Session 8: Medical imaging and cartilage

Question 1

Describe the fundamental principles of how x rays work. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 1

e- are accelerated towards a metal target. Interaction of e- with target produced photons. Some x rays pass through pt and hit detector behind them. Some are attenuated by pt. Detected x rays create image.
+: quick, portable, cheap, simple
-: radiation( but relatively low), one plane, cannot see all pathology, poor soft tissue imaging
Clinical use: checking for chest infection, fractures etc

Question 2

Describe the fundamental principles of how ultrasound scanning works. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 2

Time taken for echo to return calculated, and used to calculate where it was reflected from. Proportion of reflected waves used to calculate acoustic impedence mismatch.
+: low cost, no radiation, portable, dynamic- see movement, assess blood flow etc
-: operator dependant, cannot see well, difficult with obese patients
clinical uses: pregnancy dating, fetal growth, stones, masses etc

Question 3

Describe the fundamental principles of how medical resonance imaging works. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 3

MRI scanner creates strong magnetic field, aligns H+ atoms in pt. Radiofrequency pulse applied, tipping alligned h+, which creates detectable magnetic field. This induces current in coils of MRI. Varying signal intensities are produced by diff tissues, and they create images. High signal- bright, low signal-dark.
T1 weighting: fat bright, water dark
T2 weighting: water very bright, fat quite bright
+: no radiation, good contrast resolution
-: expensive, time consuming, fewer machines
clinical use: prostate imaging for cancer screening

Question 4

Describe the fundamental principles of how computerised tomography( CT)scanning works. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 4

X-ray tubes and detectors move around patient, creating cross-sectional images. X-rays produced, -ray tube on side of rotating gantry and detectors on opposite side. Pt table moves through gantry. Same principles of -ray attenuation as before. Cross-sectional slices of pt produced. Dected signal processed by comp does this.
+: quick, good resolution, can scan most parts of the body
-: radiation, affected by artefact like movement, overuse- fishing for diagnosis
Clinical use: determine causes of pain? cancer? weight loss? internal bleeding?

Question 5

Describe the fundamental principles of how positron emission tomography works. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 5

Radionuclides used emit positrons during decay. Emitted positrons collide with nearby e- in pt, producing 2 annihilation gamma photons, which are detected by the gamma camera.
+: good contrast and resolution, can analyse anatomy and function
-: radiation dose to pt, risk of radiation to others( public safety), expensive and time consuming
Clinical use: oncology-detecting, staging, response to treatment

Question 6

Describe the fundamental principles of how fluoroscopy works. Give advantages and disadvantages of the technique and a clinic example of where it can be used most efficiently

Answer 6

Similar to x-ray, but pulsed or continuous rays are used which creates moving images. Images enhanced using contrast( barium/ iodine).
+: real time, can carry out intervention, quick
-: higher radiation dose than single x-ray, radiation exposure to clinician, others similar to x-ray
Clinical use: coronary, after putting stent in to keep valves open, to check for blockages

Question 7

Describe the composition of cartilage in terms of its cells and extracellular components

Answer 7

Made of cells called chondrocytes, which are surrounded by a dense network of collagen and elastic fibres. Cartilage is avascular, nutrients and gases reach the chondrocytes by leaving blood vessels of the perichondrium( connective tissue that envelops cartilage when not at a joint) and by diffusing through extracellular material. Fibres, water and ground substance constitute the cartilage matric that gives cartilage its resilience, firmness, flexibility and strength.

Question 8

Classify 3 major types of cartilage and describe the structural differences between them

Answer 8

Hyaline: matrix contains collagen type 2. Present in epiphyseal growth plates during childhood and adolescence. Matrix is dense tissue containing fluid( water)
Elastic: matrix contains many elastic fibres and collagen type 2 in elastic lamellae( layers)- tough but flexible tissue
Fibrocartilage( fibrous): matrix contains lots of type 1( mostly) and some type 2 collagen fibres.

Question 9

Relate the different anatomical distribution of 3 major types of cartiligage to their different functions

Answer 9

Hyaline: cartilage in nose, articular cartilage of joint, trachea. Keeps airways open, and it tough for protection
Elastic: pinna of ear, eustachian tube, epiglottis. Returns tissue to original position, confers elasticity

Question 10

Recognise the following in histological photographs and state their functions

Answer 10

Hyaline cartilage: trachea. C shaped cartilage helps to reinforce trachea, and protect and maintain airway.
Hyaline articular cartilage: articulating ends of bones. Impt point of attack in RArthritis. Does not proliferate enough in adult cells to repair damage so fibroblasts lay down scar tissu instead. Cartilage calcifies with age, loss of flexibility.
Elastic cartilage: epiglottis,prevents food from entering airway, provides extra flexibilty and support.
Fibrocartilage: intervertebral disk, provides resistance to compression, durability, and tensile strength.