general radiology Flashcards
- formation and characteristics of X-rays + biological effects
FORMATIONS
o The x-ray is an electromagnetic wave made in X-ray tube by focusing a beam of high energy electrons on a tungsten target.
o X-ray tube: High voltage electric current is passed across a vacuum tube. This induces a stream of electrons from a cathode to an anode.
When the beam of electrons strikes the anode, X-rays are produced.
Approx. 99 % of the energy (electrons) is converted to heat, only 1 % to X-ray.
o Attenuation: X-ray beam ↓ acc. to density and atomic No of tissue when passing.
o X-ray turns X-ray film black. Low density 🡪 more X-ray pass through 🡪 darker (lung)
CHARACTERISTICS
part of electromagnetic spectrum (photon radiation)
short wavelenght : 0.01 -10nm
high frequency : 30 petahertz -30 exahertz
wavelength and frequency (energy of wave depends on frequency) shorter wavelength - higher frequency - the higher energy - greater ability to penetrate objects
objects closer to X-ray beams will be magnified (appear larger)
has ionizing effect
no mass / no charge / invisible
BIOLOGICAL EFFECTS
high energy radiation - ionizing - displace elctrones
effect on dividing cells
direct damage : radiation hits DNA molecule (genetic effect ) cell damage/cell death
indirect damage : free radicals- can cause for example -radiation burns , leukemia…
classification of biological effects according to:
stochastic - random effect /late/no threshold/not
dependent on radiation dose
risk increases with dose , not severity
either develop cancer or not /genetic defects
deterministic effect - dose dependent
severity of effect increases with dose (once
threshold is met
effects: fetal abnormality/ sterility/ cataracts…
- principles of radiation protection
radiatio protection Basic principles of radiation protection: ALARA (as low as reasonably achievable) o Justification of practice. o Optimization of protection. o Individual dose limits.
- Protection against exposure to ionizing radiation:
1. TIME:
o Acute dose vs. fractionated doses (in smaller doses with one or more rest periods, fewer cells die, gives time for repair in the body
- DISTANCE:
o The intensity of radiation decreases the further you are from the source. o Inverse square law: d= 1 m 🡪 4 mSv/h, d= 2 m 🡪 1 mSv/h.
o Radiation intensity α! - SHIELDING:
o X/gamma rays are diminished in intensity by any absorber but not totally stopped. o Materials with high atomic number can absorb more photons than lighter elements.
o For X and gamma emitters, shielding is usually lead.
- Summary-radiation safety:
o Goal: keep radiation exposure ALARA.
o Dose rate and fractionation, radiation quality, and temp can modify radiation effect. - Attend to life-threatening injuries first.
- imaging techniques: fluoroscopy - radiography -tomography - tomosynthesis
FLUOROSCOPY:
allows dynamic realtime imaging of patients
o plain X-ray images do not permit continuous observation of processes in a patient.
- fluoroscopy devices, are used with an image amplifier :
x-ray beams pass through the body and then registered on the amplifier
which amplifies primary image (creates brighter image) thats is captured by videocamera and displays it on a secondary fluoroscopic screen.
RADIOGRAPHY: (practical 1)
o Uses electromagnetic energy in the form of X-rays to create medical images. The resulting images is negative view density tissue.
o Low density = Soft tissue = Low absorption = More intensity of black colour
TOMOGRAPHY :
o is imaging by sectioning or sections, through the use of any kind of penetrating wave. A device used in tomography Is called tomography and image produced is called tomogram
TOMOSYNTHESIS: (physics webpage)
o Is an imaging technique in which multiple x-rays of one object are taken from a discrete number of angles. These cross-sectional images are used to reconstruct 3-D images of the object being scanned. It differs from computed tomography because the range of angles used is less than 360 degrees, which is used in CT.
- DSA : principles - indications - contraindications
o Classic invasive method to visualize vessels. Special angiographic x-ray devices are used for the procedure.
o Intraarterial administration of iodine contrast medium
o Able to visualize pictures by “freeze frame” of the column of the dynamic blood
o The non-contrasted image is subtracted from the contrasted one so that other structures are no longer visible. This means that it is also necessary to make a pre-contrast image
o Indications: angioplasty (opening narrowings and blockage), arterial stent, coronary angiogram, femoral angiogram, nephrostomy, diagnosis (hemorrhage, thrombus, aneurism)
o No ABSOLUTE CI! (but poor renal reserve and allergy to contrast medium should be taken into consideration)
o Technique: Arterial access into femoral artery with local anesthesia. Seldinger is the name of the puncture technique
o Complications: rare, but hematoma most common
- USG : principles - indications - limitations
Ultrasound: (Lecture 1 and book)
o US imaging uses ultra-high-frequency sound waves to produce cross-sectional images of the body. The ultrasound wave spreads within tissue as a longitudinal wave (in zones of high pressure and low pressure)
o The frequency is measured in hertz (one hertz equals one vibration per second) and range from 2 to approx. 15 MHz
principle:
o The ultrasound beam originates from mechanical oscillations of numerous crystals in a transducer, which is excited by electrical pulses (so called piezoelectric effect). The transducer converts one type of energy into another (electrical 🡪 mechanical/sound)
o 🡪 The ultrasound waves are sent from the transducer through different tissues and then return to the transducer as reflected echoes. The returned echoes are converted back into electrical impulses by the transducer crystals and are further processed to form the ultrasound image presented on the screen
o It does not create ionizations
o Has wide variety of medical applications
o Doppler ultrasound can detect a frequency shift in echoes, and determine whether the tissue is moving toward or away from the transducer. This is invaluable for evaluation of some structures such as blood vessels or the heart
o Usually the first investigation procedure to be performed and most common used image diagnostic technique
o Advantages: economical (more available), no radiation, non-invasive (can be repeated), multiplanar sectional imaging, visualization of blood flow, not been associated with carcinogenesis, few contraindications,
o Disadvantages: investigator-dependent, susceptible to artifacts, no continuous documentation, training is required to accurately conduct an ultrasound exam, not capable of evaluating tissue types with high acoustical impedance (bone, air), potential risk of thermal heating or mechanical injury to tissue, limited by abnormally large body habitus
o Indications: great diagnostic value for depicting the anatomy and pathology of parenchymatous organs (heart liver, spleen, pancreas, kidneys, muscles, connective tissue, tendons etc.). Also, an excellent method for the diagnosis of vessels
- CT : principles - indications - contraindications
o Computed tomography (CT) is an imaging technique whereby cross-sectional images are obtained with the use of X-rays.
o Uses x-ray energy and sophisticated software to create images of the body
o 1971, was the first patient scan performed 🡪 Hounsfield and Cormack nobel prize
o Hounsfield units are unites of x-ray attenuation used in CT. Each pixel is assigned a value on a scale from -1000 to + 1000
o Bone = +1000, Soft tissue +40, Blood + 40-80, Water 0, Fat – 50, Air – 1000
o Different substances have different relative densities, thus different Hounsfield units (so use it if you´re not sure what you are looking at
o Basic principles: Bundle of rays penetrates body perpendicular to its longitudinal axis. The detector system consists of a series of about 1000 individual detector elements. The source of radiation and the detector system rotate around the patient’s body
o Conventional CT: make the layers step by step during moving of the examination table with the patient
o Helical CT: investigate during continuous exposure of the patient slowly passing through the opening in the gantry
o Disadvantages: Ionizing radiation, artefact from adjacent bony structures obscures normal anatomy, hazards of intravenous contrast, high cost
o Indication: Useful for initial and acute investigation of severely ill patients (multi trauma). It provides images of the brain, chest organs with vessels, parenchymatous organs of the abdomen as well as the skeletal system with high spatial resolution.
o Neruological indications includes: stroke (differentiate between ischemic cerebrovascular syndrome, hemorrhage and subarachnoid hemorrhage), trauma to brain or skull (hematomas or fractures), tumors, inflammation – non-contrast best in hemorrhage, else with iodine
o Chest: disease of lung or mediastinum (with contrast because of different densities in chest area), High resolution CT (HR-CT) to investigate lung with thin slices for lung diseases as fibrosis, sarcoidosis, pneumoconiosis, emphysema, bronchiolitis, but not to investigate lymph nodes or metastasis!
o Abdomen: Barium contrast in GI tract, and Iodine nearly in all other cases. Acute abdomen, abscesses, lesions, parenchymatous tissues such as pancreas, liver and kidneys
o CT angiography: Non-invasive imaging of vessels by CT with i.v injection of contrast medium. For evaluation of renal arteries (stenosis), thoracic and abdominal aorta (aneurism, dissections), cervical arteries (carotid), pulmonary artery (embolism), cerebral (stroke)
o Interventional: CT-guided biopsies of lungs, liver or pancreatic lesions and CT-guided drainage of abscesses
o Contraindications for use of iodinated contrast media: allergy to iodine, toxic goiter of the thyroid, planned radioiodine treatment of thyroid cancer
o Contraindications generally: No absolute, but caution in pregnant women, repeated may increase risk for cancer, claustrophobia
- MRI : principles - indications - contraindications
Uses the energy of high-strength magnetic fields and radio waves to create images of the human body
o Principle: MRI makes use of the magnetic properties of certain atomic nuclei. Hydrogen nucleus present in water molecules, and therefore in all body tissues! The hydrogen partially aligned by a strong magnetic field in the scanner and can be rotated using radio waves. They subsequently oscillate in the magnetic field while returning to equilibrium. Simultaneously they emit a radio signal, which is detected using antennas (coils). Very detailed images can be made of soft tissues
o T1: relies upon the longitudinal relaxation of a tissues net magnetization vector (iknow it´s fucked up). Basically, spins aligned in an external field (Bo) are put into the transverse plane by an RF pulse. They then slide back toward the original equilibrium of Bo. Not all tissues get
back to equilibrium equally quickly and a tissues T1 reflects the amount of time its protons spins realign with the main magnetic field. Fat appears bright and water appears dark o T2: Relies upon transverse relaxation of the net magnetization vector. Fluid has high signal intensity (white), white matter of brain (dark)
o Indication: for most examination of most ailments of the brain including tumors, sport injuries, musculoskeletal problems, most spinal conditions/injuries, vascular abnormalities, female pelvic problems, prostate problems, some GIT conditions, certain ear, nose and throat conditions, soft tissue and bone pathology/condition
o It uses the magnetic properties of the hydrogen atom to produce images o Creates no ionizing radiation
o Advantages: Excellent soft tissue contrast, lack of artefact from adjacent bones, multiplanar capabilities and lack of ionizing radiation, many details without i.v contrast
o Limitations: Cost, artefacts, metal foreign objects, reduced sensitivity for certain substances, lack of fine bone detail (but more sensitive in the detection of infiltrative disorders of bone marrow), difficult with patients with claustrophobia, movement causes blurry images
o MR – contrast: Brain = metastases, multiple sclerosis, tumors (meningioma), tumor recurrence
o Contraindications: cardiac pacemaker, certain clips in your head from brain operations, cochlear implant, metallic foreign body in your eye or joints, pregnancy
- MRI: MRA - MRS - fMRI - other types of MRI
MRI types: Lecture 1, practical 1, book p. 514, radiopedia, radioinfo.org
o fMRI: functional MRI has same technology as MRI and looks at blood flow. It is a technique for measuring brain activity and works by detecting the changes in blood oxygenation and flow that occurs in response to neural activity. So the difference from MRI is that it views metabolic function, calculates oxygen levels and has long-distance resolution. Indication: brain anatomy examination, determine which parts of brain handling critical functions, evaluate the effects of stroke or disease
o MRA: provides images of vessels in high resolution when using ultrafast sequences and after administration of contast medium. Technical advancements in MRI devices has caused DSA to be largely replaced by MRA for diagnostic purposes. They provide reproducible images of vessels which are largely similar to those of subtraction angiography. Non-invasive and absence of radiation! MRA can provide overwiev angiography or selective imaging of vessels. Overview (thoracic aorta with supraaortic branches, the abdominal aorta and iliofemoral angiography). Selective (supraaortic vessels with images of cerebral arteries or celiac trunk, mesenteric artery and branches, selective renal angiography etc.)
o MRS: MR spectroscopy allows tissue to be interrogated for the presence and centration of various metabolites. Basic principle: distribution of electrons around an atom cause nuclei in different molecules to experience a different magnetic field. This results in slightly resonant frequencies, which in turn return a different signal. It is identical to NMR (nuclear magnetic resonance) as used in analytical chemistry. Example (lactate resonates at 1.3 ppm, lipids 1.3 ppm, creatine 3.0 ppm). Indication: Glioma (creatine and choline decrease, lipids and lactate increase), ischemia (lactate and lipids increase), infection (lactate, alanine increased) o NRM (nuclear MR): is a powerful technique which involves placing nuclei within an external magnetic field enabling thus them to undergo precession.
- contrast agents overview
o Used to enhance the visibility of internal structures in x-ray based imaging techniques such as CT, radiography and fluoroscopy.
o MRI functions through different principles and thus utilizes different contrast agents. These compounds work by altering the magnetic properties of nearby hydrogen nuclei
o The density of hollow organ can be reduced by filling it with gas or air, CO2, O2 providing NEGATIVE contrast.
o The average atomic number is increased POSITIVE contrast (iodine based, barium sulfate)
o Desirable features: easy to administer, no toxicity/carcinogenicity, stable compound, concentrates in area of interest, proper demonstration of the organ system, rapid elimination, minimal distress to patients, cost effective
o BARIUM: usually water soluble solutions, but also 1 common insoluble used for examination of upper and lower GIT (better coating properties than iodinated). 🡪 barium swallow, barium meal, enterolysis, barium enema.
Adverse effects: constipation, abdominal pain, toxicity, encephalopathy, peritonitis, adhesion, granuloma, endotoxic shock, aspiration pneumonia, allergy
o IODINE: usually classified as ionic or non-ionic. Both types are used most commonly in radiology due to harmless interaction with the body and its solubility. Primarily used to visualize vessels and changes in tissues on radiography and CT. Administration: orally, rectally, intravenous, intracavitory
o MRI contrast agents: gadolinium, iron oxide, iron platinum, manganese. They are not seen directly on MRI image, but influence adjacent protons by small magnetic fields that they establish within the MRI magnetic field required for the image procedure (paramagnetism)
o GADOLINIUM: strong paramagnetic effect, free ion is toxic therefore it is bound to chelating agents (be careful if allergy and renal diseases
o Ultrasound contrast media: albumin microspheres, galactose particles, filled liposomes, gas filled micropacticles are used. These causes greater sonic reflection and thus enhance the signals of sanguineous structures. Result is better imaging of the vascularity and perfusion of tissu
- contrast agents : side effects (+ prevention & treatment)
o Should be as hemoisotonic as possible not causing side effects (no CM fulfils this requirement), but frequency of SE has been reduced by use of low-molecular contrast media for intravenous as well as intraarterial injection
o Majority of side effects are based on the physical and chemical properties, especially their hyperosmolarity.
o Anaphylaxis in the actual sense of the term are rare
o Mild, moderate and severe side effects
o Usually occurs within 5 minutes after injection (some cases delayed up to 48h after)
o Mild: sensation of heat, reddening (face, neck), itching, urticarial, nausea, vomiting, cough, anxitiy, hypotension, bronchospasm, sneezing
o Severe: Edema, bronchospasm, cerebral spasm, cardiovascular collapse, shock, cardiac arrest
o Prevention: Before administration it is important to talk with patient and collect data on medical history as well as explain the benefits and risk of administering CM. In case of possible contraindication or absence of a favorable risk-benefit ratio, one should use alternative investigation procedures (such as MRI or ultrasound)
o Special care: known side effects, allergy, asthma, renal diseases, thyroid diseases, breast feeding period, non-insulin dependent diabetes, pheochromocytoma
o Treatment: monitor patient after injection. Treat the specific reactions (anaphylaxis with O2, epinephrine, antihistamines), ringer-solution in hypotension etc.
