CHEST XRAY

INTRODUCTIONXray is one of the oldest & widely used imaging modalities.

Wilhelm Röntgen

Plain chest radiograph• Diagnostic in 80% cases• Standard views

1. Postero-anterior(P/A)2. Lateral (right/left)

• Additional views1. Oblique view(ribs)2. Apical lordotic view3. Expiration view4. Decubitus view

Technical aspects of chest xray• A CXR obtained by faulty technique may create a fake impression of

disease.• Thus following points must be considered:

a) AP vs PA

b) Exposure or penetration

c) Rotation

d) Inspiration vs expiration film

e) Scapular position

f) Beam angulation

Cxr pa view

Patient positioning for a standard PACXR. The 180 cm (6 ft) x-ray tube to cassette distance results in a beam that isminimally divergent. In effect, the x-rays are parallel when they impact on thethorax.

Cxr ap view

The distance from the xray source to theCassette is much less than 180cm(6ft)

Frail patient

AP vs PA VIEWS• The AP CXR should always be interpreted with caution.The

following factors may cause misleading appearances-----

1) The medistinum is magnified

2) When lying supine a patient is often unable to take full inspiration. Also he

may be rotated because of difficulty in co-operating. Therefore AP cxr is inferior than

PA view.

Cont..

Why magnification?

EXPOSURE OR PENETRATION

It was standard practice to produce a CXR using a tube voltage of 50-70kv,such images have

considerable contrast but fail to show up to a third of the lungs ‘hidden’ behind the heart and

diaphragm.

Using 120-140kv produces a spectrum of xray energies that are higher & therefore more penetrating.

In this way a greater number of Xray pass through the dencer parts of the chest,i.e the mediastinum.

Above 140kv radiograph is overexposure..

Cont..• The lower thoracic vertebrae should

be visible through the heart.

• The bronchovascular structures

behind the heart(trachea,aortc

arch,pulmonary arteries etc) should

be seen.

underexposure• In an underexposed cxr the cardiac

shadow is opaque, with little or no

visibility of thoracic vertebrae.

• The lungs may appear denser &

whiter, much as they might appear

with infiltrates present.

overexposure• With greater exposure of the cxr, the

heart becomes more radiolucent & the

lungs become proportionately darker.

• In an overexposed cxr the air filled lung

periphery becomes extremely

radiolucent, & often gives the

appearance of lacking lung tissues,as

would be seen in condition such as

emphysema.

rotation• The patient is not rotated if a

vertical line drawn through

the centre of the vertebral

bodies(T1-T5) is equidistant

from the medial end of each

clavicle.

Rotation to rt side

• Rotation to the right on a PA cxr-the

manubrium and or SVC or vessels

may become usually prominent on

the right. This can simulate a

mediastinal mass.

Rotation to lt side• The aortic arch may appear enlarged

& rotation is a common cause for one

lung appearing blacker than the

opposite side.

Inspiration• If the ant aspects of at least 6 ribs do

not lie above the lt dome of diaphragm, then suspect a shallow inspiration.

8to10 ribs posteriorly

Shallow inspiration• The diaphragm is attached to the

undersurface of the heart & this muscle pulls the heart downwardson a full inspiration. This downward pull is less in shallow respiration. Consequently the side to side diameter of the heart will appear larger.

• This also cause crowding of vessels at lung bases & may simulate basal lung infection.

Scapula position

Perfect Imperfect

Beam angulation• On occasion the xray beam may not

be perpendicular to the patient’s chest,but may be angled upwards. Angulation can cause the left dome of the diaphragm to be ill defined.

• Solution- rept cxr

anatomy

Pa anatomy

Hidden areas in cxr

Checking the four tricky hidden areas: apices (brown), superimposed over the heart (green), around each hilum (yellow), and below the domes of the diaphragm (blue). It has been shown that these are the four sites where small (and also large) lesions are most commonly overlooked.

Lateral cxr

anatomy

Cont..

fissures

Retrosternal line

Heart borders

ivc

Pulmonary artery

Lateral cxr pitfall• Fake mass anteriorly. Sometimes the

shadow of a high right dome of the

diaphragm and the shadow of the

posterior margin of the heart overlap

and create a well-defined density

that mimics an anterior mass.

Cont..• Age related aortic unfolding . In

young people the descending aorta is situated posteriorly within the mediastinum and it is not visualised on the lateral CXR.

• In middle age the aorta unfolds and extends laterally to the left. Consequently its anterior and posterior walls are then outlined by the surrounding left lung. This produces a tubular opacity on the lateral CXR.

Cont..• Another fake mass anteriorly. The

apex of the heart and adjacent

epicardial fat intrudes into the left

hemithorax and displaces the most

infero-medial and anterior aspect of

the left lung. This often produces a

shadow which can simulate a mass

lesion. This appearance is often

referred to as the cardiac incisura.

Lobes & fissures

Zones of the lungs• It is based upon the relationship

between the pressure in the

alveoli , in the arteries & in the

veins.

Cont..• Zone 1: No blood flow

Reason: More negative intrapleural pressure alveoli size↑ & lower arterial pressure due

to gravity → decrease diameter of vessels

• Zone 2: Intermittent blood flow

Reason: arterial pressure is greater than alveolar and venous pressure. Whereas, venules

pressure are less than alveolar pressure venules are collapsed

• Zone 3: Continuous blood flow

Reason: Due to gravity, there is high pressure → vasodilation → more blood flow

Ventilation and Perfusion

ZONE OF VENTILATION• Zone 1: 1.92 L/minute

Reason: Increase size of alveoli

• Zone 2: 4 L/minute

Reason: intermittent size of alveoli

• Zone 3: 6.5 L/minute

Reason: Decrease size of alveoli

Ventilation/Perfusion (V/Q) Ratio

• It is the ratio of alveolar ventilation and the amount of blood that perfuse the alveoli.

Calculation:V/Q= alveolar ventilation ÷ pulmonary blood flowAlveolar ventilation= 4200ml/minutePulmonary blood flow=5000ml/minuteSo, V/Q= 0.84

Zone 1: Ventilation(V) >>>

Perfusion(Q)

V/Q= 3.4 (high)

Zone 2: Ventilation(V) = Perfusion(Q)

V/Q= 0.8 (average)

Zone 3: Perfusion(Q) >>> Ventilation(V)

V/Q=0.63(low)

Bronchovascular markings

Plethoric lungs• ASD

• VSD

• PDA

• TAPVC

• Trancus arteriosus

oligaemia• TOF

• PULMONARY STENOSIS

Hila & hilar abnormality1)99% of each hilar shadow is due to vessels-pulmonary arteries and to a lesser extend veins.

2)There are no lumpy,bumpy elements to a normal hilum.

3)95% left hilum is higher than right5% @ the same level.

THE LEFT HILUM SHOULD NEVER BE LOWER THAN THE RIGHT

PURIST APPROCH TO HILAR POINT

PRAGMATISTS APPROCH• We have always found the purist’s description of the hilar point just a little bit

confusing. So we adopt a more practical approach. We look for the vee on

each side as follows. First, identify the lower lobe pulmonary artery. Each

lower lobe artery curls gently downwards and medially and has the

approximate diameter of your little finger. Now look for the site where the

most superior upper lobe vessel — either vein or artery — crosses the lateral

margin of the little finger. The point of crossing forms a horizontal vee. The

apex of the vee at the left hilum should be higher than the apex of the vee at

the right hilum . Occasionally, the two vees will be at the same level.

PRAGMATISTS APPROCH

BENJAMIN FELSON

Hilum overlay sign

Cervicothoracic sign

The normal hila

Collapse of the left lower lobe

Cont…

Collapse of the middle lobe

Collapse of the rul

Collapse of lul

Pitfalls of collapseCollapse Imposters

RUL Azygous fissureUnfolded neck vessels

Pitfalls of collapse

Collapse Imposters

RUL Azygous fissureUnfolded neck vessels

Middle lobe Depressed sternumFat touching the heart border

RUL Epicardial fat padAccessory fissure(developmental varriant)

LLL Unfolded aortaHiatus hernia

LUL Is unique……no impersonators

PLEURA

PLEURAL EFFUSION

SUPINE CXR

PLEURAL PLAQUE

PNEUMOTHORAX RULES