Chapter 10 Clinical Application of the Chest Radiograph

Learning Objectives After reading this chapter you will be able to: Describe how a chest radiograph is produced Define terms radiolucent and radiopaque Identify the four densities seen on a chest radiograph Explain how the relationship between the x-ray source and the patient affects the images viewed on the radiograph

Learning Objectives (cont’d) State standard distance between x-ray source and film for posteroanterior chest film Identify clinical indications for a chest x-ray Explain the technique, indications, and advantages and disadvantages of the following chest radiographic views: posteroanterior, left lateral, anteroposterior, lateral decubitus, apical lordotic, oblique, expiratory

Learning Objectives (cont’d) Describe correct position for endotracheal tube placement as seen on a chest x-ray Identify the value in assessing a chest radiograph in the following situations: Central venous pressure line insertion Pulmonary artery catheter placement Nasogastric tube placement Chest tube insertion Thoracentesis Pericardiocentesis Bronchoscopy

Learning Objectives (cont’d) Explain the technique, indications, and advantages and disadvantages for computed tomography (CT) scanning Discuss the use and indications for magnetic resonance imaging in lung disease

Learning Objectives (cont’d) Explain the technique and indications for performing nuclear medicine lung scans Describe how these problems affect lung scans: thromboembolism, atelectasis, pneumonia, emphysema Describe proper technique to assess the following to evaluate chest x-ray: depth of inspiration, placement on view box, adequacy of exposure, patient rotation

Learning Objectives (cont’d) Explain the technique and indications for the use of pulmonary angiography Know proper technique for performing a systematic descriptive evaluation (interpretation) of a chest x-ray Explain the significance of these special radiographic evaluation signs: silhouette sign, air bronchogram

Learning Objectives (cont’d) Discuss limitations of a chest radiograph Appraise clinical and chest radiographic findings for the following lung disorders: Atelectasis Pneumothorax Hyperinflation Interstitial lung disease Congestive heart failure Pleural effusion Consolidation Pneumonia

Overview Physics related to radiographs Standard and special views Techniques for interpreting the chest film Common pathologic abnormalities seen on chest x-ray films

Production of the Radiograph X-rays: Electromagnetic waves that radiate from a tube that an electric current has passed through Tube made of a cathode attached to low-voltage electron source (transformer) End of cathode wire is inside the vacuum-sealed tube As electrons flow through the wire they strike the anode

Indications for CXR Examination Detecting alterations of the lung caused by pathologic processes Determining the appropriate therapy Evaluating the effectiveness of treatment Determining the position of tubes and catheters Observing the progression of lung disease

Radiographic Views Standard views Special views Posteroanterior Anteroposterior Special views Lateral decubitus Apical lordotic Oblique Expiratory

Anteroposterior View Portable chest film Film cassette placed behind patient’s back X-ray beam moves from front to back (anterior to posterior) 4 feet from beam’s origin More magnification artifact than PA chest x-ray

Anteroposterior View (cont’d) Indications for AP portable films Evaluate the lung status Evaluate lines and tubes See results of invasive therapeutic maneuvers

Postprocedural CXR Evaluation Tracheal intubation Thin radiopaque strip along entire length of ETT Inferior tip of ETT 3 to 5 cm above the carina Accidental placement in right mainstem or esophagus must be recognized Reposition Secure Follow-up CXR

Postprocedural CXR Evaluation (cont’d) Central venous pressure (CVP) Placed in R or L subclavian vein or jugular vein Tip just above confluence of SVC and RA Accidental lung puncture must be recognized AP chest film required before initiating fluid therapy

Postprocedural CXR Evaluation (cont’d) Pulmonary artery catheter Tip at the right midlung near the hilum Catheter is sutured into place if chest film demonstrates proper position of catheter tip Accidental rupture of inflatable balloon may rupture pulmonary artery Area of pulmonary infarction on CXR

Postprocedural CXR Evaluation (cont’d) Nasogastric feeding tubes Ensure tip placed at the stomach or small bowel Chest films to recognize misplacement Into the trachea Into mainstem bronchus Deep into the lung

Postprocedural CXR Evaluation (cont’d) Chest tubes To drain excess air, blood, or pleural fluid from the pleural cavity Tip of the tube should be posterior and near the apex of lung so drainage can occur Periodic portable CXRs to ensure tube’s correct position

Procedures Requiring Evaluation with an AP Portable Film Thoracentesis Pericardiocentesis Bronchoscopy After transtracheal biopsy or needle aspiration

Computed Tomography Mathematical modeling of tissues Standard CT Electron beams pass through tissue Slice of body equivalent to a slice of bread Standard CT High-resolution CT

Computed Tomography (cont’d) Lung tumors Differentiate lymph nodes or tumor As small as 2 to 3 mm Chronic interstitial disease Superior to conventional CXR AIDS Early detection of pneumonias, abscesses, and cavities

Computed Tomography (cont’d) Occupational lung disease Parenchymal and pleural changes Pleural plaques in asbestosis Pneumonia Cost has restricted its use for pneumonias Bronchiectasis COPD Remarkable clarity and detail

Magnetic Resonance Imaging Superior to CT scan in: Evaluating of mediastinal and hilar masses Differentiating lymph node enlargement from enlarged blood vessels Evaluating chest wall invasion by lung cancer

Radionuclide Lung Scanning Gamma radiation emitted from the chest after radiopharmaceuticals injected into the bloodstream and inhaled into the lung Evaluation of suspected pulmonary embolism Normal ventilation and abnormal perfusion Pneumonia and atelectasis Poor ventilation and perfusion

Positron Emission Tomography Also called PET scan Determines metabolic activity of tissues Tumors and areas of infection have high metabolic activity = hot spots Evaluation of local and distant metastasis

Pulmonary Angiography To evaluate thromboembolic disease of the lungs Performed after V/Q lung scanning is nondiagnostic Injection of contrast medium into pulmonary artery CT angiography has reduced frequency of conventional angiography

Evaluation of the Chest Radiograph Recognition of anatomic landmarks Review clinical findings before viewing CXR Placing the chest film Patient facing clinician Cardiac shadow more prominent on the left side

Determine Quality of the Film Visualize vertebral bodies through cardiac shadow If easily seen: overexposed; recognize rotation of the patient Spinous processes to medial ends of clavicles Degree of patient’s inspiratory effort 10 posterior ribs on PA film

Interpretation X-ray penetration inversely proportional to density of structure Normal lung tissue has low density Cavities, blebs (darker) Consolidation increases density Pneumonia, tumor, collapse (white patch) Greatest density in the chest: bones Systematic review of all structures A through Z

Silhouette Sign and Air Bronchogram Infiltrate that obliterates heart border or diaphragm must be located in anterior segments of the lung Air bronchogram Visible bronchi when surrounded by consolidated alveoli Confirms intrapulmonary disease

Limitations of the Chest Radiograph Small lesions may not be seen Often normal in patients with significant respiratory symptoms Asthma

Clinical and Radiographic Findings in Lung Diseases Atelectasis Hyperinflation Interstitial lung disease Congestive heart failure (CHF) Pleural effusion Consolidation

Atelectasis Compressive atelectasis Obstructive atelectasis Pleural effusion, pneumothorax, hemothorax If severe: mediastinal shift Obstructive atelectasis Tumor, aspirated foreign body, mucus plugging Postoperative atelectasis Microatelectasis CXR: lung volume loss, mediastinal shift

Pneumothorax Often causes atelectasis Tension pneumothorax Mediastinal shift Tracheal deviation away from involved side Pleural line

Hyperinflation Obstructive lung disease Increased AP diameter Large restrosternal air space Flattening of diaphragm CXR neither sensitive nor specific for COPD Provides supporting evidence

Interstitial Lung Disease Substance activates patient’s immune system = scar or fibrosis Months to years Sarcoidosis Large hilar and paratracheal lymph nodes Asbestosis Calcified pleural or diaphragmatic nodules

Interstitial Lung Disease (cont’d) End-stage pulmonary fibrosis Honeycomb-size cavities Bronchiectasis Large air bronchograms with thick walls

Congestive Heart Failure Redistribution of pulmonary vasculature Engorgement of upper lobe vessels Fluid collection in dependent portions of the lungs Increased cardiothoracic (C/T) ratio (>0.5)

Congestive Heart Failure (cont’d) Kerley’s B lines Right base, <1 mm thick, 1 to 2 cm long, horizontal Miscellaneous signs Increased interstitial markings, pleural effusion

Pleural Effusion Usually >100 ml of fluid Small volume effusion: Blunting of the costophrenic (CP) angle Small meniscus sign Partially obscured and elevated diaphragm Large volume effusion Complete or nearly complete whiteout Complete obscuring of the hemidiaphragm Confirm with lateral decubitus

Consolidation Minimal volume loss Lobar or segmental distribution Homogeneous density Air bronchograms See Figures 10-17 and 10-18

Summary Dense body tissue appears white on CXR (radiopaque); air-filled body tissue appears black (radiolucent) Increasing ventilator pressures may indicate a pneumothorax and should prompt an order for a CXR CT scans show structural information using x-rays, but provide more detail and more specific information about densities 71

Summary (cont’d) MRI uses a strong magnetic field rather than x-rays to provide images of the body V/Q lung scans helpful only if normal or highly suggestive for pulmonary emboli PET scan uses radioactively tagged sugar water injection to demonstrate metabolically active tissue

Summary (cont’d) CXR interpretation requires evaluation of: Proper placement of the film on the view box Proper film exposure Proper patient rotation and lordosis Systematic review of structures 73

Summary (cont’d) Silhouette sign allows one to know whether a pulmonary opacity is touching the heart or diaphragm rather than residing in lung tissue anterior or posterior to those tissues Air bronchograms suggest fluid in the lung tissue surrounding patent airways