Medical Imaging And Cartilage Flashcards
Describe the fundamental principle of how X-Rays work
Within an X-ray tube electrons are accelerated towards a metal target (tungsten). Some of the X-rays, then hit a detector behind the patient. Some are attenuated by the patient (absorbed p, scattered p, or lose energy as they pass through). Amount of attenuation is dependent on the density number of tissue/material, and energy of X-ray beam. The detected X-rays are digitised and processed creating an image which is uploaded to the picture archiving and communication systems.
Describe the fundamental principles of how ultrasound scanning works
Ultrasound utilises sound waves. Crystal in the transducer probe oscillates creating high frequency sound waves. These travel through tissues and are reflected back from boundaries between tissues of different density. The probe detects reflected sound waves (echos) and converts them into electrical signal.
The time taken for echo to return is used to calculate where it was reflected from. The proportion of reflected waves is used to calculate the acoustic impedance mismatch in that place and intensity is displayed as greyscale.
Hyperechoic means more reflection and more white on image. Hypoechoic means less reflection and more dark on image. Acoustic shadowing means large acoustic impedance mismatch = sound waves are completely reflected back, none pass through, dark area behind bone, air, stones.
Describe the fundamental principles of how MRI works
An MRI scanner creates a strong magnetic field that aligns hydrogen atoms within the patient. A radio-frequency pulse is applied which ‘tips’ the aligned hydrogen atoms which creates a detectable magnetic field. This field induces an electoral a current in nearby coils in the MRI machine.
Varying signal intensities are produced by different tissues, these are then processed to create images. After the pulse ends, the hydrogen atoms relax back into alignment with the magnetic field of the MRI machine.
Describe the fundamental principles of how CT scanning works
X rays produced. There is an X ray tube on one side of a rotating gantry and detectors on the opposite site. The patient table moves through the gantry, process is similar to X rays. Cross-sectional slices of the patient is imaged. Detected signals is processed by computer to produce cross-sectional images
Describe the fundamental principles of how PET scan works
Administration of radiopharmaceutical:
- Pharmaceutical part - takes the compound to tissues of interest.
- Radionuclide part - sends signal from tissue of interest.
Nuclear decay of radionuclide occurs within tissues of interest emitting gamma radiation which is detected. Y a gamma camera close to patient. Gamma camera contains a scintillator (which converts signal into light). Light signal is amplified and processed by computers to produce images.
It gives functional and anatomical information
Describe the fundamental principles of how Fluoroscopy works
Process is similar to X-ray except pulsed or continuous X-rays are used creating moving images.
This can be used to examine anatomy, pathology, motion and function.
Images are often enhanced using contrast (barium/iodine), as they have a high atomic number which is a good absorber of X rays so it appears dense on image.
Explain the advantages and disadvantages of X rays
Advantages:
- Quick
- Portable
- Cheap
- Simple
Disadvantages:
- Radiation (but relatively low)
- One plane, two dimensional
- Cannot see all pathology
- Poor, soft tissue imaging
Explain the advantages and disadvantages of Ultrasound scanning
Advantages:
- Lack of radiation
- low cost
- Portable
- Dynamic (can see movement, assess blood flow).
Disadvantages:
- Operator dependent
- No bone or gas penetration
- Difficult with obese/frail/unwel patients
- Theoretical risk of overheating if misused
Describe the advantages and disadvantages of MRI
Advantages
- No radiation
- Good contrast
Disadvantages:
- Expensive
- Time consuming
- Fewer machines, fewer radiographers
- Contraindications (pacemakers, cochlear implants, metal, claustrophobia, lack of mental capacity)
- Contrast reactions
- Image quality relies on magnetic field strength.
- Contrast reactions
Explain the advantages and disadvantages of CT scanning
Advantages:
- Quick
- Good spatial resolution
- Can scan most parts of the body well (but not all)
Disadvantages:
- Radiation
- Does. It delineate sof tissue well
- Affected by artefact (movement, metal
- Requires breath holding (not all patients can)
- Overuse (fishing for diagnosis)
- Incidental findings
- Contrast reactions
Explain the advantages and disadvantages of PET scanning
Advantages:
- Good contrast and spatial resolution
- Can analyse anatomy and function
Disadvantages
- Physiological uptake of radiopharmaceutical
- Radiation does to patient
- Risk of radiation to others
- Radioactive waste produced
- Expensive and time consuming
- Radionuclide shortages
Explain the advantages and disadvantages of Floroscopy
Advantages:
- Dynamic studies, real time can assess function, carry out intervention
- Quick
Disadvantages
- Higher radiation dose than single X ray
- Radiation exposure to interventional clinician
- one plane, two dimensional
- Cannot see all pathology
- Poor soft tissue imaging
Give a clinical example of where X rays can be used
Chest X ray
Indications: Dyspnoea, cough, haemoptysis, chest pain, follow up post pneumonia
Diagnosis: Infection, pulmonary oedema, pleural effusion, pneumothorax, cancer.
Abdomen/Pelvis X ray
Indications: Neonatal, passing of urinary tract calculate, checking for presence of foreign bodies
Diagnosis: Obstruction, volvulus, perforation, colitis, calculate, abdominal aortic aneurysms
MSK
Indications: Trauma, pain, deformity, swelling, post relocation of joint, post reduction
Diagnosis: Fracture, dislocation, effusion, soft tissue injury, tumour, infection
Give a clinical example of how ultrasound scanning can be used
Solid organs - Appearance of tissue/organ, masses, bleeds, etc
Hollow structures - function, stones, flow, obstructions etc
Breast- Assessing lumps abnormally seen on screening mammogram
- Obstetrics - Pregnancy dating, foetal anomaly, placental location, foetal growth
- Musculoskeletal - Assessing muscles, tendons, ligament, joints, nerve, soft tissue masses.
Interventional - US guided injection/biopsies/drains/aspirations.
Give a clinical example of how MRI can be used
- Central nervous system ( brain and spinal cord)
- Head and Neck imaging
- MSK imaging, bones/joints/soft tissues
- GI e.g., MRCP, MRI liver
- Cardiac MRI, MR angiography
- Gynaecological imaging, prostate imaging
- In paediatric/pregnancy to avoid radiation
