Current Protocols in Magnetic Resonance Imaging最新文献

Magnetic Resonance (MR) imaging of the brain following head injury is used in two distinct clinical contexts, (1) acutely, within days of the injury, to evaluate an unexplained neurologic deficit or to obtain prognostic information, and (2) chronically, to assess the degree of brain injury and explain neurologic or neuropsychologic findings. In this unit, two basic protocols are presented, one for acute imaging and the other for chronic imaging. Advanced MR imaging sequences, such as MR spectroscopy (MRS) and diffusion-weighted (DW) imaging can provide additional prognostic information in the acute setting and are also described. MR angiography (MRA) and direct vessel wall imaging techniques are mentioned briefly.

One of the most significant impacts of magnetic resonance imaging (MRI) has been its ability to exquisitely depict normal and pathologic anatomy of the spine. This unit presents a basic protocol for conventional fast spin echo imaging of the spine. An alternate protocol is presented for gradient recalled echo acquisitions that may be used in the sagittal and/or transverse planes to clearly distinguish between discs and soft tissue and to clarify the spinal neural foramen in the cervical region. A second alternate protocol is presented for contrast enhanced MRI acquisitions.

Contrast agents in general are exogeneous substances employed to alter natural tissue contrast. The motivation behind the use of contrast agents in MR imaging is to further enhance contrast between normal and diseased tissue types and indicate functionality of an organ. The focus of this unit is to give to the basic mechanisms of contrast agents in MR without going into their clinical applications.

Magnetic Resonance Angiography (MRA) is a robust and noninvasive technique for evaluating the vascular system with respect to deep venous thrombosis (DVT) of the lower extremities. This unit presents basic protocols for imaging the pelvic and lower extremity veins for evaluating DVT. A protocol is also provided for defining the sequence for imaging the pelvic and lower extremity veins with a stepping table.

Contrast (Azim Celik, General Electric Company, Milwaukee, Wisconsin and Weili Lin, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina). SNR (signal-to-noise ratio) determines the effectiveness of an imaging experiment. However, even the highest SNR does not guarantee the usefulness of an image. An important aim of imaging for diagnostic purposes is to be able to distinguish between diseased and neighboring normal tissues. If the imaging method used does not have a signal-manipulating mechanism which produces different signals for the diseased and normal tissues, then distinguishing the two tissues is not possible. This unit provides a detailed discussion of the contrast-producing mechanisms that arise from the signal dependence on a wide variety of tissue parameters.

Signal-to-Noise Ratio as a Function of Imaging Parameters (Azim Celik, General Electric Company, Milwaukee, Wisconsin and Weili Lin, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina). The degree to which noise affects a measurement is generally characterized by the signal-to-noise ratio (SNR, as measured by the ratio of the voxel signal to the noise standard deviation). This unit describes the importance of SNR in describing image quality. SNR is the key parameter for determining the quality of any given imaging experiment. If the SNR is not high enough, it becomes impossible to differentiate tissues from one another or the background. The dependence of SNR on imaging parameters such as the number of repetitions, the number of k-space samples (Nx, Ny, and Nz), the readout bandwidth, and voxel dimensions (Dx, Dy, and Dz) is explained in detail.

MRI techniques continue to evolve rapidly, but the basic components of a liver examination, and the clinical role of each component, have changed little. The three most important considerations for choosing techniques for imaging the liver continue to be contrast, motion artifact, and coverage. This unit presents a for liver imaging for General Electric (GE) scanners. However, these basic approaches to hepatic MR imaging are quite similar, with most details relating to minor vendor-specific differences.

Magnetic Resonance Imaging (MRI) has become a mainstay in the assessment of internal derangement of the knee. MRI prior to surgery increases diagnostic confidence. It also influences clinical practice by identifying alternative diagnoses, e.g., for an osteochondral injury that clinically may mimic meniscal tears, different surgical approaches exist for many cases. This unit presents the standard protocol for imaging injured knees in a clinical setting. The parameters given in this unit are derived from a 1.5 T machine and may need to be altered slightly depending on the main magnetic field strength and the equipment manufacturer.

Benefiting from superior tissue contrast, multi-planar capability and lack of bone artifact, MRI readily depicts complex anatomy in and about the pituitary gland. This unit presents three basic protocols for common indications relating to pathology of the sella and parasellar region. The protocols differ in emphasis more than in concept, and share a basic theme of thin slice high-resolution imaging including the use of gadolinium. With the possible exception of dynamic imaging, all protocols may be readily performed on any MR scanner.

Shoulder pain is a common clinical presentation. Though the spectrum of disorders affecting the shoulder is quite diverse, emphasis is often placed on abnormalities of the rotator cuff and glenohumeral joint instability. The rotator cuff plays an important role in both the function and stability of the shoulder. Moreover, its pathology, with early and accurate diagnosis, is amenable to treatment, which can markedly affect patient outcome. This unit presents an MR imaging protocol for evaluation of the glenohumeral joint. Though specific emphasis is placed on the rotator cuff, it can also be used for global assessment of the shoulder.