Cardiovascular  Domain  Imaging Modalities Imaging modalities commonly used in the evaluation of the cardiovascular system include: Plain Radiographs: PA and lateral radiographs are used to evaluate the chest for cardiovascular disease. This examination is helpful in the evaluation for cardiomegaly and pulmonary edema. It is most commonly used in the acute setting. Chest radiography is only sensitive for the late stages of cardiovascular disease. Normal Chest Radiograph CHF- Interstitial Edema Ultrasound (AKA- echocardiography & sonography): The most common form of ultrasound used is two dimensional sector scanning with Doppler. As bones and air obscure sonographic visualization, "sonographic windows" are imperative in ultrasound and make this examination operator dependent. Two-dimensional ultrasound visualizes the anatomic structures of the heart. Doppler signals can be reflected off the red blood cells measuring velocity through frequency changes as per the Doppler equation. Doppler signals can be mapped spectrally in a graph-like mode or with color on the two-dimensional sector scan. Measurements and calculations include quantified pressure gradients (as across a valve), evaluation for regurgitant flow, measurement of cardiac output and estimation of stenosis in certain arteries.  In addition to cardiac evaluation, ultrasound is used in the evaluation of  vessels including the carotid arteries, aorta, peripheral arteries and veins. Ultrasound- Carotid Ultrasound- Venous Radionuclide studies: Cardiac perfusionimaging: This is a physiologic test. Thallium 201 is handled by the myocardial cells similar to potassium. Its uptake is relative to blood flow so regions of decreased blood flow are seen as reduced uptake. A patient can be stressed and evaluated with a concurrent radionuclide injection. A resting scan is also obtained to establish a baseline. Thallium Radionuclide angiography: also known as MUGA (multiple gated scanning) can evaluate for ejection fraction and wall motion. Red blood cells are tagged with a 99m technetium pertechnetate and then injected. Images are gated with an ECG. This allows individual frames to be summed up in a cine mode providing a dynamic view of cardiac motion on a computer screen. From this, wall motion is evaluated and ejection fraction calculated. MUGA V/Q scan: ventilation-perfusion imaging uses radionuclide to evaluate lung ventilation and lung perfusion, separately. Ventilation is evaluated with either xenon (a gas) or aerosolized technetium. Perfusion is evaluated with small albumin particles tagged with technetium known at technetium MAA. These exams are done sequentially and images are obtained with a gamma camera. Normal V/Q Scan Computed Tomography: is typically used to evaluate great vessels of the chest and abdomen. New helical acquisitions now allow for CTA (computed tomographic angiography) after the injection of intravenous contrast for the evaluation of smaller vessels. Normal CT- Chest and Heart Magnetic Resonance Imaging:   has been effectively used in the evaluation congenital heart disease. Complex vascular anomalies of the chest and abdomen can be interrogated with magnetic resonance imaging as well. More recently, functional imaging including wall motion and perfusion analysis have been attempted and are likely to become more common in the future. Normal MRI- Chest and Heart Breath-hold Anatomical Cardiac MRI Coronary Anatomy Left Right Perfusion Acquisition Normal Abnormal Myocardial Perfusion Reserve Image Contrast Angiography: arteries are opacified with contrast intra-arterially and radiographs obtained. Contrast is introduced via catheter, which is typically percutaneously placed through the femoral artery. This is the traditional technique by which the coronary arteries are evaluated. It also is used to evaluate the aorta and peripheral arteries. Abnormal Thoracic Aortogram- Aortic Transection Venography: is a simple procedure by which contrast is injected into a cannulated vein and radiographs obtained to evaluate venous patency; usually in the evaluation for deep venous thrombosis. DVT manifests as filling defects in the veins. Left Lower Leg Venogram - Iliac DVT Left Lower Leg Venogram - Baker's Cyst Subclavian Venogram Heart Disease Heart size: Cardiomegaly is defined as the transverse diameter of the heart being greater than half the internal diameter of the chest, as seen on the PA chest radiograph. AP technique magnifies the heart and therefore cannot be used to assess cardiac size. Enlargement is commonly from ventricular dilation. Cardiac Valvular Disease: is best initially evaluated with echocardiography. Cardiac valves can be visualized with two-dimensional echocardiography. Pressure gradients can be estimated with Doppler and the degree of stenosis and regurgitation demonstrated. Ventricular contractility: is best evaluated dynamically with real time echocardiography or with radionuclide angiography. Focal motion abnormality due to ischemia or scarring can be demonstrated as well as generalized contractile abnormalities. Pulmonary edema: Pulmonary edema is generally divided into cardiogenic and non-cardiogenic causes. Cardiogenic pulmonary edema is most commonly related to left ventricular heart failure. The first sign of edema recognized on plain chest radiographs is interstitial edema with Kerley B lines. These are horizontal lines seen along the lateral lower zones of the lungs. More pronounced edema presents as alveolar edema with filling of the alveoli and is seen as air space disease on the chest radiograph. Alveolar edema is typically seen as the bilateral batwing radiodensity on chest radiographs. Both the aforementioned radiographic findings are typically accompanied by a cardiomegaly. Heart failure typically manifests on the chest x-ray as follows: Cardiomegaly, enlargement of the vessels of the upper zones of the lung secondary to increased pulmonary venous pressure. Pulmonary edema, either interstitial or alveolar. Plural effusions. Ischemic heart disease: ischemic heart disease can be screened through a number of modalities including echocardiography with stress, gated radionuclide images with stress, and via radionuclide perfusion imaging with stress. In each case, the patient is stressed on a treadmill or pharmacologically. Radionuclide angiography (MUGA) and Echocardiography- ischemia is suggested when there there is focal wall motion abnormality on stress, which is not seen at rest. This is an indirect sign of ischemia. Perfusion abnormality: ischemia is demonstrated on stress as decreased uptake of radionuclide (thallium)  that perfuses normally at rest. An area of decreased perfusion on both stress and rest signifies a region of non-vital tissue or scarring. Abnormal Thallium- Myocardial Ischemia Arterial patency: Arterial patency is best evaluated with coronary angiography. Recent studies show that the large proximal coronary arteries can be demonstrated with MRI, but not reliably. Angiography is not a screening examination, and is reserved for those patient's with a higher probability of disease and for preoperative planning. Congenital heart disease: Common congenital lesions include atrial septal defects, ventricular septal defects, and patent ductus arteriosus. Indirect signs of these can be demonstrated on plain radiographs by evaluating for cardiac contour abnormality. However, congenital heart disease is better screened with echocardiography rather than chest radiographs. A common congenital anomaly is tetralogy of Fallot in which there is decreased pulmonary perfusion due to pulmonary artery stenosis. A right-sided aortic arch can be seen in 25% of these patients. The tetralogy includes ventricular septal defect, right ventricular outflow obstruction, right ventricular hypertrophy, and an overriding aorta.   Pulmonary Embolism Pulmonary emboli originate from thrombi originating in deep veins, typically of the leg, and can be screened with V/Q scanning. Plain radiographs are usually negative in a patient with pulmonary embolism. In severe cases, either oligemia (decreased vasculature on CXR) from pulmonary artery obstruction can be seen (Westermark Sign) or focal peripheral radioopacity representing pulmonary infarction is demonstrated (Hampton's Hump). These findings are uncommon. The most common scenario is a patient presenting with an unexplained shortness of breath with a normal chest radiograph. The initial screen is typically ventilation-perfusion imaging (V/Q). V/Q Imaging: if an area ventilates normally but does not perfuse, this is called a mismatch and is a sign of a embolism. This has been statistically evaluated in national multicenter trials known as PIOPED. Two large areas of mismatch are considered high probability for pulmonary embolus. No perfusion defects are considered normal and very small areas of abnormality are considered low probability. Essentially, the rest is considered intermediate or indeterminate. This is a test of probability and those with a high probability scan have approximately 90% chance of having PE while those with a low probability scan have an approximately 10% of having PE. Bottom line- large mismatches (ventilated but not perfused) are seen in PE. Abnormal V/Q- High Probability for PE Pulmonary angiography: is considered the "gold standard" for the diagnosis of pulmonary embolism. A catheter is placed via the femoral vein into the pulmonary outflow tract. Pulmonary arteries are opacified with contrast. This evaluates for intra-arterial thrombi within the pulmonary arteries, which are seen as filling defects. The disadvantages of this examination are its expense and invasiveness. Ultrasound:  is used to evaluate for deep venous thrombosis. Ultrasound on a basic level simply evaluates for clot within veins as seen sonographically such that the veins will not compress. Normal veins collapse when pushed by the transducer. Arteries are more difficult to compress due to their muscular walls. Doppler also assists in this examination. Normal Venous US Abnormal Venous US - Popliteal DVT Venography:  is the gold standard for the evaluation of deep venous thrombosis. It has a low complication rate but is uncomfortable, more expensive, and is still more invasive than venous ultrasound. The veins are opacified and evaluated for filling defects - which represent thrombus. Abnormal Venogram - Acute Iliac DVT Abnormal Venogram - Subclavian Thrombosis Abnormal Venogram - Baker's Cyst Other modalities: helical computed tomography is now being used to evaluate for pulmonary embolism in the pulmonary arteries in place of conventional contrast angiography.  First pass contrast enhanced pulmonary MR angiography is also being evaluated for the diagnosis of pulmonary embolism.  These techniques have yet to gain wides acceptance. Pulmonary MRA\ Peripheral Arterial and Venous Disease Arterial: traditionally the peripheral arteries have been evaluated with conventional contrast angiography. However, more recently CT and MRI have been used to evaluate for arterial disease. Ultrasound with Doppler is also used to screen for arterial disease. Both CT and MRI are established as methods for evaluating the great vessels, especially the aorta. Both are ideal for the evaluation aortic aneurysms and dissecting hematoma. Abnormal CT- Aortic Dissection Normal carotid MRA Aortoiliac MRA Venous: peripheral venous evaluation is most commonly performed non-invasively with ultrasound (see above). Venography is utilized less frequently but remains the "gold standard" for documenting venous disease. Reading: Armstrong and Wastie.  Diagnostic Imaging. Third Edition. Chapters 3 and 16. Revised by Gerald R. Aben, MD. January 2, 2002