Current Protocols in Magnetic Resonance Imaging最新文献

Although contrast angiography is still considered the “gold standard” for evaluation of the aorta and its major branches, Magnetic Resonance Angiography (MRA) has quickly gained popularity as an imaging tool for the assessment of the entire aorta. MRA serves as an alternative imaging modality that can be utilized in patients with impaired renal function and with allergies to iodinated contrast medium (iodinated contrast medium is required in contrast angiography and computed tomography, CT). The purpose of this unit is to present fundamental MRA techniques useful in the evaluation of the thoracic and abdominal aorta based on experience on a 1.5 T GE LX scanner.

The glenohumeral joint boasts the greatest range of motion of any peripheral joint in the body, but not without cost; it is also the most frequently dislocated joint in the body. Stability of this articulation is limited for two major reasons. The articulating surface of the glenoid is significantly smaller than that of the humeral head, and the joint capsule is redundant and provides little support. This unit presents a basic MR arthrography protocol for evaluation of glenohumeral joint instability.

This unit outlines basic MRI protocols for evaluating the most common bone stress injuries including those of the tibia, femoral neck, femoral shaft, metatarsal, and navicular bone. The protocols concentrate on the lower extremity, as the majority of stress injures occur in this region. These protocols were developed using a 1.5 T system (Signa, General Electric Medical Systems). However, the sequences described could be adapted to low- or mid-field scanners using STIR (short tau inversion recovery) sequences to acquire the T2-weighted images. This technique would thus require longer scan times and lower resolution matrices.

Magnetic Resonance Imaging (MRI) for the evaluation of patients infected with human immunodeficiency virus (HIV), as with most other forms of intracranial inflammatory or infectious diseases, is a powerful though largely nonspecific diagnostic tool. For imaging of these complex patients with the varied and numerous pathologies they may harbor, the standard protocol is utilized to include gadolinium-enhanced sequences. This unit presents optional imaging sequences, including magnetic resonance diffusion (dMRI), magnetic resonance perfusion (pMRI), and magnetic resonance spectroscopy (MRS), that can be employed should patient tolerance allow and if specific the clinical situation requires further clarification.

Imaging goals for intracranial cerebral vascular disease are (1) to assess the degree of parenchymal injury and identify intraparenchymal hemorrhage; (2) to determine if there are areas of altered perfusion that may be at risk for future injury; and (3) to assess the intracranial arteries (patency as well as direction of flow). This unit describes a that can be used to evaluate stable patients with acute, subacute, or chronic cerebrovascular symptoms. An is also given for cases of hyperacute strokes or cerebrovascular symptoms in an unstable patient.

This unit presents a basic protocol for conventional and fast spin echo imaging of spine for visualization of the spinal compartment to assess the extent and degree of spinal cord or cauda equina compression frequently associated with primary and metastatic neoplasia. An alternate protocol is presented for the cases e.g., neurofibromatosis with multiple bilateral neoplasms extending through the neural foramina, where a coronal acquisition may be helpful to analyze the perispinal tissues for tumor extension either inward to, or outward from, the central spinal canal.

This unit discusses nulling of remaining signal from a RF pulse prior to the next RF pulse. This is to avoid mixing leftover signal with the signal generated from the next RF pulse. The slice select profile is also discussed in detail. The power of the RF pulse and its limit imposed by the Food and Drug Administration (FDA) is also discussed.Normal.

When a spin system is repeatedly disturbed by a fast repetition of RF pulses, the transverse magnetization after each new RF pulse approaches a steady-state value which is smaller than the thermal equilibrium value. The spin system takes a finite number of pulses before this steady-state is reached in a time that depends on both the T1 of the tissue and the flip angle of the RF pulse. The focus of this unit is on understanding the build-up of the magnetization to steady-state and the practical implementation of the simplest forms of imaging in the steady-state. Sequences utilizing a steady-state approach can be broadly classified as steady-state coherent (SSC) and steady-state incoherent (SSI) sequences. The SSC behavior is the subject of this unit.

This unit presents a basic protocol for fast spin echo sequences for imaging to diagnose stenosis of the spinal canal. Spinal stenosis is defined generally as a narrowing of one or more of the following: the central canal, foramina, and lateral recesses of the lumbar spine. Specifically, this stenosis can be classified into three types as defined by location: (a) stenosis of the central spinal canal, (b) stenosis of the intervertebral spinal neural foramen or foramina, and (c) stenosis of the lateral recess(es) of the central spinal canal.