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