Biomedical subjects
Publications and source records attributed to A Hampshire.
Since its introduction, gamma knife radiosurgery has become an important treatment modality for cerebral arteriovenous malformations. This paper is a brief overview of the technique used, of the clinical results achieved and of the experience gained in Sheffield.
OBJECTIVE: To evaluate the clinical results achievable using current techniques of gamma knife stereotactic radiosurgery to treat sporadic unilateral acoustic neuromas. METHODS: A retrospective review of 234 consecutive patients treated for unilateral acoustic neuromas between 1996 and 1999, with a mean (SD) follow up of 35 (16) months. Tumour control was assessed with serial radiological imaging and by the need for surgical intervention. Hearing preservation was assessed using Gardner-Robertson grades. Details of complications including cranial neuropathies and non-specific vestibulo-cochlear symptoms are included. RESULTS: A tumour control rate in excess of 92% was achieved, with only 3% of patients undergoing surgery after radiosurgery. Results were less good for larger tumours, but control rates of 75% were achieved for 35-45 mm diameter lesions. Of patients with discernible hearing, Gardner-Robertson grades were unchanged in 75%. Facial nerve function was adversely affected in 4.5%, but fewer than 1% of patients had persistent weakness. Trigeminal symptoms improved in 3%, but developed in 5% of patients, being persistent in less than 1.5%. Transient non-specific vestibulo-cochlear symptoms were reported by 13% of patients. CONCLUSIONS: Tumour control rates, while difficult to define, are comparable after radiosurgery with those experienced after surgery. The complications and morbidity after radiosurgery are far less frequent than those encountered after surgery. This, combined with its minimally invasive nature, may make radiosurgery increasingly the treatment of choice for small and medium sized acoustic neuromas.
We have characterized phosphatase activity present on the external surface of Trichomonas vaginalis, using intact living parasites. This enzyme hydrolyzes the substrate p-nitrophenylphosphate (p-NPP) at a rate of 134.3+/-14.8 nmol Pi/h per 10(7) cells. This phosphatase activity decreased by increasing the pH from 6.8 to 8.4, a pH range in which cell viability was maintained for at least 1 h. Experiments using classical inhibitors of acid phosphatases, such as ammonium molybdate and sodium fluoride, as well as inhibitors of phosphotyrosine phosphatase, such as sodium orthovanadate, [monoperoxo(picolinato)oxovanadate(V)] (mpV-PIC) and [potassiumbisperoxo(1,10-phenanthroline)oxovanadate(V)] (bpV-PHEN), showed a decrease in this phosphatase activity, with different patterns of inhibition. Cytochemical analysis showed the localization of this enzyme on the parasite surface (cell body and flagellum) and in intracellular vacuoles. Phosphatase reaction products were also observed in exocytosed membrane-bound material.
OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.
BACKGROUND: Action research has been used successfully to promote change in disciplines other than medicine, but there are few examples of its use in primary care. OBJECTIVE: We aimed to discuss the benefits and difficulties of using action research in primary care using the example of child health surveillance provision in general practice. METHODS: Twenty-eight general practices were randomly allocated into two groups. Action research was used to promote change in 14 practices by facilitating practice meetings and by providing written feedback. The other 14 practices received written feedback alone. The two groups of practices were compared using the following: (i) semi-structured interviews with one health visitor and GP from each practice; (ii) observation of baby clinics; (iii) questionnaires to parents; and (iv) return rates of child health surveillance reviews from the personal child health record. RESULTS: All 14 practices in the action research arm of the study met as individual practice teams and decided to make changes to their provision of child health surveillance. Ten practices audited their child health surveillance as a result. More health visitors in the action research practices than in the comparison practices reported changes to child health surveillance, audit, communication and use of the personal child health record. The majority of health visitors and GPs thought involvement in the action research process was beneficial. However, we were unable to show a statistically significant difference between the two groups of practices in baby clinic provision, parent satisfaction or the return rate of child health surveillance reviews. CONCLUSION: Our study suggests that action research is a successful method of promoting change in primary care. However, measuring the impact of change is difficult.
OBJECTIVE: To compare the accuracy of stereotactic localization using magnetic resonance imaging (Siemens 1.5-T Magnetom; Siemens, Erlangen, Germany) with two-dimensional and three-dimensional data acquisition techniques. METHODS: A phantom study was performed in which the coordinates of an array of rods were determined from images in both two-dimensional and three-dimensional studies and compared with measured values in a series of transverse, coronal, and sagittal images. RESULTS: The results demonstrated a distinct advantage in using three-dimensional acquisition; an error greater than 2 mm was identified in only 0.8% of the imaged volume, compared with 12% of the imaged volume in the two-dimensional study. CONCLUSION: The results indicated that more accurate stereotactic localization is achieved with a three-dimensional acquisition.
This phantom study assesses the accuracy of stereotactic localization using the Leksell G frame (Elekta Instruments AB, Stockholm, Sweden) with T1-weighted magnetic resonance imaging (Siemens 1.5 T Magnetom; Erlangen, Germany). The coordinates of an array of solid perspex rods were determined and compared with measured values in a series of transverse, coronal, and sagittal images. The maximum absolute errors observed (X = 2.7 mm, Y = 7.0 mm, Z = 8.0 mm) were discouraging. However, the more reasonable mean errors (X = 0.4 mm, Y = 0.7 mm, Z = 1.3 mm) reflect considerable variation in accuracy throughout the volume assessed and limitation of maximum errors to specific areas. We present details of the spatial variation and discuss possible mechanisms for improving accuracy. The overall results are of direct relevance only to the scanner used. These results are, however, an indication of the need to approach with caution stereotactic localization using magnetic resonance imaging and to emphasize the requirement for quality assurance and for a comprehensive study of the scanner's characteristics.
The accuracy of stereotactic localisation using magnetic resonance (MR) imaging has been assessed in a phantom study. Parallel studies compared the accuracy obtained. First, a series of two-dimensional (2D) MR slices (transverse, coronal, and sagittal) was acquired sequentially to image the three-dimensional (3D) volume of the phantom. Then, the same volume was imaged in a 3D MR study in which the entire volume was excited simultaneously and 2D slices in transverse, coronal, and sagittal planes were then reconstructed from the 3D data set. The results showed that the 3D acquisition gave superior results in all three planes, and overall it was found that only 1% of the phantom volume was affected by an error greater than 2 mm, compared with 11% for the 2D study. New facilities for image quality assurance provided in GammaPlan version 3.0 have been tested against images from the 2D study with known distortion and consequent localisation errors and successfully identified all images in which the localisation errors were likely to be greater than 3.7 mm.
Electrical impedance tomographic spectroscopy (EITS) images have been recorded from a group of 12 normal subjects using frequencies from 9.6 kHz to 1.2 MHz. The impedance changes with frequency have been modelled on a pixel by pixel basis to produce parametric images as a means of characterizing tissue. The modelling was based on the Cole equation. The lungs are seen as areas of high characteristic frequency and low time constants SC and RS. The R/S images are much less uniform over the region of the lungs. Values characterizing the lung and cardiac regions are given. The results appear to be consistent with a model for the lungs whereby the model parameters can be related to alveolar structure and composition.
A phantom study has been carried out to assess the accuracy of stereotactic localisation, using magnetic resonance imaging. The stereotactic coordinates of an array of Perspex rods within the phantom were determined and compared with measured values, in a series of transverse, coronal and sagittal images. In the transverse plane, the maximum errors experienced were X = 2.3 mm and Y = 10.7 mm. If the third fiducial plate, at the front of the frame, were not used in the scaling of the images, there was considerable improvement in the Y direction (maximum error Y = 2.1 mm). However, some deterioration in the accuracy in the X direction resulted, particularly at the extremes of Z (maximum error X = 3.5 mm). In the coronal plane, the maximum errors were X = 1.8 mm and Z = 8.0 mm. With the third plate off, the errors decreased to X = 1.9 mm and Z = 3.3 mm. In the sagittal plane, the maximum errors recorded were Y = 1.1 mm and Z = 7.5 mm. It is not possible to calibrate in this plane without the third plate.
Reinstallation of the Sheffield Gamma Knife Unit was completed in early November, 1991, following the replacement of the cobalt sources. Two methods were used to evaluate the isodose configuration within the replenished unit. The first method used a scanning microdensitometer to interrogate films exposed within a spherical phantom, whilst the second relied upon a series of measurements obtained with an array of diodes. The results produced by the latter method compared more favorably with the computer-generated theoretical curves. The two sets of results are presented and some possible explanations for the discrepancies are proposed.