5 курс / Пульмонология и фтизиатрия / Clinical_Manifestations_and_Assessment_of_Respiratory

FIGURE 8.10 Overview of normal lung window computed tomography scan. The apex appears in the two views in the upper right corner of this figure; the diaphragm at the base of the lungs appears in the lower right view.

FIGURE 8.11 Close-up of a normal lung window computed tomography (CT) scan. (A) The red arrow indicates the portion of the chest undergoing CT scanning. (B) The actual cross-sectional slice or axial view of the chest. Note the carina and both mainstem bronchi (arrow).

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FIGURE 8.12 Close-up of normal computed tomography (CT) mediastinal window. (A) The red arrow indicates the portion of the chest the CT scan is taken. (B) The actual cross-sectional slice or axial view of the chest. Note that the lungs are overexposed and appear mostly black. The bone and mediastinal organs appear mostly white.

Finally, for poorly defined lesions evident on the standard radiograph, the CT scan is a useful supplement in determining the precise location, size, and shape of the lesion. The CT scan is especially helpful in confirming the presence of a mediastinal mass, small pulmonary nodules, small lesions of the bronchi, pulmonary cavities, a small pneumothorax, pleural effusion, and small tumors (as small as 0.3 to 0.5 cm). The CT scan can be done with contrast material in the vessels to delineate vascular structures.

Positron Emission Tomography

Positron emission tomography (PET) shows the metabolic activity of the tissues and organs scanned and the anatomic structures themselves. Used in conjunction with a chest x-ray and CT scan for comparison, the PET scan is an excellent diagnostic tool for early detection of malignant lesions. The unique aspect of the PET scan is its ability to evaluate highly metabolic cells that may be cancerous. In other words, the PET scan is able to detect cancerous cells in the tissues of the body before changes develop in the anatomic shape of the organ itself.

Before undergoing the scan, the patient is injected intravenously with a solution of glucose that has been tagged with a radioactive chemical isotope (generally fluorine-18 fluorodeoxyglucose or F18-FDG compound). Cancer cells metabolize glucose at extremely high rates. The PET scan measures the way cells burn glucose. If present, the cancer cells rapidly consume the tagged glucose. As the glucose molecules break down, end-products that emit positrons are produced. The positrons collide with electrons that give off gamma rays. The gamma rays are converted to dark spots on the PET scan image. These dark spots are commonly referred to as hot spots. The presence of a hot spot on a PET scan is likely to confirm a rapidly growing tumor.

Clinically, a PET scan is an excellent tool to rule out suspicious findings (i.e., a possible malignant lesion) that are identified on either the chest radiograph or CT scan. For example, Fig. 8.13 shows a chest radiograph that identifies two suspicious findings: one small nodule in the right upper lung lobe and a larger density in the left lower lung lobe, just behind the heart. Fig. 8.14 shows two CT scans that also identify the two suspicious findings and their precise location. Figs. 8.15, 8.16, and 8.17 show PET scan images that all confirm a hot spot (likely to be cancer) in the lower left lobe. However, the PET scan image shown in Fig. 8.18 confirms that the nodule in the right upper lobe is benign (i.e., no hot spot noted).

FIGURE 8.13 Chest radiograph identifying two suspicious findings: in the right upper lobe (white arrows) (A) and in the left lower lobe (B), just behind the heart (red arrows).

FIGURE 8.14 Same chest radiograph as shown in Fig. 8.13. Note that the computed tomography scan also identifies the suspicious nodules and their precise location.

FIGURE 8.15 Positron emission tomography scan: coronal views. The last three views show a hot spot in left lower lobe.

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FIGURE 8.16 Positron emission tomography scan: sagittal view. The encircled images show a hot spot in the lower left lobe.

FIGURE 8.17 Positron emission tomography scan: axial view. A hot spot is further confirmed in left lower lobe.

FIGURE 8.18 Positron emission tomography scan: axial view. This image confirms that the small nodule identified in the upper right lobe in the chest radiograph and computed tomography scan is benign (i.e., no hot spot is evident).

Although the PET scan is relatively painless (i.e., tantamount to the discomfort associated with an intravenous needle insertion), it is lengthy. It may take up to 90 minutes to complete the scan. After the injection, the patient quietly rests in a reclining chair for 30 to 60 minutes before the scan is performed. This allows time for the body to absorb the compound. This step may be difficult or impossible for patients who are unable to remain motionless for long periods. PET scans are very expensive to perform, compared with CT or magnetic resonance imaging (MRI) studies.

Positron Emission Tomography and Computed Tomography Scan

As described in the preceding sections, PET and CT are both standard imaging tools used by the radiologist to pinpoint the location of cancer or infection within the body before developing a treatment strategy. Individually, however, each scan has its own benefits and limitations. For example, the PET scan detects the metabolic activity of growing cancer cells in the body, and the CT scan provides a detailed picture of the pulmonary anatomy that shows the precise location, size, and shape of a tumor or mass. By contrast, because the PET scan and CT scan are done at different times and locations, variations in the patient's body position often make the interpretation of the two images difficult.

Technology has now been developed that allows both the PET scan and the CT scan to be merged and performed at the same time. The image produced is called a positron emission tomography and computed tomography scan (PET/CT scan) (also known as a PET/CT fusion). The PET/CT scan provides an image far superior to that afforded by either technology independently. When combined, the CT scan provides the anatomic detail regarding the precise size, shape, and location of the tumor, and the PET scan provides the metabolic activity of the tumor or mass. The PET/CT image provides excellent image quality and high sensitivity and specificity in detecting malignant lesions in the chest. Fig. 8.19 shows a PET/CT scan alongside a CT scan and a PET scan; all the images show the same malignant nodule in the right upper lung lobe.

FIGURE 8.19 Merged positron emission tomography (PET) and computed tomography (CT) scan (PET/CT scan) (center). The CT scan, PET/CT fusion, and PET scan are all showing the same malignant nodule in the right upper lobe (white arrow). NOTE: The PET/CT fusion is normally presented in color (e.g., red, blue, yellow).

The benefits of a combined PET/CT scan include earlier diagnosis, accurate staging and localization, and precise treatment and monitoring. With the high quality and accuracy of the PET/CT image, the patient has a better chance for a favorable outcome, without the need for unnecessary procedures. In addition, the PET/CT scan provides early detection of the recurrence or metastasis of cancer, revealing tumors that might otherwise be obscured by scars from previous surgery or radiation therapy. Thus the combined PET/CT scan provides the radiologist with a more complete overview of what is occurring in the patient's body, both anatomically and metabolically at the same time.

Magnetic Resonance Imaging

MRI uses magnetic resonance as its source of energy to take cross-sectional (transverse, sagittal, or coronal) images of the body. It uses no ionizing radiation. The patient is placed in the cylindric imager, and the body part in question is exposed to a magnetic field and radiowave transmission. The MRI produces a high-contrast image that can detect subtle lesions (Fig. 8.20).

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FIGURE 8.20 Anatomy of mediastinum on magnetic resonance imaging scan. (A) Ao A, Aortic arch; Es, esophagus; LBCV, left brachiocephalic vein; RBCV, right brachiocephalic vein; T, trachea. (B) Az V, Azygos vein; D. Ao, descending aorta; Es, esophagus; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (From Armstrong, P., Wilson, A. G., & Dee, P. [1990].

Imaging of diseases of the chest. St. Louis, MO: Mosby.)

MRI is superior to CT scanning in identifying complex congenital heart disorders, bone marrow diseases, adenopathy, and lesions of the chest wall. MRI is an excellent supplement to CT scanning for study of the mediastinum and hilar region. For most abnormalities of the chest, however, CT scanning is generally better than MRI for motion (patient motion causes loss of resolution in the MRI), spatial resolution, and cost reasons.

Because the magnetic resonance imager generates an intense magnetic field, objects made of ferromagnetic material are strongly attracted to it. Therefore patients with ferromagnetic cerebral aneurysm clips, metallic artificial joints, or ferromagnetic prosthetic cardiac valves should not undergo MRI because the magnetic force of the imager can cause these devices to heat, shift, and harm the patient. The magnetic force of the imager also can interfere with the normal function of cardiac pacemakers and most ventilators.

Pulmonary Angiography

Pulmonary angiography is useful in identifying pulmonary emboli or arteriovenous malformations. It involves the injection of a radiopaque contrast medium through a catheter that has been passed through the right side of the heart and into the pulmonary artery. The injection of the contrast material into the pulmonary circulation is followed by rapid serial pulmonary angiograms. The pulmonary vessels are filled with radiopaque contrast material and therefore appear white. Fig. 8.21 shows an abnormal angiogram in which the major blood vessels appear absent distal to pulmonary emboli in the left lung. Today, the spiral (helical) volumetric computed tomography pulmonary angiogram (CTPA) (also called a CT pulmonary angiogram) with intravenous contrast has largely replaced pulmonary angiography and is fast becoming the first-line test for diagnosing suspected pulmonary embolism. The CTPA is now a preferred choice of imaging in the diagnosis of a pulmonary embolism, because the only invasive requirement for the scan is an insertion of an intravenous line (see Chapter 21).

FIGURE 8.21 Abnormal pulmonary angiogram. Radiopaque material injected into the blood is prevented from flowing into the left lung past the pulmonary embolism (arrow). No vascular structures are seen distal to obstruction.

Ventilation-Perfusion Lung Scan

A ventilation-perfusion lung scan can be used in determining the presence of a pulmonary embolism. The perfusion scan is obtained by injecting small particles of albumin, called macroaggregates, tagged with a radioactive material such as iodine-131 or technetium-99m. After injection the radioactive particles are carried in the blood to the right side of the heart, from which they are distributed throughout the lungs by the blood flow in the pulmonary arteries. The radioactive particles that travel through unobstructed arteries become trapped in the pulmonary capillaries because they are 20 to 50 µm in diameter, and the diameter of the average pulmonary capillary is approximately 8 to 10 µm.

The lungs are then scanned with a gamma camera that produces a picture of the radioactive distribution throughout the pulmonary circulation. The dark areas show good blood flow, and the white or light areas represent decreased or complete absence of blood flow. The macroaggregates eventually break down, pass through the pulmonary circulation, and are excreted by the liver. The injection of these radioactive particles has no significant effect on the patient's hemodynamics because the patent pulmonary capillaries far outnumber those “embolized” by the radioactive particles. In addition to pulmonary emboli, a perfusion scan defect (white or light areas) may be caused by a lung abscess, lung compression, loss of the pulmonary vascular system (e.g., emphysema), atelectasis, or alveolar consolidation.

The perfusion scan is supplemented with a ventilation scan. During the ventilation scan the patient breathes a radioactive gas such as xenon-133 from a closed-circuit spirometer. A gamma camera is used to create a picture of the gas distribution throughout the lungs. A normal ventilation scan shows a uniform distribution of the gas, with the dark areas reflecting the presence of the radioactive gas and therefore good ventilation. White or light areas represent decreased or

complete absence of ventilation. Fig. 8.22 presents an abnormal perfusion scan and a normal ventilation scan of a patient with a severe pulmonary embolism. An abnormal ventilation scan also may be caused by airway obstruction (e.g., mucous plug or bronchospasm), loss of alveolar elasticity (e.g., emphysema), alveolar consolidation, or pulmonary edema.

FIGURE 8.22 Fat embolism in a patient with dyspnea and hypoxemia after a recent orthopedic procedure. Perfusion (P) and ventilation (V) radionuclide scans show multiple peripheral subsegmental perfusion defects suggestive of fat embolism. (From

Hansell, D. M., Lynch, D., McAdams, H. P., et al. [2010]. Imaging of diseases of the chest [5th ed.]. Philadelphia, PA: Elsevier.)

This test is slowly being replaced by more sensitive and rapid tests, such as the spiral computed tomography pulmonary angiogram scan.

Fluoroscopy

Fluoroscopy is a technique by which x-ray motion pictures of the chest are taken. Fluoroscopy subjects the patient to a larger dose of x-rays than does standard radiography. Therefore it is used only in selected cases, as in the assessment of abnormal diaphragmatic movement (e.g., unilateral phrenic nerve paralysis) or for localization of lesions to be biopsied during fiberoptic bronchoscopy.

Bronchography

Bronchography entails the instillation of a radiopaque material into the lumen of the tracheobronchial tree. A chest radiograph is then taken, providing a film called a bronchogram. The contrast material provides a clear outline of the trachea, carina, right and left mainstem bronchi, and segmental bronchi. Bronchography is occasionally used to diagnose bronchogenic carcinoma and determine the presence or extent of bronchiectasis (Fig. 8.23). CT of the chest has largely replaced this technique. Radiation safety techniques need to be used by the respiratory therapist assisting in the performance of this technique.

FIGURE 8.23 Bronchogram obtained using contrast medium in a patient with a history of bronchiectasis. Arrows indicate the carina and the dilated and thickened bronchi leading to the posterior basilar segment of the left lower lobe. (From Rau, J. L., Jr., &

Pearce, D. J. [1984]. Understanding chest radiographs. Denver, CO: Multi-Media Publishing.)

Ultrasound

Ultrasound imaging (also called ultrasound scanning or sonography) is a quick, noninvasive diagnostic examination that produces images of organs and structures inside the body. The ultrasound transducer, which is placed on the skin over the area to be examined, sends ultrasound waves into the body. The sound waves bounce off the organs, tissue, or fluid like an echo and return to the transducer. The transducer processes the reflected waves, and a computer transforms the waves into an image of the structures being examined. Because the ultrasound uses high-frequency sound waves, as opposed to ionizing radiation, it is a safe tool for examination.

As shown in Fig. 8.24, an ultrasound is most associated with the test used to examine a baby in pregnant women. However, it is also very commonly used to examine a large multiplicity of other organs and conditions throughout the body. For example, chest ultrasound is used to examine the trachea, lungs, mediastinum, heart and its large vessels, esophagus, thymus, and lymph nodes. In addition, the chest ultrasound is often used to assess the presence of fluid in the pleural space or other areas of the chest, especially when the amount of fluid is small. When there is a large amount of fluid in the pleural space, ultrasound can be helpful in determining if the fluid is an exudate (e.g., fluid caused by inflammatory or cancerous conditions) or a transudate (e.g., caused by fluid that has leaked from blood or lymph vessels). The chest ultrasound is also used to help guide a needle during a thoracentesis or to obtain a lung biopsy sample, assess the movement of the diaphragm, and diagnose a variety of heart conditions (see the following section on the echocardiogram).

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FIGURE 8.24 Fetal Ultrasound.

The echocardiogram is commonly used in conjunction with other types of diagnostic methods, such as CT scanning, x- rays, and MRI to assess a particular condition.

Echocardiogram

An echocardiogram (also called cardiac echo or simply echo) is a type of ultrasound that produces images of the heart (Fig. 8.25). Today, echocardiography is a very common, noninvasive diagnostic tool for real-time imaging of cardiac structures and function. For example, the echocardiogram is used to assess the extent of an enlarged heart, the size and shape the ventricular cavities, the thickness and integrity of the interaterial and intraventricular septa, the origin of an abnormal heart sound, the functional status of the heart's valves, the cause of unexplained chest pain or pressure, and the source of an irregular heartbeat. It may be performed at the patient's bedside and thus has been increasingly used in the intensive care setting.

FIGURE 8.25 Echocardiogram. LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (Echocardiogram from Kacmarek, R. M., Stoller, J. K., & Heuer A. J. [2017]. Egan's fundamentals of respiratory care [11th ed.]. St. Louis, MO: Elsevier.)

An echocardiogram is also used to calculate the heart's pumping capacity, including the stroke volume, cardiac output, ejection fraction, and diastolic function. In pregnant women known to be at high risk, a pediatric cardiologist who is

specially trained in fetal cardiac evaluation commonly performs a fetal echocardiogram to detect congenital heart defects. The test is typically performed by placing the transducer over the mother's abdomen to visualize the fetal heart. Box 8.1 provides an overview of some of the specific problems that can be identified with the echocardiogram.

Box 8.1

Specific Conditions That Can Be Identified With the Echocardiogram

•Pericardial effusion

•Cardiac tamponade

•Idiopathic congestive cardiomyopathy

•Hypertrophic cardiomyopathy

•Mitral valve regurgitation

•Mitral valve prolapse

•Aortic regurgitation

•Aortic stenosis

•Vegetation on the valves

•Intracardiac masses

•Ischemic heart muscle

•Left ventricular aneurysm

•Ventricular thrombi

•Proximal coronary disease

•Congenital heart disease

•Interventricular thickness

•Pericarditis

•Aortic dissection

The different types of echocardiograms are as follows:

•Transthoracic echocardiogram (TTE): Provides a noninvasive, highly accurate, and quick examination of the heart. The transducer is placed on the patient's chest while ultrasound waves create images of the heart. It is the standard method to view the heart. The transthoracic echocardiogram is the most common echocardiogram method.

•Transesophageal echocardiogram (TEE): Commonly used when the quality of the transthoracic echocardiogram images is poor. A flexible tube containing a transducer is passed down the esophagus and positioned close to the heart. The TEE provides a cleaner and sharper image of the heart because the various structures between the outside of the chest and heart (i.e., sternum, ribs, and lung) are not between the transducer and the heart. Conscious sedation and localized numbing medication are usually applied during this procedure.

•Stress echocardiogram: Is performed before and after the patient's heart is stressed by either exercise or the injection of an agent that stimulates the heart to beat harder and faster.

•Doppler echocardiogram: A special ultrasound method used to examine both the direction and velocity of blood flow through the heart chambers, heart valves, and great vessels. There are three types of Doppler ultrasounds:

•Color Doppler uses a computer to convert Doppler measurements into an array of colors to show the speed and direction of blood flow through a blood vessel. Fig. 8.26 provides a color Doppler recording of a severe mitral regurgitation.

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FIGURE 8.26 Color Doppler recording demonstrating severe mitral regurgitation. The regurgitant jet seen in the left atrium (LA) is represented in blue because blood flow is directed away from the transducer. The yellow components are the mosaic pattern traditionally assigned to turbulent or high-velocity flow. The arrow points to the hemisphere of blood accelerating proximal to the regurgitant orifice (proximal isovelocity surface area [PISA]). The size of the PISA can be used to help grade the severity of regurgitation. LA, Left atrium; LV, left ventricle. (Courtesy Sheldon E. Litwin, MD, Division of Cardiology, University of Utah. In Benjamin, I. J.,

Griggs, R. C., Wing, E. J., et al. [2016]. Andreoli and Carpenter's Cecil essentials of medicine [9th ed.]. Philadelphia, PA: Elsevier.)

•Power Doppler is a newer technique that is used to obtain images that are difficult to obtain with the standard color Doppler. This method provides greater detail of blood flow, especially in vessels that are located inside an organ or have little or minimal blood flow. The power Doppler, however, does not determine the direction of blood flow. The determination of blood flow is done with color Doppler and spectral Doppler (see later).

•Spectral Doppler displays blood flow measurements graphically, in terms of the distance traveled per unit of time, rather than as a color picture. It also can convert blood flow information into a distinctive sound that can be heard with every heartbeat.

•Three-dimensional echocardiography (also called four-dimensional echocardiography when the image is moving)—is now possible. This method uses an array of ultrasound probes to create detailed images to assess cardiac pathology, valvular defects, and cardiomyopathies. Real-time three-dimensional echocardiography is used to guide the physician to the location to obtain a right ventricular endomyocardial biopsy or to reach the precise position for the placement of catheter-delivered valvular devices.

Although echocardiography does not offer continuous monitoring and assessment of the cardiac function, the portability of the equipment readily provides quality studies at the patient's bedside. However, it may be difficult to obtain a satisfactory image of the patient who has excessive chest bandages, is obese, is unable to turn or maintain a certain position, or has air trapping in the lungs (e.g., emphysema).

Radiation Safety

All health care workers near the area where an x-ray is being generated must observe the proper safety precautions. The potential harmful effects caused by radiation are directly related to the amount of the exposure, the duration of the exposure, and the area of the body exposed. Simply stated, the less time one is exposed to radiation, the lower is the radiation dose; the further one is away from the radiation source, the lower is the radiation dose; and the more shielding between the health care worker and the radiation source, the better.

Radiation shields include both fixed protective barriers (e.g., lead screens) and personal protective equipment (e.g., lead gowns). Even though it is the responsibility of the radiographer to manage the radiation dose and ensure the safety for both the patient and the surrounding staff, it is also the responsibility of every health care practitioner in the immediate vicinity to take all the appropriate safety precautions necessary. For example, many respiratory therapy departments require their respiratory therapists to wear radiation badges. Other protection strategies include:

•If pregnant, leave the area

•Have only the personnel needed for the x-ray procedures present in the room

•When in the room during the x-ray procedures, stand behind portable or fixed lead panels, or wear the following:

•Lead aprons

•Lead safety glasses

•Thyroid shields

•Leaded gloves

Radiation Safety Techniques

The role of the respiratory therapist is important. The intent of this chapter is not to suggest that the respiratory therapist function as a “junior radiologist.” Instead, the following areas are worthy of consideration. The therapist must: