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You are in Home >> Exams >> MCQ/EMQ

Imaging and Technology EMQ 1

Created: 5/1/2008
Updated: 11/1/2008

 
Radiology and radiopharmaceuticals

A Diethylene triamine pentaacetic acid
B CTKUB
C CT Urogram
D Mercapto Acetyl Tri Glycine
E Dimercaptosuccinic acid
F Mag 3 Renogram
G 99 Technetium
H IVU
I Chest xray
J 123 Iodine
K I-Hippuran
L Abdominal xray
M 131 Iodine


1 Effective dose of 4.7 mSv
2 Effective dose of 5.2 mSv
3 Equal to a background radiation dose of approximately 10 days
4 Localises to the proximal convoluted tubule
5 Has a half-life of 6 hours
6 Effective dose of 44 mSv
7 Handled mostly by tubular secretion
8 Equal to a background radiation dose of approximately 6 months
9 GFR dependant for clearance

Statistics

The table below gives the diagnostic performance of a test in a population of 1000 people

   Disease positive  Disease negative  Totals
 Test positive  90  180  270
 Test negative  10  720  730
 Totals  100  900  1000

A 80%
B 66%
C 6.5
D 33%
E 10%
F 4.5
G 99%
H 10
I 12.5
J 50%
K 25%
L 90%

10 What is the specificity of the test?
11 What is the positive predictive value?
12 What is the sensitivity of the test?
13 What is the likelihood ratio for a positive test?
14 What is the negative predictive value?

Statistics continued??!!!?

A Type I error
B Sensitivity
C Null hypothesis
E Specificity
F Positive predictive value
G Alternative hypothesis
H Type II error
H Power
I Confidence interval
J Median

15 Assumes no difference exists between 2 groups being studied
16 Refers to the proportion of those patients with a positive test who actually have the condition
17 Also referred to as an alpha error
18 Rejection of the null hypothesis when it is true
19 The ability of a test to correctly identify patients with the disease
20 Accepting the null hypothesis when it is false

Answers
1B 2F 3I 4E 5G 6C 7F 8H

10A 80% (720/900)
11D 33% (90/270)
12L 90% (90/100)
13F 4.5 (90/270)/(180/900)
likelihood ratio is the likelihood that a given test result would be expected in a patient with a disorder compared to the likelihood that that same result would occur in a patient without the target disorder
14G 99% (720/730)

   Disease positive  Disease negative  Totals
 Test positive  a  b  a + b
 Test negative  c  d  c + d
 Totals  a+c   d + b  

sensitivity a/(a+c)
specificity d/(d+b)
PPV a/(a+b)
NPV d/(c+d)

15C The null hypothesis assumes there  no difference exists between the groups being studied whereas the alternative hypothesis assumes a difference does exist between the groups being studied

16F The positive predictive value refers to the proportion of those patients with a positive test who actually have the condition whereas the negative predictive value refers to the proportion of those patients with a negative test who do not have the condition

17A Alpha error refers to a type I error and beta error refers to type II error

18A Type I error occurs when the null hypothesis is incorrectly rejected and there is no difference between the groups whereas a type II error occurs when the null hypothesis is incorrectly accepted when in fact there is a difference between the groups being studied

19B Sensitivity refers to the ability of a test to correctly identify patients with the disease whereas the specificity refers to the ability of a test to correctly identify those patients without the disease

20H See above for explanation

UrologyUk comment: It is always difficult to remember some of the statistical definitions, however they do come up. Look them up the night before the exam - both written and viva sections.

Another area which causes problems is the power of a study:

The power of a study refers to its ability to reject the null hypothesis when it is in fact false ie. it is the abililty of not committing a type II error

Its is given by 1 - beta and has a value between 0 and 1 - 1 is max and 0 is min - the closer to 1 the better 
 
ArticleDate:20080105
SiteSection: Article
 
   
    
                                            



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