Imaging/Diagnostic Techniques Flashcards
define x-ray
a photographic or digital image of the internal composition of something, especially a part of the body, produced by X-rays being passed through it and being absorbed to different degrees by different materials
describe process of x-ray generation (briefly)
- High energy electrons passed from 1 electrode to another
- deflected down through patient to x-ray film
- X-ray can then be viewed
what does intensity of x-rays vary with
tube current, antomic number of target, tube voltage
3 possible x-ray interactions with matter
- scatter
- transmission
- absorption
attenuation
what increases it
process by which radiation loses power as it travels through matter and interacts with it
* inc with atomic number, density and thickness
attenuation coefficients
Air < Fat < Muscle < Bone < contrast agents/metal implants
why do different anatomical structures have different appearances on x-ray
different densities (and thus, attenuation)
describe the x-ray film
Luminescent screen - film emulsion - Luminescent screen
Emulsion contains silver halide; clumps form after exposure to light generated on luminescent screens
Ultrasound
- Non-ionising as sound waves
- use gel as can’t pass through air (doesn’t transmit)
- echo transmitted back to probe
explain barium
- radio-opaque contrast agent used for outlining the gastro-intestinal tract
- high atomic number means absorbs more x-ray photons than surrounding tissues
- declining use
explain computed tomography (CT)
- rotating x-ray tube
- multiple beams with single axis of rotation
- digital geometry processing… axial image
- often give iodinated contrast (intravenous, oral)
- IV contrast can lead to kidney failure?
Applications of CT
- trauma
- cancer staging and response to treatment
- guidance for procedures
Great for defining bony detail but exposure to radiation
ionising radiation and unit
particle/wave with sufficient energy to ionise a neutral atom/molecule and leave them with either a positive or negative charge - Sievert used to descibe the absorption of radiation by the human body
what can ionising radiation cause
cell damage:
* repair
* cell death
* mutating —> transformation
how to minimise radiation exposure
- inc distance
- minimise time exposed
- use lead shield to protect staff/patients
fluroscopy
medical procedure that makes a real-time video of the movements inside a part of the body by passing x-rays through the body over a period of time
iodinated contrast media
drugs containing iodine that are given to patients to enhance the ability to see blood vessels and organs on medical images such as X-rays or computed tomography (CT) scans. Provide greater detail.
MRI
- don’t show bone well but good with soft tissue
- slower than CT
techniques used to diagnose and stage cancer
- plain radiographs
- barium studies
- CT
- MRI
- PET
functions of cross sectional imagine (e.g. CT, MRI, PET)
- initial diagnosis and staging of dieseae
- biopsy of the lesions
- monitoruing response to treatment
- evaluation of residual mass after treatment
- recognition of complications of treatment
- when there is concernt for disease relapse
- treatment (minority of cases)
CT and radiation
- ALARA (as low as resonably possible)
- ensure whether examination is necessary
- adequate clinical inforation is essential for appropriate protocol
- avoid repeat examinations
MRI - how it works
- strong magnetic field aligns protons in the body in one direction
- radiofrequency pulse displaces protons and images created by displaing time take for protons to “relax” back to the original alignment
MRI cons
- claustrophobic and noisy
- motion artefact
- cannot image patients with pacmakers, aneurysm clips
Screening
- Diagnose disease at an earlier stage, before symptoms start
- cancer is easier to treat and most likely to be curable
- NHS screening programme Breast, Bowel, cervix
purpose of screeing
- test should detect disease at an early stage where treatment can alter outcome
- test should cause no harm
- test should have high sensitivity and specificity
- benefit to the individual and the population should outweigh the cost
scrrening for breast cancer
mammography
MRI safety concerns
radiation: burns, hearing, muscle twitch…
MRI contrast agents
Gadolinium DTPA is an IV contrast medium which causes changes in local magnetic field and so alters the tissue signal
Vascular lesions nd some tumours can be more easily seen
why should be limit imaging investigations
can be expensive and should only bbe requested when appropriate
what can inform the judicious use of imaging
guidlines
what can help to decide which radiological tests
would be most useful to distinguish between diagnoses or between normal and abnormal
basic statistical concepts
molecular imaging
- Radionuclide imaging
- Positron emission tomography (PET)
- Magnetic resonance imaging (MRI)
- optical imaging
what do gamma rays occur from
radioactive decay of unstable isotopes
what is molecular imaging
a field of medical imaging that focuses on imaging molecules of medical interest within living patients
radionuclide imaging vs x-ray
diagnostic X-rays are used primarily to study anatomy. Nuclear imaging is used to study organ and tissue function
properties of ideal isotope
- half-life similar to length of examination
- gamma emmitter (rather than a/B)
- radionucleotide should be readily available at hospital site
- easily bound to pharmaceutical component
- energy of gamma rays should be 50-300 keV
- radiopharmaceutical should be easy to prepare
- radiopharmaceutical should be eliminated in similar half-time to duration of examination
radiopharmaceutical
radioactive and pharmaceutical elements - designed to attach to part of body we are looking at
gamma camera
an imaging device used to image gamma radiation–emitting radioisotopes
used in CTs?
Single Photon Emission Computed Tomography (SPECT)
- CT version of nuclear medicine
- Gamma cameras rotate around area of interest
- routinely used for brain and cardiac studies
- can be applied to any site of interest in other studies (e.g. spine in bone scan or in lung scintigraphy)
Positron Emission Tomography (PET)
- molecular imaging
- uses radionucleotides that decay by postiron emission (Proton —> neutron + positron)
- These can be used to image biologically interesting processes
- can be used for absolute quantitation but requires arterial sampling
- all scanners now PET-CT
PET and inflammation
- rheumatoid arthritis
- aortitis
- ulcerative colitis
Risks/benefits of radiation
Risk: ionising radiation - induce fatal cancer
Beneits: diagnosis, management change, treatement
reasons to request laboratory investigations
- Diagnosis (to rule in or rule out a diagnosis/ confirm/reject clinical diagnosis)
- Monitoring (eg, the effect of drug therapy/ natural history or response to treatment)
- Screening (detection of sub-clinical diagnosis)
- Prognosis (prediction of course or outcome of the disease)
individual laboratory medicine specialities
- clinical biochemistry
- immunology
- microbiology
- haematology
- histopathology/cytopathology
- genetics
why is it important to adhere to laboratory sample acceptance policy
allows laboratory to produce the right result, on the right pateint, at the right time. Thus, allowing clinicans to give the right treatment in an timely manner. -good pateint care
vein to brain time
examples of use of laboratory tests in the patient pathway
Basic Metabolic Panel (BMP)
Comprehensive Metabolic Panel (CMP)
Lipid Profile.
Thyroid Test(s)
Complete Blood Count (CBC) with or without White Blood Cell (WBC) Differential.
Prothrombin Time (PT) with INR & Activated Partial Thromboplastin Time (PTT)
Urinalysis (UA)
pre-analytical errors that can contribute to erroneous electrolyte results - Vein to brain time?
not sure if right but gonna go with it
- inadequate or incomplete requesting
- issues with results not being seen in time or being icorrectly interpreted
- issues with quality of control
- interference/issues with analyser
- sample not collected on system
- delayed transit with unspun samples
