Screening for tracheobronchial diseases with digital storage phosphor radiography]

Digital storage phosphor radiography (FCR: Fuji computed radiography) has a wide dynamic range and unique postprocessing capabilities. This study was designed to test whether chest imaging with FCR and its image processing would increase the accuracy of and confidence in the diagnosis of tracheobronchial abnormalities. In a phantom study, the performance of digital images having the appearance of a conventional chest radiograph was compared with that of a conventional system in detecting simulated tracheobronchial nodules. The digital images of lower kilovoltage (ROC area = 0.647 +/- 0.035) were equivalent to the conventional radiographs (ROC area = 0.620 +/- 0.028). On the other hand, nodule detectability was significantly improved in the digital images of higher kilovoltage (ROC area = 0.826 +/- 0.020). The author also compared the impact of five postprocessing algorithms (standard image, wide latitude image, enhanced image, reversed image, and subtraction image). ROC analysis indicated that the default standard image (ROC area = 0.826 +/- 0.020) was as good as an image with a linear rather than a sigmoid gradation curve (ROC area = 0.843 +/- 0.020), an image with strong enhancement of high frequencies (ROC area = 0.804 +/- 0.020), and an image with reversed gray scale polarity (ROC area = 0.775 +/- 0.015). Therefore these specific algorithms had no effect on the detection of tracheobronchial nodules. However, digital subtraction soft tissue images (ROC area = 0.961 +/- 0.030) were significantly better than the control images. Clinical study also indicated that subtraction images improve diagnostic accuracy in tracheobronchial diseases.     

Computer processed fluoroscopic images for digital intravenous renal angiography

We investigated intravenous digital angiography using computer processed fluoroscopic images. Computer processed fluoroscopy (CPF) was compared to conventional digital subtraction angiography (DSA) in 39 patients referred for renal vessel evaluation. For assessment of CPF the anterior-posterior images were compared with the corresponding digital subtraction angiograms. 79% percent of DSA and 71% of CPF studies were diagnostic. Peripheral injection of contrast medium caused deterioration of CPF images. Skin dose measurements were obtained in 24 patients. The median dose for DSA was 8.2 rad, compared to 1.1 rad for CPF. It is concluded that sophisticated algorithms should be investigated for digital angiography, so that high image quality can be achieved with a reduced radiation exposure.     

The AAPM/RSNA physics tutorial for residents: digital fluoroscopy.

A digital fluoroscopy system is most commonly configured as a conventional fluoroscopy system (tube, table, image intensifier, video system) in which the analog video signal is converted to and stored as digital data. Other methods of acquiring the digital data (eg, digital or charge-coupled device video and flat-panel detectors) will become more prevalent in the future. Fundamental concepts related to digital imaging in general include binary numbers, pixels, and gray levels. Digital image data allow the convenient use of several image processing techniques including last image hold, gray-scale processing, temporal frame averaging, and edge enhancement. Real-time subtraction of digital fluoroscopic images after injection of contrast material has led to widespread use of digital subtraction angiography (DSA). Additional image processing techniques used with DSA include road mapping, image fade, mask pixel shift, frame summation, and vessel size measurement. Peripheral angiography performed with an automatic moving table allows imaging of the peripheral vasculature with a single contrast material injection.     

Scanned projection radiography of the chest versus standard film radiography: a comparison of 250 cases

Two hundred fifty patients who had 240 pathological changes of the lungs or mediastinum were examined using both scanned projection radiography (SPR) and standard film radiography, and the diagnostic accuracy of the procedures was compared. The use of standard film radiography led to diagnostic findings in 90.1% of the cases, while 94% of the images obtained at SPR provided diagnostic findings. The equivalent performance and, in part, the slight superiority obtained with the digital technique is a result of the better contrast resolution for objects with diameters greater than 2 mm. A further improvement in the diagnosis of thoracic disease with digital radiography may occur because of the use of special mathematical algorithms for image reconstruction and with the use of dual-energy subtraction radiography rather than by an increase of spatial resolution.     

Projected digital radiologic images for teaching: balance of image quality with data size constraints

RATIONALE AND OBJECTIVES: The authors performed this study to determine, in the context of a teaching presentation with slides, the information content needed in a digitized radiologic image for it to be equivalent in quality to an analog image. MATERIALS AND METHODS: Eleven sets of radiologic images were obtained from a teaching file collection and digitized. The images were scanned at high resolution and saved as image files. The information content of each image was then halved repeatedly with repeat sampling of the image. This procedure was repeated nine times to yield a total of 10 images with an information content that ranged from very low (32 kB) to high (12 MB). Each of these image files was made into a 35-mm slide by using a digital slide maker. The original radiographs were subsequently made into slides by using conventional photographic methods. Care was taken to make the images identical in every respect except digitization and information content. The slides were shown to radiologists, who filled out questionnaires to rate image quality. RESULTS: Digitized slides that contain an average of 416 kB of data (the equivalent of a 750 x 570-pixel matrix with 8-bit gray levels) were equivalent to analog images for 90% of viewers. At 830 kB (1,060 x 800-pixel matrix with 8-bit gray levels), 100% of viewers found no difference between digitized and analog images. CONCLUSION: Digital images become indistinguishable from analog images if a sufficient amount of information is retained in the digital image. There is a defined relationship between the perception of quality and the information content of a digital image.     

Analysis of subtraction methods in three-dimensional contrast-enhanced peripheral MR angiography

PURPOSE: To compare the effectiveness of three image subtraction algorithms designed to improve arterial conspicuity in first-pass contrast-enhanced magnetic resonance (MR) angiography. MATERIALS AND METHODS: Three subtraction methods were analyzed through computer simulations, phantom studies, and clinical studies. These algorithms were: complex subtraction, magnitude subtraction, and maximum intensity projection subtraction. RESULTS: In high resolution three-dimensional imaging, maximum intensity projection subtraction generally yields the best background suppression. Complex subtraction is effective in reducing partial volume effects in low resolution imaging. Magnitude subtraction works better in high resolution, low contrast concentration protocols. CONCLUSION: Choosing the appropriate subtraction method according to the protocol is helpful in optimizing image quality.     

Tomosynthesis applied to digital subtraction angiography

This extension of our previous work on tomographic digital subtraction angiography (DSA) describes the theory of tomosynthetic DSA image reconstruction techniques. In addition to developing the resolution limits resulting from x-ray exposure length and image intensifier field curvature, we describe one method of image formation and show tomosynthetic DSA images of animal and human anatomy. Methods for improving the present technique are discussed.     

K-edge digital subtraction arthrography of the painful hip prosthesis: a feasibility study

K-edge energy subtraction radiography is a method for detecting the presence of iodinated contrast material by subtracting two digital radiographs produced by X-ray beams with energies above and below the iodine K edge. We performed a feasibility study on the application of K-edge energy digital subtraction arthrography (KEDSA) to painful hip prostheses. During arthrography, loosening of the prosthesis is implied if contrast material is seen dissecting around the prosthesis, an often difficult detection task because of adjacent prosthesis metal or cement. In conventional arthrography a preliminary mask image is thus used from which films obtained after injection of iodinated contrast material are subtracted. Movement by the patient during this process may preclude subsequent subtraction. With KEDSA, since multiple image pairs may be obtained after the injection of contrast material, the problem of patient motion is virtually eliminated. A conventional X-ray tube operating between 55 and 65 kVp was alternately filtered by iodine and cerium filters to produce the KEDSA images. The apparatus was capable of producing a subtracted image within 3 sec. The technique was applied to phantoms and to six patients immediately after hip arthrography that had been positive for prosthesis loosening. Although of lower spatial resolution, the KEDSA images were, in all cases, positive for loosening in a pattern consistent with the conventional arthrographic images. KEDSA was shown to be successful in detecting extraarticular contrast material. During a single study, subtraction in various imaging planes as well as postexercise subtraction imaging can be accomplished-techniques not heretofore possible in routine subtraction arthrography.     

Digital subtraction cerebral angiography by intraarterial injection: comparison with conventional angiography

For 4 months, a prototype digital subtraction system was used to obtain images of the cerebral vasculature after intraarterial contrast injections. In 12 instances, the intraarterial injections were recorded with both a digital subtraction unit and conventional direct magnification film-screen system. The digital subtraction and conventional film subtraction images were compared and graded for quality and information content by three skilled observers. In addition, quantitative measurements of contrast-detail performance and spatial resolution were obtained on both the digital system and the screen-film imaging chain. In a clinical setting, both the digital subtraction and conventional film-screen systems provided similar quality images and angiographic information. Contrast-detail curves demonstrated that digital subtraction angiography outperformed conventional film technique for low-contrast objects. Digital subtraction angiography also reduced the time required to obtain the angiogram, markedly reduced film cost, and lowered the contrast agent burden.     

Digital tomography: description and preliminary clinical experience

Digital tomography was performed in 30 patients using a new prototype system with a PET-Scope image tube. Twenty-eight exposures are obtained during a single revolution of the x-ray source over the volume of tissue to be imaged. The sum of the radiation produced by the 28 exposures is about equivalent to a single routine exposure of the part imaged. The data accumulated can provide up to 200 tomographic sections at intervals of 5 mm. Reconstruction time for each section is 3 sec. The raw images may be reconstructed as often as desired. Algorithms are being developed to allow axial and sagittal reformations. Further work is required to improve spatial resolution and contrast and to develop algorithms to allow subtraction of blurred images above and below the reconstructed site. The authors believe that digital tomography may eventually replace most routine tomograms.     

Digital processing of film radiographs

Initial clinical experience with a system for the digitization, processing, and display of film radiographs is described. Film is digitized using a high-intensity laser scanner; the recorded image data may then be subjected to a wide variety of processing options, with display of processed images on television monitors. The possibilities of clinical applications to processing and display of chest radiographs and film mammograms are described. A comparison of conventional analog subtraction and digitized film subtraction angiography indicated equivalent diagnostic capability, with the advantage of flexible, interactive image processing with the digital technique. A specially designed, energy-selective cassette permits dual-energy imaging from two films effectively exposed to different x-ray energy spectra. Dual-energy imaging may be capable of the characterization of body materials, including lung nodules, and useful for eliminating obscuring radiographic shadows overlying regions of interest.     

MR subtraction angiography with a matched filter

The technique of matched filtering (MF) has been used in the past with X-ray digital subtraction angiography as a method of improving signal-to-noise ratio (SNR) in subtraction angiographic images. In this work we describe how MF can be applied to a series of images produced by cinematographic magnetic resonance (cine MR) to produce angiographic images. Likewise, a simple subtraction image can be formed by subtracting an image in which flow is not well visualized from an image at the same location but with flow visualization. Theory predicts that a subtraction image resulting from the MF technique will yield typical SNR improvements of 60% over results from simple subtraction. Twenty-one studies of the human popliteal, canine aorta, and canine carotid artery were undertaken in which MF was compared with simple subtraction. It was determined that cine MR can be used to produce subtraction angiographic images and that MF can produce a modest improvement in SNR over simple subtraction.     

Evaluation of CRT images of digitized film angiographs

X-ray sheet film images of the test chart, the vascular phantom and angiography were digitized at sampling pitch of 0.2 mm and 0.15 mm using film digitizer TFR-01 (Toshiba) and transferred to a device for image storage and display system with 1635-line display monitor (TDF-500AS, Toshiba). Comparison of image qualities between film- and CRT-images was performed in fundamental and clinical studies. Resolution of the test chart image of conventional radiography was worse on CRT than on the original film, although it was improved when film image was digitized at resolution of 0.15 mm/pixel in comparison with that at resolution of 0.2 mm/pixel. Moiré stripes which occurred due to interference were found on CRT images taken using a grid technique. On CRT images of X-ray sheet film using direct magnification technique moiré stripes were not produced because of non grid technique, and the resolution approached that of the original film. In the study using vascular phantom, the optimal image on CRT could be obtained by various image processing procedures, and image quality on CRT with resolution of 0.15 mm approached that of original film. In case of direct magnification CRT images were superior to film images. Subtraction image of the vascular phantom at resolution of 0.2 mm/pixel was obtained on CRT and compared with film subtraction image. On conventional subtraction CRT image moiré stripes impaired the image quality in comparison with the film subtraction. However, magnification subtraction image of the vascular phantom on CRT was superior to the film subtraction. The results obtained in the test chart studies and phantom studies were also confirmed in clinical studies using various kind of angiograms. In addition, ROC study using clinical angiograms showed no significant statistical differences between the original film and CRT image even with 0.2 mm matrix size. Angiographic image on CRT at resolution of 0.15 mm/pixel or less is available for clinical use in place of conventional film image.     

Digital subtraction angiography system evaluation with phantoms

Advances in digital subtraction angiography imaging demonstrate the need for critical evaluation of the performance of digital subtraction equipment. The design of a phantom set for noninvasive assessment of the imaging quality of digital subtraction equipment is described; components include a remotely controlled transport system and individual patterns to evaluate the contrast and detail properties of the image intensifier, low-contrast sensitivity and resolution of the system, geometric distortion of image, linearity, mechanical and electronic stability of equipment, and effects of bone and bowel gas on iodine perception. The performance of an add-on digital radiographic system is presented, along with radiation exposure levels at the image intensifier for a range of radiographic techniques.     

Hardcopy recordings of analog and digital images

The increase in the use of various imaging modalities demands higher quality and more efficacious analog image recordings. Laser electronic recordings with digital array prints of 4K X 5K X 12 bits using laser-sensitive film or paper are being evaluated. Dry silver paper recordings are being improved and evaluated. High resolution paper dot printers are being studied to determine their gray scale capabilities. The authors have conducted a study to evaluate the image quality, costs, clinical use, and acceptability of CT, MRI, DSA, digital radiography, and radionuclide images recorded by the seven different printers (three laser, three silver paper, and one dot) in comparison with conventional film recording. This paper describes the technical developments and instrumentation of digital laser film and analog paper recorders and presents the results of our study.     

Digital K-edge subtraction radiography.

K-edge subtraction images have been produced using a digital video image processor. Images formed by three filtered x-ray beams are detected by an image intensifier-Plumbicon system, digitilized, and combined in real time to produce bone- and tissue-free K-edge subtraction images of iodinated structures. Preliminary studies of rhesus monkey cranial, spinal, and abdominal structures are compared with those of conventional radiography.     

Fluoroscopy: recording of fluoroscopic images and automatic exposure control.

Some means of recording images is a necessary part of most fluoroscopic systems. Several methods are available for recording images during fluoroscopy. Screen-film recording methods such as use of spot film devices and automatic film changers provide high-spatial-resolution images. Recording images by using the image intensifier (fluorography) provides film or digital images at relatively lower doses but with poorer spatial resolution. Digitally recorded images have better contrast resolution than analog images but lower spatial resolution and represent a compromise between dose and image quality. Motion picture (cine fluorographic) recording requires extremely high dose rates compared with those of lower-resolution videotape recording of motion. Recording systems in fluoroscopy require automatic exposure control for optimum image quality. The same feedback system used to control fluorographic exposures can be used to control exposure rates during fluoroscopy as well. Automatic brightness control maintains intensifier exposure rates on the basis of subject thickness by adjusting various technique factors. The type of control mechanism depends on the imaging task and the complexity (age and cost) of the equipment. The operator can choose between better image quality (higher contrast) or lower radiation dose.     

Digital subtraction venography in central venous obstruction

Thirty-five patients had central venous digital subtraction venography (DSV) to assess its value in detecting central line/shunt patency (13 patients) and central venous obstruction (22 patients). All examinations were easily performed and provided diagnostic images without conventional venographic supplementation. The disadvantages of DSV are outweighted by the advantages, which include saving time and money, superior contrast resolution, flexibility of image display, and reduced dosage of contrast agent.     

SNR improvement for multiinjection time-resolved high-resolution CE-MRA of the peripheral vasculature.

Peripheral MR angiography (MRA) should ideally provide images over a large field of view with high spatial resolution and adequate temporal resolution to accommodate differences in regional filling times. Image subtraction is usually used to remove background signals. In examination protocols involving multiple injections at multiple sites, previously injected contrast present in the mask image provides a substantial decrease in the subtraction image signal. Bolus chase methods avoid this problem but provide limited time for acquisition of high-resolution images at each station. We present here a technique applied to peripheral angiography that provides high spatial and temporal resolution while maintaining high SNR in multiple injection examinations. Undersampled projection imaging was used to increase spatial resolution relative to a previously reported technique using a Cartesian acquisition technique. Late acquisition of high spatial frequencies and temporal matched-filtering were used to increase spatial resolution and SNR, respectively. Temporal correlation analysis was applied to permit multistation examinations without mask subtraction, thus providing an additional gain in SNR relative to multistation subtraction methods. Quantitative analysis is provided to evaluate the signal and noise behavior in the matched-filtering process due to multiinjection and mask subtraction.     

双能量数字减影胸片对于不同肺野区域内结节性病变的检出差异(ROC分析)

目的　评价双能量数字减影胸片和常规DR胸片对于不同肺野区域内结节性病变的检出差异。方法　 2 0名正常成年志愿者前胸粘贴模拟结节 ,拍摄双能量数字减影正位胸片 ,应用ROC分析比较常规DR胸片与减影后软组织图像的诊断结果。结果　在双上、中肺野 ,软组织图像的曲线下面积大于常规DR胸片 ;在双上肺野、双中肺野外带 2种方法具有显著性差异。结论　双能量数字减影技术对双上肺野及双中肺野外带胸部结节性病变的检出具有优势 ,故应结合减影及常规胸片 ,以助诊断。