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Biomedical subjects

D Keating

Publications and source records attributed to D Keating.

At least 37 records · Page 2Linked to original sources
PubMed1994

MR arthrography of the shoulder with gadopentetate dimeglumine: influence of concentration, iodinated contrast material, and time on signal intensity.

OBJECTIVE: MR arthrography of the shoulder with gadopentetate dimeglumine has been proved to be valuable in the diagnosis of injuries of the rotator cuff and glenoid labrum. To date, no standard protocol for the concentration of gadopentetate dimeglumine and the volume of iodinated contrast material used for intraarticular injection exists. This study compared the intraarticular signal intensities achieved with three different MR arthrography protocols with respect to the volume of iodinated contrast material, the concentration of gadopentetate dimeglumine, and the interval between injection of contrast material and the MR study. SUBJECTS AND METHODS: MR arthrography was performed with three different protocols in 38 patients (26 men, 12 women). Patients examined with protocol 1 received an intraarticular injection of 5 ml of iotrolan and 5 ml of a 5 mmol/l solution of gadopentetate dimeglumine, resulting in a gadopentetate dimeglumine concentration of 2.5 mmol/l. Patients in protocol 2 received only 0.5 ml of iotrolan plus 12 ml of a 10 mmol/l solution of gadopentetate dimeglumine, leading to a 10 mmol/l concentration. The interval between injection and MR imaging for patients in protocols 1 and 2 was 30-45 min. Patients in protocol 3 received an intraarticular injection of 10 ml iotrolan and 1 ml of a 500 mmol/l solution of gadopentetate dimeglumine, resulting in an intraarticular concentration of gadopentetate dimeglumine of 45 mmol/l. MR examinations were performed between 20 and 360 min after administration of contrast material. Patients in protocol 3 had additional conventional and CT arthrography within 30 min after injection. The contrast-to-noise ratio of the intraarticular signal intensity was calculated for all protocols. RESULTS: The contrast-to-noise ratio (mean +/- SD) was 22.7 +/- 7.4 for the 2.5 mmol/l solution (protocol 1), 47.5 +/- 11.9 for the 10 mmol/l solution (protocol 2), and 9.9 +/- 3.1 for the 45 mmol/l solution (protocol 3) within 1 hr after injection. For protocol 3, an increase in contrast-to-noise ratio was observed after 90-180 min (53.5 +/- 12.7), followed by a decrease in contrast-to-noise ratio after 180 min (17.1 +/- 8.2). The image quality of conventional, CT, and MR arthrography (90-180 min after injection) was good in all cases of protocol 3. CONCLUSION: For MR arthrography performed within 1 hr after injection, protocol 2 is sufficient. The optimal time frame for protocol 3 is between 1.5 and 3 hr after joint puncture. Protocol 3 allows the prior performance of conventional and CT arthrography. Therefore, the addition of 1 ml of a 500 mmol/l solution of gadopentetate dimeglumine to 10 ml of iodinated contrast material is advisable if a subsequent MR study is anticipated.

Adult↗
PubMed1994

Dissection of the thoracic aorta: pre- and postoperative findings on turbo-FLASH MR images obtained in the plane of the aortic arch.

This pictorial essay illustrates the pre- and postoperative findings seen in patients with aortic dissections on contrast-enhanced turbo-fast low-angle shot (FLASH) MR images obtained in the plane of the aortic arch. Contrast-enhanced images provide morphologic and functional information not normally available with conventional spin-echo (SE) MR imaging or dynamic CT. Preoperative examination of the acute dissection is often troubled by cardiovascular insufficiency and motion artifacts. Therefore most of our patients were examined postoperatively. The main reason for postsurgical imaging is the evaluation of the flow in the different lumina and the detection of complications (i.e., aneurysms or progress of dissection).

Aortic Dissection↗
PubMed1992

Steady-state visual evoked cortical potentials from stimulation of visual field quadrants. Optimizing pattern variables for the size of the field to be investigated.

The effects of check size and stimulus size were investigated to optimize the steady-state visual evoked cortical potentials from pattern-reversal stimulation of the visual field quadrants. Check sizes of 15', 30', 60', 90', 120' and 180' were investigated at a pattern reversal rate of 11.6 per second for field sizes varying from 2 degrees x 2 degrees to 24 degrees x 24 degrees. The visual evoked cortical potentials were recorded from mid occipital, right occipital and left occipital positions. In the inferonasal quadrant, the largest amplitudes were obtained with 30' and 60' check sizes; however, for these check sizes, the visual evoked cortical potential yielded limited additional information for field sizes greater than 4 degrees x 4 degrees and 6 degrees x 6 degrees, respectively. When a field size of 12 degrees x 12 degrees was investigated, a 90' check size was optimal. The results indicated that, with the above recording positions and check sizes of 15' to 120', there is an optimal number of pattern elements, 40 to 100, for stimulation of the inferonasal quadrant. This should be taken into account when a check size is selected to investigate a field quadrant of a particular size. Digital signal processing techniques were applied to analyze the visual evoked cortical potential, and the system shows promise for objective examination of the visual field.

Adult↗
PubMed1992

Visual evoked cortical potentials from transient dark and bright stimuli. Selective 'on' and 'off-pathway' testing?

The superior hemifields of five normal left eyes were stimulated by novel equal and opposite contrast pattern onset stimuli which were generated on a cathode ray tube. Patterns consisted of 144 discs, each subtending 60 min arc at the viewing distance of 40 cm and were separated by a distance equal to their diameter. Equal and opposite light changes were created by presenting the disc patterns with different luminance values on a uniform constant background (20 cd/m2). Transient visual evoked cortical potentials to the appearance and disappearance of the patterns were recorded separately and analysed. Significant amplitude differences between the responses to bright and dark stimuli were observed with light increment responses being 36-53% larger than the light decrement responses for pattern on-set and 54-80% larger for pattern off-set respectively. This finding is attributed to the difference in the input to the ON and OFF Parallel Pathways which are known to carry light increment and decrement information respectively, as well as differences in the metabolic and discharge rates of these pathways.

Adult↗
PubMed1992

The Purkinje vascular entoptic test: a halogen light gives better results.

The Purkinje vascular entoptic test is a test of macular function which employs a light directed through the sclera illuminating the fundus. This light casts shadows of retinal blood vessels on to posterior pole photoreceptors. When the light source is moved, a patient with a good macular function should be able to see a negative image of his or her retinal blood vessels. We evaluated the Purkinje test in eyes with clear ocular media. A bright 3.5 watt halogen rechargeable transilluminator was used instead of a pen torch as previously described. Sixty-eight patients (129 eyes) attending a diabetic eye clinic, were tested. The test correctly identified 91% of eyes with good macular function and 77% of eyes with poor macular function (visual acuity 6/24 or poorer). If a vascular pattern was seen, it was probable (0.89) that good macular function was present. If no vascular pattern was seen, it was probable (0.80) that the eye had poor macular function (chi 2 = 60.14, P = < 0.001). Our results were superior to those previously reported. We attribute the increased accuracy of our test to the brighter light source used.

Adult↗
PubMed1989

The Pocket Speech Aid.

A rapid-access but limited vocabulary communication aid for the non-vocal and speech impaired is useful in some well defined situations. The design and construction of such a device is described. Three distinct situations have been identified where an aid is essential and an initial evaluation has shown the Pocket Speech Aid to be very successful.

Biomedical Engineering↗
PubMed1986

Augmentation of cardiac function in end-stage heart failure by combined use of dobutamine and amrinone.

A patient with end-stage congestive cardiomyopathy had progressive hemodynamic deterioration while awaiting orthotopic heart transplantation. Attempts to support cardiovascular function by high-dose dobutamine infusions were complicated by life-threatening cardiac arrhythmias. The addition of the noncatecholamine inotropic agent, amrinone, improved ventricular performance, enabling reduction of the dose of dobutamine and resolution of the cardiac arrhythmias. Beta receptor stimulation by dobutamine combined with phosphodiesterase inhibition by amrinone may additively or synergistically augment cardiac function despite severe congestive heart failure and also have an adrenergic "sparing effect."

Aminopyridines↗
PubMed1984

Cognitive arithmetic: comparison of operations.

Adults' performance of simple arithmetic calculations (addition, multiplication, and numerical comparison) was examined to test predictions of digital (counting), analog, and network models. Although all of these models have been supported by studies of mental addition, each leads to a different prediction concerning relations between the times required for addition, multiplication, and numerical comparison. Pairs of single-digit integers were presented and reaction times (RTs) for adding, multiplying, and comparing the stimuli were collected. A high correlation between RT for addition and multiplication of the same digits was obtained. This result is consistent with a network model, but presents difficulties for both analog and counting models. A "ties" effect of no increase in RT with increases in problem size for doubles such as 2 + 2 has been found in previous studies of addition using verification procedures, but was not found with the production task employed in the present study. Instead, a different kind of ties effect was found. Reaction time for both addition and multiplication of ties increased more slowly with problem size than did RT for non-tie problems. This ties effect, and the finding that probability of making errors contributes independently of problem size to RT support a distinction between location and accessibility of information in a network.

Adult↗
PubMedDate not supplied

Comparison of repeatability of the multifocal electroretinogram and Humphrey perimeter.

Functional mapping of the retina by multifocal electroretinographic recordings is now possible. We compared the normal range, repeatability and response topography of this new technique with conventional static Humphrey perimetry to assess its suitability in clinical practice. The multifocal technique was performed on 60 age-matched controls. Measures of repeatability and reproducibility were obtained. Results were then compared with those obtained from a customized perimetry test. In both tests the coefficients of repeatability were found to decrease with eccentricity. The inherent measurement variation between techniques was comparable. Overall system variation indicates that the technique could be a useful tool at the clinical level.

Computer Graphics↗
PubMedDate not supplied

The effect of filter bandwidth on the multifocal electroretinogram.

The effect of filter bandwith on the multifocal electroretinogram was assessed by means of theoretical calculation, electronic simulation and real multifocal electroretinogram recordings. Waveform distortion by high-pass filtering on simulated square waves, normal electroretinogram waveforms and negative electroretinogram waveforms was demonstrated. The theory of the effect of differentiation on electroretinogram waveform shape by electronic filtering indicates that little effect would be observed by changing the input filter cut-off for normal electroretinographic waveform shapes. However, negative electroretinogram waveforms are differentiated when the high-pass filter setting is increased. The differentiation effect artificially recreates a positive component that could be mistaken as a b-wave component. To eliminate this effect when recording multifocal electroretinograms, a high-pass filter setting of less than 1 Hz should be used to preserve the true electroretinographic waveform shape.

Computer Simulation↗
PubMedDate not supplied

MR-guided localization of suspected breast lesions detected exclusively by postcontrast MRI.

OBJECTIVE: We describe and evaluate a preoperative MRI localization procedure for suspected breast lesions. MATERIALS AND METHODS: Fourteen consecutive patients underwent MR localization of suspected breast lesions discovered with contrast-enhanced MRI but not detected by conventional mammography or ultrasound. In each case diagnostic MRI was repeated after the application of special skin markers. A non-magnetic wire was subsequently inserted into the breast and a second MRI performed to document the position of the wire tip relative to the lesion. RESULTS: The procedure was successful in all 14 patients, enabling excision of the lesion and allowing histological diagnoses. CONCLUSION: We found the described procedure to be quite useful.

Adult↗
PubMedDate not supplied

A versatile speech output communication aid.

A portable, battery-powered communication aid with speech output, which can be operated by patients with limited finger control, is described. The device is sufficiently versatile to try out different methods of selection of words or phrases in the search for an acceptable, portable communication aid for the speech impaired.

Communication Devices for People with Disabilities↗