1.6 Advanced Imaging CT

computed tomography principles

ionizing radiation, attenuates x-rays (body absorbs), slices

CT equipment

xray tube, table, detectors, computer

CT images are viewable in

three dimensions/360

advantages to CT image viewing

body parts rotates in space, easier view of complex anatomy

disdvantage to CT image viewing

not easily viewed in hard copy

scout image

preliminary image taken to orient imager to the precise location of viewing

volumetric imaging

multi-slice scanners, multiplanar

image thickness CT scan

thicker images contain more tissues

voxel

pixel x slice thickness

if a voxel contains more than one tissue

it will average the densities of the tissues

rapidly changing anatomy will be viewed

thin

disadvantage to CT image thickness

smaller area covered, may miss referred pain, greater concentration of radiation delivered to a tissue

windowing

imaging technique to adjust the brightness for a specific tissue type

bone windowing

soft tissue looks all one color and bone has detailed coloring

soft tissue windowing

bone looks all one color and soft tissue has scaled color

quality degradation, hardening

beams passing through dense substances causes hardening artifact that appears darker

artifacts

metals and patient motion can lead to streaking

clinical uses of CT

bone - subtle or complex fractures, rapid surgical planning, loose bodies, degenerative changes (joint too), health of IVD, rehab planning for nonunion or misalignment

advantages of CT

fast image collection, less expensive than MRI

limitations of CT

limited capacity to determine cell makeup, high levels of radiation exposure, not good at detecting blood, edema or ischemia, must be static