ECP 1 Flashcards
What are 4 ways to make a diagnosis and the best way
- Pattern recognition - I know what that is and what causes it
- Hypothetic-deductive reasoning - problems most likely due to x, I’ll examine and test to verify
- Problem-oriented approach - identify all problems, all differentials for every problem
- Key abnormality method - identify main problem - identify body system associated with signs, id lesions and causative agent
What are the 3 main steps in the HEAPC process and briefly describe
1. History and Examination - identify abnormalities ○ Subjective, objective, diagnostic 2. Assessment - Problem ○ Pathophysiology (general) ○ Differential diagnoses 3. Plan ○ Diagnostic ○ Therapeutic ○ Monitoring ○ Communication
What does the H in HEAPC stand for - 8 steps
- Signalment
- Chief complaint - symptom, clinical finding
- Last normal
- Progression of the current problems
- Systems - vomiting, diarrhoea, coughing, regurgitation, sneezing, polyuria, polydipsia, AAA (attitude, appetite, activity)
- Previous pertinent history - medication or surgical
- Medications
- Environmental history
What does the E,A,P,C stand for in the HEAPC
E
1. Physical examination
2. Other diagnostic techniques
A
1. Problem list and differentials for each problem
P
1. Plan -> Diagnostic, therapeutic, monitoring, communication
C
1. Communication -> referring vets and owner
what problem would you group the following as:
- lethargy, anorexia, painful abdomen, caudal organomegaly, vomiting
Acute abdomen with vomiting
when have hyperthermia what are the 3 things you consider
1) infectious
2) inflammatory
3) neoplasia
what are some things that are possibly life-threatening
- Collapse/loss of consciousness
- Seizures
- Bleeding
- Large or penetrating wounds
- Choking or difficulty breathing
- Protracted or severe vomiting or diarrhoea
- Difficulty urinating
- Toxin ingestion
- Previous life-threatening problems
What do you consider when you first get a emergency patient
ABCs Airways - Is there a patent airway? Breathing - Is the animal making useful breathing efforts Circulation - Is there a heartbeat with pulses
Cardiovascular assessment what are the 5 main assessments and brief
1) Pulses - femoral and metatarsal
2) mucous membranes
3) capillary refill time - gum above canine
4) heart rate
Dogs 80-120 bpm
Cats 160 - 220 bpm
5) cardiac auscultation
Mucous membrane colour in dog what does cyanosis, icterus, brown and cherry red suggest
§ Cyanosis -> hypoxaemia, polycythaemia, paracetamol/acetaminophen
§ Icterus -> sclera best for mild icterus, rarely blue to green eyes in cats
§ Brown -> paracetamol
§ Cherry red -> carbon monoxide poisoning
Respiratory assessment what are the 4 main assessments in brief
1) rate -> RR: 15-25bpm
2) effort -> mild, moderate or severe dyspnoea
3) pattern
4) auscultation and lung sounds = cranioventral louder than dorsocaudal left and right the same
What is the normal inspiration pattern
On inspiration both the chest and abdomen both move out together
□ Chest expansion and diaphragmatic contraction (70-80%)
□ Fall in intrapleural pressure
□ Lung expansion
□ Dilation of intrathoracic trachea
□ Collapse of extrathoracic airways
What are 3 main signs of abnormal inspiration and 4 reasons for this
□ Increased appropriate abdominal movement
□ Abdominal effort
□ Paradoxical abdominal movement -> inspiration abdomen moves inwards
1. Upper airway obstruction 2. Diaphragm dysfunction
3. Stiff lungs
4. Rarely: severe, chronic, pleural effusion
What clinical signs suggest mild dyspnoea
□ Tachypnoea □ No or minimally increased effort □ +/- mild patient distress □ +/- anxious facial expression □ Usually increased, appropriate abdominal movement □ NOT PANTING
what clinical signs suggest “Moderate” Dyspnoea
□ Mild/moderate increased effort □ Extended neck, (abducted elbows) □ Moderate patient distress □ +/- open mouth breathing □ +/- paradoxical abdominal movement □ Glazed-eyed stare □ Often severe paradoxical abdominal movement
what clinical signs suggest severe to critical dyspnoea and what is cyanosis
□ Severely increased effort
Open mouth breathing
Cyanosis -> life-threatening hypoxaemia - ABSOULTE, at this point animal will die if don’t do anything
Neurological assessment what are the 2 main things looking for
1) Gait § Recumbency § Single or multiple limb lameness § Ataxia § Paresis or paralysis 2) Mentation § Depressed, stuporous, comatose § Hyperexcitable, dysphoric, hysterical
What are the 5 main assessments want to do in critical situation and what first
1) cardiovascular
2) respiratory
3) neurological
MOST IMPORTANT
4) abdominal palpation
5) body temperature
What are the 6 things in the structure of the consultation model
1) Preparing for the consultation
2) Initiating the consultation
3) Gathering information
4) Physical exam
5) Explanation and planning
6) Closing the consultation
When preparing for the consult what is the main goal and how to achieve this
GOAL - good first impression
- Familiarise (name, sex, signalment, problem)
- Anticipate potential conflicts or difficulties
- Create a safe and professional environment
Initiating the consultation what are the 2 main goals and briefly how to achieve
1) establish rapport - greet, introduce, demonstrate interest/concern, attend to needs of client/animal
2) identify reason for consult - open-ended question, negotiates agenda
Gathering information what are the 2 main goals and how to achieve
1) explore problems
- Encourage client to tell the story, Open and closed questions, Listen attentively, don’t interrupt, Facilitate
2) understand the client’s perspective - client ideas, beliefs, expectations
What is important to ask in a production system consultation
- ‘Signalment’ of the mob and of the farm
- Chief complaint
- Last normal
○ Has farmer observed the problem, how many affected, other mobs affected - Environment
○ Pattern, treatment, response, protective husbandry - Contacts w other animals on and off farm
Physical examination what is the goal and 3 steps
Goal: a safe and compassionate interaction
- Announce
- Ask about temperament
- Explain
Explanation and planning what are the 4 goals and how to achieve
1) correct amount and type of info
- Assess client’s starting point, “Chunks and checks”
2) aid in recall and understanding
-Organise explanation
○ Signposting ○ Repetition and summarizing ○ Concise, no jargon ○ Use visuals
3) Check for understanding
achieve shared understanding; incorporate client’s perspective
- Explanations that relate to the client’s concerns
4) client understands and is a part of process; increase commitment to the plan
- Share own thoughts, Offer choices, Encourage client to contribute, Negotiate, Check with client
Closing the consultation main goal and how to achieve
Goal: summarize and forward planning
- Recap - Safety net - Check for agreement - Say goodbye!
What are advantages and disadvantages of inhalant anaesthetics
Advantages of Inhalants
- Allow/promote use of supplemental oxygen for patient
- Easy and rapid control of patient depth
- Fairly cost effective
Disadvantages of Inhalants
- Require specialized machine to deliver
○ Initial cost $$$$
○ Can deliver via injection of liquid into system (difficult)
- Risks/hazards of exposure
○ Mutagenic/teratogenic effects in mice
○ Potential for abortions in OR personnel
what is saturated vapor pressure and what leads to it
- Molecules move and collide with each other and walls of container, these allow molecules to escape liquid surface and enter vapor phase, occurs until number of molecules in each phase are in equilibrium. This movement creates pressure leads to SVP
- SVP = measure of liquids ability to evaporate
What does knowing saturated vapor pressure get us and give example with isoflurane and sevoflurane
Knowing the SVP of an anaesthetic allows us to predict the maximum percentage of that anaesthetic that can be achieved
Sevoflurane lower saturated pressure than isoflurane
Maximum percentage is lower than isoflurane
What controlled how much inhalant given to patient and what are the 3 important partial pressures into lungs
- Modern vaporizers deliver a precision controlled concentration of inhalant anaesthetic to the patient
- Vaporizers operate in concentrations (%)
1. Concentration leaving vaporizer = 3% - Partial Pressure (PD) = 760 mmHg x 0.03 = 22.8 mmHg
2. Gas from vaporizer mixes with other gases in rebreathing system. - Concentration & PP ↓
- PI = PP that patient is inhaling
3. Gas reaching alveoli mixes with gas left in alveoli and other gases in airways. - Concentration & PP ↓
- PA = Alveolar PP
What are the 2 things that affect the amount of anesthetic reaching alveoli (at equilibrium reflects the brain)
1) inspired concetration of anaestehtic (vaporiser setting)
2) alveolar ventilation
what do time constants allow us to estimate and how does it rise
- Allows us to estimate how long it will take for the animals tissue concentration to be equal to the concentration in the system
- Concentration in the system rises by first order kinetics
What are the 3 things that increase inspired concentration and how do they work
1) increase vaporiser setting -> set higher initially to reach desired concentration faster
2) increase fresh gas flow -.> increase value on bottom of time constant -> decrease time constant
3) decrease volume of breathing circuit -> decrease number on top of time constant to decrease time constant
Alveolar ventilation what does it affect and how to increase
affects the amount of anesthetic reaching alveoli
- increases ventilation (breath deeper and more often) decreases time constant bringing more gas/inhalant into the body
What are the 3 things that affect anaesthtic uptake into the blood and what does it do to anaesthetic induction
Anything that pulls more anaesthetic from the alveoli will slow anaesthetic induction (alveolar won’t be able to fill up and build concentration gradient)
1) Solubility - MORE soluble taken up from alveoli faster therefore SLOWER induction
2) Cardiac output (CO) - INCREASED more anaesthetic picked up therefore SLOWER indution
3) Alveolar-venosus pressure gradient - INCREASED more movement SLOWER induction
How is solubility measured for inhalant anaesthetics and which is higher sevoflurane or isoflurane
Blood: Gas Partition Coefficient:
- Compares the # of anaesthetic molecules present in each “phase” after equilibration!
- Partial pressure is equal, NOT # of molecules!
Sevoflurane -> lower - LESS SOLUBLE -> faster induction
- Ratios approach 1 faster, steeper curve, equilibrium faster
Isoflurane -> higher - MORE SOLUBLE -> slower induction
- Ratios approach 1 slower, less steep, equilibrium
Distribution of inhalant anaesthetic into the tissues what are the 3 things its dictated by and what causes faster
1) % CO to tissues - INCREASED - faster
2) Volume of tissues - LOWER body weight - faster
3) solubility in tissues - INCREASED - faster
What are the 4 body compartments for inhalant anaesthetics and how long does it take for equilibrium to occur
- The VRG (vessel rich group - brain, major organs) is equilibrated in ~5-20 mins
- The MG (muscle group) is equilibrated in ~2-4 hrs
- The FG (fat group) takes many hours to days to equilibrate
- Vessel poor group (VPG) - igaments ->
You have intubated a dog and placed it on 100% oxygen with the isoflurane vaporizer set at 2%. After 5 minutes you notice that the dog’s HR, RR, and BP all start to rise. You believe the dog is becoming light. What would you do next?
Increase the vaporizer to 2.5% and provide intermittent positive pressure ventilation (squeezing the bag)
MAC what is it, what is it a measure of and the relationship, where measured how differs
The percentage of inhalant in the alveoli that will prevent movement in response to supramaximal noxious sitimulus in 50% of the population (equivalent to ED50)
- MAC is a measure of anaesthetic potency (how much concentration needed to accomplish what is needed)
- Higher MAC LESS POTENT -> higher concertation to accomplish anaesthesia
- Measured at equilibrium between alveoli and brain
- AKA - the ED50
- Differs slightly between species
What are the MAC for isoflurance and sevoflurane and therefore which has higher potency
- Isoflurane MAC – 1.3% - HIGHER POTENCY
- Sevoflurane MAC – 2.4% - LOWER POTENCY
How does MAC relate to ED95, Deep Anaesthesia and MAC BAR
- ED95 = 1.3 X MAC = Considered “Surgical MAC”
- Deep Anaesthesia = 2.0 x MAC - avoid
- MACBAR = MAC necessary to prevent adrenergic (sympathetic) response to surgical stimulation
○ Greater than MAC, takes larger amount to prevent this (don’t want to)
List 2 factors that increase MAC and many more than decrease MAC
Factors that INCREASE MAC - Drugs causing CNS stimulation - Hyperthermia Factors that DECREASE MAC - Drugs causing CNS Depression - Hypotension (<50 mmHg) - Hyponatraemia - Hypothermia - Hypoxaemia (PaO2 < 40 mmHg) - Hypercapnoea (PaCO2 > 95 mmHg) - Pregnancy (need less anaesthetic)
What are the 6 main systemic effects of inhalants
1) CNS effects
2) Respiratory Effects
3) Cardiovascular effects
4) Renal effects
5) hepatic effects
6) malignant hyperthermia
What are the 3 main CNS effects of inhalants and when dangerous
1) Dose-related CNS depression
○ Decreased EEG wave frequency
2) Decreased cerebral metabolic oxygen requirement (CMRO2)
3) Increased cerebral blood flow (CBF)
○ Halothane more than others
○ When dangerous? Head trauma, brain tumours (increase intracranial pressure)
What are the 3 main respiratory effects of inhalants
1) Minute ventilation
○ Minute Ventilation = Tidal Volume (VT) x Respiratory Rate (RR)
§ Decrease tidal volume +/- respiratory frequency
○ Inhalant anaesthetics cause a dose-dependent decrease in minute ventilation
2) Inhalants can cause bronchodilation - can be beneficial in asthmatics
3) ↑ PaCO2 -> cause hypoventilation
○ ↓ minute ventilation
○ ↓ CNS sensitivity to CO2
○ Dose dependent effect
What are the 4 main cardiovascular effects
1) ↓ CO ○ Negative inotrope - reduce contractility - Variable effects on HR 2) ↓ Arterial BP ○ Mostly d/t ↓ SV ○ ↓ SVR in humans 3) ↑ automaticity of myocardium ○ Possibility of arrhythmias 4) Sensitize myocardium to arrhythmogenic effects of catacholamines ○ Halothane ○ Less common with “newer” anaesthetics
What are the 2 main renal effects and 3 main hepatic effects of inhalants
Renal Effects: 1) ↓ RBF and GFR ○ d/t ↓ CO 2) Methoxyflurane = nephrotoxic (humans & rats) - don’t use Hepatic Effects: 1) ↓ hepatic blood flow 2) ↓ drug clearance ability 3) Halothane hepatitis
Malignant Hyperthermia what is it, what causes it and how to treat
- Pharmacogenetic Myopathy ○ Rapid rise in temp causing death - Reported in several species ○ Humans, pigs, & horses - Inhalants are “triggers” ○ Especially Halothane - Treat with Dantrolene (prophylactic?)
What metabolism do inhalant anaestehtic undergo and isoflurane vs sevoflurane
- Most modern anaesthetics are exhaled largely unchanged
○ All anaesthetics undergo some hepatic biotransformation
§ Also some metabolism in lungs, kidneys, and intestinal tract - Isoflurane less biotransformation so less effect on the liver
What is compound A and what effects and what do from
- Forms when sevoflurane is degraded by soda lime or baralyme ○ Forms in rebreathing systems - Nephrotoxic in rats - Unknown significance for others ○ Avoid sevo for long procedures??
Nitrous oxide how differs from other inhalants, what are the 2 main effects and what are the 3 main reasons we don’t use it often
- Differs from other inhalants
○ Exists as a gas at room temp
○ Has analgesic effects (NMDA antagonist) - Can reduce MAC of other inhalants
- Stimulates SNS
○ Can actually ↑ CO
Why don’t we use it more often?
1) Higher MAC in animals compared to humans
○ Not as potent
2) Diffuses in closed gas spaces (gi tract, etc)
○ Pneumothorax, GDV, Colic, Bloat -> further inflate
3) Not inactivated by activated charcoal
○ Exposure risks
○ Environmental pollution
How does nitrous oxide 2nd gas effect work
- Nitrous given as large concentration -> large concentration gradient is present so nitrous moves quickly into blood, as moves into the blood the other inhalant needs to take up that space left (needs to get to 760mmHg) so now increase the partial pressure of the other inhalant
- “Concentrates” other inhalant in alveoli - speeds up induction
What is diffusion hypoxia in terms of nitrous oxide and how to avoid
- Occurs if room air given immediately after N2O anaesthesia
- Large conc. of N2O enters alveoli, “dilutes” available O2
- Can cause death
Avoid by administering 100% O2 for 5-10 mins after stopping N2O!!
What is an X-ray
high frequency and short wavelength
What are the 2 main ways radiation cause mutations and cancer and which important to vets
1) Deterministic effects
- Cells die suddenly due to high level exposure
2) Stochastic effects - what is important
- Low level exposure - there is no exposure for what is a risk for an individual, increased risk with cumulative exposure
- Delayed effects over a long period
- Changes to cell genome -> mutations -> cancer
What are the 3 important regulations with licensing in terms of X-ray radiation
1) Each clinic must have a management license
2) Individual vets need a use license
3) Radiation exposure must be monitored using radiation badges -> optically stimulated luminescence badges (OSL badges)
○ Wear your badge every time you are taking x-rays
○ At waist or chest level, under lead aprons
○ High radiation exposures will trigger a safety investigation
What are equivalent and effective doses in terms of radiography
Equivalent dose (H) = Absorbed dose X WR (weighting factor - type of radiation used (X-rays)) Effective dose E = Absorbed dose X Wt (tissue weighting factor)
What is the effective dose limit for radiography for vets and the general public, what is the average for vets
Effective dose limit
Occupational - 20mSv per year
General public - 1mSv in a year
Average - 0.015mSv
What is the ALARA principle and the 3 important factors in terms of radiography settings
ALARA Principle
- Keep radiation exposure
- As
- Low
- As
- Reasonably
- Achievable
1) Time
2) Distance
3) Shielding
List 3 ways to reduce the cumulative time of x-ray exposure
- only take x-rays when needed - could another test be used to answer your clinical question?
- take good radiographs the first time, avoid repeat exposure
- use efficient detector systems to allow short exposure times
List 3 ways to maximise your distance from x-ray source and what equation is important
- avoid manual restraint of animals - sedate, anaesthetise, ancillary positioning devices
- use cassette holders for equine radiography
- use length of exposure cord to allow you to stand back
INVERSE SQUARE LAW -> 1/distance squared -> if move 2 meters across than 1/4 of radiation you are receiving
List some ways to shield yourself from scatter radiation
- Use personal protective equipment - lead apron, gloves, thyroid protector
- If available, stand behind lead shield
Note: PPE is only thick enough to shield from scatter radiation, and will not protect you from the primary x-ray beam!
PPE - Lead aprons MUST be worn near radiography
- Thyroid protectors are recommended
- Lead gloves MUST be worn if hands are anywhere near the primary beam
What is within the tube head of an X-ray and what is it made out of, describe the new types
X-ray tube within tub head
- Made of cathode and anode made out of tungsten metal
- Anodes
○ Rotating anodes have greater head loading capacity and higher output
○ Stationary anodes are smaller, lighter and less expensive, but limited in x-ray output
○ Angling the anode increased surface area over which electrons can hit
How does the cathode and anode work with the X-ray machine
cathode gives off electrons, anode gives of X-rays photons
- Half press -> run current through tube head
- Full press -> high potential difference, anode more positive than cathode attracts the electrons that hit anode at high speed leading to X-ray photons from kinetic energy
What makes up quantity of an X-ray and what settings controlled by
the number of x-ray photons produced
- Controlled by the mA setting: higher filament current = more electrons = more Xray photons
- Controlled by the ms setting: longer exposure time = more electrons reach the anode = more Xray photons
- mA and ms are often regarded together, as mAs
What makes up quality of an X-ray and what setting is it controlled by
is the energy of the x-ray photons - Controlled by the kVp setting higher potential difference between cathode & anode - most important for penetrating power = more rapid acceleration of electrons = higher energy electrons = higher energy x-ray photons
What is the collimator what does it do and what are the 2 types
- The collimator assembly limits the size of the x-ray beam and area of patient irradiated.
○ To reduce the amount of scatter radiation that is produced, only irradiate the area of interest
1. adjustable parallel leaf collimator (most standard x-ray machines)
2. fixed cone collimator (dental x-ray machines)
X-ray Generator what does it do, consists of and how do you control it
- The x-ray generator supplies power to the xray tube, and consists of control panel, transformer assembly and rectification circuit
○ Transformer assembly
○ Rectification circuit to keep mains electricity to positive not alternating - The control panel allows the operator to select technical factors and initiate exposure
What are the 2 things to consider when buying an X-ray machine
- Tube rating
2. Mobility
Tube rating what is it and what are the 4 things it depends on
- X-ray tube rating dictates the maximum kV and mAs that can be used without overloading the machine
X-ray tube rating depends on:
1) Focal spot size - how to dissipate heat
2) Target angle - how to dissipate heat
3) Anode rotation speed - how is dissipates heat
4) Electrical current
What are the 3 movements of xrays and what is this called
- The x-ray photon passes straight through: TRANSMISSION
- The x-ray photons can be absorbed. They undergo the PHOTOELECTRIC EFFECT
- The x-ray photons can be scattered. They undergo the COMPTON EFFECT
What does absorption of x-ray depend on an the effect involved what makes higher absorber
- Absorption of x-ray photons depends on the ENERGY of the photon and the ATOMIC NUMBER of the absorber (bone - calcium)
Photoelectric Effect - 2 things that relate to the probably of photoelectric effect occurring
○ Lower energy photon (low kVp level) hits an electron and is absorbed
○ Higher atomic number absorber = high electron density = photon more likely to collide and be absorbed
What makes absorption of X-rays dangerous and what is the main absorber in the body
- Ejects an electron so is an ionising event -> if occurs in water than can create a fee radical -> why dangerous
- Main interaction with bone -> all x-rays absorbed, none to interact with film leading to white area on radiograph
Compton effect what type of photon undergoes this and then what occurs
Compton scatter is likely to occur with dense absorbers, large volumes of tissue, and high kVp settings
- High energy photon (high kVp settings) = hits an electron and is deflected, losing some energy
- Scatter radiation has low energy
- Scatter radiation does not travel along the path of the primary beam so just darkens the image without giving useful information
Ejects an electron so is also an ionising event
What are the 3 main negative effects of scatter radiation
Scatter radiation has no use in diagnostic radiology Negative effects of scatter radiation 1. Increase operator dose 2. Increase patient dose 3. Decrease image contrast
List 2 ways to decrease production of scatter to make it 1) safer for patient 2) safer for operator and 3) improve image quality
Safer for patient
1. Select a lower kVp technique
2. Collimate to only include the area of interest
Safe for the operator
1. Wear PPE
2. Maximise distance from patient
Improve image quality - IMPORTANT
1. Place a grid (flat plate with altering strips of low density and aluminium (good for absorption)) between the patient and the detector
○ When thickness of the body is 10cm or above this is used, scatter radiation only moves through section
2. Use the air gap technique
○ Scatter have lower energy so if larger gap more likely to dissipate by the time it gets to the detector
What are the 2 main types of radiography and relative positives and negatives
1) film-screen
○ Gradually being replaced by digital radiography systems
○ Negatives
§ Not as good for high density and soft tissue opacity - not good contrast
§ Not as forgiving for over or under exposure
§ Takes up large amount of storage space and easier to lose the film
2) digital radiography
○ The future of imaging
○ Storage via a server, hard-drive backups, third-party systems
○ Positives
§ Better for contrast with soft tissue and high density bone
§ More forgiving for over or under exposure
§ More flexible options for storage, viewing and transmission of images
What are the 2 main direct digital radiography types and the main differences
- Computer radiography (CR)
□ Use a cassette with imaging plate and plate reader
Imaging plate is coated with photostimulable phosphor - Direct digital radiography systems
□ Detector connects directly to the computer monitor - immediate production of the digital image
□ Better for large animals as heavy to carry
How does the photostimulable phosphor in computer radiography work
® Energy from x-ray photon traps electrons in a high energy state, storing information in the photostimulable phosphor
® The plate reader laser releases the trapped electron and the photostimulable phosphor emits light that is detected by fibre-optics and converted into an electronic signal
What are the 2 main types of direct digital radiography systems and the types within
1) Direct detector systems
◊ x-ray energy is directly converted to an electronic signal via semiconductor
2) Indirect detector systems
◊ x-ray energy is converted to light by a scintillator, this light is then converted to an electric signal
◊ Types
1. Thin Film Transistor (TFT)
– Flat panel detector
– May have lower spatial resolution than direct due to light diffusion, depending on the type of scintillator
2. Charge Coupled Device (CCD)
– Older technology with lower cost
– Built-in detector limits use of cross-table radiography
Storage and transmission of digital images in radiography what is mandatory and the types with their characteristics
Picture Archive and Communication Systems (PACS) - mandatory
- allow efficient storage and communication of digital images
- Types
1) cloud’ - based with third party storage
○ cost
○ security of images
○ convenient for owners to log in and see!
○ convenient if multiple branches to the practice
2) local storage - back-ups on site or off-site
○ more secure
○ may be cost-effective
○ how to share images with owners? burn CD or USB?
○ What if have a fire and lose storage device
What are the 4 things that you need to consider in terms of image quality
1) Optical density
2) Radiographic contrast
3) detail
4) technical faults
What is optical density and what are the 3 things that may cause issues
- Optical density is the degree of blackness of the image
1. Radiographic exposure -> over or under exposure
2. Windowing the image -> digital radiography only
3. Film processing -> film-screen radiography only - not really covered this lecture
What leads to radiographic over or under exposure
Overexposure results in too many x-ray photons penetrating through the patient to interact with the detector.
- too high kVp setting
○ Photons have too much energy and few are absorbed
- too high mAs setting
○ too many x-ray photons generated, lots more pass through than with normal levels of exposure
Underexposure results in too few x-ray photons penetrating through the patient to interact with the detector
- Too low kVp or too high mAs (opposite to above)
Radiographic contrast what is it and what contrast do we want for chest, skeletal and abdominal radiographs
- Different in the shades of grey
- For chest radiographs we want low contrast images
○ We want to see pulmonary vessels - For Skeletal radiographs we want high contrast images
- For abdominal radiographs we want lower contrast than skeletal but higher contrast than chest
Radiographic contrast what are the 3 components and ow to change/modify
1) subject contrast
2) film contrast
3) fog and scatter
How to change/modify
- Digital radiography contrast is controlled by the viewer by windowing the image
Subject contrast what is it a component of, what is it and the 4 things that influences it
Radiographic contrast
- Is the difference in x-ray attenuation between different areas of the subject (difference between bone and soft tissue)
- What influences it
○ Thickness of absorber - different thicknesses
○ Density - difference in density
○ Atomic number - different in atomic number
○ Energy or kVp setting - want low so absorption rather than scatter - WHAT YOU CAN CHANGE
Film contrast and fog and scatter what are they components of, what are they and result
Radiographic contrast
- Film contrast
- Determined by inherent properties of the film, but also marked over- or under- exposure or development
- Can change the properties of the film based on the contrast you want - Fog and scatter
- Fog is inadvertent exposure of film to light -> before the x-ray is taken, during packaging or storage
- Scatter radiation arises from the Compton effect -> digital radiography -> leads to low contrast
What is a technique chart for radiographs and the 6 steps
- A technique chart helps you select the best factors to optimise optical density and image contrast
Basic steps in making a technique chart
1. Make series of trail exposures
2. Choose the ‘best’ exposure
3. Calculate out technical factors for different thickness
4. Make additional charts for thorax, axial skeleton, extremities etc.
5. Keep an exposure log-book for a few months
6. Modify technique chart as required
How to assess optimal exposure with digital as cna just change with editer
- Look for the exposure index -> should get a reference range from manufacturer and check to see whether in range
- Grainy images are under-exposed
- Over-exposed images have brightness adjusted to look OK - easy to overexpose patient
Detail what are the 2 things it depends on and what are they
1) Spatial resolution
- Is the ability to distinguish two adjacent contrasting objects
- Film-screen has better spatial resolution than digital radiograph
2) Edge definition
Is governed by geometric factors in image projection
Edge definition what are the 3 components and what makes edge definition is sharpest with
1) focal spot size - smaller focal spot better edge
2) focal spot to film distance - larger distance (generally 1m) the better edge
3) object to film distance -> smaller the distance the better edge definition
What are the 2 main causes of technical faults in radiographs
1) patient preparation
2) Image artefacts
Patient preparation what are important principles and the 3 main errors
- Patients should be handled gently to ensure compliance
- Sedation is often required for good patient positioning
- Remove leads & collars, bandages, tubing and wires if they will interfere with the image
- For abdominal radiographs, fast the patient and allow them to go to the toilet
1) blur images
2) distortion of anatomy
3) parallax error
what leads to 1) blur images 2) distortion of anatomy and 3) parallax error and what are they all apart of
PATIENT PREPARATION
1) Blur images
- Occur when there is poor edge definition or when there is motion
○ If motion blur -> sedate or anaesthesia, careful handling, work ‘with’ the patient, low exposure time - CAN MANIPULATE
2) Distortion of anatomy
- Occurs when there is unequal magnification of different parts of the same object
3) Parallax error
- The diverging x-ray beam provides a true projection of objects near the centre but distorts the projection at the periphery
- This is an issue with intervertebral disc spaces -> they are parallel splits and so the x-ray beams don’t hit it equally at the edge
○ If intervertebral disc disease want to put that vertebrae in the centre of the image otherwise space between distorted
Image artefact in radiographs what is it and the 6 main ones
- is a representation of something that is not a “real’ object
1) grid cut-off
2) quantum mottle
3) double exposure
4) moire artefact
5) white lines on CR image
6) excessive edge enhancement
Grid cut-off what does it arise from and how to position the grid correctly
- Arises from incorrect alignment of the grid with the primary beam
Grid positioned for: - Set film focal distance (incorrect distance causes artefact)
- Alignment of the primary beam (if put upside down then wrong alignment, or not centred (white dispered))
Periphery of the image not enough x-rays so get whiting
Not issue if grid built into the table
What is/result from with quantum mottle, double exposure and moire artefact
IMAGE ARTEFACTS
Quantum mottle
- Underexposure of a digital image -> not enough photons -> not clear depiction of anatomy -> low mAs
Double exposure
- Digital radiograph appears as two clear images
Moire artefact
- Occurs when a grid with the wrong grid ratio is used and misaligned
○ Creates a pattern of interference with the digital read-out frequency
What is/results from with white lines on CR image and excessive edge enhancement
IMAGE ARTEFACTS White lines on CR image - Indicate a dirty plate reader While reading the plate if the plate reader is dirty and has a hair then the laser will move over that section without releasing necessary energy so get white lines instead Excessive edge enhancement - causes black lines around high density
