CT cranial, facial, and cerebral procedures

examples of scan parameters

scan type

slice thickness

slice interval

DFOV

contrast

advantages of helical scan type

decreased scan time

decreased patient dose

PREFERRED FOR CONTRAST

helical disadvantages

decreased spatial resolution from image interpolation

axial advantages

increases spatial resolution

axial disadvantages

increased scan time

increased patient dose

table movement causes pt movement

technical facots set to balance

image quality and patient dose

should be used to minimize patient dose when possible

automatic mA modulation

width of each detector row used during the scan

acquisition thickness

high resolution scans use __ rows

high speed scans use __ rows

thinner

thicker

amount of anatomical data in each image

reconstruction thickness

thinner slices =

high spatial resolution

thicker slices =

lower image noise

should match the slice thickness, so all anatomy is imaged without overlap or gaps between slices

slice interval (reconstruction)

Area for processing, usually smaller than the total area being scanned

display field of view

contrast used to enhance

tissue discrimination

contrast used to differentiate between

normal tissues and abnormalities

routes of contrast

IV

oral

rectal

intra-articular

intra-thecal

as contrast goes through the body, it looks different at different times, so __ is essential

timing

scan is not limited to __ some require multiple times of scanning

one phase

First phase for any organ, peak contrast as contrast enters organ

arterial phase

Second phase for any organ, peak contrast as contrast leaves the organ

venous phase

Occurs at about 60 sec. post injection, peak enhancement of portal venous system

portal venous phase

Time after all contrast has washed out of the organs, only certain pathologies visible

delayed phase

delayed phase also called

equilibrium phase

depends on protocol selection, speed of the CT imaging system, size of the patient

volume

routine venous phase of average adult

100 mL

snmaller adults and children venous phase

1/mL per pound

arterial or angiographic volume

depends on speed and range of scan

Longer scans or slower systems require more contrast to maintain

optimal arterial enhancement (120-150 mL)

shorter scans or faster systems (>16 slices)

75-100 mL

arterial and angiographic injection rate

dense contrast bolus, 4-6 mL/sec

traditional venous injection rate

3 mL/sec

__ of vein is limiting factor

patency

maximum intraluminal pressure allowed measured in

pounds per square inch (PSI)

Volume, injection rate, max PSI can be set

pressure injectors

contains contrast and saline used during injection

syringes

single head

one syringe

dual head

two syringes (if two, one for saline one for contrast)

enhances image quality in the chest and reduce amount of
contrast needed for the exam

saline trailer

warms contrast up to 35 degrees C to reduce viscosity and reduce risk of extravasation

heating device

motor that drives plungers forward and maintains the rate

high pressure mechanism

used to set parameters

control panel

time between the initiation of contrast injection and the initiation of the scan

scan delay time (prep time)

delay time chest vs abdomen

chest: 30 seconds

abdomen: 60 seconds

most common and most accurate method for timing angiography exams

bolus tracking

used to measure enhancement of the selected vessel as contrast enters

ROi

when contrast reaches __ scan is initiated

prescribed threshold

small bolus of contrast injected into patient and
monitored at control console, after test bolus, an ROI is used to identify the team of highest contrast enhancement, time is set as scan delay time

timing bolus

CT preferred for initial evaluation of stroke, trauma, and mental status change

CT head w/o contrast

CT head scans have algorithms for viewing

bones of skull and soft tissues in brain

blockage of an artery

ischemic stroke

intracranial bleeding

hemorrhagic stroke

banana shape and follows curve of cranium

subdural

trauma and associated with skull fracture, convex shape

epidural

bleeding in the subarachnoid space, usually caused by ruptured aneurysm

subarachnoid

hemorrhagic stroke

intracerebral

help demonstrate skull fractures

volume renderings (3D)

for 3d images

thin slices

overlapping interval

smoothing algorithm

indicated for trauma and/or facial dental abscesses

CT facial bones

facial bone protocol is idential to orbits but

lower limit of scan and DFOV increase to include mandible

clear fluid-levels, esp. in maxillary sinuses

acute sinusitis

mucosal thickening without air fluid level

chronic sinusitis

CT sinuses do not include

mandible

CT sinuses use __ slices and should be performed with patient in __ position

thicker

coronal

when pt is prone

coronal images to be acquired directly and with better visualization of air-fluid levels

Used to identify small changes in mastoid ear cells, internal auditory canal (IAC) and inner ear

CT temporal bones/IAC

pt lies prone with chin for temporal bones bc

coronal images acquired directly with higher spatial resolution

examine structures in brain especially circle of willis

CTA head

why does CTA head not follow normal windowing for brain

needs to demonstrate contrast filled vessels in brain, not brain itself

when is CTA head typically requested

after CT head w/o contrast shows subarachnoid hemorrhaging

commonly performed for eval of stroke

CTA head and neck

CTA head and neck examines

arterial structures of the brain and arterial structures
supplying blood to the brain

pathologies for CTA head and neck

thrombosis, aneurysm, stenosis, dissection, assess vascular supply after neck trauma

display max. HU value within the slice, instead of the
average, increases visibility of contrast filled vessels and
creates 3D appearance

MIP

allow multiple tissues displayed together with different
colors and transparencies

VR

Image venous structures of the brain, called sinuses

CT head venogram

primary pathology of CT head venogram

cerebral sinus (venous) thrombosis
• Occlusions of cerebral veins causes stroke symptoms