The perception of mirror-reflected objects

In what ways and under what conditions does an object appear to differ from its enantiomorph (its mirror reflection)? This 'mirror question' or its popular counterpart, "Why does a mirror reverse left and right but not up and down?" is frequently encountered, but an acceptable answer is not to be found in the literature. The question is approached as an experimental problem in visual psychophysics. A mirror optically reverses the axis perpendicular to its surface. What are the perceptual consequences of this stimulus transformation? This question is examined in four experiments by using stimuli of varying complexity and familiarity. Apparent reversals are demonstrated along right-left, front-back, top-bottom, and oblique axes, depending on the perceived asymmetries of the stimulus object. Perceived asymmetry is shown to depend both on structural asymmetries and on canonical axes and orientations defined by social convention. It is concluded that an object appears to differ from its enantiomorph by an apparent reversal along the axis of least perceived asymmetry. Implications for perceptual frames of reference and for the perception of symmetry are discussed.

Three-dimensional volumetric display of CT data: effect of scan parameters upon image quality

Of the many steps involved in producing high quality three-dimensional (3D) images of CT data, the data acquisition step is of greatest consequence. The principle of "garbage in, garbage out" applies to 3D imaging--bad scanning technique produces equally bad 3D images. We present a formal study of the effect of two basic scanning parameters, slice thickness and slice spacing, on image quality. Three standard test objects were studied using variable CT scanning parameters. The objects chosen were a bone phantom, a cadaver femur with a simulated 5 mm fracture gap, and a cadaver femur with a simulated 1 mm fracture gap. Each object was scanned at three collimations: 8, 4, and 2 mm. For each collimation, four sets of scans were performed using four slice intervals: 8, 4, 3, and 2 mm. The bone phantom was scanned in two positions: oriented perpendicular to the scanning plane and oriented 45 degrees from the scanning plane. Three-dimensional images of the resulting 48 sets of data were produced using volumetric rendering. Blind review of the resultant 48 data sets was performed by three reviewers rating five factors for each image. The images resulting from scans with thin collimation and small table increments proved to rate the highest in all areas. The data obtained using 2 mm slice intervals proved to rate the highest in perceived image quality. Three millimeter slice spacing with 4 mm collimation, which clinically provides a good compromise between image quality and acquisition time and dose, also produced good perceived image quality. The studies with 8 mm slice intervals provided the least detail and introduced the worst inaccuracies and artifacts and were not suitable for clinical use. Statistical analysis demonstrated that slice interval (i.e., table incrementation) was of primary importance and slice collimation was of secondary, although significant, importance in determining perceived 3D image quality.

Data base management in radiology: a simplified approach

The increasing availability of personal and departmental computers in radiology departments has led to increasing interest in data management. Data base management software must be system compatible, simple, and flexible to insure its acceptance and constant use. Once in place, such a system streamlines the daily documentation of interesting cases for conference, follow-up, research, and quality assurance. The authors have developed such a data base program for tracking computed body tomography cases in their department, which can be run as a portable computer to maximize ease of access and therefore usage.

The acetabulum in congenital and neuromuscular hip instability

Acetabular morphology in congenital and neuromuscular hip instability was evaluated with computed tomography (CT) and plain radiography. Thirty-three unstable hips in 27 children with congenital hip dysplasia, cerebral palsy, or spina bifida were studied. Fourteen normal hips in 14 children served as controls. Unstable hips in the children with congenital hip dysplasia demonstrated anterior and superior acetabular deficiency with increased acetabular anteversion. Global deficiency was present in acetabuli of cerebral palsy and spina bifida patients with anterior, posterior, and superior deficiencies. The acetabuli in cerebral palsy patients had significant posterior deficiency and were the shallowest of the groups evaluated.

The use of graphic design in an interactive computer teaching program

The widespread diffusion of affordable computers into the scientific and educational community has provided the opportunity to design medical and scientific teaching programs illustrated either by hand or by utilizing commercially available software and manipulating existing computer generated images. The medical illustrator can provide the ideal aesthetic link between text format information and the visual representation of such knowledge in a concise presentation format. The availability of interactive multimedia programs has given the medical illustrator an environment to create and enhance Hypermedia designed specifically for the purpose of medical education. This paper will focus on the incorporation of illustration and screen design into "CT The Game," an experimental medical teaching program currently being developed in the Johns Hopkins Body CT Imaging Laboratory. The program is designed to provide an enjoyable approach to learning Computed Tomography (CT), and is directed toward an audience of medical students, residents, and fellows.

Sacral foramina: view at CT

Conventional transaxial computed tomography (CT) is superior to plain radiography in depicting the sacrum. Because of the shape and orientation of the sacrum, CT provides oblique views of the structures of interest. With easily reproducible landmarks and standard transaxial CT data, orthogonal image sets can be produced that provide a true en face orientation matching the obliquity of the sacrum. This allows optimal visualization of the paired foramina and of the sacroiliac joints for better assessment of trauma, tumor, or inflammatory disease.

Computed tomography of the hand and wrist

CT plays a limited but distinct role in the evaluation of the hand and wrist. It is most useful in assessing bone and joint anatomy and has only a secondary role in soft tissue abnormalities. The clearest value of CT is in assessing trauma and post-traumatic complications, such as malunion, nonunion, or avascular necrosis, where careful attention to position and technique can yield important information not otherwise obtainable.

Computer-based learning in radiology: a hypermedia application in CT

Multimedia is a form of computer data presentation that uses multiple formats (text, illustration, sound, and animation) to enhance attention to and retention of presented information. Hypermedia is a nonlinear, branched access version of this that allows the user to pursue information more freely and variably than a linear format does. We used the hypermedia format to create an interactive medical teaching program that we believe holds the user's interest and attention better than a straight-text style does.

Supportive care of the lung cancer patients

The care of lung cancer patients involves a specialized team approach. Complications arising from the underlying illness or its treatment are common occurrences that must be anticipated and treated properly. Psychosocial issues commonly arise in patients and their families during the course of the illness. Caregivers skilled in helping a patient and family members come to terms with this frequently fatal disease are integral members of a multidisciplinary team of cancer specialists.

CT of malignant melanoma in the chest, abdomen, and musculoskeletal system

Malignant melanoma is an aggressive neoplasm that can involve virtually every organ system. This article provides a review of the various appearances on computed tomographic (CT) scans of melanoma involving the chest, abdomen, and musculoskeletal system. Specific emphasis is placed on the typical and atypical CT manifestations of disease as well as the similarity of these findings to those for other disease entities. The importance of accurate staging of melanoma is stressed.

AIDS education in the emergency department

The prevention of the spread of acquired immunodeficiency syndrome (AIDS) depends on an educated public reducing their risk of infection. To test the hypothesis that effective community AIDS education can be based in an emergency department, we designed and evaluated two educational interventions in a high-volume urban ED. A pretest/post-test design was used in which subjects were assigned to receive either an active education program, a passive education program, or no education program. Knowledge gains and self-reported risk-reduction behavior were evaluated by follow-up testing within a five-week period. The active and passive groups had significantly greater knowledge gains than the control group (P less than .001). Significantly greater reported reductions in high-risk behavior were found in both the active and passive groups compared with the control group (P less than .01). This study demonstrates that an ED-based AIDS education program can have a significant impact on improving knowledge and reducing self-reported risk behaviors.

Adult ankle fractures: comparison of plain films and interactive two- and three-dimensional CT scans

Thirteen patients with 15 ankle fractures potentially requiring surgical reduction according to plain film criteria were studied with transaxial CT, from which static and animated interactive two-dimensional (2-D) images and animated volumetric three-dimensional (3-D) images were generated. CT criteria believed to parallel well-accepted plain film criteria for triage of ankle fractures were developed and applied. The tibiofibular, talofibular, and tibiotalar articulations were characterized and, where possible (nine cases), compared with the (presumably normal) contralateral ankle. Talocrural angle measurements were made on interactive coronal measurements and compared with standard plain film measurements. Fracture fragment displacement, rotation, and impaction were noted. Posterior tibial lip disruption was quantified. Information derived from the 2-D/3-D CT study led to cancellation of proposed surgery in three of the distal fibular fractures and in two distal tibial fractures. There was far less variation than anticipated between the talocrural angles of the injured and normal ankles, and both injured and normal ankles deviated significantly from the accepted standard of 84 degrees. Displacement at the level of the fibular fracture was a poor predictor of more distal disruption. Two-dimensional CT was found to provide anatomic detail and information superior to either plain film or 3-D CT; 3-D CT was preferred by the surgeons for final surgical planning and for integration of the 2-D data. CT altered management in five of the 13 patients studied, supporting our belief that 2-D/3-D CT can be of significant value in assessing ankle fractures.

Pneumocystis carinii involvement of the liver and spleen: CT demonstration

Patients with acquired immunodeficiency syndrome (AIDS) are subject to a variety of infections, including Mycobacteria avium intracellulare, cytomegalovirus, Cryptosporidium, and Pneumocystis carinii. Pneumocystis is most commonly associated with a potentially fatal pneumonia in AIDS patients. Other organ involvement by Pneumocystis is rare. We present a patient with hepatic and presumed splenic infiltration by Pneumocystis.

Two-and three-dimensional imaging of the painful shoulder

Fifty-six patients with musculoskeletal disorders involving the shoulder were examined using two-dimensional computed tomography multiplanar reconstruction and volumetric three-dimensional (3D) image processing. Two- and three-dimensional imaging of the shoulder demonstrated advantages over conventional radiography in clarifying areas of complex anatomy. The techniques were found most beneficial for (1) delineating complex fractures; (2) evaluating joint instability; (3) localizing foreign bodies; (4) detecting lytic lesions; (5) assessing soft tissue pathology; and (6) identifying causes for decreased range of motion. Two-dimensional multiplanar reconstruction provided superior views of the scapula and permitted a better understanding of the orientation of the glenoid. Multiplanar reconstruction displayed deep soft tissue anatomy more clearly, including the course of important neurovascular structures. Volumetric 3D imaging added several unique perspectives, providing a more comprehensive representation of the shoulder and its articulating surfaces. The ability to rotate the shoulder about he vertical and horizontal axes in an animated video loop and to edit away confusing, overlying structures provided a "real-time" 3D model of the shoulder for planning treatment.

Enhanced computed tomographic techniques for the evaluation of total hip arthroplasty

Computed tomography (CT) has revolutionized the evaluation of musculoskeletal pathology. Until recently, however, CT of the postoperative orthopaedic patient has been severely limited by its inability to provide useful information in the vicinity of acetabular and femoral implants. Typically the hardware produces extensive artifacts that can markedly degrade the whole image. Methods are now available to reduce the metal artifact. Following hip arthroplasty, these methods have been used to plan for revision arthroplasty and to evaluate the contralateral side for avascular necrosis.

Imaging of musculoskeletal trauma in three dimensions. An integrated two-dimensional/three-dimensional approach with computed tomography

Transaxial computed tomographic (CT) data can be used to generate images rapidly in the coronal and sagittal planes (two-dimensional CT) and create simulated three-dimensional images. The techniques and advantages of an integrated two-dimensional/three-dimensional CT approach to musculoskeletal trauma are illustrated and discussed.

Clinical applications of volumetric three-dimensional imaging. A report of three cases

Three-dimensional imaging has evolved rapidly. We believe that volumetric image processing (VIP) represents a major advance within this modality. VIP preserves the fidelity of the original computed tomography (CT) data and allows the viewer to interact with the images in real time. This complements and integrates the information acquired on two-dimensional CT studies, as illustrated in three representative cases.

Treated invasive cervical carcinoma. Utility of computed tomography in distinguishing between skeletal metastases and radiation necrosis

The bony pelvis should be carefully evaluated on computed tomography (CT) scans of the lower abdomen and pelvis performed for staging cervical cancer or for evaluating suspected recurrence. CT provides optimal imaging of the spine and pelvis, frequently providing a clinically relevant supplement to bone scan or plain film information. In a study of eight patients with skeletal metastases from cervical carcinoma and three cases of radiation osteitis, overlap existed in their imaging characteristics. Metastases were always lytic but nearby sclerotic areas from radiation were often present. Radiation osteitis may be lytic, sclerotic, or mixed, and both may avidly accumulate bone-scanning radiotracers. The absence of a soft tissue mass, slow progression, blastic elements, and sharply defined borders on CT suggest radiation necrosis. However, in some lesions within a radiation portal, biopsy or MRI may be required for final diagnosis.

Fidelity of three-dimensional CT imaging for detecting fracture gaps

Simulated femoral neck fractures with varying amounts of distraction were studied using four modifications in a volumetric, three-dimensional CT reconstruction program to allow an objective comparison of volumetric versus surface (thresholded) rendering. Binary classification caused spurious fusion of gaps less than 2.0 mm or, at settings preserving these gaps, produced false holes in adjacent bone. Fracture gaps were visible to 0.0 mm using volumetric CT image rendering technique.

The application of advanced CT imaging and computer graphics methods to reconstructive surgery of the hip

Advanced computed tomographic and computer graphic techniques enhance diagnostic accuracy and offer the means by which three-dimensional operative planning can be achieved. These techniques have been used to diagnose hip pathology, rehearse and evaluate surgical plans, assess postoperative results, and design individualized prostheses.

Pulmonary carcinoid tumors: CT assessment

Computed tomography assessment of 634 surgically proven solitary pulmonary nodules included 12 pulmonary carcinoid tumors. Five were central (involving or directly abutting the bronchial tree), and seven were peripheral (surrounded by parenchyma). Three central and one peripheral lesion had CT numbers indicative of focal calcifications, frequently in the periphery of the nodule. Nodule size ranged from 1.2 to 3 cm. Nine nodules were smooth and round, two were irregular and lobulated, and in one the entire peripheral contour was difficult to assess because of postobstructive atelectasis secondary to tumor occlusion of the bronchus. The calculated average CT number ranged from 80.5 to 179 HU.