During reception (right) advair diskus 250 mcg line asthma symptoms kid, the returning echo signals received by each transducer element must be time-shifted or phased before being summated and processed order advair diskus with american express asthma treatment in khewra. The wavelength of the ultrasound used, which is inversely related to ultrasound frequency, is the principal determinant of axial imaging resolution, which equals approximately half the wavelength. Imaging resolution is also dependent on the depth of the structure being interrogated. Therefore, the choice of imaging frequency involves a trade-off between image resolution and target tissue depth: higher frequencies are capable of increased resolution, but at the expense of reduced tissue penetration. The speed of ultrasound through body tissues averages 1540 meters per second (m/sec), essentially the speed of sound through water, but varies minutely as ultrasound waves traverse various body constituents. The most intense reflections occur when ultrasound strikes these interfaces perpendicularly and when the tissues differ greatly in density. When ultrasound encounters inhomogeneous tissue regions, such as myocardium, liver, or other tissues, multidirectional reflection, or backscatter, occurs and results in speckled-appearing images. The combination of specular reflections and backscatter, together with the unique interactions between ultrasound and tissue such as refraction, interference, and attenuation, contributes to the characteristic gray-scale appearance of ultrasound images. Ultrasound penetrates poorly through air and bone, which is one of the greatest challenges to echocardiography because the heart is surrounded by the lungs and the rib cage. Several advances in the past decade have improved the quality of ultrasonic imaging. The higher number of elements in phased-array transducers has increased the number of scan lines and thus lateral resolution. Tissue harmonic imaging is now the norm, in which the receiver “listens” for returning second-harmonic ultrasound signals that are twice the fundamental frequency of the emitted ultrasound. By doing so, it effectively filters out the weaker noisy signals from cardiac chambers and has substantially improved the definition of tissue interfaces, in particular that of the endocardial borders (Fig. Ultrasound causes tissues to vibrate at a the fundamental frequency (left) but also multiples (harmonics) of that frequency. By listening for the higher (second-order) frequency returning echoes, signal-to-noise ratio and tissue definition are dramatically improved (right). These techniques are based on the Doppler principle, which states that the frequency of a waveform bounced back from a moving object will be altered (shifted) from the emitting frequency, depending on whether the object is moving toward or away from the observer. Ultrasound that is reflected from red blood cells moving toward the emitter will return at higher frequency, whereas blood flow away from the transducer will cause a lower- frequency waveform to return (Fig. This difference between the frequency emitted and that received is termed the Doppler frequency shift and is dependent on the speed of ultrasound through the medium and the velocity of blood flow. The basic equation for Doppler shift (f ) is f = f V/c, where f isd d t t the transmitted ultrasound frequency, V is the velocity of blood flow, and c is the speed of ultrasound in the tissue. For cardiac ultrasound, multiplication by a factor of 2 occurs because the Doppler shift occurs twice (when the wave goes to and from the moving object). Notably, the velocity information obtained is most accurate when the ultrasound beam is aligned parallel to the direction of blood flow (i. When the angle of insonation (θ) cannot be physically corrected, the correction factor cosθ may be applied. Echoes reflected from blood cells moving toward the transducer will return at a higher frequency than the transmitted ultrasound pulse (upper panels). Doppler echocardiography instruments harness this shift in frequency to derive blood flow velocities. The direction of flow is displayed graphically as a time-velocity spectrum above or below the baseline (in spectral Doppler) or as color- coded velocities with color flow Doppler. By gating, or defining a specific time window during which the machine “listens” for reflected signal, this technique can be used to ascertain the velocity of blood flow at a prespecified depth within the heart. Thus, when an operator places the cursor (sample volume) on the 2D ultrasound image at a particular location, the equipment will assess the velocity at that point. Because it takes time for the pulses to reflect and return to the transducer, they cannot be transmitted too frequently, or the equipment will fail to discern whether a given pulse has returned, and the velocity information obtained at that depth will be ambiguous. In Doppler ultrasound, the sampling rate must be high enough to sample the Doppler shift, which is the difference between the ultrasound frequency emitted by the transducer and the ultrasound frequency returning to the transducer. As shown by the Doppler equation, , this difference, the Doppler frequency shift, is directly related to the velocity of the flow being assessed. When velocities being assessed exceed the Nyquist limit, the system cannot accurately determine these velocities, and aliasing occurs (lower panels). These higher aliased velocities will appear on the opposite side of the baseline on the spectral Doppler display or will result in mosaic patterns in color flow Doppler imaging. Because the ultrasound tone is continuous rather than pulsed, depth of the target cannot be determined from the signal received. By convention, flow moving away from the transducer is encoded in blue, and flow toward the transducer is encoded in red. Turbulent flow, in which a wide range of velocities exist, appears as a multicolored mosaic pattern (usually green and yellow). In some systems the variance in the velocities relative to the mean is color- coded in superimposed shades of green. Color flow Doppler allows direct real-time visualization of the movement of blood in the heart and is particularly useful for identifying blood flow acceleration and turbulence. Therefore, this technology is useful for delineating both regurgitant lesions, in which blood moves rapidly and opposite to the expected direction of flow, and discrete stenoses in which there is flow acceleration. By convention, blood flow moving toward the transducer is color- coded red and flow away from the transducer is shown in blue. The color velocity scale (upper left vertical bar) represents increasing velocities in either direction. Blood flow through the normal heart and great vessels is predominantly laminar, meaning that the direction and velocity of flow are streamlined and uniform, even across valves. In contrast, valvular or vessel stenoses or obstructive lesions often cause turbulent flow, in which blood moves at different velocities and in multiple directions. Left, During the cardiac cycle, most intracardiac and large arterial flows exhibit a laminar flow profile termed “plug flow” proximally that progresses distally to a more parabolic profile because of drag force and blood viscosity. Right, The narrowest range or spectrum of flow velocities is seen during the initial phases of systole or when valves open (plug flow). As the vessel becomes stenotic, the turbulence causes progressively wider variation in flow velocities and directions. On spectral Doppler this manifests as a splay in velocities both above and below the baseline. If the vector of flow is not directly in line with the ultrasound beam, the velocities calculated by the Doppler shift will be underestimated. This problem can be corrected by applying an angle adjustment that is computed in at the machine level. However, the further the angle of flow deviates from the angle of the beam, the greater the likelihood for error in the calculation.
In some very acute deaths from heroin overdose buy generic advair diskus 500 mcg asthma allergy, the urine is negative but the blood positive buy generic advair diskus online asthma definition 404. Death is not directly related to blood concentration, due to the high tolerance individuals can build up. Most deaths are accidents that result from an individual’s taking too much medication over too short a time. Propoxyphene has a narrow margin of safety, as not only does it cause respi- ratory depression as opiates usually do, but also acts as a local anesthetic with resultant cardiac toxicity. In chronic users of propoxyphene, norpropoxyphene levels are always higher than propoxyphene, often by a factor of 2 or 3 times. In individuals who die of an acute overdose, the concentration of propoxyphene is higher than nor- propoxyphene, with the propoxypnene concentration 1 mg/L and higher. In some propxyphene related deaths, the individual presents with a lethal con- centration of propoxyphene accompanied by a higher level of norpro- poxyphene, though not 2–3 times higher. This is the picture of either an individual who died of an acute overdose but survived long enough to metab- olize a signiﬁcant amount of the propoxyphene ingested to norpropoxyphene, or of a chronic user of propoxyphene who took an acute overdose. It can be taken intravenously, orally, smoked, snorted or by way of skin patches, with the intravenous route the most common. Cocaine Cocaine has replaced heroin in some areas as the most commonly abused of the hard drugs. Introduced to medicine and the public in the late 19th century, it soon Interpretive Toxicology: Drug Abuse and Drug Deaths 525 became the “third scourge of mankind. When smoked as crack, it is immediately absorbed by the lungs and reaches the brain within seconds. It takes slightly longer for its action to affect the brain when injected intravenously. Cocaine is a relatively short-acting drug such that to maintain a high, one has to take it every 15 min to an hour. Since it is a potent vasoconstrictor, snorting the drug can occasionally cause ulceration and perforation of the nasal septum with long-term use. Cocaine has also been linked to myocardial infarctions, cerebral hemorrhages and dissecting aortic aneurysms. It is more common, however, following intravenous injection and smoking of crack than snorting. Cocaine acts on the heart to increase heart rate and force of contraction by blocking the reuptake of norepinephrine at the neuroeffector junctions. It also causes increased release of catecholamines, which also stimulate the heart. Cocaine works on the alpha receptors in the coronary arteries to cause contraction, reducing myocardial perfusion. Thus, as the myocardium needs increasing amounts of oxygen, due to the stimulation of the beta-1 receptors, the amount of blood perfusing the myocardium is reduced by vasoconstric- tion of the coronary arteries. Cocaine is rapidly hydrolyzed to benzoylecgonine and other derivatives by blood cholinesterases. Continued breakdown of cocaine will continue in the test tube unless it is inhibited by the addition of ﬂuoride. If the urine screen is negative for cocaine metabolites, the blood will also be negative. Habitual, prolonged, heavy use of cocaine can make an individual aggres- sive, violent, and paranoid. A chemical paranoid psychosis may be induced by the prolonged and heavy use of cocaine. It blocks re-uptake of norepinephrine and causes an increase in catecholamine release. The euphoric effect is similar to cocaine but may last as long as ten times that of cocaine. In overdoses, meth- amphetamine causes restlessness, confusion, hallucinations, coma, convul- sions, and cardiac arrhythmias. With chronic abuse, just like cocaine, it can produce a chemical paranoid psychosis. Methamphetamine may be transformed into amphetamine hydrochloride (“ice”) which is smoked like crack cocaine. Methamphetamine has a half-life of 11–12 hours, with 45% excreted in urine unchanged over a number of days. There is substantial overlap in blood metham- phetamine concentrations in individuals dying of a methamphetamine over- dose and those in whom it is an incidental ﬁnding. Just like cocaine, individuals may die suddenly during or immediately after a manic episode. Miscellaneous Narcotics Other drugs that should be mentioned brieﬂy are morphine, meperidine, codeine, and methadone. Deaths from morphine and meperidine are uncommon and usually involve a hospital setting where an inadvertent overdose is administered. Usually an individual dying from an overdose of codeine is also intoxicated from the use of alcohol. In individuals with high concentrations of codeine in the blood very low levels of morphine will be detected; that is, the codeine is metab- olized to a very slight degree to morphine (J. If an individual lives for a few days, analysis of the bile may reveal relatively high levels of morphine and no or trace amounts of codeine. This is because the morphine is bound to glucuronide and stored in the bile, while codeine is unbound and excreted faster. Thus, detection of morphine in the bile does not necessarily indicate that an individual took either heroin or mor- phine, since it can also be formed from codeine. Methadone is a long-acting synthetic narcotic with a half-life of approx- imately 15 h. It is not preferred by addicts, but they will use it if it is the only drug available. Many times, the addicts will sell the methadone on the street for money to buy heroin. Occasionally, young children access a parent’s meth- adone and die of an overdose. Toluene, in contrast to the chlorinated hydrocarbons, rarely, if ever causes sudden death (J. Lead is found in storage batteries and was used as a constituent of paint and gasoline for many years. The symptoms of chronic lead poisoning are abdominal cramps, vomiting, constipation, lethargy, anemia, weight loss, muscle paralysis, nephropathy, and convulsions.
Data undersampling from parallel imaging leads to a reduction of signal-to-noise ratio discount advair diskus on line 911biomed asthma attack, but three-dimensional pulse sequence and increased field strength at 3 T compensate for the signal/noise loss and are already in selected clinical use buy 500mcg advair diskus mastercard asthma graph, replacing some two-dimensional methods (Fig. Automated motion correction reduces blurring from cardiac motions and has become standard in many pulse sequences because it not only improves qualitative visual displays, but also facilitates quantitative measurements. Semiautomated cardiac localization and scanning algorithms have been developed to reduce the time required in training physicians and technologists. New contrast agents hold promise in improving the assessment of myocardial or vascular physiology. Compressed sensing data acquisition and reconstruction were used to shorten the scan time. Compressed sensing data acquisition and reconstruction were used to shorten the scan time. B, Stenoses in the proximal coronary arteries (arrow) are confirmed on invasive angiography. Extracellular volume imaging by magnetic resonance imaging provides insights into overt and sub-clinical myocardial pathology. Stress Perfusion Cardiac Magnetic Resonance Imaging Effectively Risk Stratifies Diabetic Patients With Suspected Myocardial Ischemia. Prevalence and prognosis of unrecognized myocardial infarction determined by cardiac magnetic resonance in older adults. Systematic review of patients presenting with suspected myocardial infarction and nonobstructive coronary arteries. Diagnostic accuracy of myocardial magnetic resonance perfusion to diagnose ischemic stenosis with fractional flow reserve as reference: systematic review and meta-analysis. Multicenter evaluation of dynamic three-dimensional magnetic resonance myocardial perfusion imaging for the detection of coronary artery disease defined by fractional flow reserve. Prognostic value of quantitative contrast-enhanced cardiovascular magnetic resonance for the evaluation of sudden death risk in patients with hypertrophic cardiomyopathy. T1 Mapping in Discrimination of Hypertrophic Phenotypes: Hypertensive Heart Disease and Hypertrophic Cardiomyopathy: Findings From the International T1 Multicenter Cardiovascular Magnetic Resonance Study. Prognosis of Myocardial Damage in Sarcoidosis Patients With Preserved Left Ventricular Ejection Fraction: Risk Stratification Using Cardiovascular Magnetic Resonance. Effects of myocardial fibrosis and ventricular dyssynchrony on response to therapy in new-presentation idiopathic dilated cardiomyopathy: insights from cardiovascular magnetic resonance and echocardiography. Adult left ventricular noncompaction: reappraisal of current diagnostic imaging modalities. Left atrial passive emptying function determined by cardiac magnetic resonance predicts atrial fibrillation recurrence after pulmonary vein isolation. Myocardial extracellular volume expansion and the risk of recurrent atrial fibrillation after pulmonary vein isolation. Impact of mechanical activation, scar, and electrical timing on cardiac resynchronization therapy response and clinical outcomes. Assessment of myocardial scarring improves risk stratification in patients evaluated for cardiac defibrillator implantation. Infarct tissue heterogeneity by contrast-enhanced magnetic resonance imaging is a novel predictor of mortality in patients with chronic coronary artery disease and left ventricular dysfunction. Systemic right ventricular fibrosis detected by cardiovascular magnetic resonance is associated with clinical outcome, mainly new-onset atrial arrhythmia, in patients after atrial redirection surgery for transposition of the great arteries. Prospective comparison of valve regurgitation quantitation by cardiac magnetic resonance imaging and transthoracic echocardiography. Aortic regurgitation quantification using cardiovascular magnetic resonance: association with clinical outcome. Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy. Quantitative assessment of paravalvular regurgitation following transcatheter aortic valve replacement. Relationship Between Left Ventricular Structural and Metabolic Remodeling in Type 2 Diabetes. These differences result in higher tissue densities generating higher attenuation coefficients, whereas higher photon energies will result in lower attenuation coefficients. In short, the combination of organ density and photon energy determines the number of photons that pass through a patient, which can then be quantified by a series of detector arrays located 180 degrees across from the x-ray tube. After being struck by photons, a scintillation reaction occurs at the level of the detector that encourages light formation from x-rays. The resultant scintillation pattern becomes digitized to a string of binary numbers that can be reconstructed to two-dimensional (2D) and three-dimensional (3D) images and that may be visualized for medical use on an imaging computer workstation. At a minimum, a 180-degree rotation of the gantry with x-ray emission is required to generate a 3D image, a process known as half-scan integral reconstruction. Higher tube potential (kVp) allows for greater tissue penetration, whereas higher photon count (mA) increases the total number of photons that ultimately reach the detector elements. Photons are attenuated by organs in a differential pattern related to their material densities. Photons not attenuated reach multiple detectors (C) at which a scintillation reaction occurs. At each detector, a photon flux is generated that is a product of the number of photons emitted from the x-ray tube (milliamperes, mA), the photon energy (kilovolts, kV), and the organ tissue properties. When released, 64–detector row scanners across vendor platforms were generally similar, with in-plane (x and y directions) resolution of 0. This corresponds to a spatial resolution approximately two to four times lower and a temporal resolution approximately four times worse than cineangiography (see Chapter 20). Spatial resolution, which depends on both the size of the detector elements and the material properties of the detector, has been improved by addressing the latter. This is achieved by two basic advantages: improvements in the primary speed of the scintillation reaction and reduction of the “afterglow,” or the recovery time of the scintillation response, which reduces light artifacts. Improved gantry rotational speeds have resulted in half-scan temporal resolution to 100 to 140 milliseconds. By this method, gantry rotation needs to occur only through one-fourth (rather than one-half) the gantry revolution to generate a 3D image, and this method has achieved temporal resolution rates as low as 67 milliseconds. Software-based postprocessing techniques for selective reduction of coronary motion, also known as intracycle motion correction algorithms, are used to correct coronary motion artifacts by exploiting the trajectory data across time and “backtracking” to create motion-free images. Improvements in volume coverage by imaging greater lengths in the z axis, or craniocaudal direction, have been achieved by increases in the number of detector rows. This method acquires simultaneous, or near-simultaneous, imaging at a 2 low and high kVp. The use of widely disparate energies allows for harnessing two polychromatic spectra (e. From each of these methods, tissues can be reconstructed into a single monochromatic energy (in kiloelectron volts, keV), which may be used to improve current coronary and cardiac imaging interpretation.
S. Bradley. William Carey International University.