a sensory-restricted environment during the electronconvulsive shock- (ECS) retention interval following 1-trial appetitive learning will prevent or eliminate ECS-produced retrograde amnesia. The first study replicated this finding with a 1-trial aversive learning task, indicating that this effect is not task specific. The second study attempted to determine whether illumination or the restricted environment was the crucial factor in this penomenon. Rats placed in the light during the ECS-retention interval, whether restricted or in the colony, demonstrated retrograde amnesia after ECS. However, rats left in the dark during this interval demonstrated little, if any, retention deficit particularly if this condition was combined with sensory isolation. These studies further indicate that manipulation of the general environment of the animal after ECS can alter ECS-produced retention losses.

Amnesia↗

PubMed1974