Cross-Sectional Imaging Anatomy Notes

RAD6310: Cross-Sectional Imaging Anatomy

Introduction

Anatomical Structures

• Corpus callosum

• Choroid plexus of lateral ventricle

• Fornix

• Choroid plexus of third ventricle

• Third ventricle

• Red nucleus

• Substantia nigra

• Post, perf, substance

• Clastrum

Imaging Planes

• Axial

• Sagittal

• Coronal

Hounsfield Units (HU)

• Air: -1000HU

• Fat: -50HU

• Water: 0HU

• Muscle: +40HU

• Bone: +1000HU

• Metal: +3000HU

• 4000 Shades of gray available, only 256 can be displayed, which leads to overlap in grayscale.

• Each of the 256 represents ~16HU.

• Since only ~100HU separates muscle and fat, there would be very poor distinction between these tissues.

• This gives low contrast between tissues.

Windowing

• Width narrows the field, so that there can be increased contrast between the various soft tissues.

• Example: Width set to 400, each displayed shade of gray represents 2 HU. This is useful for distinctions such as muscle vs cysts vs fat, or normal muscle vs atrophic muscle with fatty infiltration. This is a good abdomen window.

• Level changes the center point of the 256 displayed shades of gray.

• Abdomen Level: width is still 400, and the level is +60HU. This is a good abdomen level.

• Bone Window: Width is 1400, and the level is now at +550HU. This allows the differentiation between normal cortical bone, trabecular bone, lytic or blastic changes.

• Lung Window: Width is still 1400, and the level is now at -400HU. This allows the differentiation between normal air space, consolidation, fibrosis, mediastinal changes, etc.