ECP 5 Flashcards
Ultrasound what does it allow you to see, and what is the specificity and safety
- Allows evaluation of the internal structure of organs
- Dynamic ultrasound evaluation can allow evaluation of function
- Often has low specificity for identifying specific diseases - don’t know what it is
Cytology and histopathology may be required for lumps
No confirmed adverse biological reactions
What is involved with preparing the patient for ultrasound and echocardiology
- sedate, clip, alcohol and gel - don’t need to clip or sedate horses if temperament allows
- Ultrasound gel - improve transmission of sound and allow probe to glide over skin
○ Need to clip a fair amount of hair up under the rib cage - Fast animals prior - doesn’t penetrate through dense tissue/food or gas filled spaces - morning generally less gas
- Echocardiography -> Can be performed without sedation, using an echocardiography table
What are 3 important reasons to sedate during ultrasound
- Reduce stress and anxiety
- Reduce panting
- Relaxed abdominal wall - US probe can be pushed into tricky places
What are the 3 types of ultrasound
1) B-mode imaging - most common - provides a real time cross-sectional 2D image
2) M-mode imaging - provides a graphical trace of motion over time and is used in echocardiography
3) doppler mode - provides information on blood flow
Doppler mode what does it provide information on, how to interpret and the 2 types
- Provides information on blood flow -> is it moving in the right direction, regurgitation
- BART - blue away red toward, green in the middle (can reflect turbulence)
Types
○ Colour doppler superimposes direction and velocity of blood flow over the B-mode image
○ Spectral doppler allows quantification of velocity -> degree of stenosis, larger stenosis faster velocity
§ Pulsed wave doppler -> measures the velocity within a well-defined area, trace overtime of velocity of blood flow
Continuous wave doppler -> accurate for high velocity flow
How are ultrasound images made
- Images are formed one scan line at a time, based on the pulse echo principle
§ Each line sends out sound that is reflected as an echo which is then detected then move across etc.
what determines the depth and brightness of displayed echo
- The travel time of pulse to echo determines the depth of the displayed echo
○ Higher travel time arise from deeper tissues
○ Velocity of sound in tissue 1540m/sec - assumed so can place the spot on the - ALL TISSUES THE SAME - The amplitude of a returning echo determines the brightness of the displayed pixel
○ Stronger reflector higher amplitude brighter pixel
○ Weak reflector lower amplitude echo darker pixel
What are the 3 interactions of sound with tissue
- Transmission - moves through
○ Occurs when tissues have similar density and velocity of sound in that tissue
○ Acoustic impedance (Z) = velocity (v) x tissue density (p) - Refraction -
○ Bending as energy passes from medium of one density to a medium of another density
○ Ultrasound probe can detect echoes that are reflected through an angle of <3degrees
○ Mostly ignores the refraction lines - Attenuation - tissue heating
A reduction in amplitude of sound due to absorption, scattering and reflection
What are the 2 things that influence the rate of sound attenuation
- Distance -> greater distance, greater depth = more attenuation
- Frequency -> higher frequency = more attenuation
Acoustic impedance mismatch what is it and what are the 2 main structures involved
- Ultrasound can’t penetrate through bone or lung due to this - use radiograph instead
- Bone: most sound is absorbed so high acoustic impedance -> casts a distal acoustic shadow -> cannot see internal structure of bone
- Lung: most sound is reflected so low acoustic impedance -> bounces between lung and detector -> thinks it’s an echo back -> reverberation artefact
What does the ultrasound transudcer do and what are the 3 types
- Converts electrical energy to ultrasound, and coverts echoes into electrical signals
- Operator selects main frequency band used which changes based on:
Types - leads to different footprints (shape of field of view)
1. Linear array-> most common in larger animals and more dense, produces rectangular field
2. Curved array -> most common in small animal, produces trapezoid-shaped sector
3. Phased array -> tend to be specific for echocardiology - B-mode with colour doppler - triangular with narrow top
Ultrasound transducer what should you consider
When selecting a transducer, consider the frequency and the footprint of the transducer.
- Low frequency transducers are used to image deep structures BUT LOW SPATIAL RESOLUTION
Spartial resolution in terms of ultrasound what are the 2 types and what makes better resolution
- Best is achieved with high frequency transducers and when imaging within the focal zone
1) Axial resolution - distinguishing 2 objects parallel to the direction of the ultrasound beam
§ Depends on the wavelength
§ High frequency transducers have short wavelength and good axial resolution
2) Lateral resolution - distinguishing 2 objects perpendicular to the direct of the ultrasound beam
§ Depends on ultrasound beam diameters
§ Narrowest with high frequency transducers and within the focal zone
Contrast resolution in terms of ultrasound what is it and what are the 2 things its controlled by
ability to display differences in echogenicity (greyness) of objects
1) Controlled by dynamic range
○ Use a low dynamic range for echocardiography
§ Difference between parenchyma and lumen
○ Use high dynamic range for abdominal ultrasound
§ Want to see all the shades of grey
2) Also our ability to perceive the different echogenicity
○ Best seen in low gain setting and in darkened conditions
Define echogenicity, anechoic, hypoechoic, hyperechoic and isoechoic
- Echogenicity - relates to the relative brightness of a structure
- Anechoic - have no echoes within them and appear back -> urine filled bladder
- Hypoechoic - darker structure when two structures are compared
- Hyperechoic - lighter structure when two structures are compared
- Isoechoic - if two structures have the same echogenicity
Nuclear scintigrapy what does it do and the 3 molecules involved
- images the distribution of a radiopharmaceutical within the body, using a gamma camera resulting in structure and function ○ Make the body radioactive 1) Radionuclide 2) Radioactivity 3) Radiopharmaceutical
What is a radionuclide, radioactivity and radiopharmaceutical
1) Radionuclide
○ radioactive atom with an unstable nucleus
○ undergoes radioactive decay and emits the excess energy as radiation
2) Radioactivity [Bq]
○ rate of radioactive decay of a radionuclide with spontaneous emission of radiation
○ Half-life = time taken for radioactivity to reduce by half
3) Radiopharmaceutical
○ chemical containing a radionuclide, suitable for in vivo use to diagnose or treat disease
What is radioactivity dosage and radiation dose
Radioactivity dosage - amount of radioactivity administered to a patient
Radiation dose - amount of radiation absorbed by the body tissues
In terms of nuclear scintigraphy what does the radiopharmaceutical do, what is it made up of and example
radiopharmaceutical = radionuclide + ligand
- radiopharmaceutical allows the radionuclide to target the area of interest
○ Ligand - determines the physiologic distribution
Ligand eg - ○ 99mTc-MDP = Technetium Methylene Diphosphonate
§ bone scintigraphy
How does technetium work in terms of nuclear scintigraphy and what is the half life
Technetium starts as Mo and undergoes beta decay -> Tc which emits gamma rays as transitions from metastable to stable state (we get Tc at the metastable state)
HALF LIFE of 6 hours from metastable to stable state -> want to order the day before doing the study as doesn’t last as long
Generally at background levels within 24 hours
What are the 2 types of nuclear scintigraphy and what information do they provide
1) static acquisition - anatomic information - common to localise lameness in horses
2) dynamic acquisition - provides functional information - get multiple reading over time so see the movement of the radiopharmaceutical
Static acquisition nuclear scintigraphy what information does it provide and what used for
- Static acquisition anatomic information - common to localise lameness in horses
○ Bone scan -> able to see an increase in uptake of radiopharmaceutical in areas of active bone turnover -> problem area
Dynamic acquisition nuclear acquisition what information does it provide and the 2 main types
Dynamic acquisition provides functional information -> get multiple reading over time so see the movement of the radiopharmaceutical
1) Renal scintigraphy to measure GFR -> much more common in cats but still not as common
§ may be important to see when removing a kidney that the other kidney is functioning and won’t lead to kidney failure
§ Time activity curves allow you to quantify the GFR
2) Portal scintigraphy to diagnose portosystemic shunt - not as common anymore mainly just for laboratory testing
§ With a shunt over time the peak of radiopharmaceutical the peak occurs in the heart first and then liver or sometimes no peak in the liver -> BOTH SENSITIVE AND SPECIFIC FOR THIS DIAGNOSIS
Dynamic acquisition what are the main advantages and disadvantages
Advantages
- Provides functional information
- May be very sensitive -> sensitive at detecting physiologic processes
Disadvantages
- Poor anatomic resolution
- May have poor to moderate specificity
○ May be a “Hot spot” in the right shoulder = increased bone turnover but is it neoplasia, osteomyelitis, fracture
○ THEREFORE scintigraphy is usually followed up with other images modalities and/or biopsy
- The patient emits gamma radiation
○ Technetium is excreted by urine, faeces and saliva
What is important in terms of safety with nuclear scintigraphy
○ Follow the ALARA principle to be safe around animals - SAFETY
§ TIME - minimise the amount of time you handle the radioactive patient
§ DISTANCE - isolation for 24 hours until radiation has reduced to background levels
□ Horses -> area of equine barn isolated
§ SHIELDING - wear gloves, PPE to prevent contamination with urine, saliva if around scintigraphy
Computed tomography how works, and the 2 main types
- Uses x-rays to produce cross-sectional images
○ Very tightly collimated beam and can detect what is happening within a slice of the patient
Types
1. Multiple detector array - rotate X-ray source and detector
2. Stationary ring of detectors - stationary x-ray but rotary detector - Both used to recreate the internal structures with multiple slices used
Helical CT scanners what does it allow and the 2 main types
- Allow fast CT acquisition and can cover larger areas of the patient
- Types
1) Multi-slice helical CT Scanners = the best
§ Quicker to acquire information than single slice § Better resolution for reconstructed image using multiple scanner into sagittal plane
§ Can do 3D reconstruction as can reconstruct in any plane
2) Single slice scanner =
§ All information in transverse plane -> hard to reconstruct into sagittal plane
Concepts of nuclear scintigraphy what is a pixel element and the matrix and what does this influence
- Pixel element forms basis of 2D images, but represents information from a voxel (3D volume element - represent level of thickness)
- Matrix is the number of pixels used to reconstruct the image
○ 256 x 256 small matrix = poorer spatial resolution
○ 512 x 512 large matrix = better spatial resolution
§ But signal from the image becomes less as smaller voxel
§ Data file is also much larger -> how are you going to store this information
Concepts of nuclear scintigraphy what is the slice thickness and how does this change resolution
- Slice thickness - can influence the
○ Thicker slice - more x-ray absorption information so better contrast resolution, less quantum mottle but end up with volume averaging artefact (cause thick may have area of lung and heart but needs to average out these tissue - represents the in-between and therefore reduced spatial resolution
§ With the nose - have fine turbinates so not good to have thicker slices
CT number what is it and how does it relate to window width and level, what do you want with bone and soft tissue
The CT number measures the degree of x-ray attenuation (HU units) within a voxel
Air - very low -1000HU
Bone - very high +1000
- Window width and level can be adjusted to optimise the image for different tissues
○ Bone window: WW 100 -> wide window, high centre (high level of HU)
Soft tissue window: WW 250 -> narrow window, low centre
CT what are the 4 main advantages
- Acquisition is rapid
- Post processing can produce different series, long after the animal has gone
- Multiplanar reformates allow the image to be evaluated in ANY plane
- 3D reconstructions allow a global overview of the anatomy
CT when is it useful and safety
CT is useful when:
- Superimposition prevents identification of lesions
- Soft tissue information is required
- Lesions are suspected but not demonstrated on radiology or ultrasound
Safety
- ALARA principles apply
- CT involves much higher doses of radiation than radiography
- ABSOLUTELY no manual restraint
MRI - magnetic resonance imaging how does it work
- Shows distribution of hydrogen atoms throughout the body
○ Water is an abundant source of hydrogen atoms THEREFORE MR imaging is water imaging - Hydrogen atoms rotate and act as a magnetic dipole
○ Normally they are all randomly aligned so no net magnetic moment
○ HOWEVER -> when in a strong magnet in hydrogen atom lines up -> become magnetised - SLIGHTLY POSITIVE IN THE DIRECTION OF THE MAGNETIC FIELD
○ If apply radio frequency wave at the right frequency knock the hydrogen atoms out of the alignment , as they return they release energy that is detected
§ RF coil emits the frequency wave AND detects the energy
MRI sequences what is it, the main sequence and how long does it take
MRI sequences are the pattern of radiofrequency pulses with different sequences emphasising different tissues
§ A study may then take 40-50 minutes to complete -> have to have a general anaesthetic
○ T2 weighted sequences - most important
§ Sensitive at detecting increased fluid with oedema, inflammation, neoplasia
MRI sequences what are the 3 main advantages and 2 main disadvantages
Advantages - Anatomic information - Very sensitive to pathology as most pathologies involve an increased water content (tumours, inflammation etc) - Great detail within superimposition Disadvantages - Takes long time to perform - Expensive
What are the 5 basic considerations for MRI safety
- Static Magnetic Field
○ Don’t bring in metal objects into the room!! - Switching Gradient Fields
○ Can induce electrical currents in wires placed on the patient and cause burns - Specific Absorption Rate (SAR)
○ Energy is deposited within tissue and may cause heating of tissue - Helium
○ From machine may leak into room -> decrease oxygen level - Noise
○ If in the room while occurring wearing head protection is recommended
Small mammal examination what are the 4 things you need and 3 other possible equipment
- Small scale (grams)
- Paediatric stethoscope
- Oral speculum (otoscope) -> larger green
- Pen torch (ophthalmoscope)
Possibly: - Sedation - to do full clinical examination and sometimes when taking blood
- Slides.
- Scalpel blade.
Small mammal examination what is important
- ‘Over the stable door’ observations first.
○ Demeanour, respiratory rate, effort and pattern, movement, environment and owner interaction, cage, food, bedding, droppings/urination etc.
§ Get owner to take from the cage -> see how interact and if they will bite
ALSO normal examination - TPR, weight, hydration, palpation, mouth (last on all animals besides ferrets)
Venepuncture where take from in rabbits, ferrets, rats and mice and guinea pigs
- Rabbits: Lateral saphenous (cephalic, lateral auricular - NOT ARTERY, jugular)
- Ferrets: Jugular, lateral saphenous (cephalic, Cranial vena cava)
- Rats & Mice: Lateral tail vein (vena cava)
- Guinea Pigs: Lateral saphenous (femoral if sedated, jugular too short, cephalic small)
Rabbits what are important considerations when examining and where are the main problem areas
- Care: Fractured back or jumping off table.
- Place back into cage backwards.
- Husbandry issues: Bedding (not enough bedding - feet issues), stress
○ diet - fibre main issue - need heaps of hay, oxbo pellet SMALL AMOUNT, leafy greens - not lettuce
PROBLEMS - mouth, gut (gut stasis EMERGENCY) and feet main issues (all areas can be an issue)
