Plain Film Tomography George David Associate Professor Department of Radiology Medical College of Georgia Resident Physics Lectures

Body Section Tomography Not CT Body Section Imaging Goal àkeep plane of interest in focus àblur all other plans »enhances contrast Popularity decreasing because of àCT àMRI

George David Tomography History Predates CT by decades Used to be popular for inner ear studies Still used at MCG for IVP’s

Tomography Blurring Blurring accomplished by synchronous movement of tube & film àtube & bucky physically connected by rod àrod pivots around fulcrum àtube moves one direction àfilm moves in other direction

George David Conventional Tomography Blurring Image produced on film Objects above or below fulcrum plane change position on film & thus blur

Tomography Blurring the further from the fulcrum an object is, the more it blurs!

Tomography Blurring objects shaped & oriented in direction of motion àelongate àdo not blur

Tomographic Blurring Blurring improved by use of complex motions circular tri-spiral elliptical Hypocycloidal

George David Complex Blurring The more complex the blurring motion àthe sharper the tomographic image »better blurring àthe more expensive the machine $

George David Tomo Patient Doses Tomo can be high dose procedure àseveral rads not unusual one image per cut with film àcuts at many levels routinely employed to find cut of interest àeach cut exposes entire field Can do multiple images per cut with digital receptor

Thickness of Cut Same as thickness of region in focus Determined by angle tube moves Larger angles yield thinner cuts àmore motion = more blurring Smaller angles yield thicker cuts à0 o (stationary) yields conventional film

Thickness of Cut Smaller Angle; Thicker Cut Larger Angle; Thinner Cut

George David Cut Thickness Approximate cut thickness for linear tomo Tomo Angle Thickness of Cut (mm) (degrees) Infinite (non-tomo)

George David Grids & Tomo Linear grid used Grid lines parallel with table for linear tomo Grid must change orientation (rotate) in complex motion tomo àeliminates grid cutoff