Rad Overview
1. DISCOVERY- 1895,Wilhelm Röntgen (or Roentgen), working in a darkened laboratory in Würzburg, Germany- Fluorescence , x-rays; very first Nobel Prize for Physics in 1901
2. Conventional Radiography (CR, Plain Films)
-Images produced through the use of ionizing radiation, i.e., the production of x-rays, but without added contrast material like barium or iodine, are called conventional radiographs or, more often, plain films or x-rays
-source = x-ray machine; recorder = film, cassette, or photosensitive plate; processor = chemicals or digital reader
-combination of ionizing radiation and light striking a photosensitive surface produces a latent image that is subsequently processed to become visible
-PACS system: picture archiving communications and storage- images from all modalities can be stored and retrieved
-advantages- quick, inexpensive, easy to obtain
-disadvantages- reliance on ionizing radiation, limited range of densities; cancer potential
-common uses- cxr, abdominal films, initial skeletal system imaging for fractures or arthritis
-the five basic densities- air, fat, fluid or soft tissue, calcium, metal
-air: absorbs the least xrays and appears the blackest; decreased density, increased lucency
-fat: gray, somewhat blacker than soft tissue
-calcium: the most dense/ most opaque naturally occurring material eg bones, absorbs most xrays
-metal: usually absorbs all the xrays and appears the whitest
3. Computed Tomography (CT, CAT Scans)
-first introduced in the 1970s
-a gantry containing a rotating x-ray beam and multiple detectors in various arrays (which themselves are rotating continuously around the patient), along with sophisticated computer algorithms to process the data, a complete 3D set of images can be obtained
- CT image composed of pixels
-CT number from -1000 to +1000 Hounsfield units- after Godfrey Hounsfield; varies according to the density of tissue scanned and is a measure of how much xray beam is absorbed
-water = 0 hounsfield number; air = -1000; fat = ~-40 to -120; soft tissue = ~+20 to +100; bone = ~ +400 to +600; metal = ~+1000 or higher
-window = preselected range of Hounsfield numbers to best demonstrate the tissues being studied
-denser substances = higher CT numbers = increased attenuation = whiter appearance on CT
-post-processing allows for additional manipulation of the raw data to best demonstrate the abnormality without repeating a study or reexposing the patient
-three standard imaging planes in cross-sectional imaging: axial/ transverse, coronal, and sagittal
-axial/ transverse: divide body into upper and lower sections
-coronal/ frontal plane: divides the body into anterior and posterior sections
-sagittal plane: divides the body into right and left sections; midsagittal, parasagittal
-CT advantages: markedly expands the gray scale, markedly reduce any overlapping of structures that may obscure underlying pathology, patients with implantable devices contra to MRI can safely use CT, widely available
-CT disadvantages: utilizes ionizing radiation, expensive scanner, large space, sophisticated computer processing software
-CT is the cornerstone of cross-sectional imaging; can display any body part in any plane including 3D rendering in colour
4. Ultrasound (US)
- probes use acoustical energy above the audible frequency of humans to produce images
-the probe or transducer both produces ultrasonic signal and records it; the signal is processed by an on-board computer and the images recorded digitally and easily stored on PACS system
-advantages: relatively inexpensive, widely available, can be portable, does not use IR so particularly useful in imaging women of child-bearing age during pregnancy and in children
-disadvantages: cannot penetrate bones, large gas filled structures disrupt the ultrasound signal, difficult to visualize deep structures in the obese, operator-dependent
-study of first choice in imaging the female pelvis, paediatric patients, differentiating cystic vs solid, non-invasive vascular imaging, imaging foetus and placenta during pregnancy, in real-time image-guided fluid aspirations and biopsies
-other common uses- breast masses, thyroid nodules, tendons; assessing brain hips and spine in newborns
5. Magnetic Resonance Imaging (MRI)
- utilizes the potential energy stored in the body’s hydrogen atoms- mostly those in water
- hydrogen atoms contain a single proton that can be made to act like a small magnet
- extremely strong magnetic fields and radiofrequency pulses can manipulate the hydrogen atoms to produce enough localizing and tissue-specific energy to allow highly sophisticated computer programs to generate 2D or 3D images
- gadolinium used primarily for better detection of lesions such as tumours abscesses or metastases
-bone is black, fluid is white
-advantages: no ionizing radiation, superior contrast between soft tissues to CT and can differentiate better between fat, water, muscle, and other soft tissues, can characterize and discriminate among tissues using their physical and biochemical properties (e.g., water, iron, fat, and extravascular blood and its breakdown products); Blood flow, cerebrospinal fluid flow, and contraction and relaxation of organs, both physiologic and pathologic, can be evaluated
-other advantages: Because calcium emits no signal on most MRI images, tissues surrounded by bone, such as the contents of the posterior fossa and the spine, can be imaged; MRI can produce images of equal resolution in any projection without moving the patient; MRI protocols can be programmed to acquire data on physiologic phenomena such as the velocity of moving blood or the diffusion of water (useful in detecting stroke).
-disadvantages: not as widely available, expensive, high ongoing operating cost, safety issues with the extremely strong magnetic fields, side effects from radio-frequency waves produce by the scanners, possible adverse effects from some MRI contrast agents
-widely used in neurologic imaging; particularly sensitive in imaging soft tissues like muscles tendons and ligaments
6. Fluoroscopy (Fluoro)
- utilizes ionizing radiation in performing real-time visualization of the body in a way that allows for evaluation of the motion of body parts and positioning changes of bones and joints
-images can be viewed in real-time on video screens and captured for archiving either as a series of static images or as motion images
-requires xray unit specially fitted to allow for controlled motion; fluoroscopic tables are made to tilt and the fluoroscopic tube is able to move freely back and forth to image the patient
- spot films combined with other images obtained by an overhead x-ray machine in multiple projections during barium studies
- in interventional radiology iodinated contrast is selectively injected into blood vessels, tubes, or other ducts that can be fluoroscopically imaged to demonstrate normal anatomy, pathology, or the positioning of catheters or other devices
- advantages: units can be made mobile
-disadvantages: uses ionizing radiation- radiation doses can be substantially higher- reduce by using shortest possible fluoroscopy time
- used extensively to follow the location and path of externally administered barium or iodine contrast agents in real-time through the gastrointestinal and genitourinary tracts and blood vessels.
-Because of its real-time acquisition of images, it can be used for localization of tissues for biopsy and for guidance and confirmation of medical device placement
7. Nuclear medicine
- radioisotopes used referred to as radionuclides, radiotracers, or sometimes simply tracers; can be produced artificially or occur naturally; vast majority used are produced artificially
- Naturally occurring radioisotopes include uranium and thorium
- Radiopharmaceuticals are combinations of radioisotopes attached to a pharmaceutical carrier that is chosen for its binding properties, which allow the radiopharmaceutical to concentrate in (i.e., target) certain body tissues, e.g., the lungs, thyroid, or bones
- thyroid takes up iodine, the brain utilizes glucose, bones utilize phosphates, and particles of a certain size can be trapped in the lung capillaries
- After the radiopharmaceutical is carried to a tissue or organ in the body, usually via the bloodstream, its radioactive emissions can be measured and imaged using a detection device called a gamma camera
- Single photon emission computed tomography (SPECT) uses a gamma camera to acquire many 2D images from multiple angles, which are then reconstructed by computer into a 3D dataset that can be manipulated to demonstrate thin slices in any projection; camera rotates around the patient.
- Positron emission tomography (PET) scans- positron (positive electron)-producing radioisotope attached to a targeting pharmaceutical-- operate on a molecular level to produce 3D images that depict the body’s biochemical and metabolic processes.
- The most commonly used target molecule in PET scanning is an analog of glucose called fluorodeoxyglucose (FDG).
- PET mostly used in the diagnosis and treatment follow-up of cancer
-in nuclear imaging, on posterior views, the patient s right side is on your right
-uses: frequently used to locate hidden metastases or detect recurrence from a known tumour; used for cardiopulmonary imaging to assess function and anatomy of the heart and lungs; used to evaluate bones, especially for metastatic disease, fractures, and infections; used in treating certain thyroid abnormalities
-advantage: produce less patient exposure to radiation
-disadvantage: the patient themselves can briefly be the source of radiation exposure to others (e.g., technologists) utilizing nuclear medicine studies
- to limit exposure to others: decrease the time in proximity to the patient, increase the distance from the source (the patient), and appropriate shielding
8. Artificial Intelligence
-traditionally involved supervised learning, whereby a programmer or radiologist teaches the computer
- the future of AI in radiology lies in deep learning- allowing the software to teach itself using a complex system that mirrors the working of human neutral networks