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Biomedical subjects

G C Hart

Publications and source records attributed to G C Hart.

At least 19 recordsLinked to original sources
PubMed2001

Scattered radiation during fixation of hip fractures. Is distance alone enough protection?

We measured the scattered radiation received by theatre staff, using high-sensitivity electronic personal dosimeters, during fixation of extracapsular fractures of the neck of the femur by dynamic hip screw. The dose received was correlated with that received by the patient, and the distance from the source of radiation. A scintillation detector and a water-filled model were used to define a map of the dose rate of scattered radiation in a standard operating theatre during surgery. Beyond two metres from the source of radiation, the scattered dose received was consistently low, while within the operating distance that received by staff was significant for both lateral and posteroanterior (PA) projections. The routine use of lead aprons outside the 2 m zone may be unnecessary. Within that zone it is recommended that lead aprons be worn and that thyroid shields are available for the surgeon and nursing assistants.

Anesthesiology↗
PubMed1999

A 'one-stop' vascular clinic: initial experience of an out-patient immediate-access radioisotope limb blood flow service.

The availability of an 'immediate-access' nuclear medicine service has facilitated the introduction of a 'one-stop' vascular clinic, enabling radioisotope limb blood flow and Doppler ankle:brachial index tests to be performed within 2 h of each other for new patient referrals. The test results are available to assist clinical management decisions during the same clinical session. A patient satisfaction survey was undertaken in 71 patients to assess their perspective of this service provision. Fifty-one (72%) patients returned the questionnaire. All respondents preferred to have attended the 'one-stop' clinic to having to return for investigations on a separate occasion. The patient satisfaction survey has identified patient perceived advantages of improved diagnostic efficiency, reduced number of visits, reduced patient worry and the minimization of patient travel costs. During the study period, 83% of allocated gamma-camera imaging slots were utilized, demonstrating that immediate-access nuclear medicine service provision linked to specific clinics can be a practicable solution to reducing waiting times for investigative tests. This is believed to be the first reported immediate-access nuclear medicine service, as opposed to the emergency investigations normally offered to clinically urgent requests.

Ambulatory Care Facilities↗
PubMed1997

Ramp test objects for slice sensitivity profile measurement in spiral CT.

Spiral CT is increasingly becoming a routine imaging technique in the UK. The ability to scan whole organs within a single breath-hold often demands that the scan pitch (ratio of the patient translation distance per tube rotation (d) to the collimated slice thickness) be increased within technically acceptable limits. It is known that the full width at half maximum height (FWHM) of the slice sensitivity profile (SSP), degrades with increasing scan pitch and also varies with interpolation algorithm. Published literature frequently reports values for FWHM of the SSP for spiral acquisitions which have been measured with a ramp test tool. However, it has previously been shown that a ramp is inappropriate for SSP measurements in spiral CT. This is because of the physical basis of the premise for this measurement and the large artefacts generated by the application of the interpolation algorithm to the ramp spiral projection data. We present experimental evidence confirming the unsuitability of the ramp test tool in spiral CT. A cyclical variation (d/2) of the data is demonstrated; the magnitude of the measured SSP being dependent upon scan pitch and the interpolation algorithm used, as well as on the longitudinal position of the reconstruction plane.

Humans↗
PubMed1996

Survey of the variation in ultraviolet outputs from ultraviolet A sunbeds in Bradford.

Concerns have been expressed for some time regarding the growth of the cosmetic suntanning industry and the potential harmful effects resulting from these exposures. Recently published work has appeared to confirm a link between sunbed use and skin cancer. A previous survey in Oxford some years ago demonstrated significant output variations, and we have attempted to extend and update that work. Ultraviolet A, UVB and blue-light output measurements were made on 50 sunbeds using a radiometer fitted with broad-band filters and detectors. A number of irradiance measurements were made on each sunbed within each waveband so that the uniformity of the output could also be assessed. UVA outputs varied by a factor of 3, with a mean of 13.5 mW/cm2; UVB outputs varied by a factor of 60, with a mean of 19.2 microW/cm2; and blue-light outputs varied by a factor of 2.5, with a mean of 2.5 mW/cm2. Outputs fall on average to 80% of the central value at either end of the sunbed. Facial units in sunbeds ranged in output between 18 and 45 mW/cm2. Output uniformity shows wide variation, with 16% of the sunbeds having an axial coefficient of variation > 10%. UVB output is highly tube-specific. Eyewear used in sunbeds should also protect against blue light.

Beauty Culture↗
PubMed1996

Programmable dynamic line phantom control: an initial assessment of quantitative potential as a gamma camera test tool.

The dynamic line phantom (DLP) produces various test patterns for the qualitative assessment of gamma camera performance, by stepper motor control of the translatory movement of a radioactive rigid line source. The addition of a V24 serial interface port has allowed external control via an RS-232 connection to a personal computer. Programmability has enabled the DLP to be used as a quantitative test tool. One such program produces a variable contrast 'hot' and 'cold' bar pattern. The addition of a Quick Basic computer program modifies the line source movement to compensate for variation in line source activity. This maintains a test pattern with fixed, absolute contrast levels, giving the potential for the measurement of variations in long-term imaging performance. A modulation transfer function (MTF) pattern has been designed which encompasses a sinusoidally varying intensifying function with a changing spatial frequency component. Repeated measurements on two gamma cameras demonstrated poor reproducibility (CV of up to 50% dependent upon spatial frequency) and significant differences between the MTF obtained from line spread function measurements (percentage deviation of up to 23%, dependent upon spatial frequency). Neither test pattern has been adopted for routine quantitative assessment of gamma camera imaging characteristics. The reproducibility of results is poor (dominated by counting statistic limitations), making the techniques insensitive to small changes in camera performance.

Gamma Cameras↗
PubMed1994

Measuring leg ulcers using a laser displacement sensor.

A non-contact method for the measurement of a skin ulcer's area and volume has been developed. A commercially available laser displacement sensor is scanned across the ulcer's surface to produce a displacement image. From this image the healthy normal skin's surface is reconstructed and the area and volume found. Results of measurements made with phantom ulcers show that the method has a precision and accuracy +/- 5% of the total size. This compares favourably with results from other non-contact methods that have been published. The method of measurement is simple and reliable. At present, the time taken to produce a displacement image is lengthy but this is due to a limitation in the instrumentation, rather that a failing of the technique. The result of a preliminary measurement made on a patient's leg ulcer is presented.

Humans↗
PubMed1994

Airborne radioactive contamination following aerosol ventilation studies.

Lung aerosol ventilation studies may be accompanied by airborne contamination, with subsequent surface contamination. Airborne contamination has been measured prior to, during and following 59 consecutive 99Tcm-diethylenetriamine pentaacetate (DTPA) aerosol studies using a personal air sampler. Airborne contamination ranging between 0 and 20 330 kBq m-3 has been measured. Airborne contamination increases with degree of patient breathing difficulty. The effective dose equivalent (EDE) to staff from ingested activity has been calculated to be 0.3 microSv per study. This figure is supported by data from gamma camera images of a contaminated staff member. However, surface contamination measurements reveal that 60% of studies exceed maximum permissible contamination limits for the hands; 16% of studies exceed limits for controlled area surfaces. The EDE from ingestion is low, but protective clothing is essential to prevent body and clothing contamination. Ingested activity and surface contamination results from this study have been compared with results from a Technegas study.

Aerosols↗
PubMed1991

Regulation of the Xenopus laevis transcription factor IIIA gene during oogenesis and early embryogenesis: negative elements repress the O-TFIIIA promoter in embryonic cells.

Expression of the Xenopus laevis transcription factor IIIA (TFIIIA) gene is developmentally regulated. In this study we have used defined nucleotide mutations to map cis-elements involved in transcriptional regulation of the promoter for oocyte-TFIIIA (O-TFIIIA) in stage II-IV oocytes, stage VI oocytes, and tail bud embryos. During oogenesis O-TFIIIA mRNA levels decline 5- to 10-fold, and during early embryogenesis O-TFIIIA mRNA levels decline approximately 10(6)-fold per cell. In stage II-IV oocytes we find evidence for at least three distinct positive-acting cis-elements that contribute to the efficient expression of O-TFIIIA. These elements are located between -1800 to -425, -280 to -235, and -235 to -220. The most distal cis-element(s) appears to be developmentally regulated during oogenesis, since deletion of nucleotide sequences from -1800 to -425 does not reduce O-TFIIIA expression in stage VI oocytes. However, the two cis-elements located between -280 to -235 and -235 to -220 are required for the efficient expression of O-TFIIIA in stage VI oocytes. In tail bud embryos we find evidence for several developmentally regulated positive and negative cis-elements involved in O-TFIIIA expression. The positive-acting cis-elements are located between -159 to -110 and -110 to -58. The negative-acting cis-elements are found at positions -425 to -350 and -200 to -159. In addition to the developmentally regulated elements controlling O-TFIIIA gene expression in tail bud embryos, the positive-acting cis-elements active during oogenesis (located between -280 to -235 and -235 to -220) are also active during early embryogenesis. Thus, transcription from the O-TFIIIA promoter appears to be regulated by a combination of constitutive positive factors and developmentally regulated positive and negative factors during oogenesis and early embryogenesis.

Animals↗
PubMed1990

Activities of 3'-azido-3'-deoxythymidine nucleotide dimers in primary lymphocytes infected with human immunodeficiency virus type 1.

The relative antiviral potencies of five nucleotide heterodimers of 3'-azido-3'-deoxythymidine (AZT), 3'-azido-3'-deoxythymidilyl-(5',5')-2'-3'-dideoxy-5'-adenylic acid (AZT-P-ddA), 3'-azido-3'-deoxythymidilyl-(5',5')-2',3'-dideoxy-5'-inosinic acid (AZT-P-ddI), and the corresponding 2-cyanoethyl congeners AZT-P(CyE)-ddA and AZT-P(CyE)-ddI, were determined in primary human peripheral blood mononuclear cells infected with human immunodeficiency virus type 1. The homodimer 3'-azido-3'-deoxythymidilyl-(5',5')-3'-azido-3'-deoxythymidilic acid (AZT-P-AZT) was also included for comparison. The potencies of the compounds were AZT-P-ddA greater than or equal to AZT-P-ddI greater than AZT-P(CyE)-ddA greater than or equal to AZT-P(CyE)-ddI greater than or equal to AZT greater than AZT-P-AZT. Whereas AZT-P-ddA and AZT-P-ddI had in vitro therapeutic indices greater than that of AZT, the homodimer of AZT had a low therapeutic index. AZT-P-ddI exhibited the lowest toxicity in peripheral blood mononuclear, Vero, or CEM cells. Combination studies between AZT and 2',3'-dideoxyinosine (ddI) at nontoxic concentrations indicated a synergistic interaction at a drug ratio of 1:100. At higher ratios (1:500 and 1:1,000), the interactions were synergistic only at concentrations that produced up to 75% virus inhibition. At higher levels of antiviral effects, this combination was antagonistic, as determined by the multiple drug effect analysis method. AZT-P-ddI was about 10-fold less toxic than AZT to human granulocyte-macrophage progenitor cells. However, no significant difference was apparent when the compounds were evaluated against cells of the erythroid lineage. The greater antiviral activity and lower toxicity of this compound could not be attributed to the extracellular decomposition of the dimer in media at physiological temperature and pH. However, in acidic solutions, AZT-P-ddI decomposed in a pH-dependent manner. Advanced preclinical studies with this heterodimer of two clinically effective antiretroviral agents should be considered.

Cell Survival↗
PubMed1989

Dynamic radionuclide imaging with 99mTc-sucralfate in the detection of oesophageal ulceration.

Standard oesophageal scintigraphic techniques using 99mTc-colloids rarely identify oesophageal mucosal damage. Sucralfate can be labelled with 99mTc for the detection of oesophageal mucosal ulceration. This method uses two separate supine swallows of 10 MBq 99mTc-colloid in 10 ml, followed by a single supine swallow of 30 MBq 99mTc-sucralfate. The data are processed to give time-activity curves, mean transit times and condensed dynamic images. When oesophageal ulceration is detected, the time-activity curves using sucralfate show residual activity in the oesophagus after the transit time indicated by the colloid swallow. The condensed dynamic image shows a persistence of activity at the level of the ulceration. Erect sucralfate images taken immediately after the dynamic sequence show no oesophageal localisation. The results from a study of 62 patients have shown excellent correlation between the dynamic 99mTc-sucralfate images and endoscopy findings. Sequential sucralfate studies for healing also correlate well. The use of labelled sucralfate to detect oesophageal ulceration could modify the indications for endoscopy in gastrooesophageal reflux disease.

Adolescent↗
PubMed1988

Improved sensitivity in bone scintigraphy using quantitative spinal profile analysis.

Full-length skeletal scintiscans were acquired onto a data processor in a series of 256 X 256 matrices. A series of interactive computer programs enables the operator to select profiles down the spine and to standardize them by interpolation to a standard length and by normalization to a given count level. The counts within any section of a profile can then be calculated and the profile examined for any significant deviation from a reference 'normal' curve. In a study of 68 patients, 66% of the spinal profiles were judged abnormal, compared with 26% of scans assessed by visual inspection alone. Of 14 patients with positive profiles and negative or equivocal visually assessed scans, 11 had developed metastases within 14 months of the scan. All five patients with positive profile and raised alkaline phosphatase have died of metastatic disease. The technique appears to increase the sensitivity of bone scintigraphy.

Bone Neoplasms↗