advanced imaging Flashcards
Conventional ct vs cbct vs mri image
Conventional ct: see outline of bony structures and soft tissue. Bone appear white.
Cbct: outline of bony structures, appear white. Soft tissue homogenous grey
MRI: bone appear dark, soft tissue appear white
What is the most commonly used generation of ct
3rd gen
Features of the third gen ct
No translation
Rotate-rotate movement
Fan beam
Faster scan times
What is pitch (ct)
How much the table travels per x ray tube rotation aka image thickness
Advantage and disadvantage of lower pitch
Better spatial resolution
Higher radiation dose (overlapping of anatomy)
Compare CT and CBCT in terms of image acquisition and equipment
Similar components (detector, x ray source) which patient located in the middle
CT multiple rotations, CBCT one rotation
CT beam fan shaped, CBCT beam cone shaped
What does pre patient collimator do
Restrict the size of the x ray beam entering the patient’s body, specifying thickness of cross sectional slice. Minimise radiation dose to patient
What does post patient collimator in ct do
Restrict x ray beam from entering detector assembly at arbitrary angles. This reduces the amount of scatter —> improve image contrast (hence soft tissue contrast on CT better)
What is Hounsfield unit
Representation of tissue density relative to water
Which views are available on CT
Orthogonal ie axial, sagittal, coronal
Oblique, surface render, MIP
No serial cross sectional, no panoramic
Which modality has bone and soft tissue windows
Ct
What is the average radiation dose of head ct
534-1100usv
Contrast agents are used for what modality
CT and mri
What do contrast agents do
Enhance soft tissue and vessels
Contrast agents contraindicated in patients with
Iodine allergy
Renal impairment
Indications for CT
Evaluate pathology eg soft and bony tissue involvement
Infection — soft tissue, osteomyelitis
Spitch
Evaluate trauma
Craniofacial evaluation
Paranasal sinuses and temporal bone evaluation
Investigate symptoms of headache, stroke (symptom investigation not indication for CBCT)
Principles of mri image acquisition (what does the magnetic field do)
In their natural state, atoms spin in random directions around their individual magnetic fields
Magnets in MRI scanner align hydrogen nuclei to the stronger MRI magnetic field
Radio frequency pulses emitted by MRI scanner intermittently. Hydrogen nuclei respond to RF pulses absorb and release energy at different intensities.
MRI coil detects these signals and processed by algorithm to form image
What is high SI in T1 pulse timing
MRI. High SI = white. T1 is weighted +/- contrast
Fat, blood, contrast, melanin, protein
(CSF dark)
What is high SI in T2 weighted image
Fluid, CSF, kidney, gallbladder
Strengths of mri
No ionising radiation
Excellent soft tissue detail
Use of of paramagnetic contrast agents can enhance soft tissue
Limitations of mri
Long scanning time 1.5-2hours
Expensive
Susceptible to metal artefacts which can severely distort appearance of MRI image, making diagnosis difficult
Contraindications for mri
Metal containing implants eg pace maker, cochlear implant. If patient unable to provide good history may do x ray to check
Metallic foreign body eg bullet shrapnel
Braces and dental implants not contraindicated as tend not to be magnet but can cause image distortion
Pregnant, strength of magnetic field biological effect on fetus
Impaired renal function — contrast risk of nephrogenic systemic fibrosis or side effect from contrast agents
Claustrophobic
Indications for mri
Soft tissue pathology
Malignant spread to lymph nodes
Edematous changes
Perineural involvement
Evaluation of TMJ articular disc
Evaluate vascular lesions
Plenav
What is the main use of nuclear medicine
Provide functional information (rather than morphological information), using radionuclides which are taken up and metabolised. Measure radioactivity of radionuclides.
Bone scans are 2d or 3d
2d
What are the application of bone scans
Bone activity eg Paget’s disease, condylar hyperplasia
Skeletal tumours, metastases
Infection, osteomyelitis
Fracture
Eg orthognathic surgery for patient with hemimandibular hypertrophy, see whether jaw growth has stopped
How do pet scans work
Positive emission tomography scans use fluorodeoxyglucose, taken up by glucose metabolising cells
Applications of PET scan
Diagnose and stage cancer and metastases
Infection, osteomyelitis
Oblique lateral mandible x ray can be used in evaluation of
Mandibular trauma
What is waters view used for
Paranasal sinuses and zygomatic arch
