A Medley of Midbrain Maladies: A Brief Review of Midbrain Anatomy and Syndromology for Radiologists

The midbrain represents the uppermost portion of the brainstem, containing numerous important nuclei and white matter tracts, most of which are involved in motor control, as well as the auditory and visual pathways. Notable midbrain nuclei include the superior and inferior colliculus nuclei, red nucleus, substantia nigra, oculomotor nuclear complex, and trochlear nucleus. In addition, white matter tracts include the brachium conjunctivum, medial and lateral lemniscus, spinothalamic tracts, and the fiber tracts within the cerebral peduncles. Although neurologically vital, many of these small midbrain nuclei and white matter tracts are not easily individually identified on neuroimaging. However, given their diverse functions, midbrain pathology often leads to distinct clinical syndromes. A review and understanding of the location and relationships between the different midbrain nuclei and fiber tracts will allow more precise correlation of radiologic findings with patient pathology and symptomatology. Particular syndromes associated with midbrain pathology include the Weber, Claude, Benedikt, Nothnagel, and Parinaud syndromes. The oculomotor and trochlear cranial nerves also reside at this level. An understanding of their functions as well as their projected courses from the midbrain towards the eye allows identification of distinct locations which are particularly vulnerable to pathology

Parameter Optimization for Quantitative Signal-Concentration Mapping Using Spoiled Gradient Echo MRI

Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR) MR sequences for the use of gadolinium (Gd-DTPA) as a kinetic tracer. Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained. Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR) and the flip angle (FA). At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5%) over a physiologic range of concentration tracer concentrations. Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI

Clinical Neuroradiology

xi.272 hlm.; ill.; 28 c

Parameter Optimization for Quantitative Signal-Concentration Mapping Using Spoiled Gradient Echo MRI

Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR) MR sequences for the use of gadolinium (Gd-DTPA) as a kinetic tracer. Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained. Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR) and the flip angle (FA). At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5%) over a physiologic range of concentration tracer concentrations. Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI

Clinical neuroradiology : A case based approach

XII+272hlm.;28c

Parameter optimization for quantitative signal-concentration mapping using spoiled gradient echo MRI.

Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR) MR sequences for the use of gadolinium (Gd-DTPA) as a kinetic tracer. Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained. Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR) and the flip angle (FA). At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5%) over a physiologic range of concentration tracer concentrations. Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI

Extracranial Internal Carotid Artery Fenestration: A Case Report

Fenestration of the internal carotid artery (ICA) is an extremely rare congenital abnormality thought to be secondary to incomplete segmental fusion of vessels at the early stages of their development. Fenestration is usually asymptomatic and often misdiagnosed as arterial dissection. Distinction between the two can be challenging on both magnetic resonance angiography and computed tomography angiography, and digital subtraction angiography must often be utilized for precise characterization of the abnormalities. Certain imaging features, namely the length of the involved arterial segment, the regularity of luminal contour, the symmetry of arterial limbs, and the absence/presence of fusiform dilatation of either limb, produced by noninvasive angiography have the potential to help distinguish between an ICA fenestration and dissection. We report a case of an asymptomatic, true fenestration of a short segment of ICA and discuss its imaging characteristics