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Chest Radiography

  1. Acquiring a CXR
    1. Usually a CXR is taken by using kV between 80-120Q with a FFD of 6 feet (1.85 m) reduces magnification and produces sharper image.
    2. Using a low kVp (60-80 kV) produces a high contrast film with miliary shadowing and calcification being seen more clearly.
    3. With high voltages (120-170) the filmsQ are of lower contrast with increased visualization of hidden areas of lung, better penetration of mediastinum and better demonstration of normal, vessel markings and abnormal opacities.
    4. One CT thorax (8 m Sv) is equivalent to 400 CXRQ
  1. Special Chest Radiographic Views
    1. Good visualization of the apices of lung require projection of clavicles upward, as in the apical view (apicogram) with the X-ray tube angled up 50-600, or downward, as in the lordotic view with the patient in lordotic PA position in which a middle lobe collapse is seen clearly as a well-defined triangular opacity. A lordotic view is useful to detect lesions of middle lobe (like collapse) and collection on in fissure and subtle infiltrates in Upper zones. Q
    2. Lordotic View:

  1. Oblique views are taken usually to demonstrate the retrocardiac space, the posterior CP angles and the chest wall, with pleural plaques being clearly demonstrated.
  2. Decubitus view shows small amount of pleural fluid, which is not seen on PA view.
  3. Paired inspiratory and expiratory views are important in demonstrating air trapping, small pneumothorax, interstitial shadowing, diaphragm movements, and inhaled foreign body in children.
  4. Retrosternal space is best seen in lateral view while the retrocardiac space is seen well on oblique view.
  5. Paired views (inspiratory and expiratory films) are very important children with a possible diagnosis of an inhaled foreign body. Q
Interpretation of a Chest X Ray
To derive maximum information from a chest X-ray, a systematic approach should be followed.
  1. Situs
    1. Viscero atrial Situs. Normally systemic venous atrium lies on the right side, gastric fundus on the left and liver & IVC on right. Ascending aorta is on the same side as the systemic venous atrium & opposite to that of gastric fundus.
    2. Situs solitus-
      Liver, IVC, RA& right sided bronchus are on right side and gastric fundus, spleen and left sided bronchus on the left side.
      Cardiac position is determined by position of apex.
    3. Situs ambiguous-
      Atrial situs is uncertain. The most common lesions are right or left isomerism in which both atrial chambers have features of the same-sided atrium. In isomeric lesions, there is often an endocardial cushion defect with varying degrees of atrioventricular septal defect (AVSD).
      Right isomerism is usually associated with bilateral (short) right bronchi, trilobed lungs and bilateral right atrial appendages, asplenia and a midline liver.
      Left isomerism is usually associated with bilateral left (long) bronchi, bilobed lungs, left atrial appendages, polysplenia and IVC interruption. All of these abnormalities can be determined with MRI, particularly 3D balanced-SSFP techniques. Both right- and left-sided isomerism are associated with gut malrotation.
      The atrial appendages are the best method of determining atrial identification. The right atrial appendage is triangular with a wide base, whilst the left atrial appendage is a tubular structure. The presence of the terminal crest and pectinate muscle in the appendage are more specific internal characteristics of the right atrium and its appendage.
    4. Situs inversus-
      1. The mirror image of the normal anatomy is present
      2. Dextrocardia with Situs inversus-associated cardiac defects (0.7-5%)
      3. Dextrocardia with Situs solitus-associated cardiac defects (98%) 
  2. Cardiac position in thorax and cardiac silhouette
    Normally 2/3rd of heart is seen to the left of midline & 1/3rd to the right of midline. Cardiac silhouette depends on the built of the subject-
    1. Hypoasthenics: long & narrow
    2. Hyperasthenics: transverse type
    3. Moderate built: oblique / globular
  3. Cardiac size
    It can be commented upon by cardiothoracic ratio on chest x-ray PA view if following criteria are satisfied.
    1. The film is taken at a FFD of 6 feet
    2. The patient either sitting or standing and chest X-ray being taken in full inspiration i.e. anteroinferior end of 6th rib lies at the level of peak of right dome of diaphragm.
    3. No rotation i.e. medial ends of clavicles are equidistant from line drawn through spinous processes.
    4. No bony deformity.
Measurement of C/T ratio
Midline is drawn by joining the spinous processes from the midline measure max transverse diameter of right side of the heart(a) and left side of the heart(b) transverse thoracic diameter is measured(D) by drawing a line to measure maximum inner thoracic diameter.
Cardiothoracic ratio in %=  a+b/D
Normal values-
  1. neonates - 60%
  2. infants - 55%
  3. adolescents & adults- 50%
The CT ratio may be affected by technical factors and patient related factor:
  1. Technical factors:
    1. C/T ratio may increase with decrease FFD, decrease OFD
    2. Rotation
  2. Patient factors:
    1. Expiration: diaphragm goes up; heart is pushed up and rotates to left. An oblique type of heart is converted to transverse type. So, there is apparent cardiomegaly.
    2. Supine patient: diaphragm goes up; film is taken with FFD of 100cm, so there is apparent cardiomegaly.
    3. Obesity: heart is transverse type and lies in 5th intercostals space.
    4. Prominent epicardial fat pad: If present C/T ratio cannot be measured accurately.
  3. Cardiac contour: On PA view is formed by
    1. Right heart border: SVC, RA, IVC from above downwards.
    2. Left heart border- from above downwards
    3. Posterior part of arch of aorta called knuckle
    4. Pulmonary trunk - Flat or concave, May be prominent or convex in children & young females
    5. Left ventricle-lowest & most lateral aspect of cardiac border i.e. Cardiac apex
    6. Left atrial appendage- Lies below left main bronchus which separates it from main pulmonary   trunk. It is embedded in epicardial fat and doesn’t form a discrete shadow unless enlarged.
    7. Inferior border: formed by RA (1/4), RV (2/4), and LV (1/4)
Lateral view:
  1. RV form the anterior cardiac border merging with PA above.
  2. Ascending aorta becomes visible where it crossesthe pulmonary artery, then curves backwards to form the aortic arch.
  3. Posterior cardiac border is formed by left atrial appendage above and below by the superimposed RA & LV.
  1. Aorta
    1. Normal ascending aorta does not contribute to cardiac silhouette.
    2. Only when it is dilated or elongated in old age, it is seen to bulge to right beyond SVC shadow.
    3. The ascending aorta and superior vena cava emerges from the pericardial sac together.
    4. The SVC on an average lies 1 cm to the right than the aorta and its inner border is superimposed on the aorta thus, the base of the vascular shadow on the right side is a combination of SVC and aorta 1” to 1 1/2” above the outlet from pericardium. The ascending aorta curves inwards over the spine and is no longer visible in the PA view.
    5. The assessment of heart is incomplete without concomitant assessment of pulmonary vasculature. Main pulmonary artery forms the floor of Pulmonary artery segment (PAS) which is normally straight or concave. Pulmonary hilum is formed by the descending pulmonary artery and upper lobe vein. The intra-pulmonary branches gradually taper towards the periphery, the lower lobe vessels being larger than upper lobe vessels due to the effect of gravity.
Increased pulmonary blood flow is said to be present when-
  1. Prominent upper and lower zone vessels
  2. 6 vessels in peripheral 1/3rd of lung field
  3. The presence of shunt vessels, end-on vessels more than two times the diameter of the accompanying bronchus.
  4. En-face vessels below the tenth posterior rib
  5. Prominent vessels below the crux of the diaphragm
  6. RDPA diameter more than that of trachea.
  7. RDPA >16mm in diameter.
  8. Prominent hilar vessels on lateral view.
  9. In infants and children, generalized mottling may be seen.
Decreased pulmonary blood flow or oligemia is said to be present when-
  1. Concave or absent M
  2. Overall appearance of an over-penetrated film
  3. < 4 vessels in peripheral 1/3rd
  4. Small hilar, lobar and segmental vessels
  1. Differential diagnosis of Unilateral Hypertranslucent of lungQ
    1. Normal (Increased density of contralateral lung, e.g. pleural effusion/thickening, consolidation)
    2. Rotation or scoliosis
    3. Mastectomy
    4. Congenital, absence of pectoralis major
    5. Polio
    6. Pneumothorax
    7. Congenital hyperinflation (Macleod’s syndrome, congenital lobar emphysema)
    8. Compensatory emphysema (lobar collapse, lobectomy)
    9. Obstructive emphysema (foreign body, tumor)
    10. Bullous emphysema
    11. Absent or hypoplastic pulmonary artery
    12. Obstructed pulmonary artery (tumor, embolus)
  1. Differential diagnosis of opaque hemithoraxQ
    1. Technical          :       Rotation, scoliosis
    2. Pleural              :       Massive/large hydrothorax, pleural thickening, and mesothelioma
    3. Pulmonary        :       Collapse, consolidation (massive) fibrosis
    4. Congenital        :       Pulmonary agenesis
    5. Mediastinal       :       Gross cardiomegaly, tumors
    6. Surgical            :       Pneumonectomy, thoracoplasty Diaphragmatic hernia
  1. Differential diagnosis of Miliary mottling:Q
    1. Infection
      1. TB
      2. Coccidoidomycosis
      3. Blastomycosis
      4. Histoplasmosis
      5. Chickenpox
    2. Dust inhalation
      1. Tin
      2. Barium
      3. Beryllium
      4. Silicosis
      5. Coal Worker’s Pneumoconiosis
    3. Hemosiderosis
    4. HMD
    5. Histiocytosis X
    6. Metastasis
    7. Alveolar microlithiasis
    8. Bronchiolitis obliterans
    9. Sarcoidosis
    10. Secondary hyperparathyroidism
    11. Amyloidosis
    12. Miliary carcinomatosis
  1. Differential diagnosis of calcific foci in lungs:
    1. Infective:
      1. Tuberculosis
      2. Histoplasmosis
      3. Coccidioidomycosis
      4. Chicken pox
      5. Actinomycosis
      6. Abscess (Chronic)
    2. Tumors: Metastasis (osteosarcoma, chondrosarcoma, cystadenocarcinoma)
                     Benign (AV malformation, hamartoma, Carcinoid)
    3. Miscellaneous (hematoma, infarction, mitral valve disease, Broncholith, alveolar microlithiasis)
    4. Rare (hypercalcemia, silicosis, sarcoidosis, RA, amyloidosis, Osteopathia racemosa)
  2. Differential diagnosis of Cavitating pulmonary lesions
    1. Developmental: Sequestration, bronchogenic cyst, CCAM)
    2. Traumatic lung cyst
    3. Pulmonary hematoma
    4. Infections (TB, staph, klebsiella, Histoplasma, amoebic, hydatid, fungal)
    5. Pneumatocele
    6. Abscess
    7. Sarcoidosis
    8. Pulmonary infarct
    9. Bullae, blebs
    10. Malignant: Primary, secondary, lymphoma, metastasis
    11. Pneumoconiosis
    12. Connective tissue disorders: Wegener’s granulomatosis, RA, Caplan syndrome
  3. QCauses of honeycombing in lungs include:
    1. Sarcoidosis
    2. Interstitial lung disease
    3. Extrinsic allergic alveolitis (Cryptogenic)
    4. Idiopathic (UIP)
    5. Storage disorders
    6. Histiocytosis (eosinophilic granuloma)
    7. Amyloidosis
    8. Pneumoconiosis
    9. Drugs  Bleomycin, Busulfan, Nitrofurantoin
    10. Collagen vascular diseases SLE, Scleroderma, RA, Sjogren's syndrome
    11. Cystic fibrosis
    12. Oxygen toxicity
    13. Tuberculosis
  4. QAirbronchogram Sign

Parenchymal lung consolidation may result in visualization of the intrapulmonary bronchi, which are otherwise not visible on normal chest radiograph. This occurs because the air within their lumens will then stand out in contrast to the surrounding opaque lung, known as airbronchogram.

Differential diagnosis of airbronchogram sign:
  1. Normal person with phase of long exposure
  2. Consolidation
  3. Atelectasis (except in obstructive type)
  4. Alveolar cell carcinoma
  5. Pulmonary alveolar microlithiasis
  6. Pulmonary edema
  7. Pulmonary infarction (temporary)
  8. Pulmonary lymphoma of alveolar type
  9. Pulmonary hemorrhage
  10. Aspiration
  11. Sarcoidosis
  1. QSilhouette Sign
    1. Described by Felson and Felson (1950), the “silhouette sign” is loss of interface by adjacent disease and permits localization of lesion on film.
    2. Diaphragm, cardiac and aortic outlines, which are normally seen as adjacent lung is aerated, and difference in radiodensity is demonstrated.
    3. When aerated alveolar spaces are replaced by fluid/soft tissue, there is no longer a difference in radiodensity between that pert of lung and adjacent structures. Thus, the silhouette is lost and “silhouette sign” is seen.
    4. Conversely if border is retained and abnormality is superimposed, the lesion must be lying either anteriorly or posteriorly.
    5. Obliteration of these borders may occur with pleural, mediastinal or pulmonary pathology.
  • Examples of the sillhoutte sign:​
    1. Obscuration of right heart border = RML Consolidation.
Structure De silhouetted


Right heart border Right middle lobe pathology
Left heart border Lingular lobe pathology
Aortic knuckle Apicoposterior segment of LU
Right aortic border Right middle lobe
Hemidiaphragm Basal segments of lower lobe

Obscuration of right heart border = middle lobe pathology.Obscuration of Left heart border = Lingular segment pathology.

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