Volumetric rendering of MR images

The authors developed new techniques for three-dimensional display of magnetic resonance (MR) images that preserve soft-tissue definition, are fully automatic, and work with routinely used section thicknesses. MR images are segmented, selectively enhanced, and displayed by means of a volumetric rendering algorithm. These techniques were used to illustrate normal anatomy of the brain, knee, and liver. Three-dimensional rendering of balanced spin-echo images shows the ventricles and extracerebral veins and of T1-weighted images, the sulci and gyri. The large hepatic and portal vessels can be seen with these enhancement techniques. Three-dimensional views of the knee reveal articular surfaces of the tibia and clearly depict menisci and posterior and anterior cruciate ligaments. These techniques make it possible to image multiple soft tissues simultaneously while preserving the detail contained in the original images. Three-dimensional presentation of complex, overlapping anatomic regions is helpful in surgical planning and should lead to improved diagnosis.     

MR imaging of the cervical spine: techniques for two- and three-dimensional imaging.

This review briefly describes two-dimensional (2D) and three-dimensional (3D) MR imaging of the cervical spine and focuses on the current and potential clinical usefulness of 3D sequences in the evaluation of cervical spine abnormalities. The practical advantages of 3D imaging are several, and include an increase in signal-to-noise ratio over 2D imaging, thin contiguous slices, more accurate slice thickness, and optimal computer postprocessing. Different 3D techniques can provide either high- or low-signal-intensity CSF, with excellent suppression of CSF pulsation artifacts.     

Fast MR imaging: techniques and clinical applications

Fast MR imaging has matured in the past few years and is now of established value for several aspects of clinical MR imaging. The initial impetus for rapid imaging was to reduce scan times. Today its usefulness includes reducing motion artifacts, improved contrast per unit time, three-dimensional (3-D) imaging, real-time imaging, cine-mode imaging, and flow imaging. The focus of this review is on short-TR steady-state gradient-echo imaging. We discuss the basic sequence design of the mainstream fast techniques. Many important applications exist, including gadopentetate dimeglumine-enhanced MR imaging of the brain and spine, subsecond imaging of real-time applications, myelographic imaging of the spine, cardiac cine-mode imaging; 3-D musculoskeletal (knee) imaging, 3-D pituitary imaging; two-dimensional and 3-D body imaging; 3-D carotid and intravascular imaging, and reformatting 3-D images into arbitrary planes.     

3-Tesla imaging of the wrist and hand: techniques and applications

MR imaging of the wrist is complicated by its size and small critical ligamentous structures, such as the triangular fibrocartilage complex, intrinsic and extrinsic radiocarpal ligaments. 3-T magnetic resonance (MR) imaging with its nearly linear increase in signal-to-noise ratio allows for imaging the wrist with small fields of view and high spatial resolution, which in turn has potential to improve visualization of these small ligaments. Dedicated radiofrequency coils and appropriate imaging tools are required to optimize the potential of high field imaging of the wrist. Early results suggest improvement in diagnostic accuracy for the wrist when compared with 1.5 T in small studies; as larger series are acquired this will certainly become more evident. As experience with 3 T for the wrist and hand grows, it is becoming clear that it is the new standard for MR imaging of these small joints.     

CT和MR肝脏灌注成像技术及其临床应用

近年来随着CT、MR功能成像研究的发展,国内外有不少学者尝试使用CT、MR肝脏灌注成像评价肝脏功能及肝脏病变的血液动力学特征。综述了近来国内外CT、MR灌注成像在肝脏评价中的应用现状,重点是图像分析方法及临床应用。     

Clinical comparison of three-dimensional MP-RAGE and FLASH techniques for MR imaging of the head.

Three-dimensional (3D) MP-RAGE (magnetization-prepared rapid gradient-echo) imaging was evaluated as a high-resolution 3D T1-weighted brain imaging technique for patients with suspected neurologic disease. Fourteen patients were studied. In five, 3D MP-RAGE images were compared with 3D FLASH (fast low-angle shot) images. Signal difference--to-noise ratios and T1 contrast were not statistically different for 3D MP-RAGE images as opposed to 3D FLASH images. Advantages intrinsic to the application of 3D MP-RAGE sequences include decreased imaging time and decreased motion artifact. With this technique, it is possible to perform a relatively motion-insensitive, T1-weighted screening brain study with voxel resolution of 1.0 x 1.4 x 2.0 mm or smaller, in an imaging time of 5.9 minutes or less--permitting offline (poststudy) reconstruction of high-resolution images in any desired plane.     

颅神经三维磁共振成像技术的现状及展望

颅神经迂曲纤细,且毗邻复杂,很多疾病与其相关.三维磁共振成像技术具有较高的空间分辨力,且能够任意角度各向同性成像,已逐渐取代二维磁共振成像检查技术,成为颅神经成像的常用方法.对三维磁共振成像显示颅神经的现状及进展予以综述.     

颅神经三维磁共振成像技术的现状及展望

颅神经迂曲纤细,且毗邻复杂,很多疾病与其相关。三维磁共振成像技术具有较高的空间分辨力,且能够任意角度各向同性成像,已逐渐取代二维磁共振成像检查技术,成为颅神经成像的常用方法。对三维磁共振成像显示颅神经的现状及进展予以综述。     

Surface of the brain: three-dimensional MR images created with volume rendering

Image processing and volume rendering have been applied to magnetic resonance (MR) images to produce three-dimensional views of the surface of the brain. Four healthy volunteers and 17 patients with a variety of disorders underwent MR imaging of the head, and these images were processed and subjected to volume rendering. The resulting three-dimensional views depict abnormalities of the brain surface, as well as important landmarks of normal brain surface anatomy such as precentral, postcentral, superior temporal, and inferior frontal gyri, which are difficult to identify on cross-sectional images.     

CT and MR imaging of the thoracic aorta: current techniques and clinical applications

Disease of the thoracic aorta can present with a broad clinical spectrum of symptoms and signs. The accepted diagnostic gold standard, selective digital subtraction angiography, is now being challenged by state-of-the-art CT angiography (CTA) and MR angiography(MRA). Currently, in many centers, cross-sectional imaging modalities are being used as the first line of diagnosis to evaluate the cardiovascular system, and conventional angiography is reserved for therapeutic intervention. Understanding the principles of CTA and MRA techniques is essential to acquire diagnostic images consistently. This article reviews current CTA and MRA methods used in the evaluation of thoracic aortic disease.     

Noninvasive coronary imaging using electron beam CT: surface rendering versus volume rendering

OBJECTIVE: Three-dimensional data for noninvasive imaging of the coronary arteries are acquired from electron beam CT, multidetector CT, or MR imaging. Most commonly, surface rendering is used for three-dimensional processing, but recent advances in hardware and software technology have made it possible to use volume rendering. Our objective was to compare volume rendering with surface rendering for the visualization of the coronary artery tree. CONCLUSION: Our experience in the comparison of both techniques shows that because of intrinsic problems associated with surface rendering, volume rendering produces better image quality.     

Effects of window and threshold levels on the accuracy of three-dimensional rendering techniques in coronary artery electron-beam CT angiography

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate the effect of window level and gray-scale threshold on the demonstration of coronary artery lumina at three-dimensional electron-beam computed tomographic (CT) angiography. MATERIALS AND METHODS: Forty-four coronary artery branches in postmortem pigs were evaluated with electron-beam CT angiography, and the findings were compared with those from conventional angiography. Images from electron-beam CT angiography were reconstructed with maximal intensity projection (MIP), multiplanar reformation (MPR), and shaded-surface display (SSD). Four categories of window level and gray-scale threshold were evaluated. RESULTS: Three-dimensional electron-beam CT angiography accurately depicted the luminal diameters of the coronary arteries compared with conventional angiography (r = 0.83-0.90, P < .0001). The length of lumina visualized at electron-beam CT angiography was significantly shorter than that visualized with conventional angiography (P < .001). The use of MPR enabled visualization of longer segments of coronary arteries than did the use of MIP or SSD (P < .05). The higher the window level and gray-scale threshold used, the smaller the coronary luminal diameters measured (P < .05). The most accurate window level and gray-scale threshold (82.6 HU +/- 29.8 and 89.5 HU +/- 29.7, respectively) were found to correspond to the attenuation of the lumina (275.8 HU +/- 58.8). Results of simple linear regression showed a strong correlation between luminal attenuation and window level (r = 0.89, P < .0001) or gray-scale threshold (r = 0.95, P < .0001). CONCLUSION: Electron-beam CT angiography shows promise in the visualization of coronary artery lumina. For accurate display of lumina, a proper window level and gray-scale threshold for three-dimensional rendering techniques should be determined and used on the basis of the attenuation of the target vessel.     

Bronchial atresia: three-dimensional CT bronchography using volume rendering technique

We report a case of asymptomatic bronchial atresia of the anterobasal and laterobasal segments of the right lower lobe. Because of the absence of typical bronchial mucocele on chest radiograph, it was difficult to base the diagnosis on chest radiography alone. Helical CT images demonstrated the characteristic appearance of bronchial atresia, and three-dimensional (3D) CT bronchography using the volume rendering technique helped us to comprehend the spatial relationship between the dilated bronchus distal to the atresia and the more proximal bronchus.     

Gd DTPA. Future applications with advanced imaging techniques

In this admittedly preliminary view of the future, the authors present a number of new concepts in MR imaging and consider their possible advantages and limitations.