QA/acceptance testing of DEXA X-ray systems used in bone mineral densitometry.

New developments in dual energy X-ray absorptiometry (DEXA) imaging technology [fan beam and cone beam (CB)] result in higher exposure levels, shorter scan times, increased patient throughput and increased shielding requirements. This study presents the results of a European survey detailing the number and location of DEXA systems in SENTINEL partner states and the QA (quality assurance) currently performed by physicists and operators in these centres. The results of a DEXA equipment survey based on an in-house developed QA protocol are presented. Measurements show that the total effective dose to the patient from a spine and dual femur DEXA examination on the latest generation DEXA systems is comparable with a few microSv at most. Scatter measurements showed that the use of a mobile lead screen for staff protection was necessary for fan and CB systems. Scattered dose from newer generation systems may also exceed the exposure limits for the general public so structural shielding may also be required. Considerable variation in the magnitude and annual repeatability of half value layer was noted between different models of DEXA scanners. A comparative study of BMD (bone mineral density) accuracy using the European Spine Phantom highlighted a deviation of up to 7% in BMD values between scanners of different manufacturers.

Development of training syllabi for radiation protection and quality assurance of dual-energy X-ray absorptiometry (DXA) systems.

The use of dual-energy X-ray absorptiometry (DXA) scanners for measuring bone mineral density (BMD) is on the increase. A single DXA scan is a relatively low-dose diagnostic X-ray examination; however, radiation protection (RP) issues should not be trivialised. One objective of the EU 6th Framework SENTINEL co-ordination action was to develop training syllabi in RP and quality assurance (QA) for BMD, and this study presents the results. An EU-wide survey was carried out which confirmed that there was a need for an accredited DXA RP training course in many EU states. There is also limited published guidance on acceptance testing/QA for DXA. Two training syllabi were developed: one on RP and one on QA of DXA systems. A training course was delivered in Ireland in 2006 by the Medical Physics & Bioengineering Department of St James's Hospital, Dublin. Following the training course, a PC-based training CD was developed and will be made available. A harmonised approach to training will promote consistent approaches to radiation safety across the EU.

An automated ocular microtremor feature extraction using the Gabor thresholding technique.

Ocular Microtremor (OMT) is a very fine continuous eye movement which has potential in monitoring and identifying a number of clinical conditions. There is a need for improved analysis and processing techniques to extract useful, quantifiable parameters from the OMT signal. A number of papers have shown the clinical significance of looking at the 'bursts' and 'baseling' patterns of the OMT signal. Analysis to date relies on visual inspection alone. This paper introduces an automated approach to burst/baseline identification based on a time-varying filter using the Gabor transform.

Commissioning and quality assurance protocol for dual energy X-ray absorptiometry (DEXA) systems.

This study reports on the development and evaluation of a protocol for testing DEXA systems, which can be incorporated into a routine medical physics/engineering service. Methodologies are reported for (1) scatter measurement, (2) estimation of reference dose and (3) enquiry into potential sources of overexposure. Results show that fan-beam and cone-beam systems require shielding if the walls or operator are within 1 m of the table. Patient reference dose was estimated using the dose-area product (DAP). This varied over an order of magnitude from 2 to 36 mGy cm2 in the range of systems studied. The inquiry into potential sources of overexposure revealed some weaknesses in current practise including a design which prevents the inclusion of DAP metres; beam non-uniformity; incorrect specification of patient dose and the risk of overexposure when tube operates during patient positioning.

Gender and the integration of acoustic dimensions of prosody: implications for clinical studies.

This study was conducted to detect the existence of a relationship between spectral and temporal prosodic cues and to examine gender differences in any such relationship. The rationale for the investigation was to gain a greater understanding of normal prosody and the requirements for control groups in clinical studies of prosody. Ten male and 10 female speakers with no known speech or neurological deficits participated in the study. They performed a reading task which involved delivering 10 sentences first with a declarative and then repeated with an interrogative intonation (20 sentences per speaker). Intrasubject and intersubject analyses of the speech data revealed a dependence of pitch on duration that differed between male and female speakers. Significant differences between the genders were also found in speech rate, pitch range, and pitch slope. The findings suggest that an integrated treatment of acoustic cues may provide a more invariant feature of normal prosody against which clinical groups may be compared. The data also imply that in clinical studies of the production of prosody gender should be carefully controlled.

Effect of age on ocular microtremor activity.

BACKGROUND: Ocular microtremor (OMT) is a high-frequency tremor of the eyes. It is present in all individuals and is related to brainstem activity. The OMT signal appears as an irregular oscillatory movement with intermittent burst-like components. The clinical interest in OMT has centered on its use in the assessment of the comatose patient, with broad agreement among authors of its prognostic value. The purpose of this study was to examine the changes in OMT activity related to aging. METHODS: OMT was recorded from 72 normal healthy subjects using the piezoelectric strain gauge technique. The subjects ranged in age from 21 to 88 years (54.22 +/- 20.43 years, mean +/- SD). RESULTS: Our results show that the overall frequency and frequency content of the bursts falls with age (p < .002 and p < .001, respectively). There is a highly significant drop in all three frequency parameters of OMT (p < .0001) in subjects older than 60 years of age. CONCLUSIONS: These results suggest that different values of normality should operate for subjects over 60 years of age when considering the clinical application of OMT.

Ocular microtremor (OMT): a new neurophysiological approach to multiple sclerosis.

Using a piezoelectric transducer, the frequency and pattern of ocular microtremor (OMT) between 50 normal subjects and 50 patients with multiple sclerosis were compared. Controls were age matched. All records were analysed blindly. The frequency of OMT in the normal group was 86 (SD 6) Hz, which was significantly different from that of the multiple sclerosis group (71 (SD) 10 Hz, p<0.001). Those in the multiple sclerosis group with clinical evidence of brain stem or cerebellar disease (n=36) had an average OMT frequency of 67 (SD 9) Hz (p<0.001) compared with normal (n=86), whereas those with no evidence of brain stem or cerebellar involvement (n=14) had a frequency of 81.2 (SD 6) Hz (p<0.05, n=64). The differences between the two multiple sclerosis groups were also significant (p<0. 001, n=50). At least one abnormality (frequency and pattern) of OMT activity was seen in 78% of patients with multiple sclerosis. In the presence of brain stem or cerebellar disease 89% had abnormal records whereas in the absence of such disease 50% had abnormal records. This is the first report of the application of this technique to patients with multiple sclerosis. The results suggest that OMT activity may be of value in the assessment of multiple sclerosis.

The application of d.c. electrical stimulation in evoking and recording gustatory brain potentials.

Evidence exists which supports the hypothesis that electrical stimulation of appropriate parameters can fulfil the fundamental requirements for an effective evoked potential taste stimulus. Nevertheless, it had previously been considered that electrical taste stimulation is inadequate for evoking gustatory brain potentials. Consequently, the majority of the earlier attempts to record gustatory evoked potentials (GEPs) reported in the literature have employed chemical stimulus techniques. The design of an electrical taste stimulator and its interface to an evoked potential recording unit is described. The first human brain potentials recorded with this system are presented, among which are those attributable to taste pathway activation. Following future work to unequivocally confirm that taste evoked brain potentials are achievable with this system, it has potential to become a clinically valuable tool.

Ocular microtremor in brain stem death

OBJECTIVE: This study was undertaken to establish whether measurement of ocular microtremor (OMT) activity could be used as a method to establish brain stem death. Presently, the diagnosis of brain stem death can be made using clinical criteria alone. OMT is a high-frequency, low-amplitude physiological tremor of the eye caused by impulses emanating from the brain stem. There have been a number of reports indicating that the recording of OMT may be useful in the assessment of comatose states and in establishing brain stem viability or death. METHODS: We obtained the OMT recordings of 32 patients suspected of having brain stem death using the piezoelectric strain gauge technique. This method involves mounting the piezoelectric probe in a headset and lowering the rubber-tipped end piece onto the anesthetized scleral surface of the subject. The signal produced is recorded on audiomagnetic tape and later played back and analyzed on an electrocardiographic tape analyzer. RESULTS: In 28 patients, initial clinical assessment confirmed the diagnosis of brain stem death and no OMT activity was recorded from these subjects. In three patients in whom initial clinical assessment demonstrated brain stem function, OMT activity was present; when brain stem death was subsequently diagnosed in these three patients, no OMT activity could be demonstrated. In the remaining patient, two of three OMT recordings demonstrated activity in spite of the absence of clinical evidence of brain stem function. A post mortem revealed bacterial cerebritis in this subject. CONCLUSION: The results suggest that OMT is a sensitive method of detecting brain stem life and that it could play an important role in the assessment of brain stem death.

Dominant frequency content of ocular microtremor from normal subjects.

Ocular microtremor (OMT) is a high frequency tremor of the eyes present during fixation and probably related to brainstem activity (Coakley, D. (1983). Minute eye movement and brain stem function. CRC Press, FL.). Published observations on the frequency of OMT have varied widely. Ocular microtremor was recorded in 105 normal healthy subjects using the Piezoelectric strain gauge technique. The dominant frequency content of a signal was determined using the peak counting method. Values recorded ranged from 70 to 103 Hz, the mean frequency being 83.68 Hz (S.D. +/- 5.78 Hz).

Ocular microtremor in patients with idiopathic Parkinson's disease.

Abnormalities in the oculomotor control mechanism of patients with idiopathic Parkinson's disease are well recognised. In this study the effect of Parkinson's disease on tonic output from oculomotor nuclei was studied by using oculomicrotremor as an index of such output. Oculomicrotremor readings were taken from 22 parkinsonian patients and 22 normal healthy volunteers using the piezoelectric strain gauge technique. There was a slower overall tremor frequency, baseline, and burst frequency in the parkinsonian group. There was also a significant increase in the duration of baseline, with a decrease in the number of bursts a second and a decrease in average duration of bursts in the patient group compared with the normal group. One patient, whose medication was withdrawn, showed a marked decrease in mean frequency and baseline frequency with a decrease in number of bursts and increase in baseline duration compared with readings taken when treatment recommenced. These results suggest that variables measured in oculomicrotremor are altered compared with normal subjects, reflecting altered tonic output from oculomotor nuclei in patients with idiopathic Parkinson's disease.

Ocular microtremor in oculomotor palsy.

OBJECTIVES: Ocular microtremor (OMT) is a high frequency tremor of the eyes present in all individuals. Recent reports suggest that OMT may be a useful indicator of brainstem function. However, the actual origin of ocular microtremor remains controversial. This study aims to provide evidence that OMT has a neurogenic origin. MATERIALS AND METHODS: The OMT activity of five subjects with unilateral oculomotor nerve palsy and one subject with complete unilateral internal and external ophthalmoplegia were recorded from both eyes of each subject using the piezoelectric strain gauge technique, with the normal eye acting as a control. Five parameters of OMT activity were studied in each subject: the peak count, the power of the high frequency peak, the percentage power between 60 and 100 Hz, the percentage power between 70 and 80 Hz, and the 10 dB cut-off point. RESULTS: In the five subjects with oculomotor nerve palsy, the mean peak count in the normal eye was 88.4 Hz (SD+/-16.9) and in the affected eye was 59 Hz (SD+/-8.6), P < 0.0096. There was also a fall in the peak power, the power between 60 and 100 Hz, and the power between 70 and 80 Hz. In subject six, who had complete opthalmoplegia, there was no evidence of OMT activity in the denervated eye. CONCLUSIONS: These results suggest that innervation of the extraocular muscles is necessary for normal OMT activity, and OMT therefore has a neurogenic origin.

Arterial closing pressure correlates with diastolic pseudohypertension in the elderly.

BACKGROUND: Pseudohypertension has frequently been reported in the elderly population, with the diastolic measurement being the most frequent source of error. There is no satisfactory noninvasive method of calculating the error in the blood pressure reading. We investigated the role of arterial closing pressure in the diagnosis of diastolic pseudohypertension. METHODS: Indirect and direct blood pressure were measured in 24 elderly patients. Brachial artery closure was visualized by ultrasound in all subjects. Arterial closing pressure (ACP) was recorded as zero if the vessel was seen to close spontaneously when it was isolated from central arterial pressure. If the vessel did not close spontaneously, a water cuff was applied externally over the artery and the additional pressure required to close it was recorded. RESULTS: Diastolic pseudohypertension was noted in 8 subjects. Spontaneous closure of the brachial artery occurred in the 16 without pseudohypertension; i.e., ACP = 0. Additional pressure of the water cuff (range: 30-158 mm Hg) was required to collapse the artery (ACP) in those with diastolic pseudohypertension. ACP correlated with the extent of diastolic pseudohypertension (range: 5-17 mm Hg); r = .85, p < .001). CONCLUSION: We propose that ACP may be used to diagnose the presence and extent of pseudohypertension.

Sources of variance in ocular microtremor.

This study presents a preliminary investigation of the sources of variance in the measurement of ocular microtremor frequency in a normal population. When the results from both experienced and relatively inexperienced operators are pooled, factors that contribute significantly to the total variance include the measurement procedure (p < 0.001), day-to-day variations within subjects (p < 0.001), and inter-subject differences (p < 0.01). Operator experience plays a role in determining the measurement precision: the intra-subject coefficient of variation is about 5% for a very experienced operator, and about 14% for a relatively inexperienced operator.

Ocular microtremor measurement system: design and performance.

The frequency of ocular microtremor (OMT) is related to the functional status of the brain stem, and thus OMT may be useful in the diagnosis and management of brain stem disorders. The paper discusses the design of an OMT measurement system and reports quantitative specifications for three portable systems. All systems use a piezo-electric element as the transducer, which measures the displacement of the sclera during eye rotations. The systems differ in the manner in which the signal is recorded. All systems can detect eye movements corresponding to displacements of the sclera ranging from 12 to over 3000 nm. The frequency responses of all systems are flat (< 2 dB deviation from peak response) between 20 and 150 Hz. The phase response shows deviations (< pi) at the extremes of this range, but qualitative comparison of input and measured signals demonstrates that phase distortion is not excessive. Thus all systems are acceptable for clinical studies involving OMT.

Measurement of arterial closing pressure.

It has been suggested that certain artifacts in blood pressure measurement by auscultation stem from stiffness of the tissues underneath the pressure cuff, resulting in a component of cuff pressure being required to overcome resistance to brachial artery collapse. This paper describes a technique for measuring the pressure required to collapse a segment of the brachial artery which has been isolated from central arterial pressure. This measurement is termed the arterial closing pressure. In a study of eleven elderly subjects, the artery collapsed spontaneously (zero closing pressure) after being isolated from central pressure in seven subjects. The remaining four required external pressures ranging from 4.6 to 10.7 kPa (35 to 81 mmHg) in order to collapse the artery. Thus arterial closing pressure may frequently be a significant fraction of arterial blood pressure in the elderly population, and may contribute to error in the measurement of blood pressure by auscultation. Arterial closing pressure may be a useful tool for investigating the origin of differences between indirect and direct blood pressure measurements, and also in the investigation of spontaneous arterial closure.

Observing the brachial artery through a pressure cuff.

A technique is described which enables ultrasonic imaging of the brachial artery whilst pressure is applied via a pressure cuff. This involves a new instrument--a sphygmomanometer, which uses water as opposed to air as the pressure medium, in order to permit ultrasonic imaging through the cuff. The technique was found to be acceptable in the clinical setting, and gave a measurement of the systolic blood pressure which correlated with the conventional cuff measurement in eleven elderly subjects (r = 0.89, p < 0.001). The technique should have an important role to play in studying the origin of differences which occur between direct and indirect blood pressure measurements.

High frequency eye tremor: reliability of measurement.

Recent reports suggest that high frequency eye tremor or ocular microtremor (OMT) may be a useful indicator of brainstem function. The method of record analysis, and in particular the amount of record subjected to such analysis, has varied widely. We have recorded OMT from 10 normal subjects. Using these records we have performed 42 distinct replication reliability studies. We suggest seven parameters of OMT (including overall frequency of tremor) which may be of value in comparing abnormal with normal records. For each parameter we have determined the optimal duration of the record to analyse and the reliability of such analysis. Our results suggest that at least 5 s of OMT should be analysed to yield an acceptable estimate of all seven parameters.

The fast flush test: evaluation in radial artery catheter-manometer systems.

The 'fast flush test' is commonly used to determine the dynamic response of catheter-manometer systems in vivo. We compared the fast flush test with an established bench top test in vitro. The results of the two tests were compared in fifteen underdamped radical artery catheter-manometer systems. There were significant differences between the results, (P less than 0.001 for both resonant frequency and damping factor), and the variance of estimates within measurement systems was significantly greater in the case of the fast flush test (P less than 0.05 and P less than 0.005 for resonant frequency and damping factor respectively). Nevertheless, the differences between the tests were small by comparison with the errors associated with either test; in addition there was a significant linear correlation between the results of the two tests (r = 0.91, P less than 0.001 and r = 0.85, P less than 0.001 for resonant frequency and damping factor respectively). In the in vitro situation, therefore, the fast flush test provides a crude estimate of the dynamic parameters of underdamped catheter-manometer systems.