Now You See It, Now You Don’t: Visual Illusions in Radiology

Abstract

Visual illusions are distortions, alterations, or alternatives in the appearance of reality that result primarily from the sensory and perceptual processing mechanisms of the human visual system. These illusions are common phenomena in radiology, and it is important to understand them because they can create the illusion of disease, leading to incorrect image interpretation. Visual illusions in radiology can be organized according to the point in the visual system at which they emerge. Illusions of sensation, including Mach bands and background effect, are "lower-order" visual phenomena that occur as the eye and brain translate light into neural activity. Illusions of perception, such as ambiguous figures and distortion, occur in "higher-order" brain structures that are responsible for coalescing sensory input into a mental image interpreted by the mind. Illusions of image formation (eg, parallax), as the name implies, result from the way images are generated. Some visual illusions occur with all modalities, whereas others tend to be modality specific. The authors discuss a variety of visual illusions, describing their underlying psychologic and neuroscientific basis and demonstrating their relevance to radiology. A thorough understanding of visual illusions in radiology enhances diagnostic accuracy by minimizing the risk of mistaking illusions for disease.

Central venous catheterization for acute trauma resuscitation: Tip position analysis using routine emergency computed tomography

“…Regarding the precision of the CVC tip location, CT is superior (due to its three-dimensional nature) compared with conventional chest radiography, which includes the risk of misinterpreting the ray projection (parallax effect) and inter-individual differences in CVC tip position interpretation. [20][21][22] However, CT is not applicable for routine CVC tip position analysis due to the many-times-higher radiation exposition compared with conventional chest radiography.…”

Error in radiology—where are we now?

“…Simple optical illusions demonstrate how the human eye can be deceived and radiologists are as susceptible as anyone else. 7 We have to learn, for example, that juxtaposition of regions of different attenuation on a cranial CT scan can distort our perception, rendering us more or less likely to make a correct diagnosis of haemorrhage. Similarly our visual appraisal of the size of a lung lesion on sequential imaging must often be verified by direct measurement in order to avoid making an incorrect assessment of growth or shrinkage.…”

Zenker’s Diverticulum: Can Protocolised Measurements with Barium SWALLOW Predict Severity and Treatment Outcomes? The “Zen-Rad” Study

“…a Anteroposterior view, with measurement of pouch width; b lateral view, with measurement of maximum oesophageal depth, pouch height, cricopharyngeus length, pouch neck and pouch depth; c zoomed-in lateral view demonstrating maximum cricopharyngeal thickness For the AP view the BB was moved taped in a more lateral position at a rough estimation of the position of any ZD. This enabled an estimate of the ZD parameters by calibrating a known dimension in a similar plane to the ZD, from which other measurements could be extrapolated, and to minimise radiographic parallax error [8].…”