Evaluation of the cerebral vasculature by intraarterial DSA-with emphasis on in vivo resolution

Summary Comparative study was performed between IA DSA and stereoscopic magnification angiography in relation to small vessel resolution, image quality of the vessels and image quality of various pathologic lesions. The vessels of various diameters, accurately measured by stereoscopic magnification angiography, were localized on IA DSA and their resolution was carefully assessed. The vessels more than 1 mm in diameter were equally visualized on IA DSA and conventional angiography. The vessels between 1 mm and 0.5 mm showed fair resolution on IA DSA, whereas IA DSA did not resolve the vessels smaller than 0.5 mm in diameter to good advantage. In addition, image quality of the vessels on IA DSA was compared with the conventional methods. Cerebral gyrus, venous sinuses, and intracerebral veins are often shown better on DSA. The small vessels such as lenticulostriate, small cortical, thalamoperforate and meningohypophyseal arteries were not defined on DSA. Equal or better image quality was obtained in more than 85% of cases with pathologic lesions. Examinations were performed faster with lower cost and lower complication rate. Information provided by DSA was often sufficient for managements of patients. Combined use of DSA and conventional angiography will improve diagnostic accuracy and decrease the complication rate.     

Image quality in mammography with special reference to anti-scatter grids and the magnification technique

Some of the parameters determining image quality in mammography are analyzed: the effects of primary photon spectra, focal spot size and screen-film systems on spatial resolution are discussed as are scattered radiation, development temperature and absorbed dose. The parameters limiting spatial resolution and contrast are evaluated for the standard and magnification techniques. Methods of reducing scattered radiation to improve contrast are evaluated. Scatter to primary ratios for different scatter reducing methods are compared, using the physical quantity energy imparted. For the standard technique the spatial resolution has been found to be limited by the fluorescent screen. With magnification technique the focal spot is the weakest link for the spatial resolution. The contrast is mainly set by the amount of scatter using the standard technique considering the use of a low tube potential (approximately 25 kVp). Using the magnification technique the amount of scatter is so small, that the tube potential is the limiting factor. We have found the optimized standard mammographic technique to be achieved under the following conditions: 25 kVp, 0.3 to 0.6 mm focal spot, film-focus distance 500 mm, anti-scatter grid, developing temperature 36 to 38 degrees C and 4 minutes total processing time with the screen-film system we have used. In magnification technique an air gap of at least 20 mm is desired. With an FFD of about 500 mm this will give a magnification ratio of 1.8 to 2.0 and a 0.1 mm X 0.1 mm focus spot is mandatory. With this technique, it is necessary to use a faster screen-film system than that used in standard mammography.     

Effects of breast thickness and lesion location on resolution in digital magnification mammography

This study aimed to examine the resolution effects of breast thickness and lesion location in magnification mammography by evaluating generalized modulation transfer function (GMTF) including the effect of focal spot, effective pixel size, and the scatter. Polymethyl methacrylate (PMMA) thicknesses ranging from 10 to 40 mm were placed on a standard supporting platform that was positioned to achieve magnification factors ranging from 1.2 to 2.0. As the magnification increased, the focal spot MTF degraded, while the detector MTF improved. The GMTF depended on the trade-off between the focal spot size and effective pixel size. Breast thickness and lesion location had little effect on the resolution at high frequencies. The resolution of small focal spot did improve slightly with increasing PMMA thickness for magnification factors less than 1.8. In contrast, system resolution decreased with increasing PMMA thickness for magnification factors greater than 1.8 since focal spot blur begins to dominate spatial resolution. In particular, breast thickness had a large effect on the resolution at lower frequencies. A low-frequency drop effect increased with increasing PMMA thickness because of the increase in scatter fraction. Hence, the effect of compressed breast thickness should be considered for the standard magnification factor of 1.8 that is most commonly used in clinical practice. Our results should provide insights for determining optimum magnification in clinical application of digital mammography, and our approaches can be extended to a wide diversity of radiological imaging systems.     

Depth determination on stereoscopic digital subtraction angiograms

The determination of depth on stereoscopic digital subtraction angiographic (DSA) images was evaluated. A "plus" phantom that contained simulated blood vessels of various sizes with various concentrations of contrast medium was used for the study. The vessels ranged in diameter from 0.46 to 1.35 mm, with concentrations of contrast material of 1.6%-25%. The images were evaluated by seven radiologists and six radiologic technologists. The detectability of depth separation increased as the iodine concentration and the vessel size increased. With stereoscopic DSA, correct identification of depth is possible more than 80% of the time for vessels approximately 1 mm in diameter and containing 3.1% contrast medium when the vessels are separated by more than 2.8 mm.     

Abdominal angiography with stereoscopic magnification

A new technique for stereoscopic magnification angiography has been developed and combined with routine abdominal angiography. The technique utilizes two divergent x-ray beams at a 34° angle, with a 3.5 cm focal spot separation at a 94 cm focalfilm distance, produced by a synchronous arc rotation of a microfocus x-ray tube. The synchronous motion of the tube is maintained by using an electromechanical device. A magnification factor of 2.0 to 3.0 is used, and 12 films are exposed in a series, the fastest sequence being 1.5 films per second. This technique provides the advantages of magnification and stereoscopic angiography, with excellent demonstration of small arterial branches and abnormal vascularity in three dimensions.     

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.     

Enhanced pancreatic CT imaging utilizing a geometric magnification technique

Computed tomography (CT) using a geometric magnification technique was found to improve spatial resolution in phantom studies when compared with conventional third-generation geometry images. The clinical feasibility of using geometric magnification, small focal spot size, and dynamic contrast enhancement was studied in 143 patients referred to CT for clinically suspected pancreatic disease. This population included 46 patients with a normal pancreas and 36 patients subsequently proven to have primary pancreatic carcinoma. Using this new technique in conjunction with dynamic contrast enhancement resulted in high quality pancreatic images. Despite the limitations in tube current associated with a small focal spot size and low total heat capacity of the system, clinical imaging was not adversely affected. Use of the geometric magnification technique is recommended in departments where it is technically feasible.     

Focal spot size and scatter suppression in magnification mammography.

The improved image quality using magnification in film-screen mammography is related to a complicated interplay between focal spot size, x-ray tube output, detector resolution and sensitivity, air gap size, and target dimensions. Preliminary clinical evaluation of magnification mammography indicates that accuracy of diagnosis has been considerably enhanced. Additional technical and clinical evaluations are continuing, as suggested by mathematical modeling, in order to determine the best possible magnification protocols. While a small focal spot (less than 300 micrometers) is highly recommended for both contact and magnification with the film-screen systems, the smallest focal spot sizes (150 micrometers and smaller) may neither be necessary nor the best in all situations of reduced dose magnification mammography.     

Fluid equations applied to blood flow measurement using digital videodensitometry.

RATIONALE AND OBJECTIVES. Time-dependent fluid flow is computed from projection radiographs without bolus tracking by applying the fluid equations of continuity and incompressibility. METHODS. The fluid equations are combined and integrated to yield an equation that describes instantaneous mass conservation within a vessel segment. The technique is demonstrated using phantom images and patient data obtained using a digital subtraction angiography (DSA) system. RESULTS. Instantaneous and mean flow rates are successfully computed with this algorithm, but the uncertainties are overestimated. In a 1.0-cm diameter tube, instantaneous and mean velocities corresponding to 7.3 cm per frame are computed within 13% uncertainty using a 4.0-cm segment length. Mean flow rates computed from standard diagnostic angiograms taken from three different projections agree within 16%. CONCLUSIONS. This technique can successfully compute time-dependent flow rates from DSA image sequences with large fluid displacements between frames. The accuracy is strongly dependent on the magnitude of the contrast density gradient.     

Trends in image quality in high magnification digital specimen cabinet radiography

Advances in microfocus X-ray tube design together with the availability of high resolution charge coupled device (CCD) detectors have led to the introduction of high magnification digital specimen cabinets for the examination of tissue samples. This paper explores the effect that the high magnification geometry permitted by such units has upon image quality in terms of phase contrast edge enhancement, spatial resolution and the appearance of test phantom images. Phase contrast effects and spatial resolution were studied using a previously established method (using edge profiles) and by computing the system spatial frequency response at various geometries. It was demonstrated that the magnitude of the phase contrast enhancement effect reaches a stable maximum at a magnification of x 4. It has also been shown that a continual increase in both the spatial resolution together with an improved signal to noise ratio occurs up to the maximum permissible magnification geometry, with effects of focal spot blur being negligible. In practice, the limited size of the digital detector and the difficulty of object alignment can constrain the use of the very high magnification option.     

Comparison of image quality obtained with optical and radiographic magnification techniques in fine-detail skeletal radiography: effect of object thickness.

High-resolution radiography may be done using either optical or radiographic magnification. In the former technique, industrial Type M film was used without screens and the image was viewed with 4-10X optical magnification. In the latter technique, RP film was used with Detail screens and 4X geometric magnification together with a microfocus x-ray tube having a nominal focal spot size of 50 mum. The imaging properties of both techniques were evaluated by means of H & D curves, modulation transfer functions, and Wiener spectra. It was found that for thin objects such as the hand, optical magnification provides better bone images than radiographic magnification; whereas for thicker parts such as the knee, radiographic magnification is superior.     

Magnification survey and spot view mammography with a new microfocus X-ray unit: detail resolution and radiation exposure

The aim of our study was to evaluate a mammography unit capable of magnification of up to fourfold at an equivalent or lower dose than with current systems. A prototype mammography tube with an electron-beam-focusing technology resulting in a focal spot size of 40–120 μm was combined with a highly intensifying screen-film system. To evaluate contrast-detail resolution, phantom radiographs were performed with the prototype magnification mammography system using a magnification factor of 1.7 for survey views and a magnification factor of 4.0 for spot views. They were compared with unmagnified survey views and magnification spot views (magnification factor 1.9) of a state-of-the-art mammography system. The radiation exposure was measured and mean glandular doses were calculated. The contrast-detail resolution with both prototype (m = 1.7) and conventional (m = 1.1) survey views was equivalent while the entrance dose and the mean glandular dose were approximately 50 % lower with the prototype. For spot views, the contrast-detail resolution was substantially higher for the prototype than for conventional magnification while the dose was equivalent. Dose reduction and improved detail resolution are possible with this new technology. Received 3 April 1997; Revision received 22 July 1997; Accepted 3 September 1997     

Neonatal magnification radiography using standard-focus x-ray tubes

Radiographic examination of the chests of premature newborn infants is complicated by the small size and poor object contrast of the structures to be evaluated. Magnification radiography can improve image quality significantly in this situation. Unfortunately, high-quality magnification radiography requires dedicated microfocus equipment that is not available in most neonatal intensive care units. The use of standard-focus x-ray tubes (up to 1 mm focal spot size) for moderate magnification radiography (1.5 times) by using the anode side of the x-ray field of the standard mobile x-ray unit is proposed. In addition to the cost advantage of using existing standard mobile x-ray equipment, the high tube current allows for short exposure times and long target-film distances. This reduces most motion unsharpness and allows for a large air gap that results in improved image contrast. Although focal spot size at the anode side of the field is smaller in only one dimension, the magnification radiographs are superior to those obtained using the central part of the x-ray beam and superior to standard contact radiographs using the same equipment. Improvement in image quality is due primarily to decreased noise and improved contrast in the magnified image.     

Stereoscopic digital subtraction angiography in neuroradiologic assessment

Digital subtraction angiography (DSA) with stereoscopic imaging was performed in 40 patients for evaluation of a variety of cerebrospinal disorders. It was facilitated by a C-arm mounted x-ray tube and imaging chain with 7 degrees angulation between image pairs. Stereoscopic digital imaging proved particularly useful in the preoperative assessment of aneurysms, arteriovenous malformations, and primary and metastatic tumors. The technique was also found to be useful as a real-time adjunct to therapeutic radiographic procedures, as an aid in stereotaxic procedures, and in follow-up of postsurgical patients. Although the intravenous route was occasionally used, especially in postoperative follow-up of aneurysms, the procedure was most often carried out via an intraarterial approach. Stereoscopy was useful in supplying depth information regarding the relations between lesions and surrounding normal and abnormal vasculature. This technique combines the demonstrated advantages of intraarterial DSA with the unique advantage of stereoscopic imaging to demonstrate three-dimensional detail, thus contributing significantly to diagnostic confidence. Disadvantages are discussed. Further refinements in the equipment are expected: generation of stereo images with one injection, thus increasing procedure efficiency and patient safety; a video stereoscopic viewing unit; and the ability to obtain precise measurements via computer of depth, position, distance between, and true size of objects.     

Direct magnification mammography in combination with computed radiography. First clinical results

Summary Introduction: The combination of direct magnification mammography and computed radiography provides an improvement in spatial resolution of storage phosphor-based digital systems. A clinical study comparing conventional and digital direct magnification mammograms was performed. Methods: 100 survey mammograms in 1.5- or 1.7-fold magnification and 50 4-fold spot magnification views were obtained with a prototype direct magnification mammography system and a storage phosphor-based digital system. An intraindividual comparison of these with previous conventional radiograms of the same patients was carried out. Results: The diagnostic value of digital survey mammograms using the direct magnification technique is comparable to that of conventional radiograms of the breast, especially with regard to the identification of microcalcifications and lesions and the clinical consequences. Spot magnification views performed with this combination of techniques allowed improvement in the evaluation of microcalcifications. In 15 % of cases, diagnostic procedures were adjusted accordingly. Conclusion: The combination of the direct magnification technique with digital storage phosphor radiography systems allows the performance of digital mammography by improving the overall spatial resolution. The diagnostic value of digital direct magnification survey mammograms was comparable to that of conventional mammograms. Digital 4-fold spot magnification views improved visualisation of the morphologic aspects of microcalcifications.      

Automated tracking and computer reproduction of vessels in DSA images

We are developing an automated vessel-tracking method based on the double-square-box region-of-search technique, for efficient tracking of the connected vascular tree in a digital subtraction angiography (DSA) image. Tracking points and branch vessels are located by searching of the perimeter of boxes, which are centered on previously determined tracking points. The most accurate results (90% true-positive rate with six false-positives per image) are obtained by tracking using the double-square-box method. In relatively straight regions of vessels, a large box is employed for efficient tracking; in curved regions of vessels, a small box is employed to ensure accurate tracking. When tracking is completed, accurate vessel information, ie, the vessel position, size, and contrast determined at each tracking point, is available for further quantitative analysis. Computer reproductions of tracked vessel trees appear to correspond well to those in DSA images.     

Neuroradiological applications of a new system of stereoscopic biplane digital subtraction angiography

A stereoscopic biplane digital subtraction angiography (DSA) system was developed, capable of obtaining frontal and lateral projections simultaneously during a single injection of contrast medium. This new system combines the advantages of both biplane and stereoscopic single-plane DSA, and permits high-quality neuroangiography.     

3.0T高分辨率CE-MRA对颈部血管狭窄的诊断价值

目的探讨三维对比增强磁共振血管成像(3D CE-MRA)在颈部动脉血管狭窄诊断中的临床应用价值。方法对23例临床拟诊颈部动脉血管狭窄行数字减影血管造影(DSA)的患者行颈部3D CE-MRA。将两种方法检查结果进行相关性比较。结果 23例患者共230个节段血管,3D CE-MRA显示了227个节段,共诊断出74处(32.6%)狭窄,其中28处轻度狭窄,22处中度狭窄,20处重度狭窄,4处闭塞;DSA共显示了230个节段的血管,共诊断出69处(30.4%)血管狭窄,其中24处轻度狭窄,23处中度狭窄,19处重度狭窄,3处闭塞。与DSA相比,3DCE-MRA对颈部动脉轻度、中度、重度狭窄及动脉闭塞的显示敏感性均为100%,特异性分别为85.71%、90.91%、90%和75%,两种检查方法对颈部动脉狭窄程度的判断有良好的一致性(κ=0.921,P=0.000)。结论 3.0T 3DCE-MRA能够可靠的评价颈部动脉狭窄性病变,基本可以替代DSA检查。     

Three-dimensional display of the orifice of intracranial aneurysms: a new potential application for magnetic resonance angiography

Our aim was to demonstrate the orifice of intracranial aneurysms by magnetic resonance angiography (MRA). The aneurysmal orifice is that part of its lumen that communicates with the parent vessel. We studied 12 patients with 17 intracranial aneurysms using three-dimensional display (3DD) MRA; 15 of the aneurysms had previously been shown by digital subtraction angiography (DSA). The overall image quality of 3DD MRA was excellent in 10 patients. The orifice was clearly demonstrated in 13 aneurysms (76%) providing unique information about its size, shape and orientation. The orifice of 2 aneurysms (12%) was not demonstrated. Two aneurysms (12%) were not detected on MRA. Although 3DD MRA has limitations this study suggests that it can accurately define the orifice of aneurysms and could be used to provide information crucial for endovascular treatment.     

自发性蛛网膜下腔出血的CTA与DSA对比研究

目的:探讨64层CTA与DSA对自发性蛛网膜下腔出血(spontaneous subarachnoid hemorrhage,s-SAH)的应用价值及其限度。方法:收集153例s-SAH患者的CTA及DSA检查资料,回顾性分析2种检查方法的图像质量(采取1³分评分制),并比较2种方法在脑动脉瘤检出方面的灵敏度、特异度及准确度。结果:图像质量评分CTA为(2.63±0.262)分,DSA为(2.73±0.254)分,二者差异无统计学意义(P>0.05)。CTA对脑动脉瘤的检出的灵敏度为96.2%,特异度为94.9%,准确度为95.9%;DSA灵敏度为97.7%,特异度为97.4%,准确度为97.6%,二者差异无统计学意义(P>0.05)。结论:在s-SAH患者中,CTA与DSA均能准确检出动脉瘤所致破裂出血。相较于DSA,CTA能多方位显示病变,对血管壁及血管周围情况的显示更具价值。