introduction to medical

1. INTRODUCTION to
MEDICAL IMAGING

2. Objectives
• List the main diagnostic imaging modalities
used in medical practice
• Explain the basic principles of the main types of
imaging modalities
• Describe advantages of the different imaging
techniques
• List disadvantages of the different imaging
techniques

3. Medical Imaging
X-Rays: ionizing radiation
Radiography
CT scan (Computed Tomography)
Gamma rays
Nuclear Medicine
Sound waves
Ultrasound
Magnetic fields/radiofrequency waves
MRI (Magnetic Resonance Imaging)

4. Who Does Imaging?
• Radiologist
– Consultant: Diagnostic, Subspecialties
– Interventionalist
• Radiation Oncologist: Treatment planning
• Cardiologist: Invasive, Non-Invasive
• Vascular Surgeon: Endovascular procedures
• Other specialists
– Usually for procedure guidance (Ob-Gyn, Internal
medicine, Orthopedics, etc.)

5. Training
• Radiologist
– Mandatory clinical internship
– 4 years general radiology residency
– Physics, radiation protection, radiobiology,
technology, diagnosis, anatomy, pathology,
physiology, etc.
– 1 year fellowship in subspecialty
• Cardiologist, vascular surgeon, others
– intergrated into training program

6. Radiography
X-rays

7. X-rays
• Dr. Wilhelm C.
Roentgen at
University of
Wurzburg, 1895
– Discovered and
named X-rays
• Awarded first Nobel
Prize for Physics in
1901

8. X-Rays
• Radiography
– Plain film radiography - without added
contrast material
– Contrast radiography – with contrast
material
– Computed Radiography (CR)
– Fluoroscopy: done in real time
• Barium studies: Upper GI, BE
• Angiography
• CT (Computed Tomography), aka CAT scans
(Computer Assisted Tomography)

9. Radiographs
• Electromagnetic waves (X-rays) are produced in an
X-ray tube by converting electrical energy into an
electromagnetic wave
• Electrons are accelerated from an electrically
negative cathode to a positive target anode
• Energy is released and converted into heat and
X-rays

10. Radiographs
• Images produced by electromagnetic waves
(X-rays)
• produced by an X-ray tube
• pass thru the body
• are absorbed by the different tissues
• reach the film and
• expose the film
Radiographic cassette

11. Computed Radiography (CR)
• Produces digital radiographic images
• Instead of film, a phosphor plate is exposed
to X-rays
• Laser beam scans the plate
• Light is released, intensified and converted to
electron stream
• Converted by computer into digital image
• Viewed on a monitor
• Transferred over networks

12. Radiographic Densities
• Air Black
• Fat Dark gray
• Water* Light gray
• Bone White
• Calcium White
• Metal Very white
*Water=soft tissue: organs, muscles, blood vessels, masses

13. Radiodensity
Radiodensity is a function of:
1. Composition (atomic number)
2. Thickness of object
3. Strength of X-ray
Radiodensity as function of
thickness of object
Radiolucency
is the opposite

14. Radiodensity
• If an object is thick and dense, less radiation
passes thru to reach the film
– Radiodense
– Film is underexposed and stays light
• Air gives no obstruction to X-rays
– Radiolucent
– Film gets overexposed and turns black
• Bone absorbs radiation, less radiation
reaches the film
– Film is underexposed and stays white

15. Abdominal Radiograph: KUB
• Air Black
• Fat Dark gray
• Water Light gray
• Bone White
• Calcium White
• Metal Very white
*Water=soft tissue: organs, muscles, blood vessels, masses

16. Radiographs
Composed of overlapping
radiodensities, overlapping shadows
Tissues stacked in front of each other
Need 90 degree projection for anatomic
placement

17. Radiographs
Perpendicular projections are necessary to
localize structures in the body

18. Roof fell on
patient

19. Patient Position for Chest X-Ray
Posteroanterior (PA) Chest: X-ray beam
passes from posterior to anterior
RT LT

20. Erect Position
Free intraabdominal air: Pneumoperitoneum

21. Portable Films
• Patient is too ill to
go to Radiology
Department
• Less optimal
• Portable X-ray unit
• X-ray film is behind
patient
• X-rays pass through
patient from anterior
to posterior

22. Abdominal Radiographs
• Erect/upright
• Supine
• Prone
• Decubitus
• Oblique/rotated

23. Contrast Radiography
• Injection, ingestion or placement of radiopaque material into the
body for contrast enhancement
• Oral, rectal contrast: Barium, gastrograffin

24. Contrast Radiography
Angiography

25. Caution: Radiation Exposure
• Radiation workers follow safety
guidelines
• Women of child-bearing age should be
questioned about possibility of
pregnancy before abdominal X-ray.
• Ask about LMP and check pregnancy
test, if in doubt.

26. Caution: Pregnancy

27. Computed Tomography
X-rays

28. Computed Tomography
• Ionizing radiation used to obtain cross-sectional
images of the body
• Table moves through large donut-shaped scanner
– Fast moving X-ray tube (thin X-ray beam rotates)
– Numerous electronic detectors
• Rapid acquisition of images
• Contrast agents necessary for most scans
– Oral
– Intravenous iodinated

29. Computed Tomography
• Multidetector CT scans
– Advancement from tomographic imaging (slices)
to volume imaging
– Produce a volume of data that can be manipulated
– Reconstruct at 1-10 mm increments
– Axial, sagittal, coronal, 3D reconstructions

30. Computed Tomography
Coronal and sagittal reconstructions

31. Computed Tomography
• Large field of view
– Entire cross-section of body
• Improved differentiation of soft tissue densities
• Excellent spatial resolution
– Small 3-4 mm lymph nodes, vessels
• Automated scanners
– Less operator-dependent
• Ultra-fast scanners
– Suspended respiration
– Less bowel motion artifact
– Trauma
ADVANTAGES

32. CT Density Differentiation

33. CT of the Female Pelvis
• Exposure to ionizing radiation
• Allergic reactions to intravenous contrast
– Mild to severe (anaphylaxis)
• Contrast nephropathy
– May cause renal failure
– Caution in diabetics with nephropathy
• Problems of dehydration
– Cautious use in multiple myeloma, sickle cell
disease
• Soft tissue differentiation not as good as MRI
DISADVANTAGES

34. CT Windows
Windowing displays the image in differing shades of gray
Correspond to brightness and contrast
Soft tissue window Lung (air) window

35. CT Windows
Soft tissue window Bone window
Windowing displays the image in differing shades of gray
Correspond to brightness and contrast

36. CT Diagnosis
• Trauma
Shattered spleen Fractured sacrum

37. CT Diagnosis
• Pulmonary embolism
• Intravenous contrast material is necessary

38. CT Diagnosis
• Angiography
• Bowel disorders
Aortic aneurysm Perforated sigmoid
diverticulitis

39. CT 3D Volume Rendering
Aorta, plaque Aortic arch
CT Angiogram

40. Diagnostic Ultrasound
Sound Waves

41. Diagnostic Ultrasound
• Audible sound 20Hz-20KHz
• Ultrasound >20Hz
• Medical ultrasound 1-20
MHz
• Transducer sends high
frequency sound waves into
the body and gathers their
reflections (echoes)
• Converts echoes into
electronic signals
• Displays images on a
monitor

42. Diagnostic Ultrasound
• Sound travels very well through fluid
• Ultrasound is good for anything containing
fluid, as long as there is no interference for
the sound beam to reach the fluid

43. Diagnostic Ultrasound
• Interferences to sound waves: air, bone,
metal, thick tissues, deep structures

44. Diagnostic Ultrasound
• Multiplanar imaging in real-time
• Non-invasive, safe, no radiation
– Pregnancy, Pediatrics
• Relatively inexpensive
• Widely available
• Portable, bedside
• Good contrast of tissue
layers in many organs
ADVANTAGES

45. Diagnostic Ultrasound
• Good contrast of tissues layers
ADVANTAGES

46. Pelvic Ultrasound versus CT
Ultrasound
CT
Ovarian Neoplasm

47. Diagnostic Ultrasound
• Relatively small field of view
• Operator dependent: inconsistent reproducibility
• Depends on sound penetration
– Air, bone, obesity
DISADVANTAGES

48. Diagnostic Ultrasound
• Trade-off between depth (beam penetration)
and resolution
– For deeper penetration need lower frequency
transducers, resulting in lower resolution
DISADVANTAGES
3.5 MHz 12 MHz

49. Doppler Ultrasound
• Evaluation of blood flow
– Patency, direction, character of flow in vessels
– Vascularity in a mass
Carotid artery Testicular flow

50. FD = (FR - FT ) = 2 • FT • v • cos 
c
v
FT
FR
The Doppler Equation
The relationship of Doppler frequency shift
to velocity of a moving object
C =1540m/sec speed of sound in tissues

51. 3D Ultrasound
1st Trimester fetus 3rd Trimester fetus

52. Magnetic Resonance Imaging
Magnetic fields
Radiofrequency waves

53. Magnetic Resonance Imaging
• Patient placed inside a large
cylinder-shaped magnet
• Radio waves 10,000 - 30,000
stronger the earth’s magnetic
field are sent thru body
• Nuclei of body’s (hydrogen)
atoms shift position
• As they move back they send
out radio waves
• Scanner detects the signals
• Creates image based on
location & strength of signals

54. Magnetic Resonance Imaging
• Large field of view
– Cross-section of entire body
– Volume imaging (from tomographic imaging,
slices)
• No ionizing radiation as with CT
• Not as operator dependent as ultrasound
• Much fewer contrast allergies and less risk of
contrast nephropathy than with iodinated
agent used in CT
• Excellent contrast resolution among tissue
layers, esp. fat, hemorrhage
ADVANTAGES

55. Magnetic Resonance Imaging
Large field of view
Excellent Contrast Resolution

56. Ultrasound vs CT vs MRI
Field of View, Excellent Contrast Resolution
Ultrasound
MRI CT

57. Magnetic Resonance Imaging
• Exquisite neuroanatomical detail
• Musculoskeletal disorders
• Cardiovascular

58. Magnetic Resonance Imaging
• Motion related artifacts
– Bowel peristalsis
– Respiratory motion
• Cost $$$
• Image production is time-consuming with
complicated protocols & scan time
• Intravenous contrast is often required to
improve tissue differentiation
• Claustrophobia
• Obesity
DISADVANTAGES

59. Magnetic Resonance Imaging
• Contraindication in patients with ferromagnetic
metallic objects, implants, foreign bodies:
– Metallic fragments in eye
– Cochlear implants
– Cardiac pacemakers
– Brain aneurysm clips
– Certain heart valves
– Neurological stimulators
• Orthopedic devices are not harmful to patient,
but create artifacts
• Intrauterine devices are safe
METALLIC OBJECTS

60. Nuclear Imaging
Gamma waves

61. Nuclear Medicine
• Uses small amounts of radioactive material
for diagnosis and treatment
• Molecular Imaging: images reflect biological
processes that take place at the cellular and
subcellular levels
• Evaluates physiological function rather than
anatomic structure
• Uses radiopharmaceuticals: agents that have
trace amounts of radioactive atoms attached
• Radiation emitted from the patient is imaged
by a gamma camera, SPECT or PET scanner

62. Nuclear Medicine Applications
• Oncology: tumor localization, staging,
metastases
• Cardiology: myocardial perfusion scans
• Gastrointestinal: acute cholecystitis, biliary
tract, GI bleeding
• Pulmonary: ventilation, perfusion
• Infectious disease: localize infections (subtle)
• Therapy, e.g. I-131 for thyrotoxicosis, thyroid
cancer

63. Common Radionuclides
• Intravenous administration
– Technetium-99m
– Iodine-123 and 131
– Thallium-210
– Gallium-67
– Fluorine-18 Fluorodeoxyglucose
– Indium-111 labeled leukocytes
• Inhaled gaseous/aerosol radionuclides
– Xenon-133
– Krypton-81m
– Technicium-99m gas

64. Gamma Camera

65. Bone Scan: Metastases

66. PET Scan: Cancer Detection
• Positron Emission
Tomography
• 18F-fluorodeoxyglucose
(FDG)
• Primarily used for
diagnosis, staging &
monitoring of cancers:
lung, breast, cervical,
colorectal, esophagus,
head & neck,
lymphoma, melanoma
Lymphoma pre and post
chemotherapy

67. PET-CT Scanner
Combined PET scanner and CT scanner

68. PET-CT
• Imaging by “fusion” of anatomy and physiology
• Superimposition of the anatomic images of a CT scan
and the co-registration of physiologic uptake of a
radionuclide agent (molecular imaging)

69. PET-CT Scans
Fusion imaging: Lingular mass
CT PET PET-CT

70. Summary
• Medical imaging is essential for medical
practice
• Interpretation of various imaging modalities
requires training and experience
• Radiologist specializes in various imaging
modalities
– Consultant
– Interventionalist

71. Sample Question
Of the following imaging modalities, which
test has the least harmful effects for a
fetus?
a. CT
b. Ultrasound
c. MRI
d. Nuclear medicine

72. Thank you for your
attention!