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Radiography of Interstitial Lung Disease

1 What radiographic features distinguish interstitial diseases from airspace diseases? Two primary characteristics radiographically distinguish interstitial diseases from airspace diseases. First, interstitial diseases displace little of the air within the lung, whereas airspace diseases displace large amounts of air. Interstitial diseases change the overall opacity of the lung very little, whereas airspace diseases in most cases dramatically increase the opacity (whiteness) of the lung on chest…

Imaging of Airspace Lung Disease

1 What is the difference between a pulmonary acinus and a secondary pulmonary lobule? The acinus (Latin for “berry”) is a structural unit of the lung distal to a terminal bronchiole, supplied by first-order respiratory bronchioles, which contains alveolar ducts and alveoli. It is 0.6 to 1 cm in size and is the largest unit in which all airways participate in gas exchange. The secondary pulmonary lobule…

Imaging of Lung Nodules and Masses

1 What is a solitary pulmonary nodule (SPN)? An SPN is a solitary focal lesion in the lung that measures 3 cm or less. A solitary focal lesion that is greater than 3 cm is considered to be a mass, and most masses are malignant. Approximately 150,000 SPNs are detected annually in the United States, often incidentally on imaging. A goal of radiologic evaluation of SPN is to…

CT Angiography and MR Angiography of the Peripheral and Visceral Vasculature

1 What are the clinical indications for computed tomography angiography (CTA) and magnetic resonance angiography (MRA) of the peripheral and visceral arteries? CTA and MRA are noninvasive methods of assessing the arteries and veins, which have all but replaced catheter angiography. The clinical indications for these examinations can be thought of in the following broad areas: Ischemia. Aneurysm Compression syndromes. Traumatic injury. 2 What is the…

Pulmonary Vascular Imaging

1 What is the normal appearance of the pulmonary vessels on computed tomography (CT) and magnetic resonance imaging (MRI)? The main pulmonary artery originates from the right ventricular outflow tract, anterior and to the left of the aortic root, and serves as a conduit for blood from the right ventricle to the pulmonary circulation. It bifurcates into the right and left pulmonary arteries. The right pulmonary…

Coronary Arterial Imaging

1 What are some noninvasive methods of coronary artery imaging? Imaging the coronary arteries is an important part of evaluating ischemic heart disease. Traditionally, this imaging has been performed using cardiac catheterization, an invasive procedure that requires arterial puncture. Newer technologies promise noninvasive, cross-sectional imaging of coronary artery patency and offer the potential to characterize coronary artery plaque. Coronary magnetic resonance imaging (MRI), using bright blood,…

Aortic Imaging

1 What is the normal imaging appearance of the aorta on computed tomography (CT) and magnetic resonance imaging (MRI)? The normal aorta on imaging can be divided into the following five parts: the aortic root, the ascending aorta, the proximal (anterior) aortic arch, the distal (posterior) aortic arch, and the descending thoracic aorta. The proximal segment of the ascending aorta is the aortic root, which begins…

Cardiac and Pericardiac Imaging

1 What forms the borders of the heart on the frontal posteroanterior (PA) or anteroposterior (AP) chest radiograph? The chest radiograph represents an important first step in the imaging workup of cardiovascular disease. On a PA frontal view of the chest, a cardiothoracic ratio (cardiac width : thoracic width) of less than 1 : 2 is considered normal in adults. Analysis of the cardiac silhouette can yield valuable information about…

Breast MRI

1 What are the indications for breast magnetic resonance imaging (MRI)? General indications for breast MRI include: Establish the extent of disease in the setting of a newly diagnosed breast cancer. Further evaluate an imaging finding that is incompletely characterized by diagnostic mammography and/or breast ultrasonography (US). Evaluate for residual disease in the setting of positive margins after lumpectomy or other operative procedure. Evaluate a patient…

Diagnostic Mammography

1 What are the indications for a diagnostic mammogram? Some indications for a diagnostic mammogram include a history of breast cancer, breast lump, nipple discharge, focal breast pain, breast implants, history of breast biopsy, history of an abnormal mammogram, and follow-up for a previously evaluated mammographic finding (BI-RADS category 3 lesion). 2 What views are performed for diagnostic mammography? How are patients who have undergone diagnostic…

Screening Mammography

1 What is a screening mammogram? A screening mammogram is a radiographic examination of the breasts performed to detect clinically occult breast cancer in asymptomatic women. 2 When should an average woman start getting mammograms? This is currently a topic of debate. The American College of Radiology (ACR) recommends that a woman get a baseline mammogram at age 40 and annual screening mammograms thereafter. The American…

Radiation Dose and Safety Considerations in Imaging

1 What is the terminology for radiation dose? Absorbed dose, equivalent dose, and effective dose are all used to describe the effects of radiation on tissue. Absorbed dose specifically refers to the energy transferred to a quantity of tissue by ionizing radiation. Equivalent dose can be derived from absorbed dose by applying a weighting factor that describes the type of radiation, in order to account for…

Introduction to Contrast Agents

1 What is a radiographic contrast agent? A radiographic contrast agent is a substance that is administered to a patient during an imaging examination to improve its diagnostic performance. Contrast agents are most often administered via the intravenous (IV) and oral routes for computed tomography (CT) and magnetic resonance imaging (MRI) examinations. However, other routes of contrast administration may be utilized, depending on the particular imaging…