Diagnostic radiology - CT, MRI Flashcards
CT vs MRI
- Radiation
- Exam time
- Bone detail
- Soft tissue detail
- Contrast
- Radiation
CT = yes, MRI = No - Exam time
CT = fast (3 min), MRI = Slow (30min+) - Bone detail
CT = good, MRI = poor - Soft tissue detail
CT = poor, MRI = good - Contrast
CT = Iodine-based, MRI = Gadolinium-based
CT vs MRI
- Hemorrhagic stroke Sensitivity
- Ischemic stroke Sensitivity
- Hemorrhagic stroke resolution
CT = excellent, MRI = poor - Ischemic stroke resolution
CT = poor, MRI = excellent
CT vs MRI to evaluate Stroke
- Availability
- Stroke induced Infarct sensitivity
- Stroke induced Hemorrhage sensitivity
- Availability
CT = good, MRI = fair - Stroke Infarct sensitivity
CT = Poor, MRI = good - Stroke Hemorrhage sensitivity
- CT = Good, MRI = Good
CT vs MRI
- Early progression of ischemic stroke
MRI can detect early edema changes in ischemic stroke much faster than CT
List 3 sequences of MRI and their indications
1) FLAIR (fluid attenuation inversion recovery)»_space;Better detection of lesions, suppress CSF
2) SPGR: Spoiled gradient recalled sequence: T1-weighted, fat attenuation»_space; Better anatomy
3) Diffusion weighted sequence»_space; Functional, observe fluid motion and perfusion
Application of MRI sequences on the CNS?
- Brain for acute stroke
- Spine for myelopathy, radiculopathy
- Infection
- Neoplasm
2 Advantages of MRI + 4 disadvantages of MRI
Adv:
- Excellent soft tissue contrast
- No radiation risk
Disadv:
- Limited availability, expensive
- Slow to perform
- Incompatible with implants, life support (ferrous metal)
- Nodular systemic fibrosis from Gadolinium chelates in renal failure patients
Assessment for fitness to use Gadolinium in MRI?
Check urine creatinine clearance to avoid Gadolinium chelates in renal failure
MRI
Principle of operation?
- Powerful magnetic fiuld align nuclear magnetixation of hydrogen atoms in water in the body
- Radiofrequency alter alignment of magnetization> produce rotating magnetic field
- Scanner detect magnetic field
- Computer reconstruct images
Hemorrhagic stroke
- Territories?
- Most significant D/dx?
Lobar territories: Frontal, temporal, parietal or occipital lobes
D/dx: Arterio-venous Malformations (AVM), common in temporal and frontal lobe, young patients with no Hypertension
Hemorrhagic stroke
- Territories?
- Most significant D/dx?
- Lobar territories: Frontal, temporal, parietal or occipital lobes
- Basal ganglia, Cerebellum, Brainstem
D/dx: Arterio-venous Malformations (AVM), common in temporal and frontal lobe, young patients with no Hypertension
Compare epidural and subdural hematoma:
- Cause
- Shape
- Bone fracture
- Cause
Epidural = Middle meningeal artery tearing (75%) or Transverse sinus tearing (25%)
Subdural: Bridging vein tearing - Shape:
Epidural = Lentiform (biconvex)
Subdural = Crescent - Bone fracture
Epidural = 90%
Subdural = no usual association
Compare epidural and subdural hematoma:
- Cross sutures
- Cross midline
- Clinical course and progression
- Cross sutures (Subdural crosses Sutures)
Epidural: No
Subdural: Yes - Cross midline
Epidural: Yes
Subdural: No - Clinical course and progression
Epidural: Rapid deterioration
Subdural: Chronic progression
Appearance of blood on CT over time?
Initial/ acute = Hyperdense (white)
Late/ chronic = Hypodense (black)
Define time for acute, subacute and chronic subdural haematoma
Acute = < 1 week
Subacute = 1-3 weeks
Chronic = > 3 weeks
Sensitivity of CT vs MRI in detecting ischemic stroke?
MRI: high - 86-100%
CT: Gradually improve sensitivity with time, Poor sensitivity for first 10 days
<1 day = 48%
1-2 days = 59%
7-10 days = 66%
> 11 days = 74%
2 main types of vessel occlusion in Ischemic stroke?
1) Small artery occlusion (<1cm = lacunar infarct, small hypodense area)
usually at basal ganglia and periventricular white matter
2) Large artery occlusion
MCA, ACA, ICA, PCA, Cerebellar or brainstem infarct
Range of Hounsfield units/ CT number in Bone, Clotted blood, gray matter, white matter, CSF, Water, Fat, Air
Hounsfield unit:
- Water = 0
- Fat = -20 to -100
- Air = -1000
CSF = 0-8 White matter = around 30 Gray matter = around 40 Clotted blood = 40-95 Bone = 80 - 1000
Multiple/ large number of lesions on CT suggests?
Metastasis
Disseminated infection
Outline 5 different shape of lesions and interpretation
1) Round/ Oval = slow displacing, growing lesion
2) Tubular = vascular or neural lesion
3) Wedge/ Triangular = Vascular territory affected
4) Polygonal/ plate = fibrosis pattern
5) Irregular/ Infiltrative = malignancy
Adverse reactions to iodinated contrast for CT
- Anaphylaxis (increased risk with prior history of contrast reaction, active asthma and allergies)
- Nephrotoxicity (increased risk with DM, renal impairment, dehydration)
- Fatal lactic acidosis- Metformin retention due to renal failure induced by iodinated contrast
Must not use metformin with Iodine contrast in CT
Name 2 contrasts for CT
Route of admin.?
Iopamiro (iodinated)
Water (oral or rectal contrast)
IV, Per-oral, Per-rectal
Typical effective dose (mSv) for CT head, chest and abdomen or pelvis
Head = 2.3
Chest = 8
Abdomen or pelvis = 10
Typical effective dose (mSv) for Barium swallow, meal, follow-through and enema
Swallow = 1.5 Meal = 3 Follow-through = 3 Enema = 7
Advantages of MDCT over conventional CT
Multi-detector CT
Advantage:
- Increase coverage with one rotation
- Improve spatial and temporal resolution
Advantage of CT over X-ray
- No superimposition
- 3D reconstruction for spatial resolution
