Hrct chest technique and interpretation


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Hrct chest technique and interpretation

  1. 1. HRCT CHEST Dr. Thambidurai
  2. 2. HRCT Technique       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. 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. 4. LOW DOSE HRCT  Used only for, 1.follow up of patients with known lung abnormalty 2.screening large populations for lung dis
  5. 5. TARGETED RECONSTRUCTION     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. 6. TECHNICAL MODIFICATIONS     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. 7. EXPIRATORY HRCT     Post expiratory Dynamic expiratory(forced expiration) Spirometrically triggered(specific,reproducible user selected lung volumes) 3D expiratory(spiral CT+8mm collimation+3D recon)
  8. 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. 9. PULMONARY VASCULAR DIS  Full inspiration supine scans with 1cm spacing  Exp scans at 3 or more levels  Contrast enhanced spiral CT
  10. 10. HEMOPTYSIS  Full inspiration supine scan with 5mm collimation thro the hila  HRCT with 1 cm spacing at other levels  Exp scans at 3 or more levels
  11. 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 
  12. 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. 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. 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 
  15. 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. 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 
  19. 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
  20. 20. 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
  21. 21. 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)
  22. 22. 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
  23. 23. Focal septal thickening in lymphangitic carcinomatosis
  26. 26. Centrilobular nodules of ground glass density-Hypersensitivity pneumonitis
  27. 27.  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
  28. 28. 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)
  30. 30. 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)
  31. 31. 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
  32. 32. 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
  33. 33. Broncho-alveolar cell carcinoma
  34. 34. 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
  35. 35. CRAZY PAVING Combination of ground glass opacity with superimposed septal thickening • • • • • • • • Alveolar proteinosis Sarcoid NSIP Organizing pneumonia (COP/BOOP) Infection (PCP, viral, Mycoplasma, bacterial) Neoplasm (Bronchoalveolarca (BAC) Pulmonary hemorrhage Edema (heart failure, ARDS, AIP)
  37. 37. CONSOLIDATION  Consolidation → Airspace disease  Pus, edema, blood ,tumor cells or fibrosis=Replace air
  38. 38. Chronic eosinophilic granuloma
  39. 39. LOW ATTENUATION PATTERN Decreased lung attenuation or air-filled lesions. These include: Emphysema Lung cysts (LAM, LIP, Langerhans cell histiocytosis) Bronchiectasis Honeycombing
  40. 40. 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
  41. 41. Panlobular emphysema  Affects the whole secondary lobule  Lower lobe predominance  In alpha-1-antitrypsin deficiency, but also seen in smokers with advanced emphysema
  42. 42. 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
  43. 43. 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
  44. 44. Langerhans cell histiocytosis
  45. 45. 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)
  46. 46. 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