Introduction to imaging techniques Flashcards
What is the difference between a radiologist and a radiographer
Radiologist: doctor specialising in imaging interpretation
Radiographer: technician who takes images
When were X-Rays first used for imaging
1895.
When was CT scanning first introduced into clinical practice
1971.
When was MRI introduced into clinical practice
1983.
What is radiology
Diagnostic Imaging
Interventional Radiology
Do not confuse with radiotherapy
Describe the importance of radiology in clinical practice
Imaging is necessary in most clinical specialities to diagnose pathological changes to tissues. It is paramount to appreciate what is normal and what is abnormal. An appreciation of how the image is obtained, what the normal variations are, and technical considerations is necessary to obtain a radiological diagnosis.
Distinguish between ionising and non-ionising radiation
Ionising Radiation
X-ray & computed tomography (CT)
Nuclear Medicine
No ionising radiation
Ultrasound
Magnetic Resonance Imaging (MRI)
What are the sources of background radiation
Radon gas from the ground- majority Buildings and the ground Artificial rays- medical sources represent 14% of background radiation. Cosmic Rays Food and Drink.
What is the problem with ionising radiation
relationship with development of cancer years after exposure; the younger the patient, the higher the mortality and incidence of cancer in later life (between 0 and 10- greater risk of cancer later in life).
Describe X-rays
X-rays are photons and are generated from a complex X-ray tube, which is a type of cathode ray tube. The X-rays are then collimated (directed through lead-lined shutters to stop them from fanning out) to the appropriate area, as determined by the radiographic technician. As the X-rays pass through the body they are attenuated (reduction in energy) by the tissues. The X-rays that pass through the tissues interact with the photographic film.
Describe the passage of X-rays through air and fat
Low density tissues
Appear black on X-ray
Describe the passage of X-rays through soft tissue
50% X-rays pass through GREY
Soft tissue
Describe the passage of X-rays through bone
Few X-rays pass through WHITE
Bone
What do different attenuations of the X-rays result in
These differences in attenuation result in differences in the level of exposure of the film.
More exposure=black
Less exposure=white
Most of the X-rays are absorbed by bone- less reach the film- which is why it appears white.
Describe the contrast between different body parts seen in X-rays
Air- Black Fat- Fairly Black Soft tissue- gray Bone, calcium- white Metal- really white.
What can be seen on a chest radiograph
Lungs full of air so are distinguishable from tissues, but cannot distinguish between heart muscle, pericardium and blood in the heart due to similar densities
Fat has a different density so can be distinguished from tissue (muscle)
Describe the abdominal radiograph
left-sided kidney may appear white due to calcium deposits
Usually taken in AP supine position
Erect PA when small bowel obstruction is suspected.
What is inherent tissue contrast improved by
Contrast agent enhances the differences between tissues of similar densities Commonly used contrast agents: Barium Iodine Various ways they are introduced Swallowed Via rectum Into artery or vein
Contrast agents appear white on X-rays
Describe the use of barium sulfate and iodine
Barium sulfate- insoluble salt, nontoxic, high-density agent- useful for examining the GI tract.
Iodine- directly in arteries or veins- high atomic mass (so markedly absorbs X-rays well)- excreted naturally via the urinary system- and so can be used in intravenous urography
Describe the safety of intra-arterial and intra-venous contrast agents
Extremely safe and well tolerated by most patients Some patients (rare) have an anaphylactic reaction to these injections and so the appropriate precautions must be taken.
Describe the importance of CT scans
Can appreciate differences between soft tissues (e.g water) unlike X-rays.
Describe how images are obtained in CT scans
The patient lies on a bed
An X ray tube passes around the body and a series of images are obtained
A computer carries out a complex transformation of the multitude of images to perform a cross-sectional map of tissue density.
Describe the appearance of different entities on CT scans
Organs are different shade of grey depending on water content; skin is white, fat is black and air is black
Describe CT windows
Enhance the CT scan to look at different areas (soft tissue, bone, lungs)- set digital imaging.
changes interpretation to expose different details based on focussing on different density depending on structure to image
Describe the contrast agent for CT scan
Iodine injected into an arm vein during the scan
There are some risks
Allergic reaction
Kidney damage- cannot be given to those with renal failure
Enhances the blood vessels and makes them much easier to see
Differentiates pathological from normal tissue
How do liver tumours appear on a CT scan
Black holes- density difference not enough to be shown on CT.
Describe how images are obtained in ultrasound
Uses high frequency sound to make images.
Ultra high frequency sound waves are generated by piezoelectric materials, such that a series of sound waves is produced.
Importantly, the piezoelectric material can also receive the sound waves that bounce back from the internal organs.
The sound waves are then interpreted by a powerful computer, and a real-time image is produced using the display panel.
Describe the role of the transducer in ultrasound
The sound is produced and detected with the same device: transducer
Transducer
Speaker: sends sound into patient
Microphone: records sound coming back from patient
No radiation hazard, completely safe
2D image
Describe a colonoscopy
Air into colon- camera up colon.
Describe MRI scan
Strong magnet, supercooled with liquid helium
Transmit radio wave pulses into patient
Listen for return radio waves caused by interaction with protons (water) in the patient’s body
Different tissues give different intensities of returned radio waves –> image
Describe how images are obtained in MRI scans
The process of MRI is dependent on free protons in the hydrogen nuclei in molecules of water. Because water is present in almost all biological tissues, the hydrogen proton is ideal.
The protons within a patient’s hydrogen nuclei can be regarded as small bar magnets, which are randomly orientated in space.
When a pulse of radio wave is passed through the patients the protons are deflected, and as they are returned to their original position they emit small radio pulses.
The strength and frequency of these emitted pulses and the time it takes for the protons to return to their pre-excited state produce a signal. These signals are analysed by a computer and an image is created.
Why does bone appear black on MRI.
protons are packed, don’t move- different to CT and X-rays.
Describe the appearance of different entities in a T1 MRI
Air- Black Bone- black Bone marrow- white soft tissue- gray (variable) Fluid- black Fat- white
Describe the appearance of different entities on a T2 MRI
Air- Black Bone- Black Bone marrow- Grey (variable) Fluid- white Fat- white
Describe the difference between T1 and T2 MRI
By altering the sequence of pulses to which the protons are subjected, different properties of the protons can be assessed. These properties are referred to as the ‘weighting’ of the scan. By altering the sequence and the scanning parameters, T1-weighted and T2-weighted images can be obtained. These two types of imaging sequences provide differences in image contrast, which accentuate and optimise different tissue characteristics.
How can you distinguish between T1 and T2- weighted images
T1- dark fluid and bright fat- CSF is dark
T2- bright signal from fluid, intermediate signal from fat- CSF is white.
Describe nuclear medicine
Involves gamma rays
Uses radioactive tracers that emit radiation
Different tracers go to different organs or parts of the body
Images are made by detecting the radiation coming out of the patient by gamma camera
What can you see on an abnormal bone scan
Black areas- tumours- bone tries to repair itself.
Describe an abnormal lung scan showing blood flow
P.E- no blood flow
Appears normal when showing ventilation (air)
Describe PET
PET detects metabolic or ‘functional’ changes in the body rather than ‘structural’ changes
Is particularly effective in identifying whether cancer is present or not (diagnosis), if it has spread (staging) and if it is responding to treatment
Describe PET/CT
Better anatomical localisation of cancers
Faster and more specific than PET alone
Describe how PET can be used to generate images
PET is an imaging modality for detecting positron radionuclides. A positron is an anti-electron, which is a positively charged particle of antimatter.
the most commonly used radionuclide is fluuorodeoxyglucose labelled with F-18 ( a positron emitter). Tissues that are actively metabolising glucose take up this compound, and the resulting localised high concentration compared to background emission is detected as a ‘hot spot’.
Describe the planes of the feet and hands
HAND- PALMAR/VOLAR AND DORSAL
FEET- Dorsal (top), plantar (bottom).
What is the issue with proximal and distal
Don’t take into account direction of flow, for example when talking about flow.
What is the key difference between gamma rays and X-rays
Gamma rays- unstable decay of nucleus
X-ray- bombarding an atom with electrons
How are areas visualised in nuclear medicine
For an area to be visualised in nuclear medicine, the patient must receive a gamma ray emitter- technetium 99-m.
It must have:
a reasonable half-life
an easily measurable gamma ray
energy disposition in as low a dose as possible in the patients’ tissues.
