HW 12 PHYSICS study Materials

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School

Medical Career Institute, Richmond *

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130

Subject

Statistics

Date

Jan 9, 2024

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pdf

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Uploaded by ColonelBadger3940

What does the acronym PACS stand for? What are the advantages of using PACS in the clinical ultrasound laborator ● Picture Archiving and Communication System ● ability to view the same set of images in multiple locations at one time What is magneto-optical storage? What are the advantages of magneto-optical storage? ● Devices that use markers which can read/write to with an optical laser. ● cheap, lightweight, portable What is an ultrasonic contrast agent? ● uses an intravenous agent that contains microbubbles. What is the purpose of ultrasonic contrast agents? ● provide enhanced echoes from the blood pool and have enabled diagnostic ultrasound to assess and quantify microvascular blood flow An ultrasonic contrast agent must meet certain criteria for use in the clinical setting. Describe five of those requirements. 1. Must be safe. 2. Must be metabolically inert 3. Hyperechoic-strong reflector 4. Contrast effect of the agent, while in the body, should persist for an adequate period of time microbubbles should be small enough to pass through capillaries Assume that while performing an ultrasound exam with a 3-MHz transducer, the sonographer activates the harmonic mode. ● 3MHz During the time that the harmonic mode is operational, what is the fundamental frequency? ● 3MHz While using the harmonic mode, what frequency is the ultrasound system using to produce the image? ● 6MHz What is the primary purpose of the harmonic mode? ● improve the quality of the image when the fundamental image is suboptimal or inferior. Harmonics

frequency undergoes less beam distortion which equals better image quality Several statistical measurements are used to assess the accuracy of diagnostic tests, including ultrasound. These statistical measurements are carried out using an adequate sample of patients who undergo both the test being assessed for its accuracy and a test already established for its accuracy (called the gold standard). One important parameter used in these measurements is whether the outcome or result, of the diagnostic test being evaluated is classified as positive or negative. o What does it mean when a diagnostic test has a positive result? o What does it mean when a diagnostic test has a negative result? ● Positive predictive value is the probability that a patient with a positive (abnormal) test result actually has the disease. ● Negative predictive value is the probability that a person with a negative (normal) test result is truly free of disease. A crucial step in establishing the accuracy of a diagnostic test is to determine whether the results of the test (i.e., positive or negative) are correct or incorrect. Statisticians refer to a correct result as "true" and an incorrect result as "false." o How do statisticians determine whether the results of the diagnostic test being evaluated are correct (true) or incorrect (false)? o What is a true positive? o What is a false positive? o What is a true negative? o What is a false negative? ● A false negative means that a subject with the disease is misclassified as not having the disease on the basis of the screening test ● A false positive means that a subject without the disease is misclassified as having the disease on the basis of the screening test ● True positive is the number of cases correctly identified as patient ● False positive i the number of cases incorrectly identified as patient. A patient, Adam, is being evaluated for possible coronary artery disease because he has been experiencing episodes of mild chest pain on exertion. He undergoes a treadmill exercise test, which is abruptly stopped when his electrocardiogram develops changes consistent with the resulting disease. He ● true negative

then undergoes cardiac catheterization, considered to be the gold standard for the diagnosis of coronary disease. This test shows that his coronary arteries are completely normal. Which of the following terms correctly describes Adam's treadmill test result? o a) true positive b) false-negative c) false-positive d) true negative A patient, Sally, comes to her doctor's office complaining of nonspecific chest pain. Her doctor suspects that the patient may have fluid around her heart, and pericardial effusion. A chest x-ray is performed but appears completely normal. The doctor then performs a two-dimensional echocardiogram, considered to be the gold standard for identifying fluid around the heart. The echocardiogram shows the presence of fluid around the patient's heart, consistent with pericardial effusion. Which of the following terms correctly describes Sally's x-ray result? o a) true positive b) false-negative c) false-positive d) true negative ● true positive Mr. Jones is concerned that he has developed diabetes because he is experiencing frequent urination. He goes to a drugstore and purchases a bottle of test strips designed to detect the presence of glucose in the urine. The test indicates that no glucose is present in his urine. Still concerned, Mr. Jones goes to his doctor, who obtains a fasting blood glucose test, one of the gold standards for diagnosis of diabetes. The blood glucose test shows that Mr. Jones has a normal blood glucose level, confirming that he does not have diabetes. Which of the following terms correctly describes the result of the urine test strips? o a) true positive b) false-negative c) false-positive d) true negative ● true positive

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Mr. Smith comes to the emergency department complaining of symptoms suggestive of a transient ischemic attack. Duplex imaging indicates that Mr. Smith has severe stenosis of the right internal carotid artery. He then undergoes angiography, the gold standard for identifying the presence of arterial obstructive disease. Mr. Smith's angiograms confirm the results of duplex imaging, and a carotid endarterectomy is performed successfully. Which of the following terms correctly describes Mr. Smith's duplex imaging results? o a) true positive b) false-negative c) false-positive d) true negative ● true positive Several statistical measurements are used to assess the accuracy of a diagnostic test. In order to determine accuracy, these measurements must be made using an adequate sample of patients. true Define the positive predictive value of a diagnostic test and explain how it is calculated. ● the ratio of patients truly diagnosed as positive to all those who had positive test results ● Positive Predictive Value (PPV) = 100xTP/(TP+FP) Define the negative predictive value of a diagnostic test and explain how it is calculated. ● the ratio of subjects truly diagnosed as negative to all those who had negative test results ● Negative Predictive Value (NPV) = 100xTN/(FN+TN) Define the overall accuracy of a diagnostic test and explain how it is calculated. ● the ability of a test to discriminate between and/or predict disease and health Several statistical measurements are used to assess the accuracy of a diagnostic test. ln order to determine accuracy, these measurements must be made using an adequate sample of patients. o Define the sensitivity of a diagnostic test ● Sensitivity is the test's ability to correctly designate a subject with the disease as positive; it is the conditional probability (Pr{T+|D+})7, denoted by the symbol S that a subject who has the disease, D+, tests positive, T+.

and explain how it is calculated. o Define the specificity of a diagnostic test and explain how it is calculated. A highly sensitive test means that there are few false negative results; few actual cases are missed. Ceteris paribus, tests with high sensitivity have potential value for screening, because they rarely miss subjects with the disease