Fluids + Imaging Flashcards
Will you see anaemia with haemorrhage? With a severe coagulopathy, what are possible ddx?
* Yes + possible hypovolaemic shock
* Anticoagulant rodenticide toxicity, hepatic failure, DIC, malabsorptive diseases
When might you see mild thrombocytopenia?
Secondary from blood loss/ increased utilisation, DIC
What is a heart murmur? Why would you see a heart murmur with anemia? What else could cause a heart murmur?
* Heart sounds produced when blood flows across one of the heart valves that is loud enough to be heard with a stethoscope– vast majority are due to turbulent blood flow brought on by high velocity blood flow
* the body has a lower than normal number of RBCs therefore the blood is thinner and flows faster than normal
* Structural abnormality (e.g. valve leaflet), fever, hyperthyroidism
In a dog with anticoagulant rodenticide toxicity, what kind of blood transfusion product would be ideal?
Fresh whole blood for the red cells, clotting factors, proteins, and platelets (lack of vitamin K reductase does not allow the activation of vitamin K and therefore lack of clotting— so fresh whole blood with stop bleeding by providing clotting factors that have been lost)
** Max is also hypovolemic and hypoxic shock from severe anemia– so supplementation of red cells is essential
What are possible complications from a transfusion?
* Acute immunological transfusion reaction- acute hemolytic reaction (type II hypersensitivity reaction), febrile non hemolytic reaction, non-hemolytic immunological reaction (type I hypersensitivity)
* delayed immunological transfusion reaction- delayed hemolytic reaction, post transfusion purpura (internal bleeding)
* acute non immunological tranfusion reactions- bacterial contamination of transfused bloods, hemolysis from damaged RBC transfusion, hyperkalaemia/hypocalcemia/hypomagnesemia after massive transfusions, hypothermia, circulatory overload
What are some things you can do to prevent transfusion reactions?
* blood typing (especially cats), cross matching major and minor (especially if second transfusion), test infusion 0.25 m/kg/h over the first 5-10 minutes, use of an in line blood filter, monitor patient parameters every 15-30 minutes during transfusion for acute reactions (demeanor, temperature, pulse rate and quality, BP, RR and character, MM colour, plasma and urine colour), ensure transfusion complete within 4-6 hours to preven bacterial growth, proper collection and storage of blood, appropriate blood donor screening
Dog with anticoagulant rodenticide poisoning, what other treatments over than an infusion?
* Vitamin K1 supplementation
* strict cage rest to prevent further hemorrhage
* oxygen supplementation
* Intravenous fluids
What are X-rays?
A form of electromagnetic radiation
EM radiations of frequencies higher than UV light have enough energy to remove an outer-shell electron from an atom and are therefore called ionising radiation (X-rays, gamma rays, and cosmic rays are ionising radiation). When ionising radiation interacts with atoms it causes the ejection of an electron and creates an ion pair which has the potential to damage cells.
** They can produce damage to molecules and induce temporary or permanent cell damage, causing problems such as mutations or cancer
What are some unusual properties of ionising radiation?
* You cannot see, smell, touch or taste it
* Penetrates all matter
* We do not develop tolerance or immunity to radiation
* There is little difference between how individuals react to a given dose
* Dose is cumulative
* Delayed effects: May take years to see the effects
What does it mean that effects of radiation are stochastic or deterministic?
* Stochastic- increased risk with increased dose– the dose of radiation you receive, a higher dose of radiation will increase the probability of a stochastic effect e.g. a genetic mutation leading to cancer– higher radiation dose or exposure will increase the chance of cancer developing (this is the one that is important in vet med)
** no threshold below which the risk of the effect will cease & effects are cumulative over a lifetime
* Deterministic- inevitable at high doses– in contrast with stochastic effects, the severity of the effect, not the probability, increases with increasing dose. Exposure below a certain threshold will not result in the effect (THERE IS A THRESHOLD). e.g. radiation induced skin burns, uncommon however in medicine
What is the direct effect of ionising radiation? Indirect effect?
* direct effects may damage DNA, protein or other macromolecules
* Indirect effects create free radicles within cytoplasm and these free radical damage macromolecules
** Cell may either repair itself or if DNA damage has occurred a mutation may result, causing cell death, cancer, or birth defects
In Victoria, the use of radiation comes under what department? And which Act? What does it state?
* Department of Health which administers The Radiation Act 2005– species that business must have a management licence to possess a radiation source and conduct a radiation practice & individuals must have a use licence
What is ARPANSA?
* A national governing body – Australian Radiation Protection and Nuclear Safety Agency– responsibility for protecting the health and safety of the people and environment from the harmful effects of ionising radiation. They publish a series of codes and standards then implement in the form of legislation.
RPS 17: Radiation Protection in Veterinary Medicine (2009)
** Also provide “Personal Radiation Monitoring Service”– monitors and records occupational exposure to radiation
What are the three basic methods of monitoring for radiation exposure?
* Thermoluminescent Dosemeter (TLD)- electrons int he crystal structure of the TLD card are excited to high energy levels as a result of irradiation and are trapped in the crystal structure. By heating the material, electrons return to their ground state and light is emitted. The amount of ligh is proportional to the radiation dose that the TLD material has received. Filters are used to allow only certain radiation to pass.
* Film badges- degree of darkening can be measured and will indicate the absorbed dose. But dose to film does not equal dose to tissue.
* pocket dosimeters– different to TLDs and film badges… pocket dosimeters can be read instantaneously– useful when high exposures are expected.
What tissues are more susceptible to radiation?
Rapidly dividing tissue
What is the recommended effective dose limit for occupational exposure? In a single year? What is the avg annual dose for veterinarians?
20 mSv per year, averaged over consecutive years
* 50 mSv in a single year
** Avg annual dose for veterinarians is around 16 microSv = 0.016 mSv
What is the ALARA principle?
* As Low As Reasonably Achievable
** Is the radiograph necessary for the patient and management of the case? Would ultrasound or a blood test answer the clinical question?
* Minimize retaking radiographs, minimize manual restraint, under no circumstances should any part of your body be within the primary x-ray beam
What are the three types of radiation encountered in medical practice?
* Useful beam
* Leakage radiation
* Scatter radiation
How can radiation exposure be minimised ?
Modifying
- Time (take good radiographs the first time around)
- Distance from the radiation source– the energy of the scatter radiation will decrease as distance from the radiation source increases, according to the inverse square law… e.g. so by doubling the distance from the radiation source, you will reduce your radiation exposure by a factor of 4. (avoid manual restraint, use ancillary positioning devices such as sand bags, stand well back)
- Shielding- concrete walls, PPE
How thick should lead PPE be?
Lead equivalent of 0.25 mm will shield scatter radiation with energy of up to 100 keV (electron volt)
What should the local radiation management plan follow?
ARPANSA RPS 17 + ALARA by observing time distance and shielding principles
How are x-rays generated? What elements are necessary for x- ray production?
* Generated in the x-ray tube by firing a high energy electron beam at a tungsten target
- A source of electrons (cathode)
- An obstacle- free path for the passage of high speed electrons
- A target (the anode) in which the electrons can interact, releasing energy in the form of x-rays
- a method of accelerating the electrons- electrical potential difference applied between the cathode and anode
What is the cathode? What is it made of?
* cathode acts as a source of electrons
* it is of a tungsten coiled filament mounted within a molybdenum focusing cup. Tungsten has a high melting point and a high atomic number. When a current is run through the cathode filament, it heats up and releases electrons.
What is the anode? What is it made of?
* when an electrical potential difference is applied across the x-ray tube, the anode has a positive charge relative to the cathode and attracts the electrons
* When electrons collide with the anode, 99% of the kinetic electron energy is converted to heat and only 1% gets converted into x-rays
Because of the heat produced anodes have a tungsten target which is resistant to heat. This is mounted on a copper base which helps conduct heat away from the target. (Either rotating– more powerful x-ray machines– or stationary– dental and portable– copper base)
What is the glass envelope?
* Contains the cathode and anode within the vacuum. The x-ray tube has a small exit window through which the x-ray photons escape. The tube is surrounded by oil which helps dissipate the heat and acts as an electrical insulator.
What is meant by quantity in regards to properties of the x-ray beam? Quality? Intensity?
Quantity= the number of x-ray photons produced
Quality- the energy of the x-ray photons, hence their penetrating power
Intensity- the amount of x radiation per unit area. The intensity is determined both by the number of photons and the energy of each photon
What does the quantity of electrons produced at the cathod filament dependent on?
The electrical current of the cathode circuit. This is an adjustable parameter that the x-ray machine operate can control, known as the Milliamperage (mA) setting. Increasing mA increases the number of electrons within the electron cloud
What does increasing mA do?
Increasing milliamperage (mA) increases the number of electrons within the electron cloud
What does the higher the kV mean? What is kVp?
* In order to accelerate the electron cloud toward the anode and produce x-rays, a potential difference or kilovoltage (kV) is applied between the anode and the cathode. The highter the kV, the greater the acceleration and thus the greater the energy of the electrons– the greater the energy of electrons– the greater the resultant x-rays which EQUALS HIGHER QUALITY X-rays
** kVp- kilovoltage peak- the maximum voltage available at the kV setting and is an adjustable paramter that the x-ray machine operator can control
What is the meant by the exposure time?
* The potential difference between the anode and cathode is only applied for a very short period of time (milliseconds)– the exposure time is an adjustable parameter that the x-ray operator can control. A long exposure time allows may electrons to impact with the anode, while a short exposure time allows fewer electrons to impact with the anode
What is the quantity of x-rays produced a function of? What determines the quality of x-rays produced?
both the mA setting and the time setting (s)
** mA determines the number of electrons produced, while time determines the number of electrons that hit the anode
** some x-ray machines allow the operator to select the mA and s independently
** kVp setting determines the energy of the electrons and therefore the energy of the resultant x-rays and thus the quality or penetrating power of the x-rays
How does the radiographer ensure the x-ray beam has the appropriate intensity?
Intensity = quality and quantity of x-ray photons
* this is so that enough x-ray photons penetrate the patient and interact with the x-ray detector to form the image
* The x-ray operator achieves this by manipulating the kVp, mA, and second settings on the machine to be appropriate for the anatomic area that is being radiographed
What is the focal spot? What does the size focal spot influence?
The area of the target with which the electrons collide… the size of the focal spot influences the detail (edge definition) of the image and also affects the heat loading capacity of the machine.
e.g. a stationary anode is limited to having a larger focal spot in order to accomodate higher temperatures. The focal spot of a rotating anode can be smaller due to the larger surface area over which electrons impact the target and superior ability of a rotating anode to dissipate heat.
Common focal spot sizes in veterinary medicine are 1-2 mm^2
What is the collimator?
The device to limit the size and shape of the primary x-ray beam
* To minimize scattered radiation, the primary beam should be confined to a size and shape that will just cover the region of diagnostic interest
What are the benefits to using the collimator to limit the x-ray beam to the area of interest?
Less scatter radiation is produced which improves image contrast and image quality and radiation safety…
What are the three main parts of the x-ray machine generator?
* The control panel- allows the operator to select appropriate setting for the voltage (kVp), tube current (mA), and the time of exposure (sec)
* The transformer assemby- step up or step down transformers to increase or decrease the voltage as required (which is needed to boil electrons from the filament and to accelerate these electrons from the cathode to the anode)
* The rectification circuit- incoming mains electricity is alternating current (AC), when x-ray exposure is made and a potential difference is applied across the x-ray tube, direct current (DC) is required. Most efficient systems produce constant positive lectrical potential, cheaper units the DC is more variable and only reaches peak voltage (kVp) for a small proportion of the time
What are the two stages that accomplish the exposure?
* Preparation- press and hold the button on the hand piece half way down; the cathode is heated by the cathode current and the anode starts rotating
* Exposure- when the system is ready, the operator fully depresses the button; this causes the potential voltage to occur for the set exposure time
What is full wave rectification?
* Converting the AC into a direct current (DC) without losing any electricity– full wave rectification creates a nearly constant electrical potential across the x-ray tube as both halves of the alternative voltage are used to produce x-rays
* A consideratlbe portion of the exposure time is still lost however while the voltage is in the valley between the two pulses
What is a three phase generator?
Present in most modern machines- produce an almost constant electrical potential difference between the anode and the cathode, which results in:
- More power available to the x-ray tube per unit time and therefore for shorter exposure
- Intensity of the x radiation generated is higher
- Radiation quality is greater because it contains less low energy x-rays
- Tube utilisation is more efficient because the target is not subjected to bombardment of low energy electrons, which only create heat
** main disadvantage is the increased cost of the machine relative to more simply rectification machines
What is the tube rating? What is it based on?
Each x-ray machine has a tube rating expressed in kilowatts– the tube rating dictates themaximum combinations of kVp, mA and time that can be safely used without over-loading the tube
Based on:
- Focal spot size
- Target angle
- Anode speed
- Electrical current
How is a radiographic image formed? What is attenuation?
Differences in attenuation between different components of the object to be radiographed. Attenuation is the proportion of x-rays that are stopped/ absorbed by a given thickness of matter
What 3 things happen when x-ray hits matter? What determines which one predominates?
- Transmission- the x-ray photon passes straight through
- Photoelectric effect- x-ray photons can be absorbed
- Compton effect- x-ray photons can be scattered
** Which one of these interactions predominates is determined by:
- energy of the x-ray beam (kVp)
- atomic number of the absorber. Remember more interactions occur with matter that has a high atomic number
- thickness and density of the part being radiographed. It makes sense that thicker or denser objects will stop more x-rays.
What is the photoelectric effect?
PE results in complete absorption of an x-ray photn by an atom and the ejection of an orbital electron, which produces a positive ion. Largely responsible for radiographic contrast. The main way x-rays are attenuated at 40-120 kV. The primary interaction between x-rays and bone.
** Probability of the PE depends on:
- Energy of the x-ray photon (must be above threshold kV)
- Atomic number of the absorber (elements with a higher atomic number are more likely to have PE absorption)
When is PE more likely to occur?
In low energy x-rays (50 to 70 kVp)
* high Z material (more in iodine, barium and lead than in oxygen, carbon or hydrogen)
** PE explains why better contrast is achieved with low kVp and why iodine and barium (used in radiographic contrast studies) stop more x-rays than organic matter
** soft tissue is made up of hydrogen, carbon, nitrogen, and oxygen– avg atomic number of 7.. vs. bone which is mostly calcium (atomic number 20)
How do you increase subject contrast?
Decrease the kVp setting
Why is PPE made from lead?
Atomic number is Z82– materials made from elements with a high atomic number are good absorbers of x-rays
What is the compton effect? Why is it not useful in diagnostic radiology? What influences the likelihood of the compton effect?
Responsible for almost all the scatter radiation produced in diagnostic radiology
No useful function in diagnostic radiation because
- Scattered radiation poses a safety threat
- Decreases contrast of the radiographic images (e.g. the difference between black and white on the radiograph is less obvious)
** Likelihood of the compton effect
- Very dense absorbers are more likely to produce compton scatter
- large volumes of irradiated tissue are more likely to produce compton scatter– thick body aprts e.g. fat dog abdomen, horse back or shoulder; or poorly collimated image will produce more scatter
- High kVp settings thuse higher energy x-ray photons are more likely to produce compton scatter
How do you absorb scatter radiation before it hits the detector?
Use a grid
They should always be used when the patient thickness is greater than 10 cm because more scatter is produced in thicker body parts
Placed between the patient and the detector- so under the patient or under the table between the patient and the cassette
How does a film screen x-ray work? What is the most commonly used x-ray films?
* x-ray film consists of a polyester base coated on both sides with a gelatin emulsion containing silver halide crystals. When visible light or x-rays interact with silver halide crystals- an invisible image is formed then processed to be made visible– by exposing the silver halide to an x-ray photon or light photon which activates the crystals which precipitate silver… which aggregates producing darkenened areas
** Most commonly used x-ray films are double emulsion- having emulsion on both sides of the base (single emulsion can be used with pocket pets)
What are cassettes?
Cassettes are used in traditional film-screen and computed radiology (can be reusable)
* rigid lightproof containers that hold both the intensifying screens and the radiographic film. Double emulsion film is used in cassettes with two screenes which therefore results in two images on either side of the film
What is screen speed?
Part of a cassette. An important characteristic of intensifying screens. Faster screens requires less radiation (lower mAs, usually achieved with shorter exposure time)– at the expense of detail however.
What is an intensifying screen? Why must the x-ray film match the intensifying screens of a cassette?
* Intensifying screens in a cassette convert x-ray photon energy into light photons, which expose the x-ray film. The use of film with intensifying screens (film-screen) is a more efficient detection system than x-ray film alone and allows a reduction in radiation exposure up to 100 times.
* X-ray films are only sensitive to one colour of light and different screen types give off different colours
What is optical density ? What is it primarily controlled by?
Measure of the blackness of film– primarily controlled by mAs
What is the relationship between optical density of a radiograph to the exposure needed to produce that density?
Sigmoidal
* Ideally, most of the radiographic image should be exposed in the linear portion of the curve. If the film is exposed at the shoulder or toe of the sigmoidal curve, the image will appear overexposed (too dark) or under exposed (too light) respectively
What is film speed?
Term used to describe how sensitive the film is to x-ray or light photons. Film that has a high speed rating is very sensitive to photons, an adequate optical density can be achieved with lower radiation exposure. The trade off for fast fil is that it has slightly lower detail/ spatial resolution compared to slower film.
What is film latitude? What is film latitude’s relationship to film contrast?
Exposure range over which acceptable optical densities are produced. Film with a wide latitude will accept a significant variation in exposure factors or processing without exhibiting any great chance in optical film density. Most x-ray film has WIDE LATITUDE making it relatively easy to avoid under or over exposure… narrow latitude film or high contrast film is less forgiving with exposure factors– FILM LATITUDE VARIES INVERSELY with FILM CONTRAST
What speed film would you want to use for cat’s manus?
Slow speed 100 to 200- higher in detail, small body part, very little movement so longer exposure times okay to use
What speed film would you use for a fat dog’s abomen?
Fast speed- 400 to 600 speed
What film speed would you want for a horse’s carpus?
400 speed- fast system. Move a lot so short exposure time
What are the steps in film processing?
- The Developer- chemical solution that converts the latent image on the film to a visible image by reducing exposed silver halide crystals to black metallic silver. ** Time and temperature dependent (chemical reaction occurs at a greater rate at higher temperatures)– usually at 20C about 3 minutes to develop
- The rings- x-ray film retains developer in the gelatin and if this were transferred to a fixer the alkaline developer would neutralize the acid fixer– so rinsing stops the developing processes and prevents carry over the fixer
- The Fixer- removes unexposed silver halide crystals. Fixation also hardens the gelatin coating so that it can be dried without damaging the film surface. Fixed fro twice the development time to ensure maximum hardening of the emulsion. An incompletely fixed film takes on a milky or cloudy appearance.
- Wash Bath- removes the remaining silver complexes and excess fixer. (20-30 minutes)
- Dry the film. Hanging.
What are the limitations to traditional film- screen?
Image can have good contrast or good latitude but not both
* And once the film has been exposed to the x-rays, the contrast and latitude can’t be adjusted
What are the three steps of Computed Radiography?
- Image acquisition- x-ray photons strike a reusable storage phosphor imaging plate (IP)– placed in a plate reader where it is scanned by a laster beam which releases the stored latent image as visible light. Then the IP plate is erased for reuse by scanning the plate with an intense white light
- Image processing- using algorithms the computer evaluates and manipulates the digital data
- Image display- the user can then apply post processing techniques such as edge enhancement, magnification, adjustment of contrast range and dynamic range
CR advantages and disadvantages?
How does direct digital radiography work?
* Direct systems use an electronic detector made of amorphous silicon or selenium or a charged couple device to capture the image. The detector is attached to the computer system via a cable. The signal is transmitted to the computer and reassembled into a digital image.
Advantages and Disadvantages of DDR
What is the major advantage of digital imagine?
Due to the wider latitude, the number of retakes due to poor exposure are reduced
BUT although digital image contrast can be manipulated by viewing software, subject contrast is still influenced by collimation, scatter and kVp settings
How does spatial resolution of digital systems compare to film-screen systems? Does this matter?
* Spatial resolution of digital systems is not as good as film-screen systems, but it is not a clinical limitation
What are the four steps to processing the digital image that occur automatically?
- Creation of a histogram- maps optical density vs. frequency which allows mathematical manipulation of the raw data- histogram is compared to an expected histogram for the anatomic area selected to be radiographed
- Data adjusted for under or over exposure- histogram shifts left or right to compensate
- Enhancement of image contrast, using a look up table
- Edge enhancement or smoothing- complex mathematical function is applied to the raw data to allow processing in the spatial frequency domain– boundaries such as bone margins can be smoothed or enhanced
What is PACS?
Archiving and distribution of digital images
What are the features of radiographic image quality?
* Optical density, radiographic contrast (subject contrast, film contrast, fog and scatter, digital image contrast), detail (spatial resolution, edge definition), technical faults
How can optical density be manipulated?
By adjusting mAs (mA or seconds) setting
What are the six basic steps in making a technique chart?
What is quantum mottle?
An underexposed digital image will have a grainy appearance
Quantum mottle is caused by the discrete nature of an x-ray photon; underexposure results in an insufficient number of x-ray photons reaching the detector to fully form the image
*** think of black paint spots outlining something
What does radiographic contrast depend on? When is high contrast preferred? When is low contrast preferred?
Radiographic contrast depends on:
- Subject contrast- due to attenuation of the x-ray beam in different tissues; low kVp will produce high subject contrast as long as the kVp is high enough to penetrate the tissue (higher kVp = more compton scattering)
- Film contrast- homogeneity in size of silver halide crystals within the film emulsion, over or under exposure– technical factors, over or under deveopment will push film contrast to the toe or shoulderof the characteristic curve and produce low contrast image
- Fog and Scatter- inadvertent exposure of the x-ray film to light
High contrast is preferred for bone images; low contrast is preferred for chest and abdominal images
Effect of kVp, mA and exposure time on the radiographic optical density and contrast
What are the five basic radiographic opacities?
What is B-mode ultrasound imaging?
What is M-mode ultrasound?
What is Colour Doppler?
What is spectral doppler?
What three things might happen when ultrasound pulses interact with the patient?
- Transmission into deeper tissues
- Refraction (bending) of sound as it passes from a tissue of one density to a tissue of a different density
- Attenuation of sound, which is a reduction in amplitude or intensity of the pressure wave
What is a B-mode ultrasound image composed of? What does the brightness of each x correspond to?
What is acoustic impedance?
* Sound reflection or transmission characteristics of a tissue, largely dependent on the density of the tissue and speed of sound within the tissue. Because we assume constant speed of sound in soft tissue, density is the most important component in this equation
** It is not exact value of acoustic impedence that matters but the difference in acoustic impedence between two tissues
** At boundaries between soft tissue and boen or soft tissue and air there are large differences in acoustic impedance resulting in little sound transmission and the image is displayed as a shadow– THIS IS WHY WE CLIP ANIMALS FUR, clean the skin and apply coupling gel– this removes air between the skin and transducer
WHat is the preferred imaging modality to assess bone or lung?
What does the ultrasound transducer do?
* converts electrical energy to acoustic energy and acoustic energy to electrical signals
* consist of piezoelectric crystals aligned within the footprint of the transducer and when a voltage is applied the crytal vibrates and produces a sound– each one has a unique frequency at which is vibrates and will produce sound of an inherent frequency. The tranducer transmits sound pulses for 1% of the time and listens for returning echoes 99% of the time.
** The operator can select the main frequency band that is used for imaging, selecting higher frequencies for imaging superficial structures and lower frequencies for deeper
What is the phased array?
What is axial resolution?
Dependent on the spatial pulse length
What is lateral resolution?
Special considerations with scintigraphy?
What is the Hounsfield scale?
The operator can choose what part of the scale to assign the central colour gray
What is an MRI sequence?
Safety issues with MRI?
What is Poiseulle’s Law? How does it relate clinically?
Physical law that governs the pressure drop in a gluid flowing through a long cylindical pipe. Clinically you can think about how it governs the pressure needed to push a volumetric rate of fluids e.g. in ml/hr through your tube (catheter)
** both length and radius have an effect on catheter flow but the radius effect is much greater than length. Double the length, you double the pressure it takes to get fluid through at the same rate…. Catheters have a high resistance to flow. 18 gauge are the biggest we use in peripheral veins.
What gauge through rabbit ear veins, bird wings and tiny kittens?
What gauge through cats and very small dogs?
Large cats and medium sized dogs?
Larger sized dogs (heeler upwards)?
What is the most appropriate description of the radiographic appearance of a positive contrast agent in comparison to soft tissue?
Appear more radiopaque– higher atomic number
Excretory urography- to look for ectopic ureters and tumors and to evaluate kidney function
Urethrocystogram
B- mode
Spectral doppler
Phased array
