CT Theory 2 Flashcards
Planes of the body
- sagittal: left/right
- coronal: anterior/posterior
- transverse (axial): superior/inferior
CT procedure start to finish
- Patient and/or rex arrives. Asses clinical info and protocol assigned
- Patient is prepared fro appropriate protocol: lab work, previous exams/artifacts, communication and consent, prepare IV
- Position patient
- Acquire scout images
- Use scout images to set scan parameters
- Perform scan
- Dismiss patient
- Post-processing and storage of images
What lab tests are performed?
- BUN
- GFR
- Creatinine
What medical history is acquired?
- allergies?
- surgeries?
- thyroid conditions
- diabetes
- hypertension/heart condition
- pregnancy and breast feeding
- renal function
Explanation of procedure?
- speak clearly
- ask questions to ensure patient understands
- be a good listener, nod, eye contact
- use language patient understands
- answer questions, seek clarification
- be aware of fears and claustrophobia
- explain as you go
NECT vs. CECT
NECT: non enhanced
CECT: contrast enhanced
Phases of contrast injection?
- Arterial (bolus): early 15-25s, late 35sec
- Venous (non-equilibrium):65-80sec
- Delayed Venous (equilibrium): excretory = 3-15min
Ways of determining when to trigger a scan post-injection?
- Smart Prep:Localizer slice taken, set parameters, set ROI, Series of images taken (usually 2secs apart) to track bolus/CT numbers, Scan is triggered when HU threshold is reached
- Timing Bolus: measures patient cardiac output
What are retorspective reconstructions?
Change DFOV and/or target to produce image series form within raw data acquired
Another name for surface rendering?
Shaded surface display
Muscles of the rotator cuff?
- Supraspinatus: lies in the fossa
- Infraspinatus: large, triangular
- Teres minor: lies just below infraspinatus
- Subscapularis: anterior of scapula
When is a CT procedure ordered?
- Bone and soft tissue tumors
- To add info to radiographs
- Complex fractures
- Pre-arthroplasty planning
Advantages of CT over plain radiographs?
- Spatial relationships
- Ability for comparison of joints
- Bone and soft tissue can both be demonstrated with one scan
- Excellent contrast resolution
- MPR and 3D imaging features
Contraindications for CT procedures?
- Extensive hardware
- Pregnancy
General rules of positioning?
- Lower extremities: supine, feet first
- Upper extremities: supine, head first
- Ensure symmetry: no rotation
- Axial plane of anatomy perp. to scanner
- Use pillows and sponges to prevent patient motion
Shoulder Exam: positioning, anatomy included, FOVs
- supine, affected arm at side, unaffected arm raised, head first
- non-contrast
- include above AC joint to scapular tip
- Scout: AP and Lateral
- SFOV: large (body)
- DFOV: 25cm
- Slice thickness: 0.5-1mm
- Slice increment: 0.5-1mm
Shoulder exam: window settings, algorithm, reconstructions
-Algorithm: bone
-WW: 2000
-WL: 500
-kVp: 140, mA: 300
-Recons:
Standard soft tissue algorithm
MPR: coronal, sagittal, oblique
Surface rendering if indicated
Elbow: positioning, anatomy included, FOVs, etc.
- prone, affected arm extended over head, or supine with arm by side
- non-contrast
- include above elbow joint to below radial tuberosity
- Scout: AP and Lateral
- SFOV: large (body)
- DFOV: 15cm
- Slice thickness/increment: 0.5-1mm
Elbow: algorithm, window settings, reconstructions
-Algorithm: bone
-WW: 2000
-WL: 500
-kVP: 140 mA: 300
-Reconstructions:
Standard soft tissue algorithm
MPR: coronal, sagittal, oblique
Surface rendering in indicated
Wist: positioning, anatomy included, FOVs, etc.
- prone, affected arm extended over head or supine, arm by side
- non contrast
- include proximal wrist joint to proximal metacarpals
- Scout: AP and Lateral
- SFOV: large (body)
- DFOV: 10cm
- Slice thickness/increment: 0.5-1mm
Wrist: algorithm, window settings, kVp, mA, recons
-Algorithm: bone
-WW: 2000
-WL: 500
-kVp: 140 mA: 300
-Recons
Standard soft tissue algorithm
MPR: coronal, sagittal, oblique
Surface rendering if indicated
Hip: positioning, anatomy included, FOVs, etc.
- supine, legs flat, DO NOT elevate knees
- non contrast
- include above SI joints to about 4cm below less trochanters
- Scout: AP and Lateral
- SFOV: Large (body)
- DFOV: 30cm (symph to skin)
- Slice thickness/increment: 0.5-1mm
Hip: algorithm, window settings, kVp, mA, recons
-Algorithm: bone
-WW: 2000
-WL: 500
-kVp: 140 mA: 400
-Recons:
Standard soft tissue algorithm
MPR: coronal, sagittal
Surface rendering if indicated, pre-op planning, most frequently
Knee/Tibial plateau: positioning, anatomy included, FOVs, Etc.
- supine, legs flat on table, feet taped, or unaffected knee up out of way
- non contrast
- include above patella to below fibular head
- Scout: AP and Lateral
- SFOV: large (body)
- DFOV: 20cm
- slice thickness/increment: 0.5-1mm
Knee: Algorithm, window settings, kVp, mA, recons
-Algorithm: bone plus
-WW: 2000
-WL: 500
-kVp: 140 mA: 300
-Recons
Standard soft tissue algorithm
MPR: coronal, sagittal
Surface rendering if indicated, pre-op planning most frequent
Ankle: positioning, anatomy included, FOVs, etc.
- supine, legs flat on table, dorsiflex affected foot, move unaffected out of area of interest
- non contrast
- include above ankle joint through calcaneus
- Scout: AP and Lateral
- SFOV: large (body)
- DFOV: 16cm
- Slice thickness/increment: 0.5-1mm
Ankle: algorithm, window settings, kVp, mA, Recons
-Algorithm: bone plus
-WW: 2000
-WL: 500
-kVp: 140 mA: 200
-Recons
Standard soft tissue algorithm
MPR: coronal, sagittal
Surface rendering if indicated
8 cranial bones?
- Frontal
- Occipital
- Temporal x2
- Parietal x2
- Sphenoid
- Ethmoid
Bones in the anterior cranial fossa?
- Frontal
- Ethmoid
- Lesser wings of sphenoid
Bones in the middle cranial fossa?
- Sphenoid
- End of carotid canal
- Temporal bones
Structures in the posterior cranial fossa?
- Jugular foramen
- Occipital bone
- Foramen magnum
What cranial bones does the sphenoid articulate with?
All of them
What is the tubercullum sellae?
The anterior wall of the sella turcica (anterior to the dorsum sellae)
What are the hypoglossal canals? How do they sit in comparison to the foramen magnum?
Anterolateral to foramen magnum
-on occipital condyles
14 facial bones?
- nasal bones x2
- lacrimal bones x2
- zygoma x2
- maxilla x2
- mandible
- palatine x2
- vomer
- nasal conchae
Meninges of brain and their characteristics?
Dura Mater: outermost, strongest, continuous with periosteum
Arachnoid Mater: thin, delicate, middle layer, transparent
Pia Mater: inner, highly vascular, adheres to brain’s contours
What space contains CSF?
Subarachnoid space: between the pia and arachnoid mater
What does the falx cerebri separate?
The cerebral hemispheres
What does the tentorium cerebella separate?
Separates the cerebrum and cerebellum
What does the flax cerebelli separate?
The cerebellar hemispheres
4 ventricles?
- Right and Left Lateral (frontal/anterior horn, occipital/posterior horns, temporal/inferior horns)
- Third Ventricle: thin, slit-like, midline just inferior to lateral ventricles
- Fourth Ventricle: diamond shaped, anterior to the cerebellum and posterior to the pons
What parts of the brain does the lateral (sylvian) fissure separate?
The frontal and parietal
Where does the corpus collosum sit? What does it form?
Sits above the ventricles, forms the roof of the lateral ventricles
What are gyri? What are sulci?
Gyri: folds
Sulci: grooves
What is the difference between grey and white brain matter?
Grey: 35-45HU, neuron cell bodies
White: 20-30HU, myelinated sheath on nerves
What is the largest and most dense collection of white matter?
Corpus callosum
4 segments of the corpus callosum?
- Rostrum: most anterior
- Genu
- Body
- Splenium: most posterior
4 cerebral lobes?
- Frontal: most anterior
- Parietal: middle, posterior to central sulcus
- Occipital: most posterior
- Temporal: anterior to occipital, separates from the parietal lobes by the lateral fissure
Major components of the diencephalon?
- Thalamus: makes up portion of wall of 3rd ventricle, large, oval grey mass
- Hypothalamus: below thalamus, forms floor of 3rd ventricle
- Pituitary gland: connected to the thalamus by the infundibulum
- Epithalamus: most posterior
Where does the pineal gland sit?
- on the roof of the midbrain
- just posterior to the 3rd ventricle
- inferior to the splenium of the corpus callosum
Major segments of the brainstem?
- Midbrain: most superior, at junction of middle and posterior cranial fossa
- Pons: middle, large, oval shaped bulge posterior to clivus and anterior to cerebellum
- Medulla Oblongata: inferior from pons through foramen magnum
Important structures of the cerebellum?
- Lateral hemispheres: folds of grey matter
- Vermis: connects the lateral hemispheres
- Cerebellar tonsils: 2 rounded prominences on the inferior surface
- Cerebellar peduncles: nerve fiber tracts connecting to the midbrain
What 2 main pairs of arteries supply blood to the brain?
- Internal carotid arteries: anterior circulation
- Vertebral arteries: posterior circulation
Where do the internal carotid arteries enter the brain? What do they branch into?
Through the carotid canal of the temporal bone
- anterior cerebral artery
- middle cerebral artery (larger)
How do the vertebral arteries enter the brain? What do they unite to form?
Through the foramen magnum
-unite to form the basilar artery
Major dural sinuses?
- Superior sagittal sinus
- Inferior sagittal sinus
- Straight sinus
In what meninge are the dural sinuses?
The dura mater
Where do the dural sinuses drain into?
The internal jugular vein
Positioning for a head CT
- head holder or molded sponge
- patient supine, head first into gantry
- normal respiration
- eyes open or closed (can blink)
- SOML or OML
Why is it preferred to line up the SOML instead of the OML when CT imaging the head?
Reduced dose to the eye
Advantages of conventional head CT?
- allow gantry tilt
- highest image quality
- reduced radiation dose (minimal overlap)
Disadvantages of Conventional head CT?
- longer exam time
- limited ability to reconstruct data
- possibility of missed anatomy, misregistration
Advantaged of Helical head CT?
- shorter exam time (contrast enhanced studies)
- improved spatial resolution
- ability to reconstruct, use 3D tools
- allows slice increment to be changed retrospectively
Disadvantages of helical head CT?
- higher radiation dose
- does not allow gantry tilt