Imaging Procedures HEAD Flashcards by Shelby Owens

Axial CTs of the head are obtained parallel to what ?

Inraorbital- meatal line

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How can you finesse a head Ct to lower dose to the orbital region and minimize beam hardening

Image 15 degrees above Infraorbital- meatal line . Parallel to skull base

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Obtaining thinner sections through the posterior fossa of the head does what for the scan?

Reduces beam hardening artifact

Artifact is usually caused by the petrous pyramids in the head ( these are temporal bones at the base of the skull shaped like a pyramid)

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What data acquisition mode will improve z axis resolution in a head ct?

What is the benefit of having higher resolution in head Ct ?

sequential mode ( also called axial mode)

better visualization of the brain during helical scanning

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What size sections are obtained from skill base to posterior fossa? From posterior fossa to vertex?

(2-5 mm)

5-10 mm

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Under what settings are thin (0.6mm) detector configurations used

thicker reconstruction settings

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what reconstruction kernal is typically used for the head

standard or soft tissue

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What are some other terms used to describe an algorithm?

filter or kernel

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What kernel can maximize bony details and help you see fractures or skeletal anomalies

high spatial frequency kernal

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What are the window levels and window widths for the following:

Gray/ white matter

Bone

Hemorrhage/ hematoma

Acute ischemia

Gray/ white matter

Bone
WL 400 WV 3000

Hemorrhage/ hematoma
WL 75 WV 150

Acute ischemia
WL 35 WV 25

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What is the doctor trying to diagnose by ordering a non contrast head ct for a trauma patient?

hemorrhage, blood clot, or acute stroke

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True/ False . The initial use of contrast in a patient with head trauma getting a CT can potentially mask a intra cranial hemorrhage

true

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What scan must be obtained before proceeding with thrombolytic therapy?

Non contrast head ct to rule out intracranial hemorrhage

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Indications for non-contrast head CT

tumors
Hydrocephalus 
abscess
bony abnormalities 
congenital abnormalities
primary neoplasms of brain 
endocrine pathologies

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What three factors aid in the high resolution imaging technique required to image temporal bones and auditory canal ?

THIN SLICES

small DFOV

High resolution kernels

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Explain the concept of MPR

the process of using axial acquisitions to create nonaxial two-dimensional images ( coronal, sagittal, oblique, or curved plane images)

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What is the benefit to the patient of conduction isotropic MPR in Ct ?

What scanners implement this technique?

Reduces added patient dose

MDCT scanners

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How do you maximize the resolution of small bony features in the inner ear ?

Acquire targeted thin slices on both sides with a small Display field of view

Small DFOV allowed for a more zoomed in picture

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What algorithm is used to acquire CT images of temporal bones

high spatial frequency algorithm / bone algorithm / bone kernel

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Imaging orbits can be obtained in two ways:

How thin are these sections near the orbits ?

along the axial plane
(parallel to IOML)
perpendicular to the axial plane

(1-3 mm)

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Acquisition of the orbit may include the following MPRs:

The oblique MPRs go through which structure?

Axial
oblique sagittal & oblique coronal

The optic nerve

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What reconstruction kernel is typically used to image the orbit?

What kernel could be used in the case of trauma ?

soft tissue or standard

bone

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What is the window level and window width of soft tissue and bone?

Soft tissue
WL 40 WW 400

Bone
WL 400 WW 3000

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In what case is contrast needed when imaging the eyes?

Looking for vascular abnormalities , inflammation, or neoplasms

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True/ False. | Its not necessary to optimize the protocol because the eyes are not sensitive to radiation

false

Axial images of the sinus cavities should be taken parallel to what structure ?

Hard palate

To capture the sinuses you need to extend the image to include all 4 sinus cavities what are they? What are there relative locations within the head ?

Sphenoid and Ethmoid sinus ( near the ears) Frontal Sinus (near forehead) Maxillary sinus ( near cheeks0

What two ways can you have the patient positioned to obtain coronal views of the sinus Direct coronal imaging is perpendicular to what plane?

1. prone 2. supine with chin tilted all the way up axial plane

Why is coronal imaging valuable when imaging the sinuses?

Helps doctor see changing air fluid levels and sinus related diseases

What complex in the sinus cavity is best visualized using coronal imaging? What's the second best MPR to see this structure?

Osteo-meatal complex Sagittal plane

The osteomeatal-complex is a common site for what diagnosis?

Sinus inflammation

What planes should be image to get a good visualization of the facial bones?

axial and coronal

What planes/ section size (mm) should be used to image the temporomandibular joint ?

Axial thin (1-3 mm) Coronal thin (1-3 mm)

True/ False . | You can only image the temporomandibular joint with the patients mouth closed

False. Open and closed

True/ False. Non contrast Ct's are usually performed to image the sinus cavity and facial bones

False. IV contrast typically used except in case of a neoplasm.

True/ False. It is common to obtain low- dose CTs of the sinus which usually consists of unlimited coronal imaging

False. Consists of limited coronal imaging

Brain CTA's identify what pathologies?

aneurysms, vessel malformation , vessel narrowing, blood clots in the brain , and traumatic brain injury

Helical scans of the brain are performed in what direction? | From what part to what part?

Caudocranial C2 --> dorsum sella (part of sphenoid bone)

Before contrast is administered what is done in the CT to evaluate the anatomy ?

survey scan of the brain; scout

What rate do you bolus inject contrast for a brain CTA

3-4 mL/sec

How does do you know when to press the scan button following the bolus injection of contrast for a Brain CTA ? ( 2 ways)

1. Identify the time at which vessel enhancement occurs 2. Use bolus tracking software . it monitors vessel opacification following administration and then scans automatically once the Hounsfield unit within the vessel has been reached.

How long of a delay should you use following contrast administration during a brain CTA

12- 20 seconds

Name three 3D techniques used in image reconstruction

Multi Imgage Projection (MIP) surface rendering volume rendering

How are thins manipulated during acquisition to maximize the quality of the MPR and 3D images

They are reconstructed with at least a 50 % overlap to them

True/ False . CT angiography images only the vessels inside the cranium

False. inside and outside the intracranial space

What does CTA SI stand for? | What is it used for ?

CT Angiogram Source images . Used for subtraction imaging. (Contrast enhanced- un enhanced ) helps see brain infarct

How can you modify CTA protocols to see the venous structures in the brain

adjust the bolus timing

What are the 3 steps of comprehensive MDCT management of acute stroke

1. pre contrast of head 2. CTA and of brain and carotid arteries 3. perfusion imaging ( looks at the flow through brain tissue)

What 3 factors are used to describe cerebral perfusion

CBV ( Cerebral Blood volume) CBF ( Cerebral Blood flow MTT ( Mean Transit Time)

What's the difference between Cerebral Blood Volume and Cerebral blood flow

CBV is the amount of blood in 100grams of tissue brain CBF is the amount of blood that flows through 100 grams of brain tissue in 1 minute

What's the normal range of Cerebral Blood Flow in the brain ?

50- 60 mL/ 100 g/ min

What is mean transit time ?

The average rate of blood flow ( in seconds) through a region of the brain

Mean transit time varies based on what factor?

arterial outflux and venous in flow over a region in the brain

What's the equation for Cerebral blood Flow?

CBF= ( CBV)/ (MTT)

three characteristics of an infarct core

Area of the brain with : 1. increased MTT 2. decreased CBF 3. Decreased CBV

What are characteristics of ischemic pneumbra Blood flow decreases by what percentage in ischemic tissue?

- moderate decrease in CBF - possible increased CBV 34%

What type of scan do you need to tell the difference between a core infarct and ischemic pneumbra? Which condition is irreparable and which still contains viable tissue?

CT perfusion of the brain core infarct - irreparable ischemic pneumbra- still has semi intact tissue

Brain tissue with a blood volume less than this value is considered infarct core

2.5 mL/ 100 g

Standard Brain CTA protocol for 64 slice scanner

a. non contrast axial scan of the head b. 50-75ml contrast . flow rate 4-5 ml sec c. Helical CTA acquisition d. 80- 120 kvp e. Reformatting of overlapping source images to produce, MIP, surface rendering and volume rendering images

What is the general difference between a CTA and CTP of the brain ?

CTA has high diagnostic value in detecting high degree of cerebral arterial stenosis whereas CTP provides high specificity in the detection of ischemia and infarct tissue of brain.

Protocol for CT perfusion acquisition and display include?

1. bolus 50 mL @ 4-7 mL/sec 2. scan at least 2mm of brain tissue for at least 45-60 seconds to be able to catch the first pass flow of contrast through the vasculature 3. Each slab of the acquisition should include major artery in the brain to accurately create the perfusion map 4. ROI placement goes over an opacified artery and an area of venous outflow 5. ROI info. creates color coded maps of CBV, CBF, & MTT

xenon ct perfusion imaging is done by injecting, ingesting, or inhaling xenon ? This test creates a brain perfusion map on the basis of what measurement?

inhaling cerebral blood flow

What is Deconvolusion ?

computer technique implied to create color coded perfusion maps from raw ROI information