Introduction: Medical Imaging Flashcards
What is radiographic anatomy?
The study of the structure and function of the body using medical imaging techniques.
Advances include availability and speed of scans.
Five main modalities
Plain conventional radiography (X-Ray)
Ultrasound Scan (USS)
Computed Tomography (CT)
Magnetic Resonance Imaging (MRI)
Nuclear Imaging
Why is it important?
Non-invasive Helps with diagnosis Disease monitoring Research Teaching
Conventional Radiography
X-Rays
2D imaging
Highly penetrating beam of X-rays which penetrate the individal and an image is produced on a detector.
How does convention radiography / x-rays work?
Different intensities on the film highlight tissues of differing densities.
Highly dense tissues absorb more radiation.
Dense substance - Radiopaque
Less dense - Radiolucent
Contrast is sometimes used. e.g. in an angiogram
Differing Densities - Colours
Air
Black
Differing Densities - Colours
Fat
Dark Grey
Differing Densities - Colours
Soft tissue / fluid
Grey
Differing Densities - Colours
Bone
Light grey
Differing Densities - Colours
Metal
White
Advantages of X-ray
Cheap
Portable
Quick and easy to use
Combined with contrast
Disadvantages of X-ray
Exposure to Radiation
Operator dependent
2-dimensional Image
Precautions pregnancy / children
Ultrasound Scan (USS)
USS uses technique that visualises superficial or deep structures in the body by recording pulses of ultrasonic waves that reflect off tissues.
Probe placed on patient’s skin with lubricating jelly.
Sound waves emitted fro the probe hit body structures of tissues
Sound waves reflect off the structures. Different tissues will reflect at differing frequencies and times.
Top of Image closest to probe.
Increased density = whiter image (e.g. bone)
Advantages of Ultrasound Scan (USS)
Non-invasive Cheap Portable No ionising radiation Produce real-time images (doppler)
Disadvantages of Ultrasound Scan (USS)
Unable to cross a tissue-gas or tissue-bone boundary.
Operator dependent
Difficult in patients with larger body size.
Uses of Ultrasound Scan (USS)
Pregnancy
Abdominal Aortic Aneurysm monitoring
Deep Vein Thrombosis diagnosis
Echocardiogram (heart ultrasound).
Computed Tomography (CT)
Description
Hounsfield (1972)
X-ray beam and a detector system move through an arc of 360 degrees
Circular doughnut known as the gantry consists of both the beam and the detector.
Gantry rotates and a cross-sectional image is obtained.
Detector is able to measure the intensity of radiation passing through the individual.
Computer system analyses the different intensities and a 3D image is reconstructed.
Appearance of CT scan
High absorption such as bone appear white and those with little absorption appear black.
Contrast medium can be used to better visualise organs.
CT scans are viewed by looking up a patients feet.
Advantages of Computed Tomography
Able to generate a 3D image
Able to utilise contrast
Relatively quick
Non-invasive unless IV contrast is used
Disadvantages of Computed Tomography
Significant radiation exposure
Not easily portable
Requires patients to be still
Relatively expensive
Reactions to contrast
Magnetic Resonance Imaging Description
Non-invasive imaging which does not use ionising radiation
Magnetic field
Human body up of mostly water
Protons (hydrogen ions) line up within the magnetic field.
Radio frequency pulsed waves are emitted which cause the protons to misalign
Magnetic Resonance Imaging (MRI)
How it works
As protons return to their aligned position they release energy which can be measured.
Different tissues emit different signals
Why we use MRI
Scanners are useful for the visualisation of soft tissues.
Intrinsic details of different modalities of MRI such as T1 weighted and T2 weighted
Looking up a patients’ feet
Advantages of MRI
3D images are created
Differentiating tissues
No radiation exposure
Safe in pregnancy / children
Non-invasive unless contrast is use
