chapter 20 review of thoracic imaging

Chapter 20

Review of Thoracic Imaging

Learning Objectives

List the four tissue densities seen on the chest radiograph.

Define the terms radiolucent and radiopaque. Describe how to evaluate the technical quality

of a chest radiograph. State the differences between the PA chest

film and the AP chest film.

Learning Objectives (cont.)

List the anatomic structures seen on the chest radiograph.

List the steps used to interpret thoracic imaging studies.

Identify the value of the computed tomography (CT) scan, high-resolution CT scan, and CT angiography.

Describe the common radiographic abnormalities seen in the pleura, lung parenchyma, and mediastinum.

Review of Thoracic Imaging: Introduction

Chest imaging is important part of diagnosing patients with lung disease

RT needs to be able to recognize significant radiographic abnormalities in certain situations

Plain chest radiograph is very popular, inexpensive, & reliable in most cases

Review of Thoracic Imaging: Overview

Chest radiograph is created by passing x-ray beam through chest

X-ray beam strikes film after passing through chest; x-rays passing through lung turn film black, while x-rays absorbed by more dense tissue (e.g., bone) leave film white

Resulting chest radiograph represent various shades of gray shadows

Review of Thoracic Imaging: Overview (cont.)

4 different tissue densities are visible on normal chest radiograph Air, fat, water, & bone

Air (lung) absorbs x-rays least & results in dark shadow (radiolucent)

Bone (ribs) absorb most x-ray energy & result in white shadow (radiopaque)

Fat & water shadows are different degrees of gray

Tissues that absorbs the least amount of energy and appear black in an x-ray film are called:

A.Translucent

B.Radiolucent

C.Transparent

D.Radiopaque

Digital technology has replaced traditional photographic film

Currently, most X-rays are recorded & display in digital format

Digital films have advantages: Can be manipulated to enhance interpretation Can be stored & retrieved quickly from any

location/time Can be copied, shared & transported quickly Image quality does not deteriorate over time

Review of Thoracic Imaging: Overview (cont.)

Review of Thoracic Imaging

All of the following are clinical indications for a chest x-ray except:

A.After an orotracheal intubation

B.Sudden onset of dyspnea

C.During cardiopulmonary resuscitation

D.Sudden drop in oxygenation

Approach to Reading Chest Film

Disciplined approach is needed First, make sure name on film matches

patient being evaluated Second, evaluate technical quality of film

(proper patient position, x-ray penetration, etc.)

Third, systematically evaluate all anatomical structures seen on film following prescribed series of steps

CXR Reading Technique

Is film properly label? Correct patient Date & time of film Right & left side identification

Is entire chest imaged on film? Was patient properly positioned? Were penetration & exposure settings

correct? (Quality of image) Overpenetration leaves lung shadows too dark Underpenetration causes lung shadows too white

PA Chest Film

PA chest film is created in radiology department, usually with patient standing

X-ray beam passes from posterior to anterior (PA) with film placed against patient’s chest

Usually results in high-quality film with minimal magnification of heart shadow

AP Chest Film

Taken with portable x-ray machine in ICU X-ray source is in front of patient & film is

behind patient AP films are often more difficult to read

because quality is not as good as PA film Heart shadow is more magnified with AP film

since heart is closer to x-ray source & farther from film

Rotation of patient is more likely

Which of the following problems is most common during a portable AP chest x-ray?

A.Patient is not centered on the film

B.Improper side labeling

C.Cardiac shadow is reduced

D.Obscured pulmonary vessels

Film Penetration

Improper penetration may conceal structures & important details

Proper penetration shows intervertebral disc spaces through shadow of heart

Under-exposed or under-penetrated films show an increase in chest whiteness (white-out xray)

Over-exposed or over-penetrated films leave lung parenchyma black without vascular markings

Chest Anatomy on Film

Normal Chest Films

Lateral View

Assessment of StructuresChest Wall & Mediastinum Symmetry of chest Rib fractures Bone changes Heart size Presence of free air

or fluid

Lung Evaluation

Size, density & symmetry

Lung edges in frontal & lateral films

Vascular markings Presence of free air or

fluid Consolidations &

infiltrates20

In the PA projection the diameter of the heart should not exceed __________ of the chest.

A.three quarters

B.one third

C.half of the diameter

D.one quarter

Advanced Chest Imaging

Computed tomography (CT) is very helpful in certain situations

CT visualizes structures cross-sectionally with great detail up to ~2 mm structures inside lung

CT scanning creates images looking like “slices” of patient’s chest (5 to 7 mm thick)

Conventional CT scanning is used to evaluate lung nodules & masses, great vessels, mediastinum, & pleural disease

Advanced Chest Imaging (cont.)

High-resolution CT (HRCT) scanning examines 1-mm slices of lung, producing greater lung detail

High-resolution CT scanning is ideal for evaluating diffuse parenchymal lung diseases: Interstitial lung disease Emphysema Bronchiectasis

CT Angiograms

Magnetic Resonance Imaging

Uses radio waves from realigning Hydrogen nuclei to generate MRI image (no x-rays are used)

Most often used to image mediastinum, hilar regions, & large vessels in lung

MRI has limitations in chest medicine Cannot be used in patients with pacemaker Metal objects (i.e., gas cylinders or regular ICU

ventilators) cannot be used near MRI machine

Ultrasound Images created by passing high-frequency

sound waves into body & detecting sound waves that bounce back (echo) from tissues of body

Ultrasonic evaluation of lung itself is rare Uses very portable equipment Commonly used to guide placement of central

& arterial catheters, & to detect & quantify pleural effusions

Very common in ICU

Ultrasound (cont.)

An ICU patient is suspected of having a pulmonary emboli. Which of the following radiological tests would you recommend to assess his situation?

A.Chest x-ray

B.Positron Emission Tomography

C.Magnetic Resonance Imaging

D.HRCT Angiography

Hydrothorax

Also called pleural effusion Blunted costophrenic angle on chest x-ray

indicates pleural effusion is present About 200 ml of pleural fluid will blunt

costophrenic angle Best chest x-ray view for detecting small pleural

effusion is lateral decubitus Pus in pleural space = empyema

Pleural Effusion

Empyema

Pneumothorax

Refers to collection of air in pleural space May occur spontaneously, with trauma, or

with invasive procedure May occur with mechanical ventilation; called

barotrauma in such cases Pneumothorax causes lung margin to pull

away from chest wall in affected region Presence of air can be better visualized by

comparing inspiratory vs expiratory CXR

Blunted or rounded costophrenic angles in an AP or PA chest x-ray may suggest the presence of:

A.Patient is not centered on the film

B.Improper side labeling

C.Cardiac shadow is reduced

D.Basilar atelectasis

Pneumothorax (cont.)

Tension Pneumothorax

Represents serious medical emergency Occurs when air within pleural space is under

pressure Air accumulates in pleural space on

inspiration but cannot exit on exhalation Chest film will show shift of mediastinum

away from pneumothorax Requires immediate decompression with

chest tube or needle aspiration of trapped air Can lead to cardiac tamponade &

hemodynamic collapse

Tension Pneumothorax (cont.)

Pulmonary Infiltrates

Seen on chest radiograph when alveoli fill with watery fluid (edema), pus, blood, or fat-rich material

Seen as white shadows in lung Air-filled airways surrounded by infiltrates will

cause “air bronchograms” Air bronchograms are hallmark of infiltrates

that fill alveoli (air space disease)

Air Bronchograms

Right Middle Lobe Pneumonia

Pulmonary Edema

Pulmonary edema due to left heart failure is common finding on chest radiograph

Left heart failure causes enlargement of pulmonary blood vessels in apex of lung (cephalization)

Kerley B-lines are often seen with pulmonary edema due to left heart failure

Chest radiograph often shows enlarged heart & pleural effusion with CHF

Pulmonary Edema (cont.)

Interstitial Disease

Chest radiograph usually shows diffuse, bilateral infiltrates

Infiltrates may look like scattered ill-defined nodules

Many different types of ILDs; 2 most common: Idiopathic pulmonary fibrosis Sarcoidosis

Because most patients with ILD have similar findings, it does not usually establish specific diagnosis

Interstitial Lung Disease

Atelectasis Common finding on chest radiograph,

especially in postoperative patient When localized to subsegmental portion of

lung - called “plate atelectasis” Lobar atelectasis occurs when major

bronchus is obstructed by mucus plug, tumor, or foreign body

Signs of volume loss = elevation of hemidiaphragm & shift of hilum towards affected side

Plate atelectasis (cont.)

Hyperinflation

Commonly seen with emphysema If more than 7 anterior ribs above diaphragm,

hyperinflation is present Other signs of hyperinflation include:

Flattening of hemidiaphragms Large retrosternal airspace Narrowed mediastinum Increased AP diameter

Emphysema causes loss of visible blood vessels in lung

Emphysema

Which of the following chest x-ray findings is consistent with a tension pneumothorax

A.Tracheal deviation towards the affected side

B.Elevated hemidiaphram in the opposite side

C.Presence of a meniscus in the affected side

D.Absence of lung markings in the affected side

Solitary Pulmonary Nodule (SPN)

Defined as parenchymal opacity smaller than 3 cm in diameter surrounded by aerated lung

Chest CT scanning offers better method for studying nodule

Nodules having central calcification are round & have smooth edge are most likely benign

Positron Emission Tomography (PET) scanning is often very useful in evaluating SPN

SPN(cont.)

Catheters, Lines, & Tubes

Chest radiograph is obtained after placement of endotracheal tube, CVP line, or pulmonary artery catheter

Film helps confirm tube or catheter is in correct position

Tip of endotracheal tube should be 5 to 7 cm above carina with patient’s head in neutral position

Endotracheal Tube Placement

Catheters, Lines, & Tubes (cont.)

Tracheostomy tubes should extend half distance from stoma to carina

Tip of CVP catheter should be in superior vena cava

Pulmonary artery catheters can be seen in Pulmonary artery about 90% of time

Chest tubes should be within pleural space following contour of chest wall or diaphragm

Intra-aortic balloon pump tip should be located just below origin of Subclavian artery

chapter 20 review of thoracic imaging

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