Radiographic measurement of femorotibial rotation in weight-bearing. The influence of flexion and extension in the knee on the extensor mechanism and angles of the lower extremity in a healthy population.

PURPOSE: A system for examination and measurement of the weight-bearing knee was developed earlier on examination equipment used for QUESTOR Precision Radiography (QPR), adapted to computed radiography and to a picture archiving and communication system. In this study the same system was used to develop a method to define "patellar variables" including measurements of the rotation of the femur and the tibia and the patellar translation, between semiflexion and extension, as well as the Q-angle. The aim of this study was to evaluate the reproducibility of these patellar variables and also to establish "normal" reference values for both the patellar variables and the variables in the original QPR system. MATERIAL AND METHODS: For evaluation of the reproducibility 10 volunteers with healthy knees were examined twice. To obtain the reference values, 80 volunteers with healthy knees, 10 females and 10 males within each decade between 20 and 59 years of age, were examined. RESULTS AND CONCLUSION: The reproducibility of the rotation of the femur and the tibia and of the Q-angle was 2--3 degrees (SD) and of the patellar translation about 3 mm (SD). The result from the healthy volunteers will be a useful tool for evaluation of disorders in the knee joint.

Femorotibial rotation and the Q-angle related to the dislocating patella.

PURPOSE: To compare the femorotibial rotation, the patellar translation, the hip-knee-ankle angle and the Q-angle in patients with a dislocation of the patella with those of healthy volunteers. Further, the clinically measured Q-angle was compared to that measured by radiography. MATERIAL AND METHODS: A system for measurement of patellar variables was previously developed and applied to 80 healthy volunteers. In the present study, 28 patients (20 women, 8 men) with dislocation of the patella were examined bilaterally. Fourteen patients had habitual dislocations (20 affected knees) and 14 patients traumatic dislocations (17 affected knees). In 20 patients the clinical Q-angle was measured bilaterally by an orthopaedic surgeon and in 9 of these patients also by a second independent orthopaedic surgeon. RESULTS: The most striking finding was that dislocating knees in both groups showed a smaller Q-angle than the healthy knees. Further, the habitual group showed greater relative rotation between the tibia and the femur and an increased patellar translation compared to the traumatic group and to the healthy volunteers. There was a poor correlation between clinical and radiographic measurements of the Q-angle and no correlation was found between two independent clinical measurements. CONCLUSION: Surgical operations aiming at decreasing the Q-angle should be challenged.

Radiation dose and image information in computed radiography. A phantom study of angle measurements in the weight-bearing knee.

PURPOSE: To establish a correlation between radiation dose and diagnostic accuracy when employing a new digital method for angle determinations. The specific intention was to determine how far the radiation dose can be reduced without losing measuring accuracy and to compare this radiation dose with that employed with our conventional method. MATERIAL AND METHODS: An image succession of an anthropomorphic phantom was generated with a computed radiography (CR) system, by reducing the exposure stepwise. The images were archived and transferred to a workstation for evaluation. The intraobserver variation of two angle determinations was used as an indicator of the evaluation accuracy. Patient radiation doses were measured with thermoluminescent dosimeters. The energy imparted, indicating the relative risk associated with exposure to ionising radiation, and the effective dose, which determines the absolute risk, were calculated. RESULTS AND CONCLUSION: No significant correlation was found between patient dose and measuring accuracy within the evaluated exposure interval. At the lowest exposure of the CR system, the energy imparted to the patient was 30 microJ. Compared with our conventional analogue method this is a reduction by 98%. The effective dose was as low as 1.5 microSv. The CR technique creates possibilities to adapt exposure parameters, and thus the radiation dose to the patient, according to the purpose of the investigation.

Assessment of image post-processing and of measuring assistance tools in computed radiography. Evaluation of the weight-bearing knee.

PURPOSE: A system for the examination and measurement of the weight-bearing knee was adapted to computed radiography (CR) and to a picture archiving and communication system (PACS). The examination and measurement system was developed on examination equipment used for QUESTOR precision radiography (QPR). For an easier and more standardised localisation of bony landmarks on the screen, 4 measuring assistance tools (MATs) were developed. The aim of this study was to evaluate the usefulness of the tools developed and of image post-processing, specifically as magnification (zoom) and filtering (edge enhancement), by determining intra-observer variation in the measurement of angles and distances. MATERIAL AND METHODS: The original QPR measurement program, generating 19 angles and distances corrected for parallax and magnification, was converted and installed on a multi-modality workstation (Imtec Image 1200). A CR system (Fuji AC-2) was used for the generation of the related images and the measurements were made on the workstation. Four unilateral examinations of weight-bearing knees were undertaken. These examinations were measured twice under 5 different measurement conditions by 4 viewers. RESULTS AND CONCLUSIONS: The most important factor in reducing intra-observer variation was the ability to magnify (zoom) the images. The MATs also reduced variation. Filtering (edge enhancement), however, did not affect precision.

Computed radiography for characterisation of the weight-bearing knee.

PURPOSE: A new method for examining and measuring the weight-bearing knee in computed radiography (CR) and picture archiving and communication systems (PACS) has recently been developed on examination equipment used in QUESTOR Precision Radiography (QPR). QPR is a method for the standardised examination of the knee, and generates 9 angles (e.g. hip-knee-ankle (HKA) angle) and 10 distances, corrected for parallax and magnification. The aim of this present study was to evaluate the reproducibility of this newly developed method and to determine intra- and interobserver variation in its measurements. MATERIAL AND METHODS: The images were generated on a CR system, archived, and transferred to a multimodality work-station that had a monitor with a resolution of 1280x1024 (1kx1k). Photostimulable phosphor plates were used to generate images with a matrix of 1760x2140 pixels (pixel size 0.2 mm, corresponding resolution 2.5 1p/mm). Ten volunteers without knee problems were examined twice, bilaterally, by 2 different radiology technologists. RESULTS: The total reproducibility of the method was good, offering an HKA reproducibility of +/-2.64 degrees in slight flexion and +/-1.62 degrees in extension, at 95% confidence. The intra- and inter-observer variations were low with a reduction of the intra-observer variations in all measurements (except one) by a factor of 2.8 on average compared with the original QPR method for conventional film-screen radiography. CONCLUSION: When QPR is modified for CR, it fulfils the requirement of reproducibility in measurements of the weight-bearing knee.

Contrast-enhanced radiography by differential absorption, using a laser-produced x-ray source.

RATIONALE AND OBJECTIVES: The authors evaluate the feasibility of differential imaging of contrast media, with division of individual pixel values obtained from digital images generated by characteristic radiation from a laser-produced plasma, bridging the K-absorption edge of the contrast agent. METHODS: Laser pulses from an ultrashort-pulse terawatt laser system were focused onto gadolinium and tantalum targets, creating a plasma from which characteristic radiation and Bremsstrahlung was emitted. The elements of the target were selected so the characteristic emission lines of one of the elements were below the K edge of the contrast agent and the emission lines of the other element above. A phantom with gadolinium and other elements in various concentrations was examined. One radiographic exposure was made using a gadolinium target source and a subsequent exposure using a tantalum source. Both images were recorded digitally and the transmission ratios calculated by division of the individual pixel values. RESULTS: When viewed separately, the two images of the test phantom appeared similar. In the differential image, only the gadolinium solutions were bright, reflecting a difference in attenuation between the two exposures. CONCLUSIONS: Element-specific radiographs can be obtained by differential imaging. When fully explored, the technique may allow for contrast-enhanced radiography with increased sensitivity and decreased contrast dose.

Spatial resolution requirements in digital radiography of scaphoid fractures. An ROC analysis.

PURPOSE: To investigate the spatial resolution requirements in digital radiography of scaphoid fractures. MATERIAL AND METHODS: Included in the study were 60 scaphoid radiographs with and 60 without fractures of the scaphoid bone. The film-screen images were digitized using pixel sizes of 115, 170, and 340 microns along with 170 microns with a 10:1 wavelet compression. The digital images were displayed on a 1280 x 1024 x 8 bits monitor, and 5 observers evaluated the images in 5 randomized sessions. The results for each pixel size were then compared to the film-screen images by ROC analysis. RESULTS: The mean area under the ROC curves was larger for the film-screen images than for the digital images at all resolutions. However, this difference was not significant when the areas under the ROC curves for the film-screen images were compared to the digital images of 115, 170, and 170 microns with 10:1 compression. There was a significant difference for the 340-microns pixel size in favour of the film-screen images. The mean ROC curves for the digital images were very similar for the 115 and 170 microns pixel sizes, although slightly better for 115 microns. At 170 microns, the compression seemed to have a relatively small negative effect on the diagnostic performance; the deterioration was greater when the pixel size was increased to 340 microns. There was no obvious correlation between diagnostic performance and the experience of the observers in using work-stations. CONCLUSIONS: The pixel size of 170 microns is adequate for the detection of subtle fractures, even after wavelet compression by a ratio of 10:1.

PACS for radiology conferences--improvement of application software.

The introduction of PACS in a radiology department means that most functions that are available in the film-based system must be included. One important function is the radiology conference. The handling and application programs of digital workstations are normally not developed for demonstrations of many images in a limited time. This paper describes a workstation with specially designed software for radiology conferences. The application is separated in preparation and presentation of the cases to be demonstrated. Very fast image handling is achieved during the conference because the function is based on the principle of prefetching of the selected images. The images are presented on a large screen with high resolution. The experiences of digital radiology conferences are good. However, reference films from previous examinations create extra work because they have to be shown on the conventional lightbox.

Generation of x rays for medical imaging by high-power lasers: preliminary results.

PURPOSE: To evaluate the use of x-ray imaging performed with a high-power laser system in biologic and medical studies. MATERIALS AND METHODS: A compact terawatt laser system based on chirped pulse amplification in titanium-doped sapphire was used. X rays were generated by irradiating a high-atomic-number target (tantalum). RESULTS: When photons with an energy below 10 keV were removed with use of 3 mm of aluminum, the half-value layer in aluminum for the remaining x rays was approximately 10 mm. The x-ray source allowed performance of biologic magnification radiography. Star-pattern tests indicated an equivalent focal spot size of less than 60 microns. Exposures of a single pulse could be obtained. The duration of a single x-ray pulse was estimated to be of the order of picoseconds. CONCLUSION: With use of subpicosecond laser pulses, x-ray generation can occur with a smaller equivalent focal spot size than with conventional x-ray sources.

Intra-operative digital angiography as a control of the in situ saphenous vein by-pass grafts.

Forty-two patients undergoing in situ saphenous vein by-pass grafting procedures, in two patients bilaterally, were examined intra-operatively with digital subtraction angiography. In 19 (43%) of the examinations the graft and the anastomoses appeared adequate. In 8 cases (18%) significant abnormalities were found, including stenoses (11%), deficient anastomoses (5%) and graft kinking (2%). Remaining arteriovenous fistulas were found in 17 patients (39%). In most cases immediate correction was possible avoiding later re-operation. At follow up 11 of the 44 grafts were occluded, 10 of these during the first five months and of these five during the first week.

Digital subtraction angiography with bandpass filtration during by-pass operation.

Experience is reported on a simple, inexpensive video processor for angiographic control during operation. In 6 patients with graft complications instant operative corrections could be performed.

Absorbed doses at CT of the kidneys and at urography.

Radiation doses to the skin, ovaries and testes were measured at urography and CT examinations of the kidneys and adrenals. The absorbed dose to the breasts and bone marrow at CT was estimated as well as the mean bone marrow dose at urography. The results were compared with previous measurements of absorbed doses and energy imparted at abdominal angiography including nephroangiography. CT of the kidneys involves a considerably lower risk for late biologic effects to the patient than urography and, in particular, angiography.