VALIDATION OF A NOVEL TECHNIQUE FOR CREATING SIMULATED RADIOGRAPHS USING COMPUTED TOMOGRAPHY DATASETS

Understanding radiographic anatomy and the effects of varying patient and radiographic tube positioning on image quality can be a challenge for students. The purposes of this study were to develop and validate a novel technique for creating simulated radiographs using computed tomography (CT) datasets. A DICOM viewer (ORS Visual) plug‐in was developed with the ability to move and deform cuboidal volumetric CT datasets, and to produce images simulating the effects of tube‐patient‐detector distance and angulation. Computed tomographic datasets were acquired from two dogs, one cat, and one horse. Simulated radiographs of different body parts (n = 9) were produced using different angles to mimic conventional projections, before actual digital radiographs were obtained using the same projections. These studies (n = 18) were then submitted to 10 board‐certified radiologists who were asked to score visualization of anatomical landmarks, depiction of patient positioning, realism of distortion/magnification, and image quality. No significant differences between simulated and actual radiographs were found for anatomic structure visualization and patient positioning in the majority of body parts. For the assessment of radiographic realism, no significant differences were found between simulated and digital radiographs for canine pelvis, equine tarsus, and feline abdomen body parts. Overall, image quality and contrast resolution of simulated radiographs were considered satisfactory. Findings from the current study indicated that radiographs simulated using this new technique are comparable to actual digital radiographs. Further studies are needed to apply this technique in developing interactive tools for teaching radiographic anatomy and the effects of varying patient and tube positioning.     

COMPARISON OF COMPUTED RADIOGRAPHY AND CONVENTIONAL FILM-SCREEN RADIOGRAPHY OF THE EQUINE STIFLE

Major advantages of computed radiography are the potential reduction of dose and the possibility of postprocessing. In our study, we compared conventional radiographs to digital radiographs of the equine stifle by subjective evaluation of diagnostic quality when using a decreasing photon flux (mAs). Twelve equine stifle joints from horses of different weight and size were examined. Conventional and digital radiographs were performed identically in a caudocranial projection with the tube angled 15 degrees. A series of four radiographs was performed in each technique with an increasing photon flux starting with 2.5 mAs and going up to 5, 10, and 20 mAs. All radiographs were evaluated subjectively in a blinded fashion by seven readers in terms of contrast, bone structure, and diagnostic value and were graded using a 1-5 scale. Results from conventional and digitized radiographs were compared, and differences between the individual observers were analyzed statistically. Contrast, bone structure, and diagnostic value from digital images were rated significantly better than from conventional images (p < .001). For both techniques, a decrease in ranking was found with a decrease of photon flux. There was only slight interobserver variability. A dose reduction up to a factor of 4 compared to a 100 speed film-screen system seems to be possible without loss of information. Weight and size of the horse are not major influences.     

Comparison of computed radiography and conventional radiography in detection of small volume pneumoperitoneum

The role of digital imaging is increasing as these systems are becoming more affordable and accessible. Advantages of computed radiography compared with conventional film/screen combinations include improved contrast resolution and postprocessing capabilities. Computed radiography's spatial resolution is inferior to conventional radiography; however, this limitation is considered clinically insignificant. This study prospectively compared digital imaging and conventional radiography in detecting small volume pneumoperitoneum. Twenty cadaver dogs (15-30 kg) were injected with 0.25, 0.25, and 0.5 ml for 1 ml total of air intra-abdominally, and radiographed sequentially using computed and conventional radiographic technologies. Three radiologists independently evaluated the images, and receiver operating curve (ROC) analysis compared the two imaging modalities. There was no statistical difference between computed and conventional radiography in detecting free abdominal air, but overall computed radiography was relatively more sensitive based on ROC analysis. Computed radiographic images consistently and significantly demonstrated a minimal amount of 0.5 ml of free air based on ROC analysis. However, no minimal air amount was consistently or significantly detected with conventional film. Readers were more likely to detect free air on lateral computed images than the other projections, with no significant increased sensitivity between film/screen projections. Further studies are indicated to determine the differences or lack thereof between various digital imaging systems and conventional film/screen systems.     

COMPARATIVE EVALUATION OF AN ULTRAVIOLET AND AN ORTHOCHROMATIC RARE-EARTH IMAGING SYSTEM FOR VETERINARY RADIOGRAPHY

The relative quality and speed of a new ultraviolet-emitting screen, ultraviolet-sensitive film rare-earth system (DuPont Ultra-Vision®) was compared to an orthochromatic rare-earth system (Kodak Lanex®) in a clinical trial. Seven different sets of radiographs of a human foot phantom, or actual canine anatomical structures (tarsus, pelvis, skull, chest, abdomen) were evaluated independently by radiologists, radiology residents and technicians who were unaware of the screen/film combinations used. The 400-speed, Ultra-Vision® Rapid/UVG screen/film combination produced supervisor image detail compared to blue/green emitting 400 and 200-speed screen/film combinations. The image detail of the Ultra-Vision® Rapid/UVG system was nearly equivalent to that produced using a 100-speed, fine-detail blue/green emitting screen/film combination. A 200-speed Ultra-Vision® system was also tested and produced thoracic and abdominal radiographs of equivalent to slightly supervisor quality than those produced using blue/green emitting system.     

RADIOGRAPH QUALITY EVALUATION FOR EXPOSURE VARIABLES—A REVIEW

Good quality radiographs are essential for making accurate diagnoses. Many factors influence the quality of radiographs including the x-ray machine specifications and settings, the darkroom environment and processing, and the choice of ancillary x-ray equipment (cassette properties, film/screen selection, use and properties of a grid). In compiling a technique chart, many of these variables are standardized so as to provide dependable guidelines for selecting the appropriate exposure settings (mAs and kVp) for a radiographic study. The systematic evaluation of image blackening, peripheral blackening, and the visibility of the gross image detail and contrast will facilitate the development of a technique chart as well as determining the source of the problem and necessary exposure setting changes for radiographs that are suboptimal. A flow diagram is described that will assist with the systematic evaluation of radiographic quality and provide guidelines for correcting exposure errors.     

COMPARISON OF FLAT-PANEL DIGITAL TO CONVENTIONAL FILM-SCREEN RADIOGRAPHY IN DETECTION OF EXPERIMENTALLY CREATED LESIONS OF THE EQUINE THIRD METACARPAL BONE

Radiographic diagnosis of equine bone disease using digital radiography is prevalent in veterinary practice. However, the diagnostic quality of digital vs. conventional radiography has not been compared systematically. We hypothesized that digital radiography would be superior to film-screen radiography for detection of subtle lesions of the equine third metacarpal bone. Twenty-four third metacarpal bones were collected from horses euthanized for reasons other than orthopedic disease. Bones were dissected free of soft tissue and computed tomography was performed to ensure that no osseous abnormalities were present. Subtle osseous lesions were produced in the dorsal cortex of the third metacarpal bones, and the bones were radiographed in a soft tissue phantom using indirect digital and conventional radiography at standard exposures. Digital radiographs were printed onto film. Three Diplomates of the American College of Veterinary Radiology evaluated the radiographs for the presence or absence of a lesion. Receiver operator characteristic curves were constructed, and the area under these curves were compared to assess the ability of the digital and film-screen radiographic systems to detect lesions. The area under the ROC curves for film-screen and digital radiography were 0.87 and 0.90, respectively ( P =0.59). We concluded that the digital radiographic system was comparable to the film-screen system for detection of subtle lesions of the equine third metacarpal bone.     

COMPARISON OF SINGLE-PHASE AND HIGH-FREQUENCY GENERATORS FOR X-RAY UNITS

The purpose of this study was to compare characteristics and performances between single-phase (SP) and high-frequency (HF) generators for x-ray units dedicated to veterinary radiology practice. A 30-kW SP and a 30-kW high HF generator connected to a rotating anode x-ray tube were used for the study. Source-film distance, screen/film combination, and film processing were kept the same during the experiment. The mAs value yielding a similar film optical density of a stair step phantom, as assessed by a densitometer and a similar dose, as assessed by a solid state detector, was estimated for different kVp values. The ratio of the mAs used with the SP generator to the equivalent mAs used with the HF generator to produce similar film density or radiation dose was calculated. Subject contrast was measured for different kVp values as the relative difference in film optical density between two steps of the phantom. The waveform of the tube current was recorded for the two generators using an oscilloscope. Motion artifact was produced on a lateral radiograph of a canine tarsus using the two generators. Reproducibility was assessed by comparing the variances of film density measurements made on the central step of the phantom on 10 consecutive images produced with the two generators. mAs ratios (SP/HF) to obtain similar film optical density ranged from 2 (for 90kVp) to 2.5 (for 70 kVp), and mAs ratios to obtain similar radiation dose ranged from 1.2 (for 100 kVp) to 1.4 (for 70 kVp). Image contrast was slightly higher for the SP than for the HF generator. Current waveform for the SP generator was half-sinusoidal and it was almost continuous for the HF generator. Motion artifact appeared as blur for the HF generator and as several regularly placed images of the subject for the SP generator. Reproducibility was significantly better for the HF than for the SP generator (P = 0.047). It was concluded that the HF generator was approximately two times more efficient, had a better reproducibility, and produced images with a lower contrast than the SP generator. Motion artifact appears differently due to different current waveform.     

EVALUATION OF TWO OBJECTIVE METHODS TO OPTIMIZE KVP AND PERSONNEL EXPOSURE USING A DIGITAL INDIRECT FLAT PANEL DETECTOR AND SIMULATED VETERINARY PATIENTS

It is important to optimize digital radiographic technique settings for small animal imaging in order to maximize image quality while minimizing radiation exposure to personnel. The purpose of this study was to evaluate two objective methods for determining optimal kVp values for an indirect flat panel digital detector. One method considered both image quality and personnel exposure as endpoints and one considered only image quality. Phantoms simulated veterinary patients of varying thicknesses with lesions of varying sizes. Phantoms were exposed to a range of kVp values (60, 81, 100, and 121), using different mAs settings for each phantom. Additionally, all phantoms were exposed to a standard test exposure of 100 kVp/2.5 mAs. Scattered radiation was recorded and used as a measure of personnel exposure. When personnel exposure was considered, a figure of merit was calculated as an endpoint of optimization. The optimal kVp value for each phantom was determined based on the highest signal difference‐to‐noise ratio with or without inclusion of the figure of merit. When personnel exposure was not considered, increasing kVp resulted in higher signal difference‐to‐noise ratios and personnel exposure increased when both patient thickness and kVp increased. Findings indicated that a single standard technique of 100 kVp/2.5 mAs was only optimal for most medium‐sized patients. Images of thinner patients should be made with a lower kVp. Very large patients require a higher kVp than 100 regardless of the optimization method used. Personnel exposure from optimized techniques was low and not expected to exceed annual occupational dose limits.     

Comparative evaluation of six different body regions of the dog using analog and digital radiography

In this study the quality of digital and analog radiography in dogs was compared. For this purpose, three conventional radiographs (varying in exposure) and three digital radiographs (varying in MUSI-contrast [MUSI = MUlti Scale Image Contrast], the main post-processing parameter) of six different body regions of the dog were evaluated (thorax, abdomen, skull, femur, hip joints, elbow). The quality of the radiographs was evaluated by eight veterinary specialists familiar with radiographic images using a questionnaire based on details of each body region significant in obtaining a radiographic diagnosis. In the first part of the study the overall quality of the radiographs was evaluated. Within one region, 89.5% (43/48) chose a digital radiograph as the best image. Divided into analog and digital groups, the digital image with the highest MUSI-contrast was most often considered the best, while the analog image considered the best varied between the one with the medium and the one with the longest exposure time. In the second part of the study, each image was rated for the visibility of specific, diagnostically important details. After summarisation of the scores for each criterion, divided into analog and digital imaging, the digital images were rated considerably superior to conventional images. The results of image comparison revealed that digital radiographs showed better image detail than radiographs taken with the analog technique in all six areas of the body.     

DISPLAY QUALITY OF DIFFERENT MONITORS IN FELINE DIGITAL RADIOGRAPHY

In human medical imaging, the performance of the monitor used for image reporting has a substantial impact on the diagnostic performance of the entire digital system. Our purpose was to compare the display quality of different monitors used in veterinary practice. Two medical‐grade gray scale monitors (one cathode‐ray tube [CRT], one liquid crystal display [LCD]) and two standard consumer‐grade color monitors (one CRT, one LCD) were compared in the ability to display anatomic structures in cats. Radiographs of the stifle joint and the thorax of 30 normal domestic shorthair cats were acquired by use of a storage phosphor system. Two anatomic features of the stifle joint and five anatomic structures of the thorax were evaluated. The two medical‐grade monitors had superior display quality compared with standard PC monitors. No differences were seen between the monochrome monitors. In comparison with the color CRT, the ratings of the color LCD were significantly worse. The ranking order was uniform for both the region and the criteria investigated. Differences in monitor luminance, bit depth, and screen size were presumed to be the reasons for the observed varying performance. The observed differences between monitors place an emphasis on the need for guidelines defining minimum requirements for the acceptance of monitors and for quality control in veterinary radiography.     

A REVIEW OF PORTAL SCREEN-FILM TECHNOLOGY AND FIVE RADIOLOGISTS' EVALUATIONS OF SOME EXISTING PRODUCTS

Portal radiographs, radiographs made to document the accuracy of radiotherapy treatment fields, are typically of poor image contrast. Recently, a new portal film and screened-cassette system was marketed, the Kodak EC-L system, with the claim of greatly improved image contrast. This new EC-L system was tested on a canine cadaver exposed to Cobalt-60 teletherapy gamma radiation, and image quality was compared to earlier marketed Kodak portal film products. The EC-L system was found to provide portal images of improved contrast/quality.     

MAGNETIC RESONANCE IMAGING OF THE CANINE BRAIN AT 3 AND 7 T

Magnetic resonance (MR) imaging of the canine brain is commonly acquired at field strengths ranging from 0.2 to 1.5 T. Our purpose was to compare the MR image quality of the canine brain acquired at 3 vs. 7 T in dogs. Low‐resolution turbo spin echo (TSE) T2‐weighted images (T2W) were obtained in transverse, dorsal, and sagittal planes, and high‐resolution TSE T2W and turbo spin echo proton density‐weighted images were obtained in the transverse and dorsal planes, at both 3 and 7 T. Three experienced reviewers evaluated 32 predetermined brain structures independently and without knowledge of field strength for spatial resolution and contrast. Overall image quality and evidence of artifacts were also evaluated. Contrast of gray and white matter was assessed quantitatively by measuring signal intensity in regions of interest for transverse plane images for the three pulse sequences obtained. Overall, 19 of the 32 neuroanatomic structures had comparable spatial resolution and contrast at both field strengths. The overall image quality for low‐resolution T2W images was comparable at 3 and 7 T. High‐resolution T2W was characterized by superior image quality at 3 vs. 7 T. Magnetic susceptibility and chemical shift artifacts were slightly more noticeable at 7 T. MR imaging at 3 and at 7 T provides high spatial resolution and contrast images of the canine brain. The use of 3 and 7 T MR imaging may assist in the elucidation of the pathogenesis of brain disorders, such as epilepsy.     

THE EFFECT OF A TECHNICAL QUALITY ASSESSMENT OF HIP‐EXTENDED RADIOGRAPHS ON INTEROBSERVER AGREEMENT IN THE DIAGNOSIS OF CANINE HIP DYSPLASIA

Experienced and inexperienced observers evaluated the assessability of 50 radiographs (25 dogs) and determined the hip status (dysplasia/nondysplasia and final scoring according Fédération Cynologique Internationale [FCI]‐criteria) individually. A radiographic technical quality assessment was performed in a separate reading session. Interobserver agreement in determining dysplasia/nondysplasia and FCI‐scoring did not significantly increase with the increasing quality of a radiograph, irrespective whether these observers are experienced or not. There was a significant agreement between the technical quality assessment and assessability (P<0.0005). Despite the effort to objectify radiographic quality and to present high‐quality radiographs to observers, interobserver agreement on dysplasia/nondysplasia and final scoring, remains low, even in the experienced group. Although increased radiographic quality narrows the range of scoring, the range remains unacceptably high.     

THE EFFECT OF DEXMEDETOMIDINE ON RADIOGRAPHIC CARDIAC SILHOUETTE SIZE IN HEALTHY CATS

Dexmedetomidine, an alpha₂‐adrenergic agonist, may be used in companion animals for chemical restraint, including cardiac evaluation. Echocardiographic changes associated with alpha₂‐adrenergic agonists have been described; however reports of radiographic changes in cats were not found at the time of this study. Aims of this observational, prospective, experimental study were to describe the effects of dexmedetomidine on the radiographic appearance of the cardiac silhouette in healthy, adult cats. Fourteen healthy adult cats received dexmedetomidine 40 mcg/kg IM. Right lateral, left lateral, ventrodorsal, and dorsoventral thoracic radiographs were obtained for each cat at three time points: presedation, intrasedation, and postsedation (≥ two hours after reversal with atipamezole). Radiographs were evaluated in a blinded, randomized fashion by two independent observers using the vertebral heart score on all four views, the number of intercostal spaces on lateral projections, and the percent width of thorax on ventrodorsal and dorsoventral projections. Median vertebral heart score on right lateral view was significantly increased intrasedation (median = 7.8; range = 7.25–8.25) compared to presedation (median = 7.5; range = 7–8 [P = 0.001]). Median percentage width was significantly higher intrasedation (70% on VD; range 65–80 [P = 0.001], and 75% on DV; range 65–80 [P = 0.006]) compared to presedation (65%; range 65–75 on both projections). Dexmedetomidine was associated with a small but significant increase in cardiac silhouette size on right lateral (vertebral heart score), ventrodorsal (percentage width), and dorsoventral (percentage width) radiographs in healthy adult cats. This effect should be taken into consideration for future interpretation of thoracic radiographs in dexmedetomidine‐sedated cats.     

Multi‐modality diagnostic imaging of a cervical articular process fracture in a Thoroughbred horse including a novel C‐Arm imaging technique

Interpretation of cervical radiographs can be challenging due to the complex anatomy and superimposition of osseous structures on either side of the vertebrae. This report describes the investigation of neck pain in a Thoroughbred gelding following a traumatic fall. Several imaging modalities were used to demonstrate the presence of a fracture of the left cranial articular process of the fourth cervical vertebra (C4), including nuclear scintigraphy, ultrasonography, oblique radiographic projections and a novel cineradiographic technique. Oblique radiographs were superior to standard lateral‐lateral radiographs in both the diagnosis and for monitoring the progression of healing of the articular process fracture in this case.     

Digital measurement of radiographic tibial plateau angle. A comparison to measurement on printed digital images.

Pre-operative digital radiographs from 50 dogs undergoing a tibial plateau leveling osteotomy were evaluated. Tibial plateau angles were measured directly on printed films and measured on digital images using two different commercial DICOM viewers. The radiographs were scored for osteoarthritis and positioning. Using pooled results, the mean TPA from the digital images employing Web1000 (26.47 degrees +/- 3.90) was significantly higher then the mean TPA using film radiographs (25.41 degrees +/- 3.51), or IQ-View Pro (25.48 degrees +/- 3.89). There was not a significant difference between mean TPA using radiographs or IQ-view. Digital TPA measurement using built-in angle calipers in the clinical setting is a valid technique compared to measurements from film radiographs, and produces reproducible results. However, before changing to digital measurements, the chosen software programme should be validated against measurements using film radiographs to determine the magnitude of differences.     

Unipodal stance influences radiographic evaluation of foot balance in horses

Lifting the contralateral forelimb (unipodal stance) is often used as a method of restraint in horses. This experimental one group pretest, posttest study was conducted to evaluate the effects of unipodal stance on quantitative radiographic parameters in equine forefeet. Seven nonlame horses were randomly selected. Lateromedial (LM) and dorsopalmar (DP) projections were acquired for both forefeet, squarely placed on blocks, using two X‐ray generators. Radiographs of each foot were acquired first in a bipodal stance, immediately followed by the same radiographic projections obtained in a unipodal stance. The following measurements were recorded for each stance: distal interphalangeal joint (DIPJ) space width on both projections; mediolateral joint balance as the difference between lateral and medial DIPJ space widths on DP projections; extensor process‐to‐middle phalangeal condyle distance; and deep digital flexor tendon angle on LM projections. A matched pairs design and Student's t‐test with a 95% confidence level were used to test for statistical significance. Compared to a bipodal stance, lateral DIPJ space width was significantly reduced on unipodal DP views, whereas mediolateral joint imbalance and to a lesser extent medial DIPJ space width were significantly increased. On unipodal LM views, there was a significant higher degree of DIPJ flexion. These findings suggest that stance should be carefully taken into consideration when measuring radiographic parameters in equine forefeet, especially if assessing foot balance and conformation, as unipodal stance significantly affects the mediolateral balance of the DIPJ on DP radiographs and significantly alters the phalangeal axis on LM radiographs.     

INITIAL INFLUENCE OF RIGHT VERSUS LEFT LATERAL RECUMBENCY ON THE RADIOGRAPHIC FINDING OF DUODENAL GAS ON SUBSEQUENT SURVEY VENTRODORSAL PROJECTIONS OF THE CANINE ABDOMEN

Identification of the duodenum and potential abnormalities on survey abdominal radiographs is often difficult unless it contains gas. This study investigated the effect of patient positioning on the presence of duodenal gas in survey abdominal radiographs. One hundred dogs receiving a three‐view survey abdominal radiographic study were enrolled in a prospective, randomized study where all dogs were divided into two groups. Group A (n = 51) dogs had a left lateral projection first, followed by a ventrodorsal projection, ending with a right lateral projection. Group B (n = 49) dogs had a right lateral projection first, followed by a ventrodorsal projection, ending with a left lateral projection. The presence of gas within the duodenum and level of distribution of gas throughout the duodenum were recorded for all three projections. In addition, the presence or absence of duodenal pseudoulcers was evaluated on all three projections for each dog. The results for the two groups were compared using Chi‐square analysis with a P‐value of less than 0.05 being considered significant. Results showed that dogs first placed in left lateral recumbency were significantly more likely to have duodenal gas on the subsequent ventrodorsal and right lateral radiographic projections compared to dogs first placed in right lateral recumbency (P‐value < 0.0001). Pseudoulcers were seen in 11 dogs that had duodenal gas making the visualization of pseudoulcers on survey abdominal radiographs somewhat commonplace. This study emphasizes the benefit of using initial left lateral abdominal projections prior to other views for subsequent evaluation of the duodenum.