2011-11-14T05:32:00.001-08:00

CHEST X-RAY

Introduction:

The chest radiograph is the most frequently performed radiographic study in the United States. It should almost always be the first radiologic study ordered for evaluation of diseases of the thorax. The natural contrast of the aerated lungs provides a window into the body to evaluate the patient for diseases involving the heart, lungs, pleurae, tracheobronchial tree, esophagus, thoracic lymph nodes, thoracic skeleton, chest wall, and upper abdomen. In both acute and chronic illnesses, the chest radiograph allows one to detect a disease and monitor its response to therapy. For many disease processes (e.g., pneumonia and congestive heart failure) the diagnosis can be established and the disease followed to resolution with no further imaging studies. There are limitations to the chest radiograph, and diseases may not be sufficiently advanced to be detected or may not result in detectable abnormalities.

Indications:

1- Aspiration. 2- Atelectasis. 3- bronchiectasis. 4- Dyspnea.

5- COPD. 6- Emphysema. 7- Cystic fibrosis. 8- Neoplasm.

9- Pleural effusion. 10- Pneumonia. 11- Tuberculosis.

12- Heart failure and other heart problems.

Patient preparation:
1- The removal of all opaque objects from the chest and neck, as clothes with buttons, hooks,
     or any objective that would be visualized on the radiography as a shadow.
2- The patient then puts on a hospital gown, which commonly has the opening in the back.
3- Long hair braided or tied together in bunches with rubber bands or other fasteners may
      cause suspicious shadows on theradiography if left superimposing the chest area.
4- Oxygen lines or electrocardiogram ( ECG ) monitor leads should be carefully moved to
     the side of the chest if possible.

Technical factors

1- kilovoltage ( KV ) :-

Generally, KV should be high enough to result in sufficient contrast to demonstrate the many shades of gray needed to visualize the finer lung marking. thus, chest radiography uses low contrast, described as a long-scale contrast, with more shades of gray. this requires high KV of 100-120.
Low KV, high contrast, will not provide sufficient penetration to visualize well the fine lung marking in the areas behind the heart and mediastinum. Too high contrast is evidence when the heart and other mediastinal structures appear underexposed, even though the lung fields are sufficiently penetrated.
as a general rule, in chest radiography, the use of high KV (above 100) requires the use of girds can be used.

2- Milliamperage and Exposure time ( mAs ):-

Chest radiography requires high mA and short exposure time to reduce the involuntary subject movement and loss of sharpness. Adequate mAs should be used to provide for optimum density of lungs and mediastinal structures, where faint outline mid and upper vertebrae and posterior ribs are seen through the heart.

3- breathing:-

Images are normally acquired on arrested deep full inspiration,which ensures maximum visualization of the air-filled lungs.The adequacy of inspiration of an exposed radiograph can be assessed by the position of the ribs above the diaphragm. In thecorrectly exposed image, it should be possible to visualize either six ribs anteriorly or ten ribs posteriorly, or the thoracic spine disc spaces should be barely visible through the heart but bony details of the spine are not usually seen.
Hold breath on second inspiration.
Expiration technique.

A radiograph may be taken on full expiration to confirm the presence of a pneumothorax. This has the effect of increasing intrapleural pressure, which results in the compression of the lung, making a pneumothorax bigger. The technique is useful Postero-anterior radiograph of chest taken using high kVp technique in demonstrating a small pneumothorax and is also used to demonstrate the effects of air-trapping associated with an inhaled foreign body obstructing the passage of air into a segment of lung, and the extent of diaphragmatic movement.

4- Rotation:-

- Rotation on PA chest radiographs can be determined by examin-ing both sternal ends of the clavicles for a symmetric appearance in relationship to the spine. On a true PA chest without any rotation, both the right and left sternal ends of the clavicles will be the same distance from the center line of the spine. Note the rota¬tion evident in by the difference in distance between the center of the spinal column and the sternal end of the right clavicle as compared with the left.

- If the patient is rotated then interpretation may become difficult. Firstly, it may be difficult to know if the trachea is deviated to one side by a disease process. It also becomes difficult to comment accurately on the heart size. Changes in lung density due to asymmetry of overlying soft-tissue may be incorrectly interpreted as lung disease.

5- central ray location:-

Central ray chest-positioning method

The vertebra prominens corresponds to the level of the T1 and the uppermost margin of the apex of the lungs. This landmark, which can be palpated at the base of the neck, is the preferred landmark for locating the CR on a PA chest . For the average female, this is down about 7 inches (18 cm); for the male, about 8 inches (20 cm).

One way of determining this distance is by an average hand spread as shown. Most hands can reach 7 inches (18 cm). The 8-inch (20-cm) distance can be determined by estimating an additional inch. If the hand spread method is used, practice with a ruler to con¬sistently determine these distances

These differences between male and female are true for near-average body-types for the general population, with crossover ex-ceptions in which certain larger athletic type females may also have longer lung fields, and some males shorter lungs. However, for pur-poses of chest positioning for the general population, these average measurements of 7 inches (18 cm) for a female and 8 inches (20 cm) for a male can be used as reliable guidelines.

Basic and special projections

Basic

Lateral

Special

AP lordotic

Anterior and posterior oblique

PA projection

Technical factors:

1- IR: 14 x17 inches.

2- Lengthwise or crosswise.

3- Stationary gird.

4- 100- 120 KV mAs 5

Patient position:

1- The patient ERECT facing the cassette.

2- Align midsagittsl plane to CR and to midline of IR with equal margins between lateral thorax and sides of IR.

3- Feet spread slightly, weight equally distributed on both feet.

4- the patient's chin is rested on the top of the cassette holder to prevent superimposing apices .

5- Hands on lower hips, palms out, elbows partially flexed.

6- The shoulders and arms are rolled forward to bring the scapulae towards the side of the chest to prevent superimposition of scapulae over lung field.

7- Top of IR will be approximately 1.5 to 2 inches ( 4 to 5 cm ) above shoulders on average patients.

Central ray:

The horizontal central beam is directed at right-angles to the cassette at the level of the eighth thoracic vertebrae (i.e. spinous process of T7), which is coincident with the lung midpoint The surface marking of T7 spinous process can be assessed by using the inferior angle of the scapula before the shoulders are pushed forward.

SID of 72 inches (180 cm).

Respiration

Exposure made at end of second full inspiration.

Image characteristics:

• Full lung fields with the scapulae projected laterally away from the lung fields.

• The clavicles symmetrical and equidistant from the spinous processes and not
obscuring the lung apices.

• The lungs well inflated, i.e. it should be possible to visualize either six ribs anteriorly
or ten ribs posteriorly.

• The costophrenic angles and diaphragm outlined clearly.

• The mediastinum and heart central and defined sharply.

• The fine demarcation of the lung tissues shown from the hilum to the periphery.

· Penetration the vertebral outlines should be visible in the mediastinum.

· Density the average density of the lungfields should be approximately 1

Anatomy Demonstrated

Lungs, trachea, heart, major mediastinal vessels, diaphragm and ribs

Lateral projection

Technical factors:

1- IR: 14 x17 inches.

2- Lengthwise

3- Stationary gird.

4- 100- 120 KV mAs 6

Patient position:

1- The patient erect facing the cassette.

2- Sagittal plane parallel and coronal plane perpendicular to the film

3- Weight equally distributed on both feet.

4- The patient’s arms are folded across the top of the head and the elbows gripped with the hand of the opposite

5- The chin is raised up.

6- The top of the film should be positioned about 5 cm above the tops of the shoulders.

Central ray:

The horizontal central ray is centered midway between the anterior and posterior skin surfaces at the level of T6/7 at a level midway between the xiphisternum and the sternal angle.

SID of 72 inches (180 CM).

Respiration

Make exposure at end of second full inspiration.

Image characteristics:

Insufficient elevation of the arms will cause the soft tissues of the upper arms to obscure the lung apices and thoracic inlet, and even the retrosternal window, leading to masses or other lesions in these areas being missed.
Rotation will also partially obscure the retrosternal window, masking anterior mediastinal masses. It will also render the sternum less distinct, which may be important in the setting of trauma when sternal fracture may be overlooked. ( posterior ribs and costophernic angle on side away from IR projected slightly ¼ to ½ inch or about 1 cm posterior because of divergent rays).
Penetration the cardiac shadow should be penetrated.
Density the average density of the lung fields should be approximately 1.

Anatomy Demonstrated

Lungs & diaphragms (superimposed), trachea, bronchus, major vessels, heart thoracic cage.

AP projection

This projection is used as an alternative to the postero-anterior erect projection for elucidation of an opacity seen on a posteroanterior, or when the patient’s shape (kyphosis) or medical condition makes it difficult or unsafe for the patient to stand or sit for the basic projection. For the latter, the patient is usually supported sitting erect on a trolley.

Technical factors:-

1- IR: 14 x17 inches.

2- Lengthwise or crosswise

3- Stationary gird.

4- 100- 120 KV mAs 4

Patient position:

· Patient is supine on cart; if possible, the head end of the cart or bed should be raised into a semierect position.

· Roll patient shoulders forward by rotating arms medially or internally.

· Place IR under or behind patient; align center of IR to CR ( top of IR about 1.5 inches above shoulder.

· Center patient to CR and to IR; check by viewing patient from the top, near the tube position.

• The median sagittal plane is adjusted at right-angles to the middle of the cassette.

Central ray:

· CR angled caudad to perpendicular to long axis of sternum (generally requires 5 caudad angle, To prevent clavicles from obscuring the apices).

· CR to level of T7, 3 to 4 inches ( 8 to 10 cm ) below jugular notch.

· SID of 40inches (100 CM) for supine.

Respiration:

Make exposure at end of second full inspiration.

N.B

For semierect position, use 72-inch (180- cm ) SID if this is possible. Always place markers on the IR or label the IR or label the image to indicate the SID used; also indicate those projections obtained, such as AP supine or semierect.

Image characteristics:

1- The heart will appear larger as are a result of increased magnification from a shorter SID and increased OID of the heart.

2- Possible pleural effusion for this type of patient will often obscure vascular lung markings when compared with a fully erect PA chest projection.

3- Usually there will not be as full an inspiration, with only eight or nine posterior ribs visualized above diaphragm. Thus the lungs will appear more dense because the lungs are not as fully aerated.

4- Correct CR angle: three posterior ribs should be seen above clavicles, indicating unobscured apical region.

Anatomy Demonstrated

Lungs & diaphragms (superimposed), trachea, bronchus, major vessels, heart thoracic cage.

AP lordotic

Indication:

To clarify anomaly seen on PA projection e.g. Interlobular effusion, Pancoast tumour (Pancoast tumor, superior pulmonary sulcus tumor, an adenocarcinoma of a lung apex causing Pancoast syndrome). Pancoast syndrome, pain and tingling of the arm over the area of distribution of the ulnar nerve, constriction of the pupil, and paralysis of the levator palpebrae superioris muscle, due to pressure on the brachial plexus by a malignant tumor in the region of the superior pulmonary sulcus.

Technical factors

1- IR: 14 x17 inches.

2- Lengthwise or crosswise

3- Stationary gird.

4- 100- 120 KV mAs 4.

Patient position:

• The patient stands AP erect approximately 30 cm from the film.

· Leaning back with shoulder, neck, and back of head against IR.

• Both patient hands on hips, palm s out, shoulders rolled forward.

• Center midsagittal plane to CR and to centerline of IR.

• Center cassette to CR. ( TOP OF IR should be about 3 inches { 7 to 8 cm} above shoulders.

Central ray:

· The horizontal central ray is centered in the midline midway between the sternal notch and the xiphisternum.

· SID of 180 cm.

Respiration

On second full inspiration.

Modification

If patient is weak and unstable and/or not able to assume the erect lordotic position, an AP semiaxial projection may be taken with the patient in a supine position. Shoulders are rolled forward and arms positioned as for lorotic position.

The cr is directed 15 to 20 cephalad, to the midsternum.

Image characteristics:

1- Limits of anatomy, superiorly the skin margins of the apices, inferiorly the T4, laterally the ribcage.

2- No rotation, The apices should be symmetrical about he midline.

3- The medial ends of the clavicles should be projected above the lung apices.

4- The apex scapulae should be clear of the lungfields.

5- Penetration the vertebral outlines should be visible.

Anatomy Demonstrated:

Lung apices and the medial ends of the first 4 ribs.

Anterior oblique position – RAO and LAO

This projection is used to separate the heart, aorta and vertebral column, thus enabling the path of the ascending aorta, aortic arch and descending aorta to be acquired on film. The projection will also demonstrate the diameter and the degree of unfolding of the aorta.

N.B the side of interest generally is the side farthest from the IR. Thus the RAO will provide best visualization of the left lung.

Technical factors:

1- IR: 14 x17 inches.

2- Lengthwise or crosswise

3- Stationary gird.

4- 100- 120 KV mAs 4.

Patient position:

1- Patient erect, rotate 45 with left anterior shoulder IR for the LAO and 45 with right anterior shoulder against IR for RAO.

2- Patient arm flexed nearest IR and hand placed on hip, palm out. And opposite arm raised to clear lung field.

3- Patient looking straight ahead, chain raised.

Central ray:

1- CR perpendicular, directed to level of T7 ( 7 to 8 inches ) below level of vertebra prominens.

2- SID of 180 cm

Respiration :

Second full inspiration.

RAO

LAO

Anatomy Demonstrated:

Both lungs from the apices to the costophrenic angles should be included. The air-filled trachea, great vessel , and heart outline.

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Positioning and Related Anatomy for X-ray Imaging