Week 1: Anatomical Concepts and Medical Imaging Flashcards
Body Planes?
Sagittal - vertical plane that divides the body into right and left sides
Mid-sagittal - Passes through the midline and divides into equal right and left sides
Parasagittal- a vertical plane that divides the body into unequal right and left sides (not through the midline)
Coronal/frontal plane: A vertical plane that divides the body into anterior (front) and posterior (back) portions
Transverse/horizontal plane: Divides the body into superior (upper) and inferior (lower) portions
Oblique: Passes through the body at any angle other than a 90 degree angle
What are body axes?
- Movements that occur sin a plan and around an axis
- Movements will occur about an axis at 90 degrees to that plane
What are the main the main body axes?
Mediolateral/Coronal/Frontal axis (sagittal plane movement)
Anteroposterior/Sagittal axis (coronal/frontal plane movement)
Longitudinal/ Vertical axis (transverse/horizontal plane movement)
Available movements and their axes?
Sagittal plane of movement around the mediolateral/coronal/frontal axes: Flexion/ extension and elevation and depression
Coronal/frontal plane of movement around the anteroposterior sagittal axis: Abduction/ adduction and lateral flexion movements
Transverse/horizontal plane of movement around the longitudinal/vertical axis: Internal rotation/external rotation and pronation/supination movements
Circumduction movements are across multiple planes and around multiple axes simultaneously
Introduction to Medical Imaging: Definition
Medical imaging is a broad term used to describe the techniques and procedures for visualizing the human body
X-ray: How does it work?
- Uses ionizing radiation
- X-ray beam is generated then transmitted through the body part
- How much of that x-ray beam that is absorbed depends on the density of the tissue e.g. bones will absorb more and air doesn’t absorb much at all
- The denser the tissue, the whiter the structure appears on the x-ray
A static 2D image is produces
X-ray projection?
The direction in which an x-ray beam passes through the body
- Anterior- Posterior (AP) projection: Beam travels from anterior to posterior (coronal plane)
- Posterior-Anterior (PA) projection: Beam travels from posterior to anterior (coronal plane)
- Lateral projection: Beam travels through the side (sagittal plane)
As a minimum, two perpendicular projections are required when looking at an area of interest
X-ray: When is it used?
- For dense structures like bones and calcifications
- When structures of different density are adjacent to each other, such as the lungs where air is against soft tissue and bone
- Pre-operative e.g. anesthetic evaluation
For assessing tube placement, particularly in hospital settings for intubated patients
X-ray: What are the risks?
- Risks of radiation
- Imaging must be justified
- Weight up risks vs benefits and only proceed if benefits outweigh the risks of exposing a patient to radiation
- Risk is higher in pregnancy and for pediatric patients (can cause radiation induced malignancy (cancer) years after exposure
Dental or chest x-rays are quite lower dose
X-ray: Advantages and Disadvantages?
Advantage:
- Cheap
- Quick, accessible, can be mobile
Disadvantages:
- Static image
- Limited detail
Care needs to be taken when used
Computed Tomography (CT): How does it work?
- Similar to x-ray as it used ionizing radiation
- Different to x-ray as it takes x-ray images from multiple angles around the part being imaged and over multiple slices
A computer then reconstructs these into multi-slice, cross-sectional images that can be reformatted into multiple planes
- Different to x-ray as it takes x-ray images from multiple angles around the part being imaged and over multiple slices
CT: When is it used?
- Diagnostic tool e.g.
- Staging and monitoring in oncology
- Preoperative planning
Provide detail of multiple structures e.g. lung, bone and soft tissue
CT: What are the risks?
- Radiation at a much more significant dose than x-ray (abdomen exposes to 10 millisieverts of radiation)
At approx. 20millisieverts there 1 in 1000 increased risk of malignancy from the radiation
CT: Advantages and Disadvantages:
Advantages:
- Relatively accessible
- Quick
- Provides detail
Disadvantages:
- Radiation dose
- Needs to be able to lie on the CT table and keep still, needs patient cooperation
- Limited use for dynamic imaging
Needs to be stable to get to the radiology department, be transferred onto the CT table, have the scan and allow for it to be interpreted
Ultrasound: How does it work?
- Ultrasound uses sound waves to create a picture (no radiation)
- A transducer probe transmits the sound wave and then records the echo that’s received back
This creates a 2D image
- A transducer probe transmits the sound wave and then records the echo that’s received back
Ultrasound: When is it used
- Assessing soft tissue structures e.g. liver, kidneys, muscles, tendons
- Provides dynamic assessment not just a static image (vessel flow, heartbeat)
NOTE: air and calcification e.g. bone, readily reflet sound waves and so create a bright line and obscure deep to them so sound waves can not get beyond this point
- Provides dynamic assessment not just a static image (vessel flow, heartbeat)
Ultrasound: What are the risks?
- Safe
- Not associated with cancer which makes it useful in: assessment of foetal structures, pediatric patients, tissues more susceptible to the risks of ionizing radiation such as thyroid or breast tissue
Ultrasound: Advantages and Disadvantages
Advantages:
- Accessible
- Safe
- Usually cheaper that CT and MRI
- Provides dynamic assessment, not just a static picture
Disadvantages:
- Limitations in the use of sound waves, both in terms of how substances transmit sound waves and the depth the sound waves will reach e.g. air, calcification,
- Some scans benefit from an element of cooperation from the patient
Hard for people with fat as the soundwave reflects off of fat
Magnetic Resonance Imaging (MRI): How does it work?
- Involves the used of magnetic fields and radiofrequency pulses to create a static image
Basic summary:- When the body is placed into a strong magnetic field, all the protons (positively charged subatomic particles within our body’s atoms) align with the magnetic field
- Radio waves are then transmitted to briefly disrupt the alignment of the protons
- The protons then return to be aligned with the magnetic field but the rate at which they realign is different for each body tissue
This information is then used to generate a picture
MRI: When is it used?
- Soft tissue structures
- Excelled for brain, spine, muscle, tendon, ligament and joints, liver pancreas
There is some scope for functional assessment of tissue however is not yet routinely used
- Excelled for brain, spine, muscle, tendon, ligament and joints, liver pancreas
MRI: What are the risks?
- Metal as MRI is a very strong magnet, needs to know whether the body has an implant
Risk in pregnancy, as it is new there is not a lot of evidence associated with its use on pregnant women, not safe in third trimester
MRI: What are the advantages and disadvantages?
Advantages:
- Provides detail of soft tissues (gold standard)
- Doesn’t use ionizing radiation
Disadvantages:
- Claustrophobia: MRI tunnel is tube like
- Loud for the patient even with headphones
- Limited accessibility due to size
- Time
- Cost
MRI: Critical points:
- X-Rays are not therapeutic and not routine
- ROT: only proceed if benefits outweigh the risks of exposing a patient to radiation
- Radiographers licensed and regulated (careful what you promise your patients)
A variety of safety considerations
Anatomical Positions:
- Frame of reference (standard anatomical position)
- SAP = head forward, palms forward close to side, feet at comfortably positioned, head facing forward, palms forward, toes forward, feet slightly apart
- Planes/ imaginary lines
Planes are imagined as a series of parallel lines
Anatomical Relationships:
- How each body structure relates to each other
- Relationship of an anatomical structure can be described in terms of where it is relative to something else
- Based from standard anatomical position
- Superior: Cephalic pr Cranial region
- Inferior: Caudal (tail, towards the toe)
- Superficial, deep, medial, lateral, proximal, distal
- Show the relationship of one organ or body part in relation to another
Left and Right = patients left or right not our own (so it is opposite)
What is a joint? What aren’t joints?
Joint is where two or more bones or cartilage meet, some that aren’t joints e.g. tongue, lips, eyes
What is dorsi and plantar flexion?
Dorsi-flexion when front part of foot are lift off the ground in an anterior direction and the angle is decreasing between the foot and the angle.
The opposite is plantar flexion bends the foot or toes towards the ground and the angle is increasing
What is hyperextension?
Movement occurs beyond normal limits of the joint which may lead to injury
What is: Abduction, adduction, circumduction and lateral flexion
- Abduction and adduction: frontal plane around anteroposterior axis
- Abduction: away or laterally from middle plane of the body. Fingers: the middle remains stable and the others move
- Adduction: Moving back to original position
Lateral flexion: Unique type of abduction, shoulders tilt or move to the right so the midline is becoming bent
What is: Circumduction, rotation (medial and lateral)
- Circumduction: Involves, circular movement, flexion, abduction, extension or adduction. Distal end of the part moves in a circle
- Rotation: body part turns or revolves around a longitudinal axis
Medial and lateral rotation: Medial: anterior surface of limb moves towards medial plane. Lateral: Anterior surface of the limb moves away from the medial plane
- Rotation: body part turns or revolves around a longitudinal axis
What is pronation, supination, inversion and eversion?
- Pronation: forearm and hand to swing the distal end of the radius medially and laterally around anterior aspects of the ulna while the proximal end of the radius rotates in place
- Supernation: Rotates radius laterally and palm faces anteriorly.
- Eversion and inversion: Soles of feet move away and towards median plane
- Eversion: Moving the outer edge of the foot away from the midline
Inversion: Moving the outer edge of the foot towards the midline/ median plane
What is opposition and reposition?
Thumbs have two movements: Opposition and reposition. These allow fine movements. Opposition brings the pad of the thumb to other fingers e.g. gripping a pencil, doing a button. Reposition: Brings the thumb back to its normal position
What is protrusion/retrusion, elevation/depression?
- Protrusion and Retrusion: Anterior and Posterior movement of a joint e.g. moving a neck in and out
- Elevation and Depression: Elevate moves body in a superior position (shrugging) Depression moves inferiorly
How are X-rays projected?
- X-ray pass through tissues interact with photographic film. Air reduces x-rays energy a little bit, fat reduces more than air but less than water and bone attenuates the ex-rays the most
- The differences in attenuation is responsible for exposure on film
- Bone appears white as it has been exposed to the least amount of x-rays whilst air is black as it has been exposed to the most amount of x-rays. Can see fractures as they appear darker in the bone
- Projections as the x-ray beam is projected through the area of interest to the other side
Different projections are defined by the orientation of the body segment relevant to the beam and body sector
What is:
Anteroposterior projection
Lateral projection
Posteroanterior projection
Axial projection
- Anteroposterior projection (AP): X-ray is projected from anterior to posterior
- Lateral: Projected from the side
- Posteroanterior (PA): Projected from posterior to anterior
Axial: Projected down the superior to inferior axis
How many projections are required? What is divergence?
- Minimum of two perpendicular projections are required to get all the evidence
Divergence: Basic principle of projection, will diverge from source projector through bone. If the light is closer to the body it will be bigger but less sharp, if it is too far away it will not be magnified and too small. Therefore it is better for it to be closer to the detector rather than the source
How does an ultrasound work? What are advantages and disadvantages?
- Transducer to detect high frequency sound wave
- Passes through tissues but comes back to the transducer
- The more denser the higher the sound wave frequency and whiter the image
- Advantages: Image soft tissues and bone, harmless, portable an inexpensive
Disadvantages: Poorer resolution, artefacts common, sound wave unable to penetrate completely through the body
How does an MRI work? Advantages and disadvantages?
- Magnetic field which resonate hydrogen atoms
- Emit a radiofrequency which collected by a receiver to show an image. Tissues classified by the hydrogen content, the more hydrogen or water atoms, the whiter it will be, and the darker the less hydrogen and water atoms.
- Does not detect bone
- Advantages: Imagery of soft tissues, not bone, soft tissue injuries, no ionizing radiation
Disadvantages: Expensive, noisy, claustrophobic, remain still, magnetic fields interact with metal which distorts the images
What is cranial and caudal?
Upper and lower of the body (head and feet)
If the aim of the x-ray is to get an unobstructed, as complete an image of both lungs as possible, which of the following x-ray projections would be best suited to achieving this?
Posterior-Anterior projection
What is the name of the body cavity where the lungs are located?
Thoracic
What type of specialised tissue lines this body cavity?
Serous Membrane
How would air in the pleural space appear on x-ray?
Black
Which of the following options is a way that CT scans are distinguishable from an x-ray?
CT scans provide multi-slice cross-sectional images
