1. Introduction to Imaging
Patrick Knott, PhD, PA-C
Physician Assistant Department

2. History 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

3. History 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

4. Ionizing vs 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

5. Ionizing 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

6. Lethal dose of radiation exposure
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

7. Radiation Exposure
Exam mrads Chest Abdomen Cervical spine LS spine series Pelvis CT scan mrads/slice

8. Maximum permissible exposure
Lifetime permissible dose: (RADS) = 5 x (age - 18)
Health care workers
Whole body/gonads/eye lens 5 RADs/yr (5,000 mrads)
Hands/forearms/feet RADs/yr
(5000 / 12 = 400mrads/month = 1 lumbar spine x-ray)

9. Ways to reduce patient exposure to ionizing rays
Eliminate unnecessary radiographs and projections
Shield the most radiation sensitive areas (gonads, eye lens, thyroid)
Reduce area irradiated
Avoid x-rays in pregnancy

10. Ways to reduce staff radiation exposure
Reduce exposure time
Increase distance from radiation
Use proper shielding
Wear radiation film badge is exposed to multiple x-rays

12. How x-rays are generated
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)

16. Film 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

19. Radiographic appearance is 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

20. Radiographic 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

24. Radiographs are “Summation Shadowgrams”
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

30. Film Penetration Over Penetrated Under penetrated
Over exposed, radiographs are too dark
Too many RADs
Under penetrated
Under exposed, radiographs are too white
Too few RADs  

31. Newer 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

32. Common Radiographic Projections
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)

33. Taking 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

34. Computerized Tomography
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 densities
Hounsfield Units (attenuation numbers)
Air = -500; bone = +500
High speed helical and spiral CT
3-D CT
Ultra-fast CT scan

43. Fluoroscopy
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

47. Diagnostic Ultrasound
Ultrasonic sound waves are generated and reflected back
Frequency of the sound wave is > 15,000 cycles

48. Advantages Easy to use and noninvasive Inexpensive Portable
Can insert in every orifice

49. Disadvantage Bone and air-filled structures interfere with image
Indications
Gall bladder disease
Arterial and venous pathology
Ob/gyn diagnostics
Neonatal

54. Magnetic Resonance Imaging
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

56. Mobile MRI (semi truck)

57. Magnetic Resonance 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

59. Axial View

60. Coronal View

61. Sagittal View

63. Magnetic Resonance Imaging
2 types of MRI phases
T1 imaging (time to recovery)
Fat appears white
Air, cortical bone, CSF appear black
T2 imaging (time to relaxation)
Blood, CSF appear white

64. T1 and T2 Images

65. T2 Image

66. T2 (top) and T1 (bottom) Axial

67. Advantages 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

68. Disadvantages 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

69. Radioisotope Scanning
Visualize living organs and tissues
The isotope emits gamma rays for a brief period of time
These rays are recorded by a gamma camera
Can identify bone cancer, occult fractures, pulmonary emboli, thyroid cancer, cardiac ischemia

71. Technetium-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

72. Technetium Technetium-99m-pertechnetate
Trapped by thyroid
Technetium-99m-macroaggregated albumin
Trapped by thyroid gland
Tc-99m-methylene diphosphonate
Trapped by bone tissue, used for bone scan

75. Thallium and Iodine
Thallium-201 for evaluation of myocardial blood flow
Iodine-131 for thyroid imaging

76. Cardiac Thallium Scan

79. Contrast 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

80. Contrast 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

81. Barium Enema

83. Hysterosalpingogram

84. 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

85. Contrast Material
Gadolinium –   Rare earth, metallic, paramagnetic contrast –   Used only for MRI enhancement –   No risk of an allergic reaction –   Nontoxic to the kidneys

86. Radiologic 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

87. 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

88. Conclusions and Questions