The document provides a comprehensive overview of radiological interpretation principles, including techniques for viewing images, evaluating radiographs, and understanding various imaging modalities like CT and MRI. It emphasizes the importance of systematic evaluation, knowledge of anatomy, and correlation with clinical data to avoid pitfalls in interpretation. Additionally, it discusses the differences between CT and MRI, their advantages, disadvantages, and key concepts in ultrasound imaging.

1. Principles of Radiological
Interpretation
Dr. Moses Acan
Department of Radiology

2. VIEWING

3. Where can you look at
images
 PACS (Picture Archiving and
Communication System) workstations
 ED
 ICUs
 WebCIS based PACS (java script)
 Web Based PACS
 Viewing boxes

4. Viewing the Radiographs
 Quite, dark room, no distractions
 At least 2 well lit view boxes
 A bright light illuminator for relatively over
exposed areas
 3 dimensional concept
– From a 2 dimensional image the 3rd
dimension must be constructed
– Orthogonal views
 Anatomy text, anatomical specimens,
notes

5. X-ray viewing station

6. Basics:
Looking at Imaging Studies:
 Adequate Study?
 Correctly labeled with patient’s name, MR#, and the date
of the study?
 Technically adequate?
 Systematic versus Focused look at a study:
 Radiologist does both!
 As the requesting clinician, you should also look at your
patient’s study (at least plain films), as well as follow up on
the final report.
 PTX, PNA, pleural effusions, SBO, free air
 Evaluate lines and tubes (especially the ones you placed!)

7. The Radiograph
 High technical quality – adequate
collimation, exposure, development and
are free of artifacts
 Is it normal, abnormal, artifactual?

8. Viewing the Radiographs
 Radiographs should be placed on the
view box the same way every time
 Laterals
 AP or PA
 Obliques

9. How do x-rays passing through
the body create an image?
 X-rays that pass through the body to the
film render the film dark (black)
 X-rays that are totally blocked do not reach
the film and render the film light (white)
 Air = low atomic # = x-rays get through =
image is dark
 Metal = high atomic # = x-rays blocked =
image is light (white)

10. 5 Basic Radiographic
Densities
 Air
 Fat
 Soft tissue/fluid
 Mineral
 Metal
1.
2.
3.
4.
5.
Name these radiographic densities.

11. Radiographic Opacities
 Metal White
 Mineral – Bone Light grey
 Soft tissue – fluid Grey
 Fat Dark grey
 Air Black

12. Evaluating the Radiograph
 Take into account the patient history
and clinical signs
 Does an abnormality exist?
– Perception of abnormal
 Where exactly is the abnormality?
 Describe the roentgen signs
 Opinion
– Rule out list of prioritized differentials

13. Roentgen Signs
 Size
 Shape
 Margination
 Number
 Change in position
 Alteration in opacity
 Change in function of organs
– Roentgen signs should be correlated with history,
physical exam, disease patterns, pathogenesis
etc.

14. Other
 Summation – some opacity do not touch
but are superimposed  the opacity
where they overlap is increased
 Silhouette sign – structures of the same
opacity touch and their margins are lost
 Contrast Media
– GI, GU, neuro etc.

15. Pitfalls to Interpretation
 Do not get distracted by a large mass
for example and forget the rest of the
radiograph
 Tunnel vision
 Must use a systematic approach - every
time

16. Summary
 Properly displayed, Viewing
environment, technical quality
 Normal or abnormal – must know
anatomy
 Systematic evaluation and correlation
with clinical data
 Correct diagnosis or send to someone
for help

17. CT: A Little History...
 In the early 1970s, Hounsfield
developed a way of computerizing
Xrays to select certain densities for
viewing.
–Plain films: black, white or a few
shades of grey
–CT: thousands of shades of grey
based on the density of the tissue
(Hounsfield Units)

18. Computed Tomography (CT)
 Lingo:
 Attenuation
 Density
 Enhancement
 Hounsfield Units
 -1000 air ***
 -100 fat
 0 water ***
 20-80 soft tissues
 100’s bone/Ca/contrast
 >1000’s metal
 Large radiation dose

19. What We Need to Know
 Air is very black (less than -1000 HU)
 Water/CSF is black (near 0 HU)
 Bone is very dense/white (500-3000
HU)
 Blood is white (60-80 HU)
 Brain is gray 35-50 HU

20. CT vs. MRI
Wide doughnut
Opening
10-20 minutes
Length
Adjust window
Technique
Axial
Plane
250,000 UGX
Cost
Bright
Bone
Long,
narrow
30-60 min
T1, T2, Pd
3-D
500,000 UGX
Dark
Magnetic fld
X-ray beam
Obtained
MRI
CT

21. Advantages to CT
 Costs less than MRI
 Better access
 Shows up acute bleed
 A good quick scan
 Good visualization of bony
structures and calcified lesions

22. Disadvantages to CT
 Resolution
 Beam-hardening artifact
 Limited views of the posterior fossa
and poor visualization of white-
matter disease

23. Magnetic Resonance Imaging
(MRI)
 Lingo:
 Signal intensity
 T1
 T2
 Enhancement
 No radiation
 Strong magnetic field
 No pacemakers
 No electronic implants
 Small, long tube
 Patients must hold still
 Relatively expensive

24. Advantages to MRI
 No radiation exposure
 Gadolinium contrast is relatively
nontoxic
 Capacity for quantitative imaging, 3-D
reconstruction, angiography,
spectroscopy

25. Disadvantages of MRI
 Cost
 Some patients ineligible
because of pacemakers, other
metal
 Claustrophobia
 Long exam
 Access

26. ABNORMAL CTs and MRI

27.  Is the scan
– Contrast or noncontrast?
– Good quality?
 Describe the abnormality

28. Describe the abnormality
 Appearance of the lesion
– Hypodense, hyperdense, isodense or
mixed for CT.
– Hypointense, hyperintense, isointense or
mixed for MRI.
 Location

29. Epidural with fracture

30.  SHAPE round, oval, linear, saucer-shaped is a
lesion that starts at the periphery of the bone.
 BORDERS, poorly / well defined with
regular/irregular borders.
 SIZE in inches or mms Measure do not
estimate.
 SYMMETRY usually indicates a variant of
normal or an inherited condition.

31. On each slice look for:
 Anatomical Symmetry,
symmetry, symmetry
• E.g in the brain - sulci , cisterns
and ventricles, grey-white
differentiation

32. Identify What Doesn’t Belong
• Hyperdensities (whiter), e.g
• extra-axial hematomas (SDH, EDH)
• ICB or contusion
• SAH in sulci, cisterns or ventricles
• Hypodensities (darker)
• pneumocephaly (air is darker than CSF)
• infarction

33. Isodense Subdural Hematoma

34. Hygroma with shift s/p SDH

35. Acute on Chronic Subdural Hematoma

36. Intraparenchymal Bleed

37. Identify What Doesn’t Belong
• Localized or diffuse lesion
• effacement of sulci or cisterns
• distortion of gray-white matter interface
• enlarged ventricles, temporal horn
• Fractures, eg
• soft tissue swelling
• fluid (blood) in sinuses or mastoid air cells
• in children, look for widened sutures
• Always look at bone windows

38. Diffuse Edema, SAH tracking across tentorium

39. Blood: Acute blood is white (60-80 HU) on
CT, due to the density of hemoglobin.
As hgb breaks down, the HU decrease (i.e.
subacute and isodense hematomas)

40.  Relationship to OTHER ANATOMY

41.  T1w T2w

42. What Is Bright
on CT?
 Blood
 Contrast
 Bone
 Calcium
 Metal
What Is Dark
on CT?
• Air
• CSF/H20

43. Artifacts
 Beam
hardening
 Bone
 Foreign body
 Motion

45. • SPECT/ PET
•Brain scans
•Bone scans
• Cardiac scans
• Renal scans
• Lung scans
• Thyroid, parathyroid scans
•
Isotope scans

46. Uses for SPECT and PET
 Acute stroke
 Identify a seizure focus-increased
flow during sz and decreased
interictal flow
 Dementia-frontal pattern in FTLD,
temporo-parietal pattern in AD
 Ligand imaging in PD, others

47. ULTRASOUND SCAN –
INTERPRETATIVE
PRINCIPLES
 Is a very important technique for
imaging soft tissues
– Real time images
 Major applications: heart, abdomen and
pelvis as well as neck, breast,
peripheries, neonatal brain and
obstetrics.

48.  Limitations
– It cannot cross a tissue gas or tissue bone
interface
– Afticactual signals
– Operator dependant.

49.  Imaging methods
– A- mode (pulse echo)
– M- mode
– B- mode (grey scale display)

50.  A-mode M-mode
www.upei.ca/~vetrad

51.  B-mode

52. Interpretation
 Shadowing and through transmission
– Acoustic shadowing
– Acoustic enhancement
– Edge shadowing
 Echogenicity
– Anaechoic…….black
– Hypoechoic …..falls in btn black n white
– Hyperechoic--white

53.  Doppler ultrasound
– Colour Doppler
– Spectral Doppler
– 2D imaging + spectral Doppler.

54.  Acoustic shadowing and enhancement

55.  Edge shadowing

56.  Hyperechoic and hypoechoic

57.  Hypoechoic

58.  Heterogenous

59. A FEW CASES…

60. Diagnosis?

62. A broken central venous catheter has
migrated into the right lower
lobe pulmonary artery

63. Can you recognize
shapes and density?

64. D
i
Diagnosis?

65. History: 11 y/o twisting
injury of the foot

67. 1.
2.
3.
4.
Please name these bones
Word bank:
Cuboid
Navicular
Medial cuneiform
Os naviculare

68. Proximal
Distal
1.
2.
3.
Word bank: epiphysis, metaphysis, diaphysis, cortex, medullary cavity
Naming the parts of a long bone

69. Summary:
 X-rays pass through the body to varying
degrees
 Higher atomic number structures block
x-rays better, example bone.
 Lower atomic number structures allow
x-rays to pass through, example: air in
the lungs.
Question: If x-rays were blocked to the same degree by all body
structures, could we see the internal parts of the body?

70. 5 basic radiographic densities from
black to bright white
 Air
 Fat
 Soft tissue/fluid
 Bone/mineral
 Metal

71. What density
are the
lungs?
Why?
The list: air, fat, soft tissue, mineral and metal

72. CT scan of the abdomen
X-rays used skin
What density is this?
air

73. Absorbed
Passed through

74. Medullary bone
Soft tissue
Metal
Note:
Right-left marker

75. 2
4
3
1
Name these
densities

76. What densit
is this?

77. Remember…..

78. The anatomical position
right left

79. Radiographic Analysis
 Any structure, normal or pathologic,
should be analyzed for:
1. Size
2. Shape and contour
3. Position
4. Density (You must know the 5 basic
densities)

80. And yes….
o CT is a great tool but provides a high does of
radiation
o Provide good indications!
o IV Contrast + Sick Kidneys = BAD
o If worried about free air in the abdomen,
order upright or decubitus films
o Radiology is a cool specialty. Think whether it’s a
good fit as you go through the year.

81. Questions for me?