hrct,ct,chest,grounglass,nodules,interpretation,technique,expiratory hrct,honeycombing,secondary nodule

1. HRCT CHEST
Dr. Thambidurai

2. HRCT Technique
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Thinnest collimation (1.0-1.5mm)
High spatial frequency/sharp algorithm/bone algorithm
kvp:120-140;mA:240
Matrix size: Largest (512 * 512)
Scan time =<1sec
Windows:-700/1000 HU or -600/1500 HU, soft tissues :
50/350

3. LOW DOSE HRCT
Study by Zwirewich et al
collimation - 1.5 mm
scan time - 2 sec
kV – 120
mA – 20 ( low dose) and 200(high dose)
RESULTS:
1. Two techniques are equally diagnostic in
97%
2. low dose failed to demonstrate ground
glass in 2 and emphysema in 1 patient

4. LOW DOSE HRCT
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Used only for,
1.follow up of patients with known lung
abnormalty
2.screening large populations for lung
dis

5. TARGETED RECONSTRUCTION
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Optional
Retrospectively targeting image image
reconstruction to a single lung , using a
smaller FOV increases the spatial
resolution by decreasing the pixel size
For 512 *512 matrix, if FOV is 40 cms,pixel
size wil be 0.78 mm, for a FOV of 15cms,
pixel size would be only 0.29mm thus
improving the spatial resolution.
Disad- requires addition time,filming and
raw data needs to be saved

6. TECHNICAL MODIFICATIONS
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PATIENT POSITION –PRONE-early lung
fibrosis
EXPIRATORY- obstrutive lung diseases
SCAN SPACING
-1 cm intervals
- 3 0r 4 cm intervals
- LIMITED HRCT-3 preselected
levels( aortic arch, carina,2cm above Rt
hemidiaphragm)
GANTRY ANGULATION- 20 degrees
caudally in bronchiectasis

7. EXPIRATORY HRCT
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Post expiratory
Dynamic expiratory(forced expiration)
Spirometrically
triggered(specific,reproducible user
selected lung volumes)
3D expiratory(spiral CT+8mm
collimation+3D recon)

8. RECOMMENDED PROTOCOLS
SUSPECTED EMPHYSEMA,AIRWAY
DISEASE OR OBSTRUCTIVE LUNG DIS
-full inspiration supine scans with 1 cm
interval from lung apices to base
-expiratory scans at 3 or more levels

9. PULMONARY VASCULAR DIS
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Full inspiration supine scans
with 1cm spacing
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Exp scans at 3 or more levels
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Contrast enhanced spiral CT

10. HEMOPTYSIS
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Full inspiration supine scan
with 5mm collimation thro the
hila
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HRCT with 1 cm spacing at
other levels
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Exp scans at 3 or more levels

11. COMBINED DIAGNOSIS OF DIFFUSE
LUNG DIS AND FOCAL
ABNORMALTIES
Full ins HRCT with 1cm spacing
 Prone scan if necessary
 Exp scans at 3 or more levels
 Spiral CT with or without contrast
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12. RESTRICTIVE OR FIBROTIC OR
UNKNOWN DIFFUSE LUNG DIS
CHEST RADIOGRAPH ABNORMAL
-full ins supine scans with 1 cm spacing
from apices to base
-exp scans at 3 or more levels
CHEST RADIOGRAPH ABNORMAL
-option 1
-option 2

13. OPTION 1
-full ins scans with 2 cm spacing in both
prone and supine from apices to base
-exp scans at 3 or more levels
OPTION 2
-full ins supine scans with 1 cm spacing
from apices to bases
- prone scans if dependant densities
present
- exp scans at 3 or more levels

14. RADIATION DOSE
CONVENTIONAL CT - 20 mGy
 HRCT – 120 Kv,200mA, 2 sec
-4.4 mGy for 1.5 mm at 10mm intervals(12%
-2.1 mGy for 20 mm intervals(6%)
-36.3 mGy for conventional 10mm scans at
10 mm intervals
Low dose HRCT at 20 mm interval=chest x ray
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15. ARTIFACTS
STREAK
- due to aliasing or correlated noise
- fine linear netlike opacities that
radiate from the edges of sharply
marginated high contrast structures
such as ribs, vertebral
bodies,bronchial wall most commonly
found paralleling pleura or posterior
chest wall

16. MOTION ARTIFACTS
PULSATION OR STAR ARTIFACT
-thin streaks radiating from vessels at left
lung base adjacent to heart
 DOUBLING ARTIFACT
-major fissure, bronchi or vessels may be
seen as double because of cardiac pulsation
or respiration and can mimic bronchiectasis
Motion artifacts can be reduced by ECG gating
of scan acquistion or spirometrically
controlled respiration
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17. HRCT-BASIC INTERPRETATION

18. SECONDARY LOBULE

19. • Basic anatomic unit
• Smallest lung unit surrounded by connective tissue
septa
• Measures 1-2 cm
• Made up of 5-15 pulmonary acini, that contain the
alveoli
• Supplied by a small bronchiole (terminal bronchiole)
in the center, that is parallelled by the centrilobular
artery
• Pulmonary veins and lymphatics run in the periphery
of the lobule within the interlobular septa
• Two lymphatic systems: central networkbronchovascular bundle towards the centre of the
lobule ; peripheral network- within the interlobular
septa and along the pleural linings

21. Centrilobular area
Central part of the secundary lobule
Site of diseases, that enter the lung through the airways
Eg: Hypersensitivity pneumonitis
Respiratory bronchiolitis
Centrilobular emphysema
Perilymphatic area
Peripheral part of the secundary lobule
Site of diseases, that are located in the lymphatics of in the
interlobular septa
Eg: Sarcoid
Lymphangitic carcinomatosis
Pulmonary edema

22. BASIC INTERPRETATION
What is the dominant HR-pattern:
 Reticular
 Nodular
 High attenuation (ground-glass, consolidation)
 Low attenuation (emphysema, cystic)
Where is it located within the secondary lobule (centrilobular,
perilymphatic or random)
Is there an upper versus lower zone or a central versus
peripheral predominance
Are there additional findings (pleural fluid, lymphadenopathy,
traction bronchiectasis)

24. RETICULAR PATTERN
Thickening of the interlobular septa / fibrosis as in
honeycombing
SEPTAL THICKENING
Thickening of lung interstitium by fluid, fibrous tissue, or
infiltration by cells results in a pattern of reticular
opacities due to thickening of the interlobular septa

26. Focal septal thickening in lymphangitic carcinomatosis

27. NODULAR PATTERN

29. SARCOIDOSIS

30. Centrilobular nodules of ground glass density-Hypersensitivity pneumonitis

31.  TREE-IN-BUD APPEARANCE:
 Irregular and nodular branching structure, most easily identified in the
lung periphery
 Represents dilated and impacted (mucus or pus-filled) centrilobular
bronchioles

32. Tree-in-bud indicates the presence of:
Endobronchial spread of infection (TB, MAC, any
bacterial bronchopneumonia)
Airway disease associated with infection (cystic fibrosis,
bronchiectasis)
Airway disease associated primarily with mucus retention
(allergic bronchopulmonary aspergillosis, asthma)

33. ACTIVE TB-TREE IN BUD

34. RANDOM NODULES
Result of the hematogenous spread of the infection
Small random nodules are seen in:
Hematogenous metastases
Miliary tuberculosis
Miliary fungal infections
Sarcoidosis may mimick this pattern, when very extensive
Langerhans cell histiocytosis (early nodular stage)

36. HIGH ATTENUATION PATTERN
 Ground-glass-opacity = hazy increase in lung opacity
without obscuration of underlying vessels
 Consolidation = increase in lung opacity which
obscures the vessels

37. Ground-glass opacity →Filling of the alveolar spaces with
pus, edema, hemorrhage, inflammation or tumor
cells→Thickening of the interstitium or alveolar walls
below the spatial resolution of the HRCT as seen in
fibrosis
 Upper zone predominance: Respiratory bronchiolitis,
PCP
 Lower zone predominance: UIP, NSIP, DIP
 Centrilobular distribution: Hypersensitivity pneumonitis,
Respiratory bronchiolitis

39. Broncho-alveolar cell carcinoma

40. MOSAIC ATTENUATION
'Mosaic attenuation' = density differences between affected
and non-affected lung areas
When ground glass opacity presents as mosaic attenuation
to consider:
Infiltrative process adjacent to normal lung
Normal lung appearing relatively dense adjacent to lung
with air-trapping
Hyperperfused lung adjacent to oligemic lung due to
chronic thromboembolic disease

42. CRAZY PAVING
Combination of ground glass opacity with superimposed
septal thickening
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Alveolar proteinosis
Sarcoid
NSIP
Organizing pneumonia (COP/BOOP)
Infection (PCP, viral, Mycoplasma, bacterial)
Neoplasm (Bronchoalveolarca (BAC)
Pulmonary hemorrhage
Edema (heart failure, ARDS, AIP)

43. ALVEOLAR PROTEINOSIS

44. CONSOLIDATION
 Consolidation → Airspace disease
 Pus, edema, blood ,tumor cells or fibrosis=Replace
air

45. Chronic eosinophilic granuloma

46. LOW ATTENUATION PATTERN
Decreased lung attenuation or air-filled lesions.
These include:
Emphysema
Lung cysts (LAM, LIP, Langerhans cell histiocytosis)
Bronchiectasis
Honeycombing

48. EMPHYSEMA
Areas of low attenuation without visible walls as a result of
parenchymal destruction
Centrilobular emphysema
 Most common type
 Irreversible destruction of alveolar walls in the
centrilobular portion of the lobule
 Upper lobe predominance and uneven distribution
 Strongly associated with smoking

50. Panlobular emphysema
 Affects the whole secondary lobule
 Lower lobe predominance
 In alpha-1-antitrypsin deficiency, but also seen in
smokers with advanced emphysema

51. Paraseptal emphysema
 Adjacent to the pleura and interlobar fissures
 Can be isolated phenomenon in young adults, or in
older patients with centrilobular emphysema
 In young adults = spontaneous pneumothorax

52. CYSTIC LUNG DISEASE
 Lung cysts: Radiolucent areas with wall thickness
of less than 4mm
 Cavities -Radiolucent areas with wall thickness of
more than 4mm and are seen in infection (TB,
Staph, fungal, hydatid), septic emboli, squamous
cell carcinoma and Wegener's disease

53. Langerhans cell histiocytosis

54. BRONCHIECTASIS
Bronchiectasis is defined as localized bronchial dilatation
Bronchial dilatation (signet-ring sign)
Bronchial wall thickening
Lack of normal tapering with visibility of airways in the
peripheral lung
Mucus retention in the bronchial lumen
Associated atelectasis and sometimes air trapping
A signet-ring sign represents an axial cut of a dilated
bronchus (ring) with its accompanying small artery (signet)

55. HONEYCOMBING
 Honeycombing is defined by the presence of small
cystic spaces with irregularly thickened walls
composed of fibrous tissue
 Predominate in the peripheral and subpleural lung
regions
 Subpleural honeycomb cysts occur in several
contiguous layers

58. DISTRIBUTION WITHIN THE LUNG

60. ADDITIONAL FINDINGS