This unit presents protocols for MR imaging of masess of the elbow using T1- and T2-weighted sequences. An alternative method using post-contrast images is also provided, which may help to differentiate cystic or necrotic lesions from solid masses by defining a nodular or peripheral enhancing component in a cystic lesion versus more diffuse enhancement in a solid mass.
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.
This unit discusses the basic spin properties of the proton. The motion of a spin in an magnetic field that give rise to magnetic moment, is also discussed. The key to grasping much of MRI lies in understanding the concept of precession. Famous Bloch equation that basically leads to the description of the precession of a spin in the presence of an external magnetic field is also explained.
This unit presents an in-depth discussion of the radiofrequency field, including how variations in the RF field will cause variations in image intensity that are independent of the physical spin density and the effect of slice select gradients.
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 Basic Protocol that can be used to evaluate stable patients with acute, subacute, or chronic cerebrovascular symptoms. An Alternate Protocol is also given for cases of hyperacute strokes or cerebrovascular symptoms in an unstable patient.
When imaging patients for intracranial arteriovenous malformations, the goals are: (1) to determine if an arteriovenous malformation is present; (2) to assess size, shape, and location of the nidus; (3) to determine potential arterial feeders and venous drainage routes (including screening for aneurysms on arterial feeders); and (4) to determine the state of the surrounding brain parenchyma, including the identification of intracranial hemorrhage. A post-contrast 3-D spoiled gradient echo (SPGR) sequence is used for sequences 1 to 3. Standard MR imaging sequences are used to evaluate the brain parenchyma. The protocol contained within this unit can be used for the evaluation of stable patients. In order to perform the optional sequences with perfusion and diffusion studies, a scanner with echoplanar capabilities is required; however, the standard anatomical MR imaging sequences included in the protocols do not require these faster gradients.
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