IMAGENOLOGIA DEL CORAZON Y GRANDES VASOS

RADIOLOGIA-UNMSM

Hallazgos de aparente cardiomegalia y congestión vascular pulmonar son posibles cuando se toma con pobre esfuerzo inspiratorio. Esto se determina por el nivel del diafragma relativo a las costillas posteriores. Con los diafragmas elevados característico de espiración forzada, es natural que la trama vascular pulmonar este mas aglomerada y de la apariencia de congestión pero no se encontraran líneas Kerley B o acentuación bronquial.

Cuando el diámetro horizontal de la silueta cardiaca basal excede la mitad del diámetro interno del tórax se califica como cardiomegalia. Verificar siempre que la placa este bien inspirada, el diafragma debe estar por debajo del nivel del arco costal posterior 9 o 10.

SPECT- Sestamibi en actividad miocárdica

Superficie de corte vertical, ha la izquierda corte coronal y sección sagital. el corte coronal ilustra la posición de las válvulas mitral y tricúspide comparada con el septum interventricular, el que en su región superior esta adelgazado corresponde al septum membranoso . Esto es evidente en el corte sagital donde el septum se adelgaza justo debajo de la válvula aortica.

La figura ilustra corte a nivel del miocardio del ventrículo izquierdo. Mayor parte del curso de las arterias coronarias mayores yace en el epicardio en la superficie del corazón, con los vasos con frecuencia envueltos en grasa. Aquí se ilustra un vaso penetrante a través de la pared miocárdica para irrigar segmentos como el septum.

La ilustración compara el tejido del corazón y grandes vasos con una representación esquemática mostrando la posición de las válvulas y la sobre posición de las estructuras derechas con el ventrículo izquierdo, la aorta ascendente y la aurícula izquierda.

Oblicua anterior izquierda: la proyección anterior del grueso miocardio ventricular izquierdo (normalmente <11 mm de grosor) comparado con la delgada pared libre ventricular derecha (generalmente menos de 3mm de grosor). Debajo de la arteria pulmonar izquierda principal esta la orejuela auricular izquierda, y adyacente a la porcion mas baja de la VCS esta la orejuela de la aurícula derecha.

Vista lateral izquierda: las estructuras fibrosas anclando la válvula mitral con la aurícula izquierda posteriormente. El flujo del ventrículo derecho se dirige anterior y superiormente muestra la delgada pared ventricular derecha anterior, y la mas alta posición de la válvula pulmonar en relación de la aortica la que se ve sutilmente a la sombra del septum ventricular membranoso.

This illustrates a cut section view through the short axis of the left ventricular cavity in a plane through the body of the papillary muscles. Note the greater trabecular pattern of the right ventricle and the thinner right ventricular free wall myocardium (3 mms.) compared to the left ventricular myocardium (up to 11 mm thick in normal septum or lateral walls). The simplified schematic shows the crescentic shape of the right ventricle in this view compared to the circular left ventricular cavity and the path of the coronary arteries anteriorly in the interventricular groove (left anterior descending artery) and posterior interventricular groove (where lies the posterior descending artery).

This illustrates a cut section view through the short axis of the left ventricular cavity in a plane through the body of the papillary muscles. Note the greater trabecular pattern of the right ventricle and the thinner right ventricular free wall myocardium (3 mms.) compared to the left ventricular myocardium (up to 11 mm thick in normal septum or lateral walls).

• Ionizing versus non-ionizing radiationMedical imaging techniques can be broadly grouped into those which use ionizing radiation versus those that do not. The ionizing radiation group consists of those images created by the use of x-rays or gamma rays. Both x-rays and gamma rays are high energy, short wavelength (less than an angstrom) electromagnetic radiation that is capable of penetrating and passing through most tissues. Gamma rays arise from the nuclear decays of radioactive tracers introduced into the body, while x-rays arise from an x-ray tube where high speed electrons bombard a small spot on a tungsten anode target. Ionizing radiation, as it passes through the body is differentially absorbed by tissues of greater thickness or higher atomic mass (e.g. calcium has a higher atomic weight than hydrogen which is a major component of tissue water). Different portions of the body tissues attenuate differing amounts of the incident radiation. One mechanism of that attenuation is ionization of the tissue atoms which make them chemically reactive and potentially capable of cell damage. Ionizing radiation is therefore not used casually but only when medically indicated. X-rays are nonetheless highly useful diagnostically and are a backbone of medical imaging by both computed tomography and film.

• It is the locally differential pattern of x-ray radiation escaping the body that creates the "shadowgram" on an x-ray film. That escaping radiation strikes a fluorescent screen inside a film cassette, and fluorescent light from those screens in turn expose the film emulsion (n.b.: if x-ray film was actually only sensitive to exposure by x-rays, we wouldn't need darkrooms for handling those films).

• Non-ionizing radiation techniques mainly use either acoustic pulses (ultrasound) for echo-ranging imaging (somewhat like radar) or radio-waves combined with high-field magnets, in the case of magnetic resonance imaging.

• Medical images can be understood to belong to one of two main groups: tomographic or projection techniques. Projection techniques, such as x-ray films are "shadowgram-like" transilluminations of the body. Because of the nature of trans-illumination, various tissues are imaged as overlapping each other and often need multiple views (thus the PA and Lateral) for visual under-standing

• Ionizing radiation is a portion of the high energy electromagnetic radiation spectrum which can penetrate and be transmitted through tissues (unlike light, which is mostly absorbed at the skin surface, failing to adequately penetrate thick body parts such as the skull). One of the chief modes by which Ionizing radiation interacts with tissues is by knocking out atomic shell electrons losing energy in the process. The resulting differential absorption can be detected by a film cassette at the opposite side of the body from the radiation entrance

Tomography is a "slicing" of the body into various sections and in various view planes. The tomographic sections when viewed in sequence or integrated by a computer allow the display and understanding of 3-dimensional anatomy.

X-ray imaging is a method of illuminating the body with a penetrating high energy ionizing radiation. The differential absorption of this radiation by the various tissues of the body creates on film an inverse shadow of the body. Less dense, lower atomic weight structures, such as the lung, allow transmission of more radiation flux producing greater fluorescence on an absorbing screen which exposes an adjacent film more densely, making those areas black. Higher atomic weight structures (bone) absorb and block the radiation, thus do not result in the exposure of the silver halide grains in the film emulsion, and so bony structures such as the ribs appear white (transparent).

As Ionizing radiation passes through the body, it is differentially absorbed by tissues of greater thickness or high atomic mass (e.g. calcium). Different portions of the body tissues attenuate differing amounts of the incident radiation. The radiographic density is mainly the result of x-ray radiation scattering or loss of the incident radiant energy by ionization.

The range of densities that an X ray can display is the key to its usefulness as a diagnostic imaging tool. The X ray tube emits a large burst of X rays, generated by bombarding a tungsten target in a vacuum tube with high energy electrons (40-150 keV). Many of these X rays when directed toward a person will pass through the body and strike a fluorescent screen in a cassette, exposing a light-sensitive film adjacent to it.

Coronary angiography requires multiple separate views to completely examine coronary anatomy and resolve potential vessel overlap. Several separate sequential injections of left (LCA) and right coronary arteries (RCA) are shown. Here, "postero - anterior" (PA), "left anterior oblique" (LAO), and "right anterior oblique" (RAO) views of a normal coronary tree are provided. The "Left Ventriculogram" is an RAO view with direct contrast injection into the cavity to examine myocardial function.

Computed tomography is a digitally based x-ray technique. Like x-ray, the resulting images arise from differential x-ray absorption of tissue, a feature that rests primarily on atomic weight (and thus the electron density) of the various tissues. The technique uses a narrowly collimated x-ray beam to irradiate a slice of the body. The amount of radiation transmitted along each projection line is collected by photo-multiplier tubes and counted digitally. By rapidly acquiring views from numerous different projections, achieved by quickly rotating the tube and detectors around the body, the transmissivity of the body from different angles can be established externally.

Nuclear medicine images arise from injected radioactive tracers which subsequently emit radiation from within body organs. The radioactive compounds tend to be designed to accumulate selectively in specific tissues. For example, lung scans used in the diagnosis of pulmonary embolus arise from technetium-labeled macroaggregated albumin, which when injected into a vein, spreads and is deposited relatively evenly throughout normally perfused lung micro-vasculature. Creates image solely of the lungs

Planar nuclear projection images of myocardial perfusion using technetium-99m sestamibi as the perfusion agent demonstrates the anterior, left anterior oblique, and left lateral nuclear images compared to comparable anatomic illustrations. The majority of the nuclear myocardial image is provided by the full thickness of the left ventricular myocardium. The right ventricular free wall and atrial walls are much thinner structures but define the outline of their cavities.

The SPECT camera is a large scintillation crystal connected to multiple photo-multiplier tubes which detect radiation emanating from the body. The technology of SPECTarises from positioning the camera head at multiple angles around the body accumulating as many as 180° of views at specific angular intervals. A certain number of counts are obtained from each view. In some cases multi-headed cameras are used to increase the speed of acquisition. Software integrates all individual projection views into a composite data set which can be re-displayed as CT slices.

Nuclear myocardial perfusion tomograms using the radioactive compound technetium-99m sestamibi are shown compared to illustrations of the heart from similar views. Note that most of the myocardial wall activity arises from the left ventricular myocardium since it is considerably thicker (11 mm) than the right ventricular free wall (3 mm). The short axis tomogram shows the left ventricular myocardium as a donut shape while the vertical long axis and horizontal long axis tomograms display the myocardial wall as U-shaped structures.

Technetium radioactive labeling of red blood cells which are stable enough to permit equilibrium imaging of the major vessels and cardiac blood pool primarily of the cardiac chambers, when gated with the electrocardium into 15 to 20 time segments between systole and diastole, create a radionuclide angiogram from which calculation of ventricular ejection fraction, regional wall motion, and general chamber sizes can be assessed. These blood pool images are known variously as MUGA

(multi-gated acquisition) or more conventionally, ERNA (equilibrium radionuclide angiogram). This technique is considered one of the most accurate for estimating left ventricular systolic function.

The medical imaging portion of the sound spectrum begins in the megahertz range, well above the maximum audible frequency of 15 kilohertz. In the 2 to 7 megahertz range used by ultrasound imaging, the wavelength of the acoustic pulses are less than a millimeter and are therefore capable of resolving fine anatomic structures.

Transesophageal echocardiography is performed by using a miniature high-frequency (5 MHz) ultrasound transducer mounted on the tip of a directable gastroscope about 12mm diameter. Using topical anesthesia and a little sedative, most individuals can swallow the probe without difficulty. Because the transducer lies in the lower esophagus in close direct fluid contact with the posterior of the heart, the images are superb since there is no interference by lung tissue.

Magnetic resonance imaging depends on immersing the body in a steady, strong magnetic field, commonly up to 1.5 Tesla (i.e. 15,000 Gauss for reference, the earth's magnetic field is about 0.5 Gauss). Some modern "whole-body" (i.e. apertures wide enough to accept a person's thorax) machines now operate at 4 or more Tesla. Hydrogen atoms, pervasive in the water which makes up about 70% of the body's mass, have a dipole property by virtue of their characteristic spins.

The cardiac silhouette is the most prominent central feature of the chest x-ray and it produces a familiar gourd shape with the apex of the left ventricle located just behind the left chest nipple. The inferior left ventricle wall lies on the left diaphragm and the superior base of the heart shows the aortic knob lying just to the left of the spine. A linear line descending from it, lying to the left of the spine, represents the lateral edge of the descending aorta.

Findings of apparent cardiomegaly and pulmonary vascular congestion must be viewed in the light of possibility of a poor inspiratory effort. This is determined by noting the level of the diaphragm relative to the posterior ribs. With the high diaphragms characteristic of a forced expiration, it is natural that pulmonary vascular markings will be more crowded and may give the appearance of congestion but the lungs will lack Kerley B lines or bronchial cuffing.

When the horizontal diameter of the lower cardiac silhouette well exceeds one half of the internal diameter of the thorax, cardiomegaly is diagnosed. It is wise to assess the depth of the inspiration by noting whether the diaphragm lies lower than the ninth or tenth rib posteriorly as it should if there is an adequate inspiratory effort.

The PA (postero-anterior) radiograph at first appears to provide reassuring evidence that the tip of the pacemaker lies in the right ventricular apex. The slightly thickened metal tip of the pacemaker is seen just lateral to the border of the descending aorta. The value of a lateral radiograph is best exemplified when the course of the pacemaker wire is followed inferior and is found to lie well posterior to the expected position of the right ventricular cavity.

Pneumonic infiltration of the lingula increases the density lung immediately adjacent to the left cardiac border. The presence of two areas of similar soft tissue density results in a loss of the conventional sharp boundary to the heart. The radiographic appearance of a sharp boundary at the left cardiac border would still be present if the lung density were located posterior to the heart, say in the left lower lobe.

This case exemplifies an acute occlusion of the right coronary artery - click the "Pre angiogram" button. After thrombolysis of the clot, the proximal obstruction was dilated by balloon angioplasty - click on "Post angiogram". Though flow was restored to the coronary, a discrete moderate stenosis is still present in mid-coronary. It was subsequently successfully dilated by balloon angioplasty.

Sequential right coronary artery (RCA) angiograms ("1", "2" and "3") showing diagnosis and treatment of a patient whose acute coronary syndrome was caused by a clot at the site of a high - grade stenosis in the proximal right coronary. Angio "1" shows the clot as a void in the contrast. Angio "2" shows balloon angioplasty of the stenosis. Angio "3" shows placement of an intra-coronary stent with complete restoration of lumen patency and flow.

Findings to be observed in normal lungs include vascular markings composed primarily of the vertically oriented pulmonary artery segments and the horizontally directed pulmonary veins toward the left atrium. The gradual decrease in size of the vessels as they branch peripherally should be noted. Close to the hilar structures the smaller bronchials seen as thin walled darker circles. Edematous thickening of these bronchial walls are one of the earliest findings of congestive failure.

Erect posterior-anterior chest radiograph PA images commonly show significant differences from AP (antero-posterior) films particularly in relation to the proportional size of the mediastinum. The PA position places the heart and upper mediastinum closer to the film with greater distance to the exposing Xray tube (generally 72 inches) making the Xrays more parallel as they enter the body and avoiding disproportional enlargement of anterior vs. posterior structures. Effects of gravity have visible effects on the pulmonary

vasculature since the pulmonary artery pressures are low (~25 mm Hg. in systole and ~12 mm Hg. in diastole) and the vessel walls are soft and compliant.

On a supine frontal Xray of the chest there are significant differences in the appearance of normal pulmonary vasculature and mediastinum. The closer distance of the exposing Xray tube (often only 40 inches from the film cassette) makes the Xrays more diverging and disproportionally enlarges the appearance of structures that are farther from the film (the anterior body structures such as the ascending aorta). Although the pulmonary artery pressures are low (~25 mm Hg. in systole and ~12 mm Hg. in diastole) and the vessel walls are soft and compliant, the upper lung arterial vessels and the lower lobe vessels are now at the same level as the cardiac chambers.

Angiograms are created by injecting an iodine solution into the bloodstream. Iodine was chosen because it is a high atomic weight material which differentially attenuates x-rays but is nonetheless well tolerated by the body (it is mostly excreted in the urine). When a catheter is threaded into the pulmonary artery and an iodinated solution ejected from its tip, the pulmonary arteries are quickly first opacified showing a relatively vertically oriented branching pattern, originating at the hilum. Normal arteries progressively reduce in diameter after multiple branches.

Observation of discrete abnormal densities within the lung fields are described as nodules. When the density is similar to that of the ribs, they can be presumed to be calcified. Confirmation of the presence of calcium can be obtained quantitatively from computed tomography which may, with its greater quantitative soft tissue sensitivity, reveal other inapparent parenchymal densities.

This 28 year old male with a history of non-seminomatous testicular ca was being followed by routine chest X-rays. The x-ray in this ex shows very little evidence of abnormality but the computed tomography scan done simultaneously show multiple nodules and demonstrate the increased sensitivity of that cross-sectional technique for small tissue density nodules in the lungs. Some of the greater visibility of these nodules on CT are due to that technique's greater range of intensity differentiation of soft-tissue densities, but some of the result is also due to the cross-sectional imaging plane it produces which avoids confusing overlapping structures.

This PA radiograph demonstrates a large wedge-shaped density in the right middle lobe. Also note a coin lesion at the right costophrenic angle. The right middle lobe large density on biopsy was determined to be a metastasis from cervical carcinoma. Note that the sharp upper boundary of the right middle lobe triangular mass is the right middle lobe fissure. In addition, there is enlargement of the right hilar structures due to metastases within the hilar lymph nodes.

The Westermark is an eponym indicating the abrupt cutoff of pulmonary vascularity distal to a large central pulmonary embolus. The presumed mechanism behind the image arises from the nearly complete obstruction of bloodflow to the pulmonary artery distal to the embolic clot. Presumably the lack of flow to these more distal vessels results in their radiographic transparency and an appearance of an abrupt truncation as is shown in this exemplary case. </TD< TR>

Enlargement of one or both hila must distinguish between lymphadenopathy vs. vascular enlargement. With few exceptions, vascular enlargement produces a branching pattern at its borders and generally is bilateral, whereas lymphadenopathy is more spherical or elipsoidal. Bilateral lymphadenopathy occurs with a variety of immunological disorders as well as sarcoid, but unilateral adenopathy results from either unilateral pulmonary infection or, more ominously, malignant tumors.

Hilar adenopathy (due to sarcoid). Hilar adenopathy must be distinguished from enlargement of the hilar vasculature (such as by pulmonary hypertension). Hilar lymph nodes appear more nodular and "lumpy" than hilar vessels which usually retain their branching pattern when enlarged. Bilateral hilar adenopathy implies diseases that are generalized and include sarcoid and lymphoma.

Normal blood flow in the pulmonary capillaries are subject to a variety of influences. The mean hydrostatic intravascular pressure in the pulmonary artery is approximately 14 mmHg. The transmural vascular pressure is the intravascular pressure minus the intrapleural pressure in the larger vessels. Pressure in the pulmonary circulation is significantly influenced by gravity.

Patients with congestive heart failure commonly will have increased density of the interstitial markings of the lung fields. Very specific patterns have been described as Kerley "B" or "A" lines. The "B" lines are most commonly cited and when identified imply the presence of interstitial edema in the pulmonary septa. The Kerley "B" lines are short, horizontal lines perpendicular to the lateral aspects of the lung.

Se pueden diferenciar las ramas ascendente y descendente de la Aorta . Pacientes ancianos con historia de HTA con frecuencia tienen una configuracion estasica de la Aorta, con un patron tortuoso de la aorta descendente. Dilatacion de la aorta ascendente puede encontrarse en el sindrome de Marfan, asi como insuficiencia aortica,dilatacion post-estenotica, y aneurismas aorticos.

The PA (postero-anterior) radiograph is only very subtly abnormal in the mediastinum. Looking through the central mediastinal density there is a suggestion of air and possibly an air fluid level in the region medial to the descending aorta. (Incidentally noted is a central venous line entering under the right clavicle and terminating in the superior vena cava). The CT scan is definitive and shows clearly the air-filled dilated esophagus posterior to the trachea. Radiodense fluid such as barium defines the esophageal space and its dilatation.

Forty-eight year-old male with longstanding moderately severe aortic insufficiency due to past endocarditis. When the volume of the regurgitant fraction is significant, there is enlargement of the left ventricle and, therefore, a globular widening of the cardiac silhouette.

These images arise from a forty-two year-old male with progressive dyspnea on exercise over a two-year period. The patient had a strong family history of cardiomyopathy with two of three siblings who died in their 30's of idiopathic cardiomyopathic disorders. The cardiomegaly visible on this frontal chest film was not present on a film taken two years before but became progressive as shown by the film of just two months previous.

Chest radiographs of patients with hypertension generally are nonspecific. In this 44 y.o. male with malignant hypertension the only suggestive finding is the prominence of the ascending aorta appearing as a bulge in the upper mediastinum on the patient's right. This is caused by an ectatic unwinding of the ascending aorta in response to the high arterial pressures. Note that the cardiac silhouette does not appear to be significantly enlarged since the major abnormality is increase in thickness in the myocardial wall rather than dilation of the ventricle.

Mitral stenosis generally creates a characteristic configuration dominated by enlargement of the left atrium. Note that the left mainstem bronchus is elevated and lies more horizontal than normal. The tissue boundary angulated away from the spinal column below the left mainstem bronchus represents the lateral boundary of the enlarged left atrium.

This radiograph was obtained from a sixty-two year-old male with sudden onset of substernal chest pain radiating to the left arm and jaw. The chest x-ray often may show a normal cardiac size and normal vasculature if the area of cardiac ischemia is limited. Large areas of myocardial ischemia or accumulations of ischemic events involving many myocardial segments or multiple coronary arteries can lead to congestive failure and a pulmonary edema pattern.

Radiography of patients with pericardial effusion will show apparent cardiomegaly when the effusion is large enough. Since the pericardial fluid is roughly the same radiographic density as blood in myocardium, it may be impossible to confirm whether the cardiomegaly is due to enlargement of the ventricular chambers or whether the fluid is located in the pericardial space

Ventricular septal defect.a) The heart is moderately enlarged and there is shunt vascularity. The distinct vessel margins indicate no interstitial edema. Cardiac catheterization showed a large shunt (2.5: 1) at the ventricular level.b) There is posterior displacement of the esophagus (arrows) by left atrial enlargement.