Diagnostic imaging Flashcards
What are the three parameters of an xray? Which ones relate to energy, and which to number?
Kilovoltage (kV) - energy
Milliamperage (mA) - number
Time (s) - number
What are the main diagnostic imaging modalities, and what basic elements do they rely on for image aquisition?
Xray - photons
Ultrasound - soundwaves
Computed tomography - photons
Magnetic resonance imaging: magnetic fields and hydrogen ions
What are the three potential outcomes for an xray beam travelling towards a patient?
Passes through the patient unaffected (black)
Absorbed by the patient (white)
Scattered by the patient (dangerous & decreased image quality)
What are the 5 radiographic opacities
MOST LUCENT
Gas
Fat
Fluid/soft tissue
Bone
Metal/contrast
MOST OPAQUE
Name three factors that will increase the amount of xray scatter
Increased area of the patient exposed to the primary beam
Increased thickness of the patient
Increasing kV
Name two ways of limiting scatter
Collimators
Grid
What does DICOM stand for?
Digital imaging and Communications in Medicine
(File format for DI)
What does PACS stand for?
Picture Archiving Communications System
In terms of kV and mA, how might you adjust these factors when radiographing the abdomen
Lower kV: enhance soft tissue structures
higher mA: compensate for low kV
In terms of kV and mA, how might you adjust these factors when radiographing the thorax?
High kV: thorax already high contrast due to air
Low mAs: keep time low as possible
What are the three principles of radiation safety?
Time (as few exposures as possible)
Distance (inverse square law, restraint)
Shielding (collimation & PPE)
What are the two main advantages of CT and MRI
Cross-sectional imaging removes superimposition (simplifies complex anatomy)
Increased contrast
Define: Hounsfield unit
In CT, the amount of the xray attenuated by a voxel is assigned a Hounsfield Unit relative to water (HU = 0)
Hyperattenuating (>0) = whiter
Hypoattenuating (<0) = blacker
List 5 advantages of CT
Simplifies complex anatomy (remove superimposition)
Increased contrast resolution cf xray
Multiplanar reformats
3D reconstruction
Fast image aquisition
List 5 disadvantages of CT
Radiation safety (more exposure than xray)
Soft tissue resolution not as good as MRI
Equipment accessability
Requires general anaesthesia
Patient size limited
List four advantages of MRI
Safe, no radiation
Extremely detailed soft tissue contrast
Eliminates superimposition
Multiplanar
List five disadvantages of MRI
Magnet is always on: interacts with pacemakers and attracts magnetic metals
Patient size limited
Equipment accessability
General Anaesthesia required for most procedures
Scans can take a long time (2 hours)
List 3 advantages of ultrasound
Safe: uses sound waves
Form of cross-sectional imaging: allows assessment of the internal structure of anatomy
Real time: assessment + guidance for sampling
List 4 disadvantages to ultrasound
Impaired by the presence of gas
Decisions need to be made at the time of examination
Not able to provide a specific pathological diagnosis
Artefacts
What three factors define an ultrasound wave
Frequency, wavelength, velocity
In ultrasonography, what is the pulse-echo principle?
The transducer sends a pulse of soundwaves, and measures the time it takes for the echo to return.
US machines assume the velocity of soundwaves in soft tissue is constant (1540 m/s)
distance = V x t /2 (to account for the time travelled to, and from, the interface)
What is acoustic impedence?
Acoustic impedence = density of tissue x velocity of sound
As the sound travels across the interface from one tissue type to another, the difference in acoustic impedence determines how much of the sound is reflected, and how much is absorbed.
Large difference in acoustic impedance = More sound refelected
Small differences are ideal, because more soundwaves are absorbed and can reach deaper depths
List two tissue interfaces where a high difference in acoustic impedence occurs
Air-tissue
Tissue-bone
What is the functional impact of chosing an ultrasound transducer with different frequencies
Increased frequency: better resolution, decreased depth
Decreased frequency: lower resolution, increased depth
What is the goal when choosing a frequency of transducer?
Choose the highest frequency that will still reach the required depth
In ultrasonography, what is B-mode and M-mode?
B mode = brightness mode (traditional US mode)
M mode = motion mode (able to tract the motion of a small slice over time)
Name six descriptors of ultrasound
Size
Shape
Margination
Location
Echogenicity
Echotexture
List four terms to describe echogenicity
Hypoechoic (darker)
Isoechoic (same)
Hyperechoic (lighter)
Anechoic (black)
These are relative terms between structures
What is this artefact?
Acoustic enhancement
Tissues distal to a fluid filled structure are hyperechoic to surrouding tissue (useful artefact)
Decreased reflection by fluid> increase sound waves penetrate distal structures > able to reflect more soundwaves
What is this artefact?
Acoustic shadowing: structures distal to a highly reflective surface are lost on the image
What is this artefact?
Mirror image: Duplication of structures across a highly reflective curved surface
Characteristic location: reflection of the gallbladder across the diaphragm
What is this artefact?
Refraction artefact: refraction (bending) of the sound wave around a curved structure
In the presence of free fluid, edge of the urinary bladder appears to have a hole
What is this artefact
Reverberation artefact: multiple hyperechoic linear structures at regular intervals
Dt repeated bouncing of sound waves between two reflective structures
E.g. between transducer and skin (use acoustic coupling gel), or transducer and superficial gas filled structure
Echocheck: List abdominal structures in increasing order of echogenicity
Fluid: urine, bile
Renal medulla
Renal cortex
Liver
Spleen
What layers of the small intestine are seen here?
Outer hyperechoic: serosa
Outer hypoechoic: muscularis
Inner hyperechoic: submucosa
Inner thick hypoechoic: mucosa
Center hyperechoic: mucous layer/lumen
What are the roentgen signs?
Size
Shape
Location
Number
Margination
Opacity
How do you assess kidney size on a radiograph?
DV projection:
Dog: 2.5-3.2x length of L2 vertebrae
Cat: 2.4-3x length of L2 vertebrae
Is this dog in R or L lateral recumbancy?
Right lateral recumbancy
Gas moves to left (nondependent) stomach (fundus)
Crura parallel
Is this dog in R or L lateral recumbancy?
Left lateral recumbancy
Gas moves to right (nondependent) stomach (pyloris)
Crura crossed
How do you identify a suspected obstruction in the small intestine on a radiograph?
Lateral projection
Dog: >1.7x height of L5
Cats: serosa-serosa measurement > 12mm
How do you identify if the pulmonary artery/veins are normal size?
Dog, lateral: no wider than 4th rib
Dog, VD: Same width at intersection of 9th rib
Cat, VD: 1.6x at intersection 9th rib
How do you identify if the cranial mediastinum is an appropriate size?
VD:
Dog: 2x width vertebrae at this level
Cat: no wider than vertebrae at this level
How do you identify if the heart in a dog is of normal size?
Lateral: width = 2.5-3.5 intercostal spaces;
Height = 2/3 thoracic cavity
VD: 2/3 width thoracic cavity
How do you identify if the heart in a cat is of normal size?
Lateral: width 2 intercostal spaces (5th-7th);
height 70% thoracic cavity
VD: 50% width of thoracic cavity
What joint is indicated by the top arrow?
Antebrachiocarpal joint
What joint is indicated by the middle arrow?
Intercarpal joint
What joint is indicated by the bottom arrow?
Carpometacarpal joint
What joint is indicated by the top arrow?
Tarsocrural joint
What joint is indicated by *+#?
Proximal intertasal joint
* Talcalcaneocentral
*Calcanoquatral
What joint is indicated by the middle arrow?
Distal intertasal joint
What joint is indicated by the bottom arrow?
Tarsometatarsal joint
Which ultrasound transducer would you choose for small animal (<40kg) abdominal ultrasound?
5-8MHz curvilinear
Which ultrasound transducer would you select for a >40kg animal abdominal ultrasound?
1-3 MHz curvilinear
Which transducer would you choose for examining superficial structures?
5-15MHz linear array
Which transducer would you choose for echocardiography?
Phased array
