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Accuracy, sensitivity and specificity analysis

Accuracy, sensitivity and specificity analysis. The main outcome of a diagnostic imaging examination is an accurate diagnosis of a patients condition so that proper treatment can be administered. It can be affected by factors such as: Image quality

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Accuracy, sensitivity and specificity analysis

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  1. Accuracy, sensitivity and specificity analysis

  2. The main outcome of a diagnostic imaging examination is an accurate diagnosis of a patients condition so that proper treatment can be administered. • It can be affected by factors such as: • Image quality • Competency of the radiologist to interpret the image

  3. Classification of a Diagnosis Positive – patients in whom the disease has been diagnosed. True positive – if the diagnosis is revealed to be correct. False positive – if study indicates that they do not have the disease despite the positive findings from the image. Negative – healthy patients with no disease present are considered negative.

  4. True negative – if a diagnosis of a negative is determined from an image and is supported by follow-up studies. False negative – if a negative diagnosis is given to a patient who later has the disease.

  5. Accuracy • Is the percentage of cases that is diagnosed correctly; it can be determined by the following equation: • Accuracy = (NTp+ NTn)/Ntotal =100 • N = number of cases • NTp= Number of cases of True Positive • NTn= Number of cases of True Negative • Ntotal = total number of cases

  6. Example Answer: 0.967 or 96.7% If a 210 total chest x-ray are performed in a month and the number of true negatives is 167 and the number of true positive is 36, then the accuracy rate of the image diagnosis is

  7. Sensitivity • Is also referred to as the TP fraction(True Positive Fraction)and indicates the likelihood of obtaining a positive diagnosis in a patient with the disease. Sensitivity is determined by the following equation. • Sensitivity = NTp/(NTp + NFn) • NFn – False Negative

  8. Example Answer: 0.92 or 92% • If a department has a true positive of 36 and has a false negative of 3, what is the sensitivity of the diagnosis.

  9. Specificity • Is also known as the TN fraction (True Negative Fraction) and indicates the likelihood of a patient obtaining a negative diagnosis when no disease is present. Specificity is determined by the following equation • Specificity = NTn/(NTn + NFp) • NFp= False positive

  10. Example Answer: 0.97 or 97% A department receiving a 167 TNs and 4 FPs has a specificity of

  11. Problem solving If a department has a total number of 300 cases , with a true positive of 157 and a true negative of 115 with a false negative of 5 and a false positive of 2. What is the accuracy percentage? What is the sensitivity percentage? What is the specificity percentage?

  12. Answer Accuracy = 157 + 115/300 x 100 = 0.906 or 90.6% Sensitivity = 157/157 + 5 = 0.969 or 96.9% Specificity = 115/115 + 2 = 0.982 or 98.2%

  13. Practice If a department has a causal rate of 12% that was caused by the processor what is the number of films used if it has a total repeat rate of 432? x/432 = 0.12 432*0.12 = x X=51.84 or 52 films

  14. Data analysis With these data shows that the department has an accuracy 90.6% to which cases of diagnosis is correct, sensitivity or detectability of 96.9% which is the likelihood of obtaining a positive diagnosis of patients with a disease. A specificity of 98.2% to which it indicates the likelihood of a patient obtaining a negative diagnosis when no disease is present.

  15. Summary The ideal for all of the values is 100%. A diagnostic imaging department is responsible for establishing its own threshold of acceptability for each value. Implementing a quality management program requires more than just equipment monitoring and maintenance. The outcome assessment of diagnostic images must also be performed to evaluate the success of the procedure.

  16. END OF MIDTERM

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