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A computational approach to medical imaging.

Notwithstanding the progress in medical imaging by means of computer-based techniques, several problems still remain unsolved in this field. In particular, a unified approach for the treatment of biological complexity and variability is lacking. Moreover, perceptive and cognitive aspects of medical vision play an important role in a computational approach to medical imaging and must be carefully considered. The recent developments of Computer Vision and Artificial Intelligence suggest that such a computational approach is feasible. As a consequence, symbolic representations of the clinical information contained in the images as well as adequate processing techniques are necessary. In this way the treatment of uncertainty and the qualitative analysis are made possible. Moreover, due to the intrinsic homogeneity of symbolic representations, the comparison of different image sources, signals and clinical data is attainable. In the paper, the basic principles of Computer Vision are summarized and the need of a specific computational theory for medical vision is emphasized. Afterwards, the main characteristics of integrated systems for computational imaging in medicine, are described. Some examples relative to the imaging of the cardiovascular system are also given. Although the development of artificial vision systems in biomedicine is still an area of research, very promising perspectives are opened by a computational approach.

Artificial Intelligence↗
PubMed1987

Readability of computer display print enlarged for low vision.

A letter counting task was presented on a Macintosh computer screen using two different versions of 24 point Times Roman print. One version, called "grainy," had 12 matrix units per font height and the other, called "smooth," had 24. A mixed group of low vision subjects and a normally sighted group had speed and accuracy measured as they performed the test task from two different viewing distances. For both population groups, the remote test distances were arranged individually so that the letters subtended an angular size scarcely larger than threshold. The close distances were fairly representative of practical working distances. It was shown that, for both groups of subjects, smooth letters allowed faster performance for the closer working distances only. Smoothing the letters helped accuracy of performance at the far distances, and at the close distances, smoothing improved the accuracy for the low vision group but not for the normals. The implications are discussed.

Adult↗
PubMed1992

Computational aspects of motion perception in natural and artificial vision systems.

In this paper a computational scheme for motion perception in artificial and natural vision systems is described. The scheme is motivated by a mathematical analysis in which first-order spatial properties of optical flow, such as singular points and elementary components of optical flow, are shown to be salient features for the computation and analysis of visual motion. The fact that different methods for the computation of optical flow produce similar results is explained in terms of the simple spatial structure of the image motion of rigid bodies. Singular points and elementary flow components are used to compute motion parameters, such as time-to-collision and angular velocity, and also to segment the visual field into areas which correspond to different motions. Then a number of biological implications are discussed. Electrophysiological findings suggest that the brain perceives visual motion by detecting and analysing optical flow components. However, the cortical neurons, which seem to detect elementary flow components, are not able to extract these components from more complex flows. A simple model for the organization of the receptive field of these cells, which is consistent with anatomical and electrophysiological data, is described at the end of the paper.

Artificial Intelligence↗
PubMed1990

3-D model of vascular network in rat skin obtained by stereo vision techniques.

The quantitative analysis of the depth of injury, penetration of therapeutic agents in tissues, and the regeneration of vascular patency after a graded degree of thermal injury requires a knowledge of the shape and spatial configuration of the vascular networks in the tissue. We have applied computational stereo vision techniques to describe the 3-D configuration of microvessels in full thickness rat skin vascular casts produced by perfusion of Yellow Microfil latex solution through the aorta. The principal concern is to describe the 3-D structure of vascular networks using a set of 3-D space curves. This representation is computed by integrating monocular and binocular processing; the 2-D curve representation of blood vessels computed through monocular analysis is integrated with disparity data to yield a space curve representation for each vessel. A connection diagram is also computed to indicate the connections existing among the computed space curve representations.

Algorithms↗
PubMed1989

Changes in colour contrast sensitivity associated with operating argon lasers.

A new test of colour vision using computer graphics has been used to obtain quantitative estimates of colour contrast sensitivity in ophthalmologists before and after they have treated patients by argon laser retinal photocoagulation. The colour vision of all subjects is normal when tested with the 100-hue test and HRR (Hardy, Rittler, Rand) plates, but colour contrast sensitivity measured along a tritan colour confusion line is selectively impaired after a treatment session. No such change occurs after a medical session spent examining patients with a fundus camera. In younger ophthalmologists the sensitivity recovers several hours after the treatment session ends, but in some persons there is a prolonged and possibly permanent elevation of threshold.

Adult↗
PubMed1988

Dysthyroid optic neuropathy. The crowded orbital apex syndrome.

The authors have reviewed the clinical presentation, visual fields, color vision testing, visual-evoked potentials, and computed tomographic (CT) findings of 58 patients (95 eyes) with dysthyroid optic neuropathy. The authors compared these findings to a control group of 60 patients (119 eyes) with thyroid eye disease who underwent CT scanning and did not exhibit evidence of optic neuropathy. Clinically, dysthyroid optic neuropathy is an insidious disease; when compared with the usual Graves' orbitopathy patient, the optic neuropathy group presented at a later age and with a later onset of thyroid eye disease. The patients in this group were more likely to be male and/or diabetic, and often presented with desaturation of color vision. Asymmetrical extraocular muscle restriction and vertical tropias were more frequent in the optic neuropathy group. The most sensitive indicators of optic nerve dysfunction appeared to be visual-evoked potentials and color vision. Computed tomographic studies confirmed that apical orbital crowding was a characteristic feature of optic neuropathy. These findings should alert the clinician to a more aggressive approach to these patients.

Adult↗
PubMed1989

Pituitary adenoma: diagnosis and management.

This article is a review and update on pituitary adenomas and their effects on the visual system. Current diagnostic characteristics and tests of importance to the optometrist are highlighted. Major clinical manifestations of pituitary adenomas during various parts of the visual examination are discussed. Neuroradiologic testing and treatment modalities are also briefly covered. Finally, a case report illustrates how routine optometric care can lead to diagnosis of pituitary adenoma in a visually asymptomatic patient. This case underscores the importance of investigating every case of unexplained vision loss.

Adenoma↗
PubMed1989

Primary optic nerve sheath meningiomas. Report of nine cases.

Between 1979 and 1987 the authors treated nine cases of primary optic nerve sheath meningioma. The definitive treatment for these lesions is surgical resection, although no single best plan for optimal management has been determined. The data indicate that only small anterior tumors may be removed with preservation of useful vision. With posterior circumferential tumors, there have been no cases of tumor removal with preservation of vision. A management strategy directed toward preservation of vision is discussed.

Cranial Nerve Neoplasms↗
PubMed1991

Problems in the diagnosis and management of unilateral retinoblastoma.

The improved prognosis for life in retinoblastoma challenges us to readdress the severe morbidity associated with late presentation and treatment, particularly in unilateral disease. Three cases of unilateral sporadic retinoblastoma are presented to illustrate the range of therapeutic options that need to be considered in management and to show that early recognition of the tumour and local treatment have the potential to minimise morbidity and to enable binocular vision to be retained.

Antineoplastic Agents↗
PubMed1988

Inverted vision after frontal lobe disease.

A case of bifrontal abscesses is reported. The patient claimed that he sometimes saw the world as if it were upside-down. A review of the literature reveals that, since 1805, 21 similar cases have been documented. The present case is unusual in that the neuropsychological status of the patient is investigated in some detail, and in that it seems to be the first report of inverted vision in a case of frontal lobe disease.

Brain Abscess↗
PubMed1986

Bilateral optic nerve sheath enlargement.

A 43-year-old man presented with progressive visual loss in each eye associated with bilateral optic nerve sheath enlargement. At surgery, the left optic nerve sheath was diffusely distended with clear fluid, but biopsy of the optic nerve and its sheath revealed only normal structures. Decompression of the right optic nerve prevented further deterioration of vision in this eye. The etiology of this condition and pathogenesis of visual loss is unknown.

Adult↗
PubMed1991

Steroid-induced visual recovery in fibrous dysplasia.

Fibrous dysplasia is a rare disorder of bone that may be associated with acute loss of vision. Surgical intervention is generally advocated and sometimes restores vision in these patients. We report a case of a patient with unilateral optic neuropathy from fibrous dysplasia who suffered two acute episodes of visual impairment. The first episode of vision loss was reversed by surgery and the second by corticosteroid treatment. A trial of corticosteroid therapy may be beneficial in cases of acute vision loss due to fibrous dysplasia.

Adult↗
PubMed1992

Human vision combines oriented filters to compute edges.

The experiments examined the perceived spatial structure of plaid patterns, composed of two or three sinusoidal gratings of the same spatial frequency, superimposed at different orientations. Perceived structure corresponded well with the pattern of zero crossings in the output of a circular spatial filter applied to the image. This lends some support to Marr & Hildreth's (Proc. R. Soc. Lond. B 207, 187 (1980)) theory of edge detection as a model for human vision, but with a very different implementation. The perceived structure of two-component plaids was distorted by prior exposure to a masking or adapting grating, in a way that was perceptually equivalent to reducing the contrast of one of the plaid components. This was confirmed by finding that the plaid distortion could be nulled by increasing the contrast of the masked or adapted component. A corresponding reduction of perceived contrast for single gratings was observed after adaptation and in some masking conditions. I propose the outlines of a model for edge finding in human vision. The plaid components are processed through cortical, orientation-selective filters that are subject to attenuation by forward masking and adaptation. The outputs of these oriented filters are then linearly summed to emulate circular filtering, and zero crossings (zcs) in the combined output are used to determine edge locations. Masking or adapting to a grating attenuates some oriented filters more than others, and although this changes only the effective contrast of the components, it results in a geometric distortion at the zc level after different filters have been combined. The orientation of zcs may not correspond at all with the orientation of Fourier components, but they are correctly predicted by this two-stage model. The oriented filters are not 'orientation detectors', but are precursors to a more subtle stage that locates and represents spatial features.

Adaptation, Ocular↗
PubMed1985

[Disorders of binocular vision in amblyopic patients working at computer terminals].

For the first time two cases are described with disturbances of binocular vision caused by subjective perception of positive scotomata in the amblyopic eye. The visual strain of working at a terminal leads to a slight increase in the squint angle; as a result, a paracentral scotoma may shift into the middle of the binocular visual field and impair the image quality of the fixing eye. Amblyopic subjects presenting with these symptoms are disqualified from working at VDUs. However, not every amblyopic is affected.

Adult↗
PubMed1987

Residual vision in patients with retrogeniculate lesions of the visual pathways.

Twenty-five subjects have been studied who, as a result of damage to the striate cortex, were 'blind' in extensive areas (scotomata) of the visual fields. Of these 25 subjects, 5 exhibited residual vision in response to transient lights presented within the scotoma, which enabled them to locate the stimuli by hand-reaching or by eye movements; the latter have been measured by electro-oculography. The residual vision underlying their responses was characterized by low flicker-fusion and by sensitivity in detection of movement which increased as target speed was raised. Discrimination for the direction of target movement was poor, but spatial resolution in the discrimination of target displacement was essentially normal. The subjects were unable to recognize or discriminate the spatial structure of targets located within the 'blind' field, and the observed dissociation between spatial discrimination of displacement and pattern is examined in relation to the 'two systems' hypothesis of visual function. There is no obvious correlation between the extent of neuronal damage as revealed by CT scans and the existence of residual vision.

Adult↗