Intro to medical imaging Flashcards
how is an image produced using X-rays
- within an X-ray tube, electrons are accelerated towards a metal target
- interaction of electrons with the target produces photons (X-rays)
- some of the X-rays pass through the patient then hit a detector behind the patient
- some are attenuated by the patient (absorbed, scattered, lose energy)
- amount of attenuation depends on density and atomic number of tissue/material and energy of the X-ray beam
- detected X-rays are digitised and processed, creating an image
imaging techniques with X-rays
- x-ray single pulse of X-rays passes through patient to detector creating one image
- fluoroscopy continuous/pulsed X-rays, creating real-time moving images
- CT X-ray tube and detectors move around patient creating cross-sectional images
how does angiography work to generate an image of CVS
- intial X-ray image taken of anatomical region of interest
- second image taken of same region after iodinated contrast agent injected into the blood vessels
- the two images are digitally subtracted leaving only the iodinated contrast outlining the blood vessels
- radiologist compares the image to normal anatomical images
clinical use of X-ray
chest
- indications: dyspnoea, cough, haemoptysis, chest pain, post-procedure
- diagnoses: infection, pulmonary oedema, pleural effusion, pneumothorax, pericardial effusion, cancer
abdomen/pelvis
- indications: neonatal, urinary tract calculi, location of foreign bodies
- diagnoses: obstruction, volvulus, perforation, colitis, AAA
MSK
- indications: trauma, pain, deformity, swelling, post joint relocation, post reduction
- diagnoses: fracture, dislocation, effusion, soft tissue injury, tumour, infection
advantages of X-ray
- quick
- portable
- cheap
- simple
advantages of X-ray
- quick
- portable
- cheap
- simple
disadvantages of X-ray
- radiation (relatively low)
- one plane, two dimensional
- cannot see all pathology
- poor soft tissue imaging
how does fluoroscopy work
- pulsed or continuous X-rays are used which creates moving images
- can examine anatomy, pathology, motion and function
- images enhanced using contrast (barium/iodine)
- high atomic number = good absorber of X-rays so dense on image
clinical use of fluoroscopy
- diagnostic and interventional
- vascular (angiography) eg. cerebral, cori=onary, embolisation, angioplasty
- GI eg. barium swallow, barium meal, barium enema
- GU eg. urogram, hysterosalpinogram, nephrostomy, insertion
- MSK eg. arthrogram, therapeutic joint injections, orthopaedic surgery
advantages of fluoroscopy
- dynamic studies, can assess in real time and carry out intervention
- quick
disadvantages of fluoroscopy
- higher radiation dose than single X-ray
- radiation exposure to interventional clinician
- one plane, two dimensional
- cannot see all pathology
- poor soft tissue imaging
how does CT (computed tomography) work
- X-rays produced
- X-ray tube on one side of a rotating gantry and detectors on opposite side
- patient table moves through gantry
- cross-sectional slices of patient imaged
- detected signal processed by computer
clinical uses of CT
- diagnosis/further investigations/management trauma, bleeding, clots, ischaemia, pain, cancer, obstruction, calculi, weight loss, fever
- monitor conditions cancer, ILD
- interventional radiotherapy, CT guided biopsies, drains
advantages of CT
- quick
- good spatial resolution
- can scan most parts of body well
disadvantages of CT
- radiation
- does not delineate soft tissues well
- affected by artefact
- requires breath-holding
- overuse
- incidental findings
- contrast reactions