Modalities Flashcards
In dental radiography why is a stationary anode used?
because only a low kVp is utilised
isocentre when undertaking a Orthopantomogram?
Dental arch
What angle is given to a xray beam on a OPT unit?
15 degrees cranially (towards the head)
How is the soft tissue detail achieved on a Cephalogram
with the use of an aluminium filter
What does INR stand for?
International normalisation ratio
What distance should a radiographer be from the pencil beam in DEXA?
1m
What is a normal Z-score?
-What T-score indicates osteopenia?
-What T-score indicates osteoporosis?
-2.0 and above
-1.0 to -2.5
-2.5 and below
What is the anode in a mammography tube made from?
Molybdenum and/or rhodium alloy. Preferred to tungsten due to low atomic numbers.
What are the standard mammography views?
Craniocaudal and mediolateral oblique
What is the name of the device used to make radioactive isotopes?
Cyclotron
What is the keV of the photon gamma rays?
511 keV
Which radiopharmaceutical is typically used in PET-CT?
18 fuoride
What is the half-life of 18 Fluoride?
110 mins
What is the parent atom of 99m-Tc?
Molybdenum-99
Through what process does 99m-Tc decay?
Gamma decay
What would a Hounsfield unit of 0 mean?
Water
What is the name of the effect the transducer uses in US?
Piezoelectric effect
What is the half-life of 99m-Tc?
6 hours
What is the propagation speed of sound considered to be in soft tissues?
1540ms^-1
What is the photon energy of 99M-Tc?
140 keV
Advantage of helical scanning in CT
enables continuous rotation of the x-ray tube and therefore permits faster rotation times and therefore faster scanning.
Purpose of compression in mammography
- To equalize breast thickness so as to produce a radiograph with relatively homogeneous density across the whole breast.
- Increase resolution
- decrease movement unsharpness
- decrease patient scatter
- increase contrast
- decrease dose
Sound waves travel via
compression and rarefraction
How much does a gamma camera amplify the incident electron
Factor of 4^10
What is a flood test in RNI
To ensure that all photomultiplier tubes are functioning correctly.
quality control tests regularly undertaken in the radiopharmacy when preparing radiopharmaceuticals
Dab tests.
Broth tests.
breakthrough test
ensures that no traces of molybdenum 99 are present in the technetium 99m
accepted upper limit of ‘missed tissue at chest wall’ that is regarded as acceptable in mammography
5 mm
advantage of non-ionic contrast media compared to ionic
Ionic contrast media is associated with 4 times the number of reactions and is 5.5 times more likely to cause a severe reaction.
How are images created in PET imaging
Coincidence detection, two gamma photons with an energy of 511 keV are emitted at 180 degrees to each other, only photons that hit the detector at the same time are ‘counted’
what is a contrast agent product license
The Product Licence defines the accepted (i.e. evaluated) range of use of the contrast agent. Not all contrast agents are licenced for all ages or for all types of examinations.
What is the difference between ‘general’ gadolinium based contrast agents used routinely in MRI e.g. for brain imaging, and contrast agents used in MRI specifically for imaging the liver parenchyma?
The general type contrast agent passes through the extracellular space and is then excreted via glomerular filtration whereas liver specific agents are taken up by liver cells and excreted by the biliary pathway.
what are ultrasound contrast agents made from?
Ultrasound contrast agents contain microbubbles of carbon dioxide that are naturally absorbed by the patient’s body.
what is the benefit of 3T MRI compared to 1.5T MRI
At higher field strengths there is a greater signal to noise ratio; this can lead to improved resolution and / or reduced scan times.
which modality is considered a disruptive introduction
MRI
Patient group directions, and / or patient specific directions.
Legal framework within which the task of administering contrast agents and other medicines used in imaging is delegated to the radiographer
What advice does the Royal College of Radiologists give about giving iodine based contrast media to parents who are breast feeding (as of January 2022)?
A very small percentage of the injected dose enters the breast milk and virtually none is absorbed across the normal gut, hence no special precaution or cessation of breastfeeding is required.
What are the 4 gradings of evidence for justification of dental radiography
A, B, C, NSR
How many focal spots are used in mammography tubes?
There are usually two focal spots in mammography. They need to be smaller than in general radiography to increase the detail seen on the image. This is so that small calculi can be recognised. A focal spot size of 0.3mm is used, with an option to use a 0.1mm focal spot for magnification.
Of what material is the tube exit port made in mammography, and why?
Beryllium is used to reduce the absorption of low energy x-rays.
Why is the anode Heel effect is so important in Mammography
In mammography it aligns the cathode over the chest wall end (thicker area to penetrate, higher energy beam) and the anode over the nipple end (thinner area to penetrate, lower energy beam), therefore give a more even exposure across the image.
Tomosynthesis?
imaging technique creating a 3-dimensional reconstruction of breast tissue through a series of projections taken at various angles. This produces slices through the breast which when put together provide us with a diagnostic, 3-D image of the breast. It differs to mammography because it is not limited into putting a 3-D image into a 2-D plane. It gives us a more accurate representation of certain cancers which mammography cannot.
BIRDS/BIRADS
BRAIDs is an internationally recognise system for the assessment of mammograms
Disadvantages of NHSBSP screening program
- Radiation dose on non-symptomatic patients
- not 100% sensitive
- anxiety of screening for patients
- High false positive rate
- potential over treatment
DSA
Digital subtraction angiography
Which arteries are most commonly used to access the circulatory system in angiography?
Femoral Artery, radial artery, brachial artery
- Why does DSA tend not to be used for cardiac angiography?
Heart movement
4 common procedures in angiography
- Angioplasty
- Stenting
- Thrombolisation
- Embolisation
Which type of artefacts is DSA imaging particularly susceptible to?
Movement
Why do we administer antispasmodics during CT colonography?
During CT colonography, adequate distension of the colon is required to allow proper visualisation of GIT mucosa. Buscopan is administered to relax the colon and allow filling of the colon
Who can administer a medicine to a patient under a PGD?
Any registered health care professional named in the PGD
What are the categories of iodine based contrast media?
- Ionicity
- No. of benzene rings
Why are non-ionic dimer contrast media not used for CT fast bolus scans?
High viscosity
Which type of iodinated contrast media is used of patients at high risk of adverse reactions?
Non-ionic dimers
which type of iodinated contrast media can be used for extravascular imaging e.g. cystography
Ionic
How are MRI contrast media categorised?
- Linear/Macrocyclic
- Ionicity
What is a disadvantage of linear MRI contrast agents?
Increased brain deposition
What is the main risk of MRI contrast in high risk patients?
Nephrogenic Systemic Fibrosis
What are the 3 categories of dose dependent adverse events to contrast media?
- Minor:
flushing, nausea, vomiting, mild rash - Moderate:
severe urticarial, facial oedema, hypotension, bronchospasm - Severe: hypotensive shock, laryngeal oedema, convulsions, respiratory and cardiac arrest
What are the two types of adverse reactions to contrast?
DOSE DEPENDENT- due to high osmolality causing; anoxia, vasodilation, BBB breach, histamine release
DOSE INDEPENDENT-
- Anaphylactic due to prior sensitization involving MAST and BASOPHIL activation. this causes respiratory distress, cardiac dysfunction, shock.
- Anaphylactoid can occur without prior exposure due to direct mast cell activation and involvement of the complement cascade. (pseudo-allergic reaction)
What types of contrast agents are used in X-ray based imaging?
IODINE
BARIUM
AIR (double contrast although being replaced largely by CT colonography)
What types of contrast agents are used in MRI?
GADOLINIUM BASED
- Paramagnetic
- Shortens T1 relaxation time
- Causes bright contrast
IRON OXIDE
- Superparamagnetic
- Decreases T2 relaxation time
- Causes dark contrast
What types of contrast agents are used in US?
- IV administration of Micro/Nanobubbles consisting of perfluorocarbon, nitrogen, or sulfur hexafluoride stabilised in phospholipid membranes.
- This increases vascular contrast during imaging due to non-linear oscillation response of microbubbles to ultrasound waves.
13 components of a CT machine
Gantry
Collimator
X-ray tube
Filter
Collimator
Detector array
Data acquisition system
Emergency stop button
Patient table
Control panel
High voltage generator
Cooling equipment (e.g. liquid or air tube housing)
Slip ring
3 types of detector in CT
Scintillation crystals and photomultiplier tubes
Ionisation chambers
Solid state detectors
An effective detector array has …
- Fast response rate
- High detection efficiency
- Low cost
- High stability
- Wide dynamic range
CT scanner generations
FIRST- head only, single detector linear scan with pencil beam, 4-5 minutes
SECOND- Single projection fan shaped beam with up to 30 detectors, 30 degree rotation, 10-90 second
THIRD- Single projection fan shaped beam with up to 300 detectors and 360 degree rotation, 2-10 seconds
FOURTH- Single projection fan shaped beam with 360 degree ring of stationary detectors, 2-10 seconds
FIFTH- Electron beam scanners for cardiac imaging, 50msec scan
SIXTH- Multiple projections, fan shaped beam with 360 degree of stationary detectors and 360 degree rotation of tube, table movement allows continuous scanning of whole body through gantry bore.
SEVENTH- Multidetector CT with >10k detectors, 0.5mm section thickness, >20 simultaneous contiguous detectors, 12-15 seconds depending on body region.
How do CT scanners minimise cross talk between detectors in the array?
- Small gap between detectors
- Pre- and Post-patient collimation
How do CT scanners overcome the anode heel effect?
The rotating anode tubes are aligned with their long axis perpendicular to the scanning plane
Hounsfield units for common tissues…
Bone (average) +1000
Liver +40-70
Kidney +40-60
Fat -100
Lungs -150-400
Air -1000
Water 0
CSF +15
Contrast +100-300
In CT What is convolution and deconvolution?
Convolution is the process of modifying pixel values via a mathematical formula, this results in smoothing or a sharpening effect on the image, it is sometimes called a mask. With the process of deconvolution being the removal of the mask and returning the pixel values to their original level via the reverse process.
CT patient based artefacts
Motion
Transient interruption of contrast
Clothing
Jewellery
CT physics based artefacts
Beam hardening
Partial volume averaging
Quantum mottle (noise)
Photon starvation
Aliasing
Truncation
CT hardware based artefacts
Ring artefact
Tube arcing artefact
Out of field artefact
Air bubble artefact
Windmill artefact
Cone beam artefact
MPR artefacts
What is the principal purpose of having a small counterweight for the undercouch x-ray tube in a fluoroscopic unit?
The counterweight is intended to make the screening unit lightweight enough to move around the patient easily during screening, but also to stay in position when the table is tilted.
unsealed source in RNI
A source of ionising radiation that is not always contained and is often in liquid form e.g. an injection of radiopharmaceutical
Window width and level to display lung fields
Window Width 1500
Window Level -600
T1 recovery
losing energy to the molecular lattice
MRI quench
A sudden loss of superconductivity when the temperature of the superconductor is raised, either deliberately, or spontaneously resulting in release of the coolant.
what CT finding is associated with a thunderclap headache
Subarachnoid haemorrhage
Iodinated contrast development oldest to newest
Ionic monomers.
Ionic dimers.
Non-ionic monomers.
Non-ionic dimers.
Why have some linear chelate gadolinium based MRI agents been withdrawn from clinical use
evidence that some of these agents were associated with nephrogenic systemic fibrosis and also with gadolinium deposits being retained in tissues such as the brain as well as other organs.
constructive technology
DR
emerging technologies fro detection of breast cancer
Digital infrared thermal imaging of the breast.
MR elastography
eGFR screening
eGFR should be checked for all non-urgent patients where possible.
risk factors other than eGFR for NSF and AKI
Diabetes,
Hypertension,
Heart failure,
Kidney failure,
Kidney problems,
Being on renal dialysis.
In fluoro what does trendelenberg and anti-trendelenberg mean
- Trendelenburg = patient supine, with head tilted downwards.
- Anti-trendelenburg = patient supine, with feet tilted downwards.
What effect, in CT scanning, causes the Hounsfield Units to be lower than they should be in the part of the image corresponding to the centre of the patient?
beam hardening
What is the most common radiopharmaceutical used in PET imaging?
18F-FDG
MRI, sequence that completely eliminates fat signal from the resultant image?
STIR (Short Tau Inversion Recovery)
What are the effective energies typically used within a DXA scanner?
around 40 keV and 70 keV
Mammography tube anodes are typically constructed of a Molybdenum alloy which results in low energy photons of which energy?
20-30KeV
which part of MRI QA is detectable through regular control testing
SNR fluctuation
When undertaking an evaluation of CT number homogeneity as part of a CT quality assuarance programme which of the following values represents an acceptable level of error?
Should not exceed ±5 HU.
Why does the effective half-life of a radiopharmaceutical matter in terms of choice of agent?
If it is too short, it may be difficult to image the required physiology, if it is too long the patient will get an increased ionising radiation dose
what affect does changing slice width have on an image and dose
The use of thinner slice widths results in high resolution images but a higher dose.
What effect does narrowing the window width have on the images?
increases image contrast
In RNI what is a collimator
A structure that is placed over the surface of the gamma camera. It consists of lead slats that form holes through which gamma photons travel. The type of collimator influences the resolution/sensitivity of the gamma camera for the procedure. It removes gamma photons that are not perpendicular to the surface of the camera.
Match the ultrasound examination with the most appropriate probe frequency:
2.5 MHz
deep abdomen, obstetric and gynaecological imaging
3.5 MHz
general abdomen, obstetric and gynaecological imaging
5.0 MHz
vascular, breast and pelvic imaging
7.5 MHz
breast, thyroid
10.0 MHz
breast, thyroid, superficial veins, superficial masses, musculoskeletal imaging
15.0 MHz
superficial structures, MSK
Why is a full bladder required for pelvic ultrasound?
It creates an acoustic window enabling the surrounding anatomy to be visualised more clearly
Which mode of contrast is used when imaging the stomach during a barium meal examination?
Double contrast
With reference to developments and trends in the science of medical imaging identify the correct order of introduction into practice of the listed developments (from oldest to most recent).
Plain film radiography - wet film processing
Plain film radiography - daylight processing
Computed radiography
Direct digital radiography
With reference to developments and trends in the science of medical imaging identify the correct order of introduction into practice of the listed developments (from oldest to most recent).
Projection radiography
Ultrasound
Magnetic resonance imaging
PET-CT
co-registration
Combining multiple complementary modalites in a single image for example to demonstrate both structure and function.
Which vein would you most commonly use for intravenous administration of contrast media?
Basilic vein
correct dose of intramuscular adrenaline needed for an acute adult anaphlyactic reaction?
500 micrograms (0.5ml of 1 in 1000)
With regard to fluoroscopy what is the difference between digital zoom and magnification?
Digital zoom is a post processing function which enlarges the acquired image whereas magnification is where the image is enlarged during acquisition due to geometry.
Which regard to MRI, which of the following describes the relationship between magnetic field strength and processional frequency of magnetic moments?
They are directly proportional.
DXA scanners measure bone mineral density by ….
Using two discrete energies of x-rays and regions of interest to adjust to bone for nearby soft tissue and provide an areal bone mineral density measurement in g/cm2.
What is the primary reason for checking for diabetes mellitus before administering intravenous gadolinium based contrast media?
diabetes mellitus is associated with increased risk of poor renal function
Which type of contrast media should be used and why for a gastrointestinal contrast study in a patient with a suspected oesophageal fistula?
Water soluble as this is absorbed by, and non toxic to, the body’s tissues.
What development within CT means that the feasibility and effectiveness of national lung cancer screening is being reviewed?
Low dose CT.
One of the three ways in which a dual energy CT scanner may be designed?
A single detector and a single tube, with the tube able to rapidly switch between high and low tube potentials.
In what way might machine learning (a form of artificial intelligence) be used in MRI?
Machine learning can be used to automatically plan sequences (i.e. position scans slices or volumes on localiser images), increasing reproducibility and reducing positioning errors.
Software developments in MRI are leading to what are being called synthetic sequences. What does this mean in general terms?
Synthetic sequences are where a single acquisition is undertaken and reconstructed to yield multiple tissue weightings, thereby saving scanning time, and being of particular use for paediatric and distressed patients.
What do the initials ARSAC stand for?
Administration of Radioactive Substances Advisory Committee.
Under which legislation does the licencing for the administration of radioactive substances fall?
IR(ME)R 2017.
With regard to the administration of radioactive substances such as radiopharmaceuticals, which of the following statements is correct?
A practitioner must hold a licence in order to be able to justify the administration of a radiopharmaceutical to a patient.
In relation to the administration of radiopharmaceuticals, which of the following is the best explanation of a DRL?
A DRL (diagnostic reference level) is a specified dose level used in Radionuclide Imaging for a standard sized patient for specific examinations and equipment, and should not be exceeded for standard procedures.
When should an amendment to a licence that covers the administration of radioactive substances (radiopharmaceuticals) be sought?
When a new procedure is being introduced, when a procedure is changing (e.g. from research to diagnostic), when a significantly greater administered activity (above the diagnostic reference level) is intended to be administered.
How is data processed in MRI
The MRI signal is analogue; it is stored in analogue form until data acquisition is complete, then digitised.
With regard to gamma cameras, what is the difference between intrinsic and extrinsic Quality Control tests, and which is more relevant to clinical practice?
Intrinsic tests are performed without the collimators in place and test the inherent capabilities of the camera and image processing system itself.
Extrinsic tests test the whole system including the collimator performance and are more relevant to clinical practice.
How are intravenous iodinated contrast agents excreted from the body?
They are excreted in urine, unmetabolised, by the process of glomerular filtration through the renal system.
Precision medicine
A patient has breast cancer. The patient has had a biopsy and both the cancer and the patient’s blood has been genotyped. The patient has had the cancer staged histologically and through imaging. The patient’s treatment plan is based on all these factors.
define restoration of a digital image
an objective process that removes additive noise and distortion returning the digital image to its original form
Why is MRI disruptive
MRI is a disruptive technology as it did not build upon existing expertise, required new technology but did significantly outperformed existing modalities.
which group of patients are at increased risk of nephrogenic systemic fibrosis during administration of gadolinium based contrast agents?
Patients with renal impairment.
Patients in the perioperative liver transplantation period.
Infants, neonates and the elderly.
When might frequency domain filtering have a specific advantage over spatial domain filtering for image restoration?
To remove periodic noise from a digital image
Aliasing occurs in a digital image when:
the pixel size is more than half the width of the minimum object in to be resolved within the image.
Cones had a lower Weber ratio and therefore have better brightness discrimination.
True
Which function can be used to perform a contrast stretch?
s = αx + β
Which parameters are plotted for an isopreference curve?
The number of bits is plotted against the number of pixels in the digital images
what must the RPA hold
he RPA (Radiation Protection Advisor) must hold a valid certificate of competence from an organisation recognised by the Health and Safety Executive.
SNR
the ratio of the average signal to the standard deviation of the background.
What are the three fundamental steps required to perform image enhancement in the frequency domain?
- Convert the image to the frequency domain using a Fourier Transform
- Multiply the Fourier domain image by the Fourier domain filter
- Convert the image back to the spatial domain image using an inverse Fourier Transform
When noise is removed from a digital image in the spatial domain what effect does changing the mask size have on the final image?
The larger the mask the more smoothed/blurred the image is in removing the noise.
Why is it not possible to perceive colour in dim light conditions?
Scotopic vision uses rods which can only differentiate light intensity.
AUC of the ROC curve
an estimate of the discriminatory performance of an imaging system where AUC=1 is a perfect discrimination and AUC=0.5 has no discrimination.
What is the purpose of the filter function, H(kx, ky)?
To selectively supress some of the frequencies in the digital image
An example of a single sensor modality is:
First generation CT
How often should MRI RF pickup coils be checked?
Daily
