Contrast-enhanced magnetic resonance angiography in peripheral arterial disease: improving image quality by automated image registration

In peripheral arterial disease, contrast-enhanced MR angiography (MRA) is a noninvasive imaging alternative for catheter-based digital subtraction angiography (DSA). In DSA, final images are generated by subtracting a native mask image from subsequent contrast-enhanced images. Image quality is routinely improved by digitally shifting the mask image prior to subtraction if the patient has moved during angiography. This study investigated whether such image registration may also help to improve the image quality of MRA. In all, 545 MRA examinations of pelvic and leg arteries in patients with symptoms of peripheral arterial disease were studied retrospectively. Standard nonregistered MRA was compared to automatically linear, affine, and warp registered MRA by visual analysis and by three image quality parameters, including vessel detection probability (VDP) of angiographic maximum intensity projections. Most MRA of pelvic and upper leg arteries showed good nonregistered image quality. However, the 15% of lower legs with a body shift of 1 mm or more had relatively low nonregistered image quality, which improved significantly with image registration (VDP gain more than 18%, P < 0.05). The visual analysis gave similar results. In conclusion, image registration can improve image quality of MRA in peripheral arterial disease, especially in the lower legs.     

An algorithm for correction of distortion in stereotaxic digital subtraction angiography

An algorithm for correction of the geometrical distortion in digital subtraction angiography (DSA) images was developed. Originally invented for 3D X-ray angiography, the algorithm was implemented in a computer program designed to fulfil the specific needs of stereotaxic DSA. The algorithm is based on transformation of an image of a grid from a distorted image back into its original pattern. The same transformation is then applied pixel-by-pixel to the angiographic images, which are acquired in direct conjunction with the grid image, without moving the gantry. The algorithm was tested in phantom studies and in the clinical situation with seven patients in ten examinations. Comparisons were made between co-ordinate determinations made on conventional full-size cut film and those performed on uncorrected and corrected DSA images, using 30- and 23-cm fields of view. With our method of measurement we could not show any remaining geometric distortion in the corrected DSA images. This distortion correction can, if properly applied, be used for high-precision stereotaxic DSA. Received: 16 September 1995 Accepted: 5 January 1996     

Three-dimensional fusion digital subtraction angiography: new reconstruction algorithm for simultaneous three-dimensional rendering of osseous and vascular information obtained during rotational angiography

This report describes three-dimensional (3D) fusion digital subtraction angiography (FDSA), a new algorithm for rotational angiography that combines reconstructions of the blood vessels and the osseous frame in a single 3D representation. 3D-FDSA is based on separate reconstructions of the mask and contrast sequences of the rotational acquisition. The two independent 3D data sets (3D-bone and 3D-digital subtraction angiography [DSA]) are fused in a single 3D representation. The algorithm uses a modification of the Feldkamp method that compensates for signal intensity inhomogeneity inherent to the reconstruction of nonsubtracted rotational acquisitions. By separately reconstructing the osseous and vascular information obtained from the rotational angiogram, 3D-FDSA provides optimal angiographic resolution and precise topographic analysis even when the studied vascular tree is in the immediate vicinity of bone.     

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.     

2-phase summation imaging of the subclavian steal syndrome using transvenous DSA

A simple method is reported to obtain a two-phase summation image in subclavian steal syndrome using digital subtraction angiography (DSA) via selection of a mask during the early arterial phase and the contrast image during delayed retrograde filling of the ipsilateral vertebral artery and the postocclusive subclavian artery. The summation image results by employing replay of the stored image information.     

Digital subtraction angiography in interventional radiology

Intraarterial digital subtraction angiography (DSA) was used an an adjunct to interventional vascular procedures (embolotherapy and transluminal angioplasty) in 56 patients. The advantages of intraarterial DSA include improved contrast resolution, instantaneous subtraction capability, and immediate image availability. A considerable reduction in contrast dose and concentration, procedure time, and patient discomfort can be expected when interventional vascular procedures are performed with the assistance of intraarterial DSA.     

Three-dimensional digital angiography: new tool for simultaneous three-dimensional rendering of vascular and osseous information during rotational angiography

Three-dimensional (3D) digital subtraction angiography (DSA) is the latest development in the neurovascular imaging armamentarium. 3D-DSA combines the anatomic resolution of DSA with 3D visualization abilities previously offered by only CT or MR angiography. 3D-DSA provides more detailed information than does DSA alone in the evaluation of neurovascular lesions, such as cerebral aneurysms. However, the inability of 3D-DSA to simultaneously image osseous and vascular structures is noted as a weakness of this technique compared with CT angiography. We describe a new 3D digital angiography reconstruction algorithm that allows the concurrent display of the cerebral vasculature and the osseous landmarks.     

Internal densitometric gating for digital subtraction angiography

Motion artifacts create a severe problem in digital subtraction angiography (DSA) studies. Periodic motion can be eliminated by "gating," matching a precontrast mask with a postcontrast image at the same phase position in the cycle. Electrocardiogram (EKG) signals are used in cardiac DSA for this purpose. An alternate method relies on the generation of a density-time curve dependent on the attenuation changes of anatomical motion. A densitometric window placed at an appropriate location records the variation, from which individual images are tagged with phase position information encoded as delay time. Results are similar to the EKG gating method for cardiac DSA when using an appropriate window location. Periodic motion caused by superimposed respiration can be suppressed by tracking diaphragm or other object attenuation changes with the same algorithms. Using these techniques permits the nonarbitrary matching of mask and contrast images without physiologic monitoring. The techniques are straightforward and relatively easy to implement on systems designed for rapid digital imaging.     

Cardiac imaging with digital subtraction angiography

Central cardiovascular anatomy and function have been evaluated with intravenous digital subtraction angiography (DSA). The subtraction techniques used for studying the left ventricle (LV) were mask mode, time interval difference and functional subtraction. Aside from contrast enhancement, a major use of digital fluoroscopy for cardiac applications has been computer-assisted quantitative analysis of LV dimensions and function. Left ventricular volumes and wall thickness determined from DSA studies have correlated closely with direct left ventriculograms and sonocardiometry measurements in patients and animals, respectively. Measurements of segmental LV contraction with DSA correlated closely with direct left ventriculography in normal patients and patients with coronary artery disease. The sensitivity of intravenous DSA for detecting significant coronary artery disease was increased by performing DSA immediately after increasing the myocardial oxygen demands by atrial pacing. The advantages and disadvantages of DSA in relation to other semi-or non-invasive imaging modalities are discussed.     

Contrast-enhanced magnetic resonance angiography in carotid artery disease: does automated image registration improve image quality?

Contrast-enhanced magnetic resonance angiography (MRA) is a noninvasive imaging alternative to digital subtraction angiography (DSA) for patients with carotid artery disease. In DSA, image quality can be improved by shifting the mask image if the patient has moved during angiography. This study investigated whether such image registration may also help to improve the image quality of carotid MRA. Data from 370 carotid MRA examinations of patients likely to have carotid artery disease were prospectively collected. The standard nonregistered MRAs were compared to automatically linear, affine and warp registered MRA by using three image quality parameters: the vessel detection probability (VDP) in maximum intensity projection (MIP) images, contrast-to-noise ratio (CNR) in MIP images, and contrast-to-noise ratio in three-dimensional image volumes. A body shift of less than 1 mm occurred in 96.2% of cases. Analysis of variance revealed no significant influence of image registration and body shift on image quality (p > 0.05). In conclusion, standard contrast-enhanced carotid MRA usually requires no image registration to improve image quality and is generally robust against any naturally occurring body shift. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Digital intraarterial subtraction technique of the extracerebral vascular system

We report the results from intraarterial digital subtraction angiography (IA DSA) of the extracerebral vessels with aortic arch injection of contrast medium via femoro-arterial puncture, instead of the more widely used intravenous digital subtraction angiography (IV DSA). Intraarterial DSA is performed using a lower contrast dose and rate, making this study less invasive and costly than the conventional arteriographic study of the aortic arch. Intraarterial DSA provides better resolution than IV DSA. The diagnostic accuracy is almost equivalent to conventional angiography and is largely superior to photographic subtraction angiography with intravenous injection of contrast media.     

全下肢动脉血管造影技术的临床应用探讨

目的比较血管造影跟踪法(bolus chasing angiography,BCA)与传统法(static digital subtraction angiography,DSA)的技术特点。方法回顾性分析了我院61例全下肢动脉血管造影患者的造影技术参数,其中31例采用BCA、30例采用DSA血管造影技术。分别对完成造影时间、对比剂用量、图像质量、患者吸收辐射剂量(dose-area product,DAP)进行对照分析。结果2种造影技术对比显示:DSA的图像质量在显示胫腓血管上优于BCA,但是DAP值高,对比剂用量多以及检查时间长。经统计学处理,二者差异均具有显著性(P<0.00)。结论BCA与DSA相比具有造影时间短,对比剂量用量少,DAP低的特点,DSA局部观察血管情况较细致。因此,先行BCA筛查,然后针对病变加做局部DSA。     

Tomographic digital subtraction angiography: initial clinical studies using tomosynthesis. Work in progress

We have developed a method for acquiring multiple tomographic subtraction images using a rapid, repetitive, circular tomographic motion. The method combines the principles of digital subtraction angiography (DSA) and electronic tomosynthesis. Fifteen patients were examined with the technique using single intravenous bolus injections of contrast material. The image sequence obtained during each injection was first processed with a nontomographic mask subtraction, and the result was then compared with the tomographic DSA scans synthesized from the same sequence. The effective section thickness was approximately 0.5 cm, with each section being 0.5-1.0 cm apart. Twelve of the intravenous DSA scans provided the necessary diagnostic or clinically useful information. Two of the three nondiagnostic scans were caused by avoidable technical reasons. In eight cases, the tomographic DSA scans were superior in quality to the nontomographic scans, exhibited significantly less artifact from patient motion and overlying bowel gas, and were effective in separating overlapping vessels. Tomosynthesis permits multiple electronic imaging of the area of interest without reinjection of contrast material and appears to be more informative than nontomographic intravenous DSA imaging.     

Dynamic MR digital subtraction angiography using contrast enhancement,fast data acquisition,and complex subtraction

A dynamic MR angiography technique, MR digital subtraction angiography (MR DSA), is proposed using fast acquisition, contrast enhancement, and complex subtraction. When a bolus of contrast is injected into a patient, data acquisition begins, dynamically acquiring a thick slab using a fast gradient echo sequence for 10–100 s. Similar to x-ray DSA, a mask is selected from the images without contrast enhancement, and later images are subtracted from the mask to generate angiograms. Complex subtraction is used to overcome the partial volume effects related to the phase difference between the flowing and stationary magnetization in a voxel. Vessel signal is the enhancement of flow magnetization resulting from the contrast bolus. MR DSA was performed in 28 patients, including vessels in the lungs, brains, legs, abdomen, and pelvis. All targeted vessels were well depicted with MR DSA. Corresponding dynamic information (contrast arrival time t_a and duration of the arterial phase t_av) was measured: t_a/t_av = 3.4/4.7 s for the lung, 10.3/4.9 s for the brain, 12.8/19.3 for the aorta, 15.2/12.6 s for the leg. MR DSA can provide dynamic angiographic images using a very short acquisition time.     

Hepatic blood supply: comparison of optimized dual phase contrast-enhanced three-dimensional MR angiography and digital subtraction angiography

PURPOSE: To optimize and determine the value of dual-phase contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography for preoperative evaluation of the blood supply to the liver. MATERIALS AND METHODS: Dual phase 3D MR angiography of the hepatic arteries and portal vein was performed in 140 patients. In 80 patients, the value of fat saturation, digital image subtraction, an anticholinergic agent, and a high-caloric meal were evaluated. In the next 60 patients, MR angiographic and digital subtraction angiographic (DSA) image quality and diagnostic value were compared. RESULTS: Fat-saturated images were of significantly better quality (P < .01) than non-fat-saturated images. Digital image subtraction was useful in only 23 of 40 patients. The injection of an anticholinergic agent was superfluous, whereas administration of a high-caloric meal helped in demonstration of the superior mesenteric artery and portal vein. Classification on MR angiograms of the arterial blood supply was correct in 57 of 60 patients. All arterial and portal venous lesions were seen on MR angiograms, and MR angiograms had a significantly higher subjective image-quality ranking than did DSA images in the evaluation of the portal vein (P < .05). CONCLUSION: Fat saturation and use of a high-caloric meal improve the results of MR angiography of hepatic vessels. MR angiography was comparable to DSA for evaluation of the arterial system and was superior for demonstration of the portal vein; therefore, MR angiography could replace intraarterial DSA.     

Digital angiography

The many available methods of digital subtraction angiography (DSA) are briefly reviewed. At present the most commonly used are temporal filtration techniques, which include conventional subtraction, integrated remasking , and various types of filtering. Their present use in intravenous, as well as intra-arterial, DSA is shown. The "moving mask" subtraction technique for cardiac and coronary studies is of particular interest. The current status of second-order subtraction techniques such as tomographic DSA and parametric digital imaging is presented. The latter method is particularly useful for demonstration of shunts. Finally, several examples of non-angiographic and future applications of digital radiography are presented.     

3D rotational digital subtraction angiography may underestimate intracranial aneurysms: findings from two basilar aneurysms

3D digital subtraction angiography (DSA) allows clinicians to review intracranial aneurysms and other vascular lesions. We report 2 basilar aneurysms that were imaged by both 3D DSA and DynaCT. These 2 techniques produced very different aneurysm appearances. Anterior portions of the aneurysms were invisible on 3D DSA but were revealed by DynaCT. These aneurysms appeared to have been flattened by image artifacts in 3D DSA. Pulsation and gravity are 2 possible causes of aneurysm underestimation.     

Digital subtraction angiography--a critical analysis

The advantages and disadvantages claimed for intravenous and intra-arterial digital subtraction angiography (DSA) are critically examined. The parameters determining image quality and the factors degrading the image in intravenous DSA are discussed. It is argued that many of the patients specifically referred for intravenous digital subtraction studies are unsuitable for this examination either because poor image quality is to be expected and/or because the large contrast load inherent in this type of examination is undesirable.     

Digital subtraction CT angiography based on efficient 3D registration and refinement.

A novel method for fast, automatic 3D digital subtraction CT angiography (DS-CTA) is presented to generate artifact-free angiograms. The proposed method consists of two steps: 3D registration to align a CT image to the CT angiography (CTA) image and subtraction-and-refinement to extract blood vessels only. For efficient and accurate 3D registration in the first step, an normalized mutual information (NMI) based algorithm is adopted, and its fast version is developed by introducing a new measure. To further improve the subtracted image quality in the second step, a novel 3D refinement algorithm is suggested to effectively remove unwanted residuals. Experimental results of seven clinical CT/CTA head datasets demonstrate that cerebral vessels are well extracted from CTA images with almost no loss. The typical processing time is 3-9 min depending on the image size in a PC with a 2.4 GHz CPU.     

三维动态增强MR血管造影对颅内动脉瘤的诊断价值

目的 评价三维动态增强磁共振血管造影(3D DCE-MRA)在颅内动脉瘤诊断中的价值。方法 对54例高度怀疑有颅内动脉瘤的病人行3D DCE-MRA检查，随后行DSA造影及可行的血管内栓塞治疗。3D DCE-MRA用超快速三维梯度回波序列(3D FISP)(钆喷替酸葡甲胺0．2mmol／kg,1次扫描时间10s)，工作站上三维重建，比较3D DCE-MRA及常规DSA在显示动脉瘤、瘤颈及与载瘤动脉关系上的优劣，及对血管内栓塞治疗的价值。结果 39例脑动脉瘤患者共45个动脉瘤，3D DCE-MRA对动脉瘤的敏感度为96％，特异度73％，准确度90％。3D DCE-MRA对动脉瘤细节及瘤颈的显示明显优于常规DSA，尤其是颈内动脉海绵窦部及椎动脉近小脑后下动脉的动脉瘤，可指导DSA显示动脉瘤方向及预先制定治疗方案。但对周边部及动脉分岔处小动脉瘤的诊断应谨慎。结论3D DCE-MRA能无创有效地诊断颅内动脉瘤，所提供的三维信息对治疗方案的制定具有极大帮助。当诊断有怀疑时，应结合DSA检查。