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OBJECTIVE: To compare fluoroscopic freeze-frame digital images with conventional 105-mm spot films during voiding cystourethrography (VCUG) with regard to diagnostic quality and radiation dose. MATERIALS AND METHODS: VCUG was performed on 57 consecutive children by a commercially available fluoroscopic digital system. Both freeze-frame digital images and conventional 105-mm spot films were obtained during 90 s of fluoroscopy. Skin radiation dose was assessed separately for spot films and for both fluoroscopy and spot films, employing thermoluminescent crystals on the anterior surface of the body. Patients were classified into three age groups: group A younger than 12 months, group B 1-5 years old and group C 5-12 years of age. RESULTS: Digital and conventional images provided diagnostically identical results in 108 out of 114 ureters examined (94.7%). Percentage reductions in skin radiation dose due to the fluoroscopic hard copies compared with the four 105-mm radiographs were 53.8%, 50.5% and 57.1% for groups A, B and C, respectively. CONCLUSION: Substitution of conventional 105-mm spot films during VCUG with digital fluoroscopic hard copies resulted in a substantial reduction in radiation dose. Digital images were as accurate as the conventional films in excluding vesicoureteric reflux (VUR). The two methods correlated well in diagnosing and grading VUR.     

Occupational medicine aspects of nasal diseases]

PURPOSE: The relations between image quality in last image hold images and dose in grid controlled fluoroscopy in comparison to the continuous mode need to be characterised and recommendations for the clinical application of this technique should be given. MATERIAL AND METHODS: Spatial resolution, signal-noise ratio and, contrast-detail visibility were evaluated by phantom measurements in grid controlled pulsed and continuous fluoroscopy. Dose was measured at the image intensifier entrance. Image quality of last image hold (LIH) images of clinical examinations was graded in relation to single shot exposures. RESULTS: Signal-noise ratio and contrast-detail visibility depend on the dose per puls. Spatial resolution and contrast-detail visibility in grid controlled fluoroscopy are superior than to in the continuous mode. Image quality of the LIH images from the grid controlled fluoroscopy was improved. Radiation exposure could be reduced to 10-46%. CONCLUSIONS: Combinations of puls-dose and -frequency are recommended for achieving extensive dose reduction and improved image quality of LIH images.     

X-ray imaging using amorphous selenium: feasibility of a flat panel self-scanned detector for digital radiology

We investigate a concept for making a large area, flat-panel detector for digital radiology. It employs an x-ray sensitive photoconductor to convert incident x-radiation to a charge image which is then electronically read out with a large area integrated circuit. The large area integrated circuit, also called an active matrix, consists of a two-dimensional array of thin film transistors (TFTs). The potential advantages of the flat-panel detector for digital radiography include: instantaneous digital radiographs without operator intervention; compact size approaching that of a screen-film cassette and thus compatibility with existing x-ray equipment; high quantum efficiency combined with high resolution. Its potential advantages over the x-ray image intensifier (XRII)/video systems for fluoroscopy include: compactness; geometric accuracy; high resolution, and absence of veiling glare. The feasibility of the detector for digital radiology was investigated using the properties of a particular photoconductor (amorphous selenium) and active matrix array (with cadmium selenide TFTs). The results showed that it can potentially satisfy the detector design requirements for radiography (e.g., chest radiography and mammography). For fluoroscopy, the images can be obtained in real-time but the detector is not quantum noise limited below the mean exposure rate typically used in fluoroscopy. Possible improvements in x-ray sensitivity and noise performance for the application in fluoroscopy are discussed.     

Evaluation of a new low-dose digital x-ray device: first dosimetric and clinical results in children

BACKGROUND: A new low-dose digital X-ray device, based on Charpak's Nobel prize-winning multiwire chamber, enables the production of images at very low doses. Objectives. To present the first dosimetric and clinical results. MATERIALS AND METHODS: The analysis was performed on 93 children with scoliosis and 47 undergoing pelvic radiography. The comparative study between conventional X-ray and the new technique focused on three points: (1) the dose delivered by each system (2) the diagnostic information provided by each system and (3) comparison of image quality criteria with European guidelines. RESULTS: The mean ratio of conventional dose to that of the low-dose technique was 13.1 for the spinal examination and 18.8 for the pelvis. There was no significant difference in diagnostic information available from each modality, but there was a slight difference in quality criteria in favour of the conventional technique. CONCLUSION: This new device allows spectacular dose reduction, consistent with adequate clinical information. Improvements of the prototype will lead to extension of potential indications and industrial development.     

Long-term outcome after sagittal synostosis operations

PURPOSE: Optimization of image quality by use of digital luminescence radiography (DLR) in voiding cystoureterography (VCU) instead of a conventional screen film system. PATIENTS AND METHODS: 53 patients with a suspected vesicouretral reflux were examined with a VCU in analogous and digital technique. The X-rays were taken in a sitting position while simultaneously measuring the bladder pressure. An intraindividual comparison was omitted for X-ray saving reasons. In the follow-up 3 patients were examined with the other system. Two radiologists and two urologists compared 60 VCU of 53 patients--30 VCU in conventional screen film and 30 in DLR technique presented in standard and edge-enhanced images--with regard to image quality according to 3-step score (A--good image quality, B--sufficient image quality, C--insufficient image quality). RESULTS: The 59 conventional films were scored 72 times with an A, 76 times with a B, and 72 times with a C, whereas the DLR films were scored 116 times with an A, 72 times with a B, and only 8 times with a C. Hereby the edge-enhanced images were the most useful for distinguishing the bladder shadow from the soft tissue of the thigh and for detecting reflux. Furthermore, the exposure dose when applying DLR could be decreased to 75% in grown-ups and to 57% in children without any significant loss of information. CONCLUSION: The DLR is highly superior to the conventional film screen system because of its relatively high tolerance towards wrong exposures, especially with respect of the sitting position during MCU. With the DLR we obtained 96% and with the conventional system only 63% films usable for diagnosis.     

Imaging factors and image optimization

Optimization of dose and image quality is task-dependent. The three main image quality parameters, sharpness, contrast, and noise, are interdependent in radiographic systems. The need to minimize patient dose imposes further couplings between these factors. This is the reason why there are no universally applicable imaging systems.     

Tailored low-dose fluoroscopic voiding cystourethrography for the reevaluation of vesicoureteral reflux in girls

OBJECTIVE: Radionuclide voiding cystography is generally advocated for the reevaluation of proved vesicoureteral reflux. The purpose of this study was to assess the efficacy of tailored low-dose fluoroscopic voiding cystourethrography for this purpose. SUBJECTS AND METHODS: Forty-five girls (2 years 9 months to 19 years 7 months old; mean, 7.4 years) who had proved reflux were examined with tailored low-dose voiding cystourethrography. The technique used a low-dose fluoroscopic system and a computer-based video frame grabber that produced frame-averaged digital video fluoroscopic hard copies. A tailored voiding cystourethrographic protocol was designed to minimize ovarian radiation dose. Digital images were compared with standard 105-mm spot films in a similar group of 25 children. RESULTS: The tailored low-dose fluoroscopic technique produced diagnostically adequate images in all patients that were comparable in quality to standard spot films. The ovarian dose was 1.7-5.2 mrad (0.017-0.052 mGy) with a mean of 2.9 mrad (0.029 mGy). This compared favorably with the lowest reported doses with the radionuclide technique. CONCLUSION: Tailored low-dose fluoroscopic voiding cystourethrography is an attractive and practical alternative to the radionuclide technique in girls with proved vesicoureteral reflux.     

On-line portal imaging: image quality defining parameters for pelvic fields--a clinical evaluation

PURPOSE: A test of several image enhancement techniques, performed on on-line portal images in real clinical circumstances, is presented. In addition a score system enabling us to evaluate image quality on pelvic fields is proposed and validated. METHODS AND MATERIALS: Localization images (n = 546) generated by an on-line portal imaging system during the treatment of 13 patients on pelvic fields were obtained by delivering a radiation dose of 6-8 cGy by an 18 MV photon beam, and recorded with a silicon intensified target video camera with adjustable gain, kV- and black level. Set-up errors were corrected before continuing irradiation. A scoring system based on the number of visible bone-soft tissue edges and transformed to a scale 0 to 5 was developed to judge image quality. A validation of this classification of images was performed with the use of transsectional bone-densities (bone-density*radiological path length) specified at the score defining landmarks. A high pass filter was used on all images, additional on-line open field subtraction was performed on 242 fields. Off-line study was performed in which a panel consisting of two groups (one composed of three radiation oncologists, the other of three radiotherapy technologists), scored 470 pelvic fields without further enhancement, and the same images with Contrast Limited Adaptive Histogram Equalization (CLAHE) (Pizer et al.). Two different clipping levels (3.0 and 5.0) were studied. RESULTS: Gender and transsectional bone-densities were the most defining patient-related factors influencing image quality. Camera settings, gantry angle, and image post-processing were important non-patient-related factors. All investigators judged CLAHE to ameliorate low contrast images and to deteriorate good quality images (p < 0.001).     

Low-dose radiography of scoliosis in children. A comparison of methods

STUDY DESIGN: Records of 1,582 conventional and computed radiographic examinations performed to evaluate scoliosis were reviewed and compared to determine differences in total radiation burden. OBJECTIVE: This study evaluated the impact of computed radiographic imaging (CRI) on radiation exposure in children undergoing serial spinal radiographs for scoliosis assessment and compared exposure from CRI with that of low-dose film-screen combinations. SUMMARY OF BACKGROUND DATA: CRI permits diagnostic radiographic studies to be performed with a dose reduction of 80%-95% compared to conventional film-screen systems. High speed film-screen systems also permit a significantly lower exposure. Each approach has unique advantages and disadvantages. METHODS: Over 6 years, we performed 1,582 spinal examinations in children 4-14 years old using reduced dosage techniques with computed radiography. The images were obtained with Fuji FCR 101 and Philips PCR/SP systems. The adequacy of diagnostic image quality in the serial evaluation of scoliosis at different exposure levels was evaluated and compared with regular and film-screen systems with speeds ranging from 250 to 1,200. RESULTS: Diagnostic-quality images for evaluating scoliosis can be obtained with doses of 5% or less than required with conventional film-screen systems. Computed radiography provides image quality and dose reduction comparable to a 1,200-speed film-screen system. CONCLUSION: CRI gives satisfactory images at 5% reduction of the standard film-screen dose. Based on comparison with a 1,200 speed film-screen system, CRI provides equal or better image quality at a similar radiation dose. The cost of CRI is higher than for film-screen radiography, but wide latitude and the ability to tailor dose with requirements for image quality are significant advantages for CRI.     

MR cholangiopancreatography of pancreaticobiliary diseases: comparing single-shot RARE and multislice HASTE sequences

OBJECTIVE: In this study, we compared the single-shot rapid acquisition with relaxation enhancement (RARE) sequence with the multislice half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence to assess the ability of each technique to show various pancreaticobiliary diseases using MR cholangiopancreatography. SUBJECTS AND METHODS: MR cholangiopancreatography was performed using both the single-shot RARE and the multislice HASTE pulse sequences in 80 consecutive subjects in whom we had proof of a range of diagnoses. The study population included healthy subjects (n = 9), patients with benign lesions (n = 41), and patients with malignant lesions (n = 30). We analyzed each image using the following criteria: the cause of the lesions, the image quality (i.e., the amount of artifact and the sharpness of anatomic structures such as the right and left hepatic ducts, the extrahepatic bile duct, and the main pancreatic duct), and the reviewers' preference of images. The images were evaluated independently by two radiologists who were unaware of the results of the other cholangiopancreatographic sequence and of the diagnosis. RESULTS: Artifacts were less prominent in images that were obtained using the single-shot RARE sequence (p = .0192); however, the sharpness of anatomic structures was the same using either sequence (p = .1673). For images that were obtained using the single-shot RARE technique, the sensitivity, specificity, and accuracy in distinguishing malignant from other abnormalities were 83%, 78%, and 80%, respectively; for the multislice HASTE technique, these values were 77%, 72%, and 74%, respectively (p > .05). Disease-specific accuracy in determining the correct diagnosis was 54% and 59%, respectively (p > .05). In patients in whom all the ducts needed to be defined, the single-shot RARE technique was preferred to the multislice HASTE technique (p < .01). CONCLUSION: The single-shot RARE technique shows fewer artifacts and is preferred to the multislice HASTE technique. However, both techniques show the same degree of sharpness of anatomic structures, both are able to reveal malignant diseases, and both provide enough information to determine a specific diagnosis.     

Evaluation of image quality using 1 : 1 pitch and 1.5 : 1 pitch helical CT in children: a comparative study

OBJECTIVE: The objective of this study was to compare the quality of 1 : 1 and 1.5 : 1 pitch helical contrast-enhanced thoracic and abdominal CT images in children who cannot cooperate for breath holding. MATERIALS AND METHODS: This is a retrospective study of 33 contrast-enhanced CT examinations in 11 children of 0-4 years of age. All children had an initial CT study using 1 : 1 pitch helical scanning followed over the next 6-36 months by one to four CT examinations with 1.5 : 1 pitch. Radiation dose with the two techniques was measured with a pencil ionization chamber. RESULTS: The two techniques provided comparable overall image quality. There was 33 % less radiation dose with 1.5 : 1 pitch helical scanning. CONCLUSION: The 1.5 : 1 pitch helical CT provides comparable quality images and a smaller radiation dose than 1 : 1 pitch in examining children aged 0-4 years.     

Visualization of colorectal polyps with spiral CT colography: evaluation of processing parameters with perspective volume rendering

PURPOSE: To evaluate two key processing steps for detection of colon polyps with spiral computed tomographic (CT) colography with perspective volume rendering (PVR): image reconstruction and opacity assignment of the attenuation data. MATERIALS AND METHODS: Spiral CT was performed in 10 patients with known polyps confirmed at colonoscopy, and detailed quantitative analyses were performed of data obtained in four. First, anatomic fidelity of three-dimensional (3D) images generated from two-dimensional (2D) source images with equal voxel dimensions (87%-90% overlap) was compared with 3D images generated from 2D source images with unequal voxel dimensions (0%-80% overlap). Next, the relative dimensions of colorectal polyps to adjacent structures were evaluated for various opacity threshold settings. Then, step and sigmoidal opacity functions were compared with respect to image smoothness and edge sharpness. RESULTS: PVR images generated after interpolation of image data reconstructed with at least 60% overlap were equivalent in image quality to PVR images generated from source images with equal voxel dimensions. Relative polyp-to-haustral fold dimensions demonstrated substantial distortions with opacity thresholds below -700 HU. The 3D PVR images generated with the sigmoidal opacity function were significantly smoother than those generated with the step opacity function (paired t test, P < .02), with small differences noted in edge sharpness. CONCLUSION: Use of highly overlapping source images (87%-90%) was not necessary to generate 3D PVR images of colorectal polyps. Image artifacts were suppressed with use of an appropriate opacity threshold and a sigmoidal opacity function without substantial loss in edge sharpness.     

Storage phosphor direct magnification mammography in comparison with conventional screen-film mammography--a phantom study

Contact mammography with current photostimulable storage phosphors is hampered by its low spatial resolution. Detail visualization can be improved by geometric magnification radiography which enlarges small details to exceed inherent image noise. This study compares storage phosphor mammography using a dedicated direct magnification system with state-of-the-art conventional screen-film mammography. Storage phosphor direct magnification survey views (1.7x) and spot views (4x) were obtained with a prototype mammography unit providing focal spot sizes of 120-40 microns. Conventional technique screen-film survey views (1.1x) and spot views (1.8x) served as comparison. A contrast detail study and a receiver operating characteristic (ROC) analysis using an anthropomorphic breast phantom with superimposed microcalcifications was performed. Contrast detail resolution in the digital and conventional survey views were equivalent. For the spot views, contrast detail resolution was significantly higher with the digital technique (p < 0.001). ROC analysis of 400 observations demonstrated a significantly higher performance (p < 0.001) with digital images versus conventional screen-film mammograms. The area under the ROC curve (Az) in the digital survey views was 0.76 +/- 0.07 versus 0.59 +/- 0.02 in the conventional technique. In digital spot views, Az was 0.82 +/- 0.07 as compared with 0.66 +/- 0.04 in the conventional spot views. These results suggest that storage phosphor digital mammography in conjunction with direct geometric magnification technique may be superior to conventional screen-film mammography in the detection of microcalcifications.     

(+)-SKF-10,047 and dextromethorphan ameliorate conditioned fear stress via dopaminergic systems linked to phenytoin-regulated sigma 1 sites

OBJECTIVE: To assess the dynamic range of radiological images captured with a personal computer frame-grabbing system coupled to an X-ray fluoroscopy machine. METHODS: A 386DX-40 MHz, IBM compatible, computer with an SVGA monochrome graphics subsystem and a 387 co-processor, installed with a Screen Machine frame-grabber and controlled by a program specially written was used. Various systems were examined and the observer's perceptions of the results assessed. RESULTS: The dynamic range available to an ordinary X-ray fluoroscopy system was found to be restricted to about 750 mV. Similar measurements showed that the dynamic range was always restricted to 3/4-1/2 of the full available signal because of a high value of the dark voltage of the TV camera's target on all seven systems measured. The dynamic range of the computer-frame grabber system was found to be significantly wider than the Image Intensifier-TV camera chain but, surprisingly, it was affected by the type of file format used for image storing on disk. Clinical images from a barium meal examination as well as CT images captured after optimisation of the frame-grabber were found to contain large quantities of noise in the first two least significant bit planes making them redundant and limiting the grey levels needed for image display to less than 64. This number was also less than the 80 grey levels that could be discriminated by the human eye on the computer monitor. CONCLUSIONS: It was concluded that 6 bit digitisation would have been sufficient for image capture. The advantages of the wider dynamic range of the frame-grabber and the processing capabilities of the computer were tested for the possibility of improving the perception of detail. However, the results were negative. The limiting spatial resolution measured with a variable density bar pattern at all magnifications was about 0.4 lp/mm lower from that measured directly on the fluoroscopic screen. A detail perception test had the same result. The perception success was significantly lower with the digital images at all but the highest of the exposure rates and despite the use of image processing filters.     

Advanced multiple beam equalization radiography (AMBER) combined with computed radiography. Preliminary evaluation

The combined use of AMBER (Advanced Multiple Beam Equalization Radiography) and a digital storage phosphor (SP) radiography system was evaluated for chest radiography in a pilot study with 4 patients. Four image modes with different dose levels were compared: the SP in combination with an AMBER equalized exposure (SP/AMBER) and 3 nonequalized exposures with dose levels corresponding to the respective calculated AMBER lung dose (SP/lung field dose), the calculated AMBER mediastinal dose (SP/mediastinal dose) and the calculated AMBER average dose (SP/average dose). All image modes were matched for Hurter and Driffield characteristics and subjectively rated according to visibility of details. The improved signal-to-noise (S/N) ratio of SP/AMBER resulted in a better visualization of structures in the mediastinum and the basal lung where SP/lung field dose scored lowest. For the central lung no quality differences were seen between techniques. The compressed dynamic range of the SP/AMBER images was more easily displayed on the hard-copy film. The combination of AMBER with SP radiography promises to overcome the dynamic range limitations of digital displays while, at moderate doses, giving better S/N and image quality than standard SP technique.     

Multiplanar imaging in the preoperative assessment of metallic intraocular foreign bodies. Helical computed tomography versus conventional computed tomography

OBJECTIVE: This study aimed to compare the effectiveness of helical computed tomography (CT) versus conventional CT in the preoperative assessment of metallic intraocular foreign bodies on axial, coronal, and multiplanar reconstruction images in clinical routine. DESIGN: Prospective comparative trial, alternate assignment of consecutive patients. PARTICIPANTS: Eighteen patients with penetrating eye injuries and suspected metallic intraocular foreign bodies were studied. INTERVENTION: Alternate patients were assigned to undergo either helical CT or conventional CT in the axial plane. Both the helical and the conventional data were transferred to a workstation, and reconstructions in the coronal and sagittal planes were performed. Additional direct coronal scanning was performed only when necessary for preoperative assessment. MAIN OUTCOME MEASURES: The quality of the directly obtained axial and coronal, as well as the reconstructed coronal and sagittal images, was assessed for each, imaging method based on the ability to detect and accurately localize foreign bodies. The size of the foreign bodies was measured and compared to the actual diameter. Total examination time and radiation dose delivered to the lens were measured for each imaging method. RESULTS: All foreign bodies were detected by each scanning method on the axial, the coronal, and on the reconstructed planes. The quality of the axial images was similar for helical and conventional CT. The helical technique provided high-quality reconstructed images comparable in quality to the directly obtained coronal planes in conventional CT. Reconstructions by conventional technique were not useful for preoperative assessment. The examination time for the total orbital volume was 18 seconds for helical CT examinations and 52 seconds for conventional CT examinations. Radiation dose delivered to the lens for the complete examination was 35 mGy for helical CT axial scanning, 56 mGy for conventional CT axial scanning, and 63 mGy for conventional CT coronal scanning. CONCLUSIONS: Helical CT multiplanar imaging offers several significant advantages for the preoperative assessment of metallic intraocular foreign bodies compared to the conventional CT technique in clinical practice, including short examination time, reduced motion artifacts, reduced radiation exposure, and the ability to obtain diagnostically useful coronal and sagittal reconstruction images without the need for additional scanning.     

Focal pachypolymicrogyria in three siblings

Low-power bright field photomicrographs often suffer from insufficient sharpness, uneven illumination, and colour hues. Using a film scanner, commercially available and designed for digitizing 35-mm transparencies, we directly scanned microscopic slides that carried dye-labelled and stained sections. The digital images covered a field of up to 24 x 36 mm and revealed excellent sharpness, absolutely even illumination and superior colour reproduction as compared to conventional photomicrographs taken with binoculars, macro lenses, or microscopes. As the method requires neither specialized instrumentation nor expert knowledge of photomicrographic techniques, it reduces costs and saves time. The high-quality digital survey micrographs can easily be used for image processing, image analysis and morphometry. Thus, this new method is valuable not only for pathology, embryology, histochemistry, and the neurosciences, but also for the exchange of low-power micrographs via the internet and for computer media that are increasingly used in medical education.     

Use of computed radiography in the study of an historic painting

The authors demonstrate the use of radiography in the investigation of an historic painting and describe the potential benefits of computed radiography compared with conventional screen-film radiography. The subject for the comparison was a 16 x 19-foot oil-on-canvas painting, Scipio Africanus Freeing Massiva, by Giovanni Battista Tiepolo. Radiographs of the painting were obtained by using a portable, industrial radiographic unit and both conventional screen-film and photostimulable phosphor plate cassettes. For this investigation, computed radiography had a number of advantages over screen-film radiography, largely due to its wider dynamic range and its capabilities for enhancing the digital images with image processing tools such as magnification, edge enhancement, colorization, and airbrushing. The ability to electronically combine images from the large painting into a single composite image file was extremely valuable, as this technique was much less cumbersome and resulted in much higher quality composite images than could be achieved with conventional radiography. An additional advantage of computed radiography includes the capability to easily archive and transmit these images in a digital format for subsequent review.     

Retinal vessels before and after photocoagulation in diabetic retinopathy. Determining the diameter using digitized color fundus slides

BACKGROUND: Retinal vessel diameter is an important parameter in blood flow analysis. Despite modern digital image technology, most clinical studies investigate diameters subjectively using projected fundus slides or negatives. In the present study we used a technique to examine vessel diameters by digital image analysis of color fundus slides. We investigated in a retrospective manner diameter changes in twenty diabetic patients before and after panretinal laser coagulation. MATERIAL AND METHODS: Color fundus slides were digitized by a new high resolution scanning device. The resulting images consisted in three channels (red, green, blue). Since vessel contrast was the highest in the green channel, we assessed grey value profiles perpendicular to the vessels in the green channel. Diameters were measured at the half-height of the profile. RESULTS: After panretinal laser coagulation, average venous diameter was decreased, whereas arterial diameter remained unchanged. There was no significant relation between the diameter change and the number of laser burns or the presence of neovascularization. CONCLUSIONS: Splitting digitized images into color planes enables objective measurements of retinal diameters in conventional color slides.     

Clinical application of region-of-interest techniques to radiologic imaging

In region-of-interest (ROI) imaging, a filter with a central aperture is used to substantially reduce patient dose outside of an ROI while maintaining or improving image quality within the ROI. The benefits of ROI imaging can be realized by using standard imaging equipment. ROI imaging has been clinically applied to gastrointestinal radiology and interventional procedures. In gastrointestinal procedures, ROI fluoroscopy without image processing can be used without adversely affecting the procedure or interfering with spot radiography. ROI fluoroscopy can reduce the dose-area product by a factor of 1.7 for gastrointestinal procedures. In interventional neuroradiologic procedures, equalized display brightness is achieved with road mapping during fluoroscopy and with standard digital subtraction techniques during angiography. In interventional radiology, ROI filters can generally reduce the patient skin dose to levels below the threshold for skin effects, thus eliminating these effects across more than 85% of the field of view.