Introduction to Introduction to ImagingImaging
History of ImagingHistory of Imaging
Wilhelm Konrad Roentgen discovered the x-ray in 1895 Using a cathode-ray tube, passed a current
through the tube and noted a black line across a piece of platinocyanide paper laying on his workbench
He termed this new invisible ray x-ray (x = unknown)
Received 1st Nobel prize in physics in 1901 Widespread use for medical imaging by 1913
History of ImagingHistory of Imaging
The first radiation fatality was Clarence Daley (Thomas Edison’s assistant) in 1904
Fluoroscopy was developed by Thomas Edison Ultrasound was first used in the 1940s but was
used for accredited medical purposes in the 1950s
Computed tomography was introduced in 1971 Magnetic resonance imaging (MRI) 1980s
Ionizing vs Non-Ionizing Ionizing vs Non-Ionizing RadiationRadiation
Non-Ionizing Radiation No known genetic
damage Modalities
Ultrasound MRI
Ionizing radiation Ionizes tissue Causes genetic damage Modalities
Conventional (plain-films) radiographs Fluoroscopy CT scans Nuclear imaging modalities
Ionizing RadiationIonizing Radiation
Effect of ionizing radiation
Radiation protection was instituted in the 1930s
Radiation absorption dose (RAD) The amount of radiation your body was exposed to
Radiation effect in man (REM) The amount of biological damage received from the
exposed radiation
Lethal dose of radiation Lethal dose of radiation exposureexposure
5000 RADs to entire body kills 50% of humans
Partial body exposure can cause organ atrophy and dysfunction
High doses can cause hematologic effects that take months to recover from
Prolonged repeated exposure leads to an accelerated induction of malignant disease
Radiation ExposureRadiation Exposure
Exam mradsChest 10Abdomen 300Cervical spine 250LS spine series 400Pelvis 100CT scan 1-4 mrads/slice
Maximum permissible Maximum permissible exposureexposure
Lifetime permissible dose: (RADS) = 5 x (age - 18)
Health care workersWhole body/gonads/eye lens 5 RADs/yr (5,000
mrads)Hands/forearms/feet 75 RADs/yr
(5000 / 12 = 400mrads/month = 1 lumbar spine x-ray)
Ways to reduce patient Ways to reduce patient exposure to ionizing exposure to ionizing
raysrays Eliminate unnecessary radiographs and
projections
Shield the most radiation sensitive areas (gonads, eye lens, thyroid)
Reduce area irradiated
Avoid x-rays in pregnancy
Ways to reduce staff Ways to reduce staff radiation exposureradiation exposure
Reduce exposure time
Increase distance from radiation
Use proper shielding
Wear radiation film badge is exposed to multiple x-rays
How x-rays are How x-rays are generatedgenerated
An anode (tungsten or molybdenum) is bombarded with electrons from a cathode
X-rays pass through the pt and expose the film
Problems X-rays are slower than light in developing film Long exposure to x-rays is needed (harmful)
Film developingFilm developing
A light-proof case containing a sheet of film
Film is surrounded on each side by a fluorescent sheet
Brief exposure by x-rays causes the fluorescent sheets to glow
Fluorescent sheets expose the film
Radiographic Radiographic appearance is appearance is determined by:determined by:
Atomic number (density)
Thickness
Overlap of structure (increase thickness)
Object’s shape
Distance from film (magnification principle)
Film turns black if x-rays completely penetrate the subject and reach the film (oxidizes the silver)
Film remains white if x-rays are blocked (by bone) from penetrating the subject
Film is various shades of gray, depending on how many x-rays reach a film through semi-solid structures
Radiographic DensitiesRadiographic Densities
Air density (most dark, radio-lucent)
Fat density
Soft tissue/fluid density
Bone density
Non-physiologic density (white, radio-opaque) Contrast agents (iodine, barium) & metals
Radiographs are Radiographs are ““Summation Summation
ShadowgramsShadowgrams”” The radiographic density is the sum of all the
densities and thickness interposed between the x-ray beam source and the film Adjacent densities are distinct and separated by a border
or line The greater the difference in adjacent densities, the
sharper the border Borders become indistinct and blend together into one
common density when similar densities are in the same plane
The radiographic projection must be properly oriented to the density border in order to show it Can see air/water border by looking at the side of the
glass, but not if you look from the top or bottom of the glass
Film PenetrationFilm Penetration
Over Penetrated Over exposed, radiographs are too dark Too many RADs
Under penetrated Under exposed, radiographs are too white Too few RADs
Newer techniquesNewer techniques
Radiographic image is digitalized and stored and viewed on a computer
Image may be digitally enhanced and magnified Image may be printed for a hard copy Image may be transmitted by phone to a
remote site
Common Radiographic Common Radiographic ProjectionsProjections
Anterior-posterior (AP)
Posterior-anterior (PA)
Lateral (right or left)
Right lateral: right side against film
Left lateral: left side against film
Oblique (right & left)
Special views (in handout)
Taking X-RaysTaking X-Rays
Place object of interest as close to the film as possible to avoid magnification
Take multiple views from different angles
Fractures require at least 2 views at 900 to each other
When ordering x-rays, standard views are usually, taken unless otherwise specified
Computerized Computerized TomographyTomography
Utilizes ionizing radiation
Allows for rapid scanning in great detail
Scans in the axial plane only
Visualize bone better than soft tissue
View the CT as if the pt was laying on back with feet toward you
Many different densitiesHounsfield Units (attenuation numbers) Air = -500; bone = +500
High speed helical and spiral CT3-D CTUltra-fast CT scan
FluoroscopyFluoroscopy
Technique that allows real-time visualization of the patient
Continuous x-ray beam through the pt to cast an image on a fluorescing screen
Uses Venous and angiographic procedures Fracture reduction
Diagnostic UltrasoundDiagnostic Ultrasound
Ultrasonic sound waves are generated and reflected back
Frequency of the sound wave is > 15,000 cycles
AdvantagesAdvantages
Easy to use and noninvasive
Inexpensive
Portable
Can insert in every orifice
DisadvantageDisadvantage
Bone and air-filled structures interfere with image
Indications Gall bladder disease Arterial and venous pathology Ob/gyn diagnostics Neonatal
Magnetic Resonance Magnetic Resonance ImagingImaging
Pt placed in the core of a large magnet
Radio waves are passed through the body in a particular sequence of very short pulses
Each pulse causes a responding pulse of radio waves to be emitted from the pt’s tissue
Location from which the signals have originated is recorded by a detector and sent to a computer
Mobile MRI (semi Mobile MRI (semi truck)truck)
Magnetic Resonance Magnetic Resonance Imaging Imaging
Computer produces a 2D picture
Hydrogen atoms in fat and water are imaged
These atoms are aligned in a magnetic field
Pulsed radiowaves knock these atoms out of alignment
H+ atoms eventually reestablish the previous equilibrium with the surrounding magnet
When this occurs, absorbed radiowaves are emitted
Emitted waves are analyzed by a computer to produce the image
Axial ViewAxial View
Coronal ViewCoronal View
Sagittal ViewSagittal View
Magnetic Resonance Magnetic Resonance ImagingImaging
2 types of MRI phasesT1 imaging (time to recovery)
Fat appears white
Air, cortical bone, CSF appear black
T2 imaging (time to relaxation)Blood, CSF appear white
T1 and T2 ImagesT1 and T2 Images
T2 ImageT2 Image
T2 (top) and T1 T2 (top) and T1 (bottom) Axial(bottom) Axial
AdvantagesAdvantages
Utilizes non-ionizing radiation
Can scan in multiple planes (axial, coronal, sagittal)
Can scan in 1 mm to several cm increments
Better soft tissue detail
Noninvasive evaluation of cerebral blood vessels
DisadvantagesDisadvantages
Poor bone detail
Scanning time is much longer than CT
Can’t be scanned if you have certain kinds of metal implants
Enclosed uncomfortable table
Poor quality images of the abdomen and chest due to breathing and peristalsis causing greater motion artifact
Radioisotope ScanningRadioisotope Scanning
Visualize living organs and tissues
The isotope emits gamma rays for a brief period of time
These rays are recorded by a gamma cameraCan identify bone cancer, occult fractures,
pulmonary emboli, thyroid cancer, cardiac ischemia
Technetium-99mTechnetium-99m
The most useful tracer Inexpensive Short half-life Readily available from portable generator High concentrations of isotope will congregate
in tissues with increased metabolism
Give less precise anatomic information
TechnetiumTechnetium
Technetium-99m-pertechnetateTrapped by thyroid
Technetium-99m-macroaggregated albuminTrapped by thyroid gland
Tc-99m-methylene diphosphonateTrapped by bone tissue, used for bone scan
Thallium and IodineThallium and Iodine
Thallium-201 for evaluation of myocardial blood flow
Iodine-131 for thyroid imaging
Cardiac Thallium ScanCardiac Thallium Scan
Contrast MaterialContrast Material
Iodine contrast– Water soluble– Can be given IV, IA, intrathecal, endobronchial, or directly into the GI tract– Risk for allergic reaction– Can cause renal failure– Contraindicated in renal insufficiency
Contrast MaterialContrast Material
Barium contrast– Water insoluble– Given PO or rectally– Good for GI tract imaging– Very irritating if GI tract is perforated– Risk of fecal impaction, aspiration, perforation
Barium EnemaBarium Enema
HysterosalpingogramHysterosalpingogram
Contrast Material Contrast Material
Gastrograffin contrast– Water-soluble, iodine-based contrast– Good for GI tract imaging, but not as good as barium– Used if GI tract perforation is suspected – Promotes peristalsis– May cause serious lung edema in cases of
esophageal-trachea fistulas
Contrast MaterialContrast Material
Gadolinium– Rare earth, metallic, paramagnetic contrast – Used only for MRI enhancement– No risk of an allergic reaction– Nontoxic to the kidneys
Radiologic ReportsRadiologic Reports
Radiology report content
Description of the findings
Summary of findings
May suggest clinical correlation or additional imaging studies to be performed
Reports are sometimes noncommittal
One should not make a diagnosis by imaging studies alone Final diagnosis and treatment requires:
Clinical information (H&P, labs) Imaging studies Differential diagnosis
Viewing Films Viewing Films
Confirm the name and date of x-ray
Did you get what you wanted?
Properly orient on the view box Orient film as if pt was facing you (chest) or
away from you (spine) R and L indicators Up and down arrows Supine vs. standing indicators
Evaluate the exposure