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Biomedical subjects

E Chiu

Publications and source records attributed to E Chiu.

At least 55 records · Page 3Linked to original sources
PubMed1996

Magnetic resonance imaging of trabecular bone structure in the distal radius: relationship with X-ray tomographic microscopy and biomechanics.

The contribution of trabecular bone structure to bone strength is of considerable interest in the study of osteoporosis and other disorders characterized by changes in the skeletal system. Magnetic resonance (MR) imaging of trabecular bone has emerged as a promising technique for assessing trabecular bone structure. In this in vitro study we compare the measures of trabecular structure obtained using MR imaging and higher-resolution X-ray tomographic microscopy (XTM) imaging of cubes from human distal radii. The XTM image resolution is similar to that obtained from histomorphometric sections (18 microns isotropic), while the MR images are obtained at a resolution comparable to that achievable in vivo (156 x 156 x 300 microns). Standard histomorphometric measures, such as trabecular bone area fraction (synonymous with BV/TV), trabecular width, trabecular spacing and trabecular number, texture-related measures and three-dimensional connectivity (first Betti number/volume) of the trabecular network have been derived from these images. The variation in these parameters as a function of resolution, and the relationship between the structural parameters, bone mineral density and the elastic modulus are also examined. In MR images, because the resolution is comparable to the trabecular dimensions, partial volume effects occur, which complicate the segmentation of the image into bone and marrow phases. Using a standardized thresholding criterion for all images we find that there is an overestimation of trabecular bone area fraction (approximately 3 times), trabecular width (approximately 3 times), fractal dimension (approximately 1.4 times) and first Betti number/ volume (approximately 10 times), and an underestimation of trabecular spacing (approximately 1.6 times) in the MR images compared with the 18-microns XTM images. However, even for a factor of 9 difference in spatial resolution, the differences in the morphological trabecular structure measures ranged from a factor of 1.4 to 3.0. We have found that trabecular width, area fraction, number, fractal dimension and Betti number/volume measured from the XTM and MR images increases, while trabecular spacing decreases, as the bone mineral density and elastic modulus increase. A preliminary bivariate analysis showed that in addition to bone mineral density alone, the Betti number, trabecular number and spacing contributed to the prediction of the elastic modulus. This preliminary study indicates that measures of trabecular bone structure using MR imaging may play a role in the study of osteoporosis.

Absorptiometry, Photon↗
PubMed1996

The effect of Huntington's disease and Gilles de la Tourette's syndrome on the ability to hold and shift attention.

Huntington's disease (HD) and Tourette's syndrome (TS) are two basal ganglia (BG) disorders, associated not simply with hyperkinetic movements but also with attentional impairments. The purpose of this experiment was to evaluate the attention deficits reported in HD and TS via the use of a vibrotactile choice reaction time (CRT) procedure involving biased probabilities of event occurrence. We attempted to ascertain whether HD and TS patients are impaired in their ability to shift their attention to an unexpected location, or when they have to hold attention to an expected location. The results demonstrate that HD patients, as compared to controls, experience difficulties in shifting their attention from expected to unexpected spatial locations; this effect was exacerbated with the adoption of a crossed arm configuration. On the other hand, TS patients' performance, although slower overall, was not qualitatively greatly different from that of the controls. We had previously found, with a similar paradigm, that Parkinson's disease patients instead manifest problems in holding or maintaining attention to an expected locus. We conclude that HD patients experience considerable difficulties in allocating attentional resources between expected and unexpected event occurrences. Perhaps due to pervasive subcortical damage and dysfunction in the circuits linking the frontal lobes with the BG. In TS, a similar if milder functional rather than structural deficit may be reflected in a pattern of responses which resembles a weaker version of the HD response pattern.

Adult↗
PubMed1996

Bradykinesia and movement precision in Huntington's disease.

To determine whether bradykinesia in patients with Huntington's disease (HD) reflects impaired force production or an increased requirement for terminal visual guidance, 11 HD patients and matched controls performed drawing movements with varying precision requirements. Participants used an electronic pen upon a WACOM SD420 graphics tablet to join targets of either 10 or 20 mm diameter which were separated by a distance of 62.5 or 125 mm. While HD patients had slower movements, exhibiting more cycles of acceleration and deceleration, patients were not disproportionately affected by variations in target size or separation. Bradykinesia did not seem to be a product of impaired force production or increased reliance upon terminal visual guidance, since neither accelerative or decelerative phases were specifically affected by HD. However, movements of HD patients were of less consistent duration, implying variability associated with internal cues regulating movement.

Adult↗
PubMed1996

Subcortical dysfunction in schizophrenia: a comparison with Parkinson's disease and Huntington's disease.

Neuropsychological performance in 20 chronic schizophrenic patients was contrasted to 25 Parkinson's disease, 12 Huntington's disease patients and 26 normal controls on measures shown to be sensitive to subcortical dysfunction. Some overlap was observed in the performance of the schizophrenic and basal ganglia groups on tasks of executive and mnestic function, but the general pattern indicated significant differences in performance. Notably, in contrast to the two basal ganglia groups, there was no evidence of slowed thinking, or impaired motor function in schizophrenia, which are considered hallmarks of subcortical grey matter disease. An association was observed between poor performance on the tests of executive function and the severity of negative symptoms. Our findings suggest that schizophrenia is not associated with primary subcortical impairment, but is more likely to reflect frontotemporal dysfunction. We consider that the similarities between this disorder and subcortical degenerative syndromes may be due to a difficulty in generating action in schizophrenia, perhaps arising from dorsolateral prefrontal disconnection.

Adult↗
PubMed1995

Reliance on advance information and movement sequencing in Huntington's disease.

To identify the focus of impairment in the performance of sequential movements in Huntington's disease (HD) patients, the extent of their reliance on external advance information was examined. Twelve patients with HD and their age-matched controls performed a series of button-presses at sequential choice points along a response board. A sequential pathway was designated, and with each successive button press, advance visual information was systematically reduced to various extents in advance of each move. HD patients, like previously studied parkinsonian patients, were particularly disadvantaged with high levels of reduction in advance information, and as a consequence, both their initiation and execution of movements progressively slowed with each successive element in the response sequence. The pattern of results was not affected whether or not patients were taking neuroleptic medication, nor did performance on a variety of cognitive measures correlate with motor performance. Control subjects' performance, on the other hand, remained constant in terms of both initiation and execution with each of the three levels of reduction in advance information. We conclude that HD patients, like parkinsonian patients, who also suffer from a basal ganglia (BG) disorder, require external visual cues to sequence motor programs effectively. Our findings suggest that with HD there may be abnormalities in a central mechanism that controls switching between movement segments within an overall motor plan. The BG, which provide internal cues necessary for component sequencing, may be disrupted, thereby impairing the ability to use such internally generated cues to guide movement.

Adult↗
PubMed1995

Impaired movement sequencing in patients with Huntington's disease: a kinematic analysis.

This experiment asked whether Huntington's disease, like Parkinson's disease, another disorder of the basal ganglia, causes a specific progressive deficit in the performance of sequential movement. Ten patients with Huntington's disease and their age-matched controls wrote the lower-case letter "l" four times in a linked cursive script, upon a graphics tablet which sampled pen position at 200 Hz. Kinematic features of sequential movement (stroke length, stroke duration, peak velocity, time to peak velocity and time from peak to zero velocity) were examined in a Group by Stroke Position (2 x 8) design, to identify which aspects of movement might show progressive disturbances. Unlike Agostino et al. [Brain 115, 1481-1495, 1992], this experiment did in fact find progressive changes in the performance of sequential movements. Kinematic analysis indicated a progressive increase in movement duration during sequential movement, that was associated with the accelerative phase of movement.

Adult↗
PubMed1995

Evaluation of technical factors affecting the quantification of trabecular bone structure using magnetic resonance imaging.

High resolution magnetic resonance (MR) techniques combined with standard techniques of stereology and texture analysis have been used to quantify trabecular structure. Using dried excised specimens from the tibia (n = 10) and radius (n = 2) we evaluate the impact of using volumetric gradient-echo (GE) and spin-echo (SE) MR imaging sequences, the relative importance of echo time in gradient-echo MR imaging, and the impact of different threshold values to segment the bone and bone marrow on the estimation of trabecular bone structure. We also investigate the inter-relationships between the different structural parameters derived from MR images. Images were obtained using fast gradient-echo and spin-echo imaging sequences, with TE values ranging from 7 to 17 ms using 4.7 and 1.5 Tesla imaging systems. In-plane image resolution ranged from 128 to 156 microns, and slice thickness ranged from 128 to 1000 microns. We derived stereological measures such as the mean intercept length, trabecular width, fractional area of trabecular bone, trabecular number, and trabecular spacing, the fractal dimension as a texture-related parameter and the Euler number as a measure of connectivity from these images. We found that the mean intercept length as a function of angle traced an ellipse with the orientation of the principal axis of the ellipse, a measure of trabecular orientation, identical when measured from the spin-echo or gradient-echo MR images. Absolute measures such as the fractional area, trabecular width, trabecular number, and fractal dimension as measured from gradient echo images were 28%, 30%, 1.3%, and 0.6% greater, respectively, than those calculated from spin-echo images, while the trabecular spacing was 14% less when calculated from gradient-echo images compared to spin-echo images. The structural parameters also depended on the echo time used to obtain the MR image. The choice of the threshold used to segment the high resolution images also affected the estimated structural parameters significantly. Our results indicate that MR may be used to visualize and quantify trabecular bone architecture; however, the different technical factors that could affect the appearance of MR images must be understood and considered in the data analysis and interpretation.

Absorptiometry, Photon↗
PubMed1995

A survey of psychiatric services for elderly people in Australia.

In 1992 a postal questionnaire identified 107 psychiatrists in Australia who, for a significant proportion of their time, were providing psychiatric services to elderly people. Only 18% were female. There were 34 psychiatrists working full-time in psychiatry of old age in the public health system. Twenty-three multidisciplinary catchment area psychiatric services for elderly people were identified, but staff to population ratios varied considerably. The ratio of psychiatrists to elderly was 1:30,000--similar to the ratio in a large part of Britain seven years previously. Psychogeriatricians are involved in a broad range of teaching and research activities. The mean number of non-medical staff in a catchment area psychogeriatric service should be increased.

Aged↗
PubMed1995

The Simon effect and attention deficits in Gilles de la Tourette's syndrome and Huntington's disease.

Tourette's syndrome and Huntington's disease have long been clinically associated with attentional deficits. In this study, we aimed to determine the nature and quantify the extent of such deficits. A technique was devised to ascertain the efficiency with which Tourette's syndrome and Huntington's disease patients could shift and direct attention away from naturally expected stimulus-response (S-R) linkages. This was done by varying the relationships formed between stimulus and response location. Attentional efficiency was indicated by relative speed of responding to relevant (congruent) and irrelevant (incongruent) stimuli, in a paradigm developed from the Simon effect. There were five conditions progressively increasing in complexity. The stimuli consisted of left and right pointing arrows and, in some cases, various conditionality manipulations were also employed, such that in the presence of a certain symbol (i.e. 'x') the nature of the response had to be reversed, whereas in the presence of an alternative symbol (i.e. '='), the response was compatible with the direction of the arrow. As predicted, Tourette's syndrome and Huntington's disease patients, regardless of medication or depression status and unlike controls, were particularly disadvantaged in responding to various conflicting S-R configurations. Tourette's syndrome and Huntington's disease patients may experience difficulties in making attentional shifts, or in inhibiting inappropriate responses; they may also be more susceptible (than controls) to the conflict that can arise when the spatial code formed for the stimulus is irrelevant for selecting the appropriate response. We conclude that our findings support the notion that cognitive deficits in Tourette's syndrome and Huntington's disease may stem from abnormalities of the major pathways interconnecting the basal ganglia and the frontal lobes.

Adult↗
PubMed1995

Intensive consolidation chemotherapy for newly diagnosed acute myeloid leukemia using a regime containing moderate dose cytosine arabinoside and mitoxantrone.

Fifty patients with previously untreated acute myeloid leukemia were treated with an induction regimen consisting of cytosine arabinoside 100 mg/m2 per day by 18 h i.v. infusion for 7 days, daunorubicin 50 mg/m2 per day by i.v. bolus injection for 3 days and etoposide 75 mg/m2 per day by 1 h i.v. infusion for 7 days. Thirty seven of them (74%) went into complete remission (CR) and they all then received two consecutive courses of consolidation chemotherapy consisting of cytosine arabinoside 500 mg/m2 per day by 1 h i.v. infusion every 12 h for 4 days (total eight doses) and mitoxantrone 12 mg/m2 daily by 30 min i.v. infusion for 3 days. They were followed by maintenance chemotherapy with cytosine arabinoside and thioguanine 2 monthly. With a median follow up time of 24 months, 20 of the 37 complete responders had relapsed (54%). The disease-free survival (DFS) of 37 CR patients and the overall survival of all patients at 24 months were 37 and 44%, respectively. Age of patients and number of courses of induction chemotherapy to achieve CR were significant factors predicting DFS. Myelosuppression was the major toxic side effects. Ten patients had prolonged marrow suppression following consolidation chemotherapy. In conclusion, despite the significant myelosuppression observed, overall improvement in treatment outcome was not demonstrable with the use of this intensive consolidation therapy.

Adolescent↗
PubMed1995

Advance information and movement sequencing in Gilles de la Tourette's syndrome.

Tourette's syndrome is a chronic neurological disorder manifested by involuntary motor tics and vocalisations. Because the basal ganglia have been implicated in the pathology underlying Tourette's syndrome, the present two procedures, both involving sequential movements, sought to determine the extent to which patients with Tourette's syndrome were reliant on, and could utilise different levels of advance information. Patients with Tourette's syndrome were found to be more reliant than controls on external visual cues to execute rather than to initiate a motor programme. When there was a high level of reduction in advance information--that is, a visual pathway to be followed was extinguished well in advance of each successive movement--executions progressively slowed as the sequence was traversed. Similarly, if no advance information was provided before each move, movement execution was slower than that of controls. The movement initiation times of patients with Tourette's syndrome were, however, similar to those of controls, as were their movement execution times when advance visual information was available. It seems that patients with Tourette's syndrome, like parkinsonian patients who are known to have a basal ganglia disorder, require external sensory cues to sequence a motor programme effectively. The present study found evidence consistent with the hypothesis that patients with Tourette's syndrome, like patients with Parkinson's disease, may be dysfunctional in internal switching mechanisms. Alternatively, with limited visual guidance, patients with Tourette's syndrome, regardless of medication or depression state, may require more time to plan and programme each next submovement, and under such conditions may require external visual cues to direct attention effectively to given targets. Although the underlying pathogenesis is still speculative, it is concluded that there is much to support the notion that Tourette's syndrome may stem from abnormalities of the major pathways between the basal ganglia and the frontal lobes.

Adolescent↗
PubMed1995

Treatment outcome and prognostic factors for primary nasal lymphoma.

PURPOSE: To report our experience managing a large series of Chinese patients with primary nasal lymphoma. PATIENTS AND METHODS: From January 1975 to December 1993, 100 patients (median age, 50 years) with newly diagnosed primary nasal lymphoma were studied. There were four low-grade, 62 intermediate-grade, nine high-grade, and 25 unclassifiable lymphomas. Immunophenotyping was performed in 45 patients: eight B cell, 35 T cell, and two uncertain. All cases of angiocentric lymphoma that were typed were T cell. Fifty-two patients had stage I disease, 15 had stage II, four had stage III, and 29 had stage IV. Only 15 patients had B symptoms (weight loss, night sweats, and/or fever), and 11 had bulky disease. Thirty-nine patients with clinically localized stage I and II disease received local radiotherapy alone (before 1980), and the remaining 28 stage I and II patients received combination chemotherapy followed by local radiotherapy. The 33 patients with advanced stage III and IV disease were given combination chemotherapy, and additional radiotherapy was given to five of them who had bulky local disease. RESULTS: Significantly higher complete remission rates were observed in patients with early stages of disease and those without B symptoms. Superior disease-free survival after complete remission was observed in patients with stage I/II disease. Univariate factors associated with a better overall survival included age less than 60 years, stage I disease, and absence of B symptoms. Survival was significantly better in the subgroup of patients with stage I disease. CONCLUSION: Patients with nasal lymphoma, especially those with advanced disease, seemed to have a poor prognosis, and their clinical outcome was not improved significantly by the use of chemotherapy instead of radiotherapy or the use of doxorubicin-containing chemotherapeutic regimens.

Adolescent↗
PubMed1995

The Life Skills Profile: a study of its psychometric properties.

Two hundred patients with severe mental illness of mixed type were assessed by treating mental health professionals a total of 730 times with the Life Skills Profile (LSP). Confirmatory factor analyses broadly confirmed the existence of the Self-care and Non-turbulence subscales. Internal consistencies were generally good but inter-rater reliabilities were of only marginal acceptability. The fit of the data to the five subscales can be improved by reassigning two items. The Communication subscale had the poorest psychometric properties. Certain LSP scale scores were found to vary with how well and how long the rater had known the patient. Validity, which was assessed by relating LSP scores to locus of care (i.e. community or hospital), Brief Psychiatric Rating Scale (BPRS) ratings and Resource Associated Functional Level Scale (RAFLS) ratings, was good. An alternative scoring system yielded rather clearer meaning for some of the subscales.

Activities of Daily Living↗
PubMed1994

Characteristics of handwriting of patients with Huntington's disease.

Patients with Huntington's disease exhibit poorer-quality handwriting, sometimes clinically exhibiting macrographia, an increase in the size of handwriting. To characterize deficits in handwriting of patients with Huntington's disease, we compared the writing of 12 young, 12 age-matched controls, and 12 patients with Huntington's disease. Subjects were asked to write the letter "l" four times, at a constant length, on a graphics tablet that sampled pen position at 200 Hz. Huntington's disease causes chorea (involuntary movement), akinesia (difficulty in initiating voluntary movement), and bradykinesia (slowness and difficulty in maintaining voluntary movement). To distinguish changes in handwriting quality due to involuntary movement from impairments of voluntary movement, handwriting samples with obvious choreic movements were analyzed separately from other handwriting samples. Several measures of quality of handwriting were considered, based on: the regularity and consistency of handwriting, the efficiency of movement trajectories, and the proportions of movement occurring at specific frequencies. Results suggested that Huntington's disease increases variability of movement parameters, and causes problems in producing smooth movements. Choreic movement was best characterized by the number of zero crossings in the velocity function relative to the prescribed number of writing strokes. We hypothesize that macrographia in Huntington's disease occurs when chorea predominates over bradykinesia. Comparisons were made between the handwriting of patients with Huntington's and Parkinson's diseases.

Adolescent↗
PubMed1994

An unrelated marrow donor registry in Hong Kong.

One of the limitations of allogeneic bone marrow transplant is the availability of HLA-compatible donors. HLA-identical or one antigen mismatched related donors can only be found for up to 40% of adult and 25% of paediatric patients in Hong Kong requiring a marrow transplant. The rest must rely on donors identified from volunteer unrelated marrow donor panels. Almost all our patients are Chinese but most volunteers in the worldwide marrow donor registries are Caucasians whose HLA profiles are different. Thus an unrelated marrow donor registry for Chinese was established in Hong Kong in 1991 and > 17,000 volunteers have participated. More than 300 local and overseas Chinese patients have so far been referred to our Registry for donor search. Suitable donors have been found ultimately for 40% of them. So far, 26 marrow transplants have been performed using unrelated donors from this registry. They include six overseas Chinese patients.

Asian People↗