Measure 15 patients 3 times or 30 patients 2 times, repositioning the patient after each scan

a) Measure 15 patients 3 times or 30 patients 2 times, repositioning the patient after each scan

b) Calculate the root mean square standard deviation (RMS-SD) for the group

c) Calculate LSC for the group at 95% confidence interval

d) All the above

d) All the above

Each of the above steps must be followed to perform a precision assessment. It is important that the patient gets off the table and is repositioned each time for accurate data.

What is drift?

a) The gradual change in measured values

b) Shift in crosshairs of positioning lazer

c) Slipping table top of scanner

d) Computer speed decreasing

a) The gradual change in measured values

Drift is the gradual change in measured values. Calibration is used to monitor drift.

True or False

BMD results from different scanners can be compared.

False

This statement is false. DXA results cannot be compared between different units without valid cross-calibration. Even then, results should not be used for serial scans in patients undergoing treatment.

What causes drift?

a) Aging of the X-ray tube

b) Aging of the detector

c) Changes in room conditions or power supply to room

d) All the above

d) All the above

All the above factors can impact drift. Constant room conditions, such as temperature and humidity values will help keep drift to a minimum. Aging of the equipment will happen with use and time.

What are the components of a Quality Control procedure?

a) Periodic phantom scans

b) Plot and review QC data regularly

c) Maintain service logs

d) All the above

d) All the above

Each of the points listed are part of QC procedures. Each scanner will have manufacturer guidelines and a phantom specific to the individual scanner. Maintaining service logs and plotting QC results are critical as well.

How is the term accuracy applied to bone density?

a) The technologist's ability to reproduce serial scans on patients

b) Insuring patient demographics, such as height and weight, are correctly entered

c) The true bone density of the measured site; applies primarily to the machine

d) Insuring the lazer positioning lights are centered

c) The true bone density of the measured site; applies primarily to the machine

Accuracy is the term used for the true bone density of the measured site. This term applies primarily to the scanner.

What is the phantom that is used in external calibration composed of?

a) A firm gel that mimics soft tissue

b) A hard plastic material

c) Known bone and tissue standards

d) Metal

c) Known bone and tissue standards

The phantom is composed of known bone and tissue standards which gives the control factors for the calibration standard.

When should a precision assessment be performed?

a) Following the installation of a new DXA system

b) With newly hired technologists

c) After a new technologist has learned basic scanning skill and completed 100 scans

d) All the above

d) All the above

Precision assessment should be preformed following all the above events.

Why is the least significant change (LSC) vital to bone density testing?

a) In order to be sure that the patient's BMD in subsequent scans can be considered true biological changes, the LSC must be a known variable.

b) As with any medical testing, the likelihood of numeric values being reproduced identically in serial testing is almost non-existent.

c) The technologist's precision error rate is used to determine the LSC

d) All the above

d) All the above

LSC is vital to bone density testing when patients are being monitored during treatment because the reading doctor must determine if the changes seen in serial exams are true changes in the BMD or due to technical factors. If the changes exceed the LSC, it can be assumed that the changes are clinically significant.

What are the most common charts used in DXA QC?

a) CUSUM charts

b) Shewhart charts

c) Bar charts

d) Scatter charts

b) Shewhart charts

The Shewhart chart is the most commonly used chart in QC programs to provide graph visuals for plotting results.

True or False

A technologist can use data from every patient scanned, with no regard to anatomical anomalies.

False

This statement is false. Patients in the study should be conforming with normal anatomy.

True or False

Technologist precision is considered research and requires approval from the institutional review board.

False

This statement is false. Precision is not considered research and does not require approval from IRB.

DXA units must be calibrated according to method of energy production. Voltage switching units rely on an internal calibration system. How does this occur?

a) The X-ray beam passes through a filter during patient scans

b) Calibration filter contains equivalents of air, tissue and bone

c) Point by point calibration

d) All the above

d) All the above

All three of these statements accurately describe the calibration techniques in oscillating energy supplies. The calibration is performed during each patient scan. This insures accurate patient results.

How is the BMD established on the phantom?

a) The manufacturer provides it

b) It is preset on the phantom

c) By scanning the phantom 5 times and finding the average

d) By scanning the phantom 10 times without repositioning and calculating the average or mean of the readings

d) By scanning the phantom 10 times without repositioning and calculating the average or mean of the readings

The BMD is established by scanning the phantom 10 times without repositioning. Calculate the mean and set the 1.5% limits.

True or False

According to the ISCD official positions, precision assessment should be clinical practice.

True

Precision should be standard clinical practice and will enhance patient care.

What is Quality Assurance?

a) The daily phantom test

b) The technologist precision test

c) The comprehensive quality program ensuring proper scanner functions and minimizing operator error

d) Daily logs of testing

c) The comprehensive quality program ensuring proper scanner functions and minimizing operator error

QA is the comprehensive quality program. It includes daily QC with the phantom and technologist precision tests.

What statistics are included in DXA scanner QC?

a) Standard deviation (SD) of the data

b) Average or mean

c) Percent coefficient of variation (%CV)

d) All the above

d) All the above

All three statistics are part of the DXA QC. %(CV)=(SD/mean)x100 is the mathematical formula to calculate the percent coefficient of variation. The smallest possible SD is desired.

True or False

External calibration for scanners with constant potential generators is performed weekly.

False

This statement is false. External calibration is done daily during the QC on the machine.

How is precision calculated in departments with multiple technologists?

a) Precision can only be calculated on an individual technologist, regardless of the number of techs performing DXA studies

b) Precision is provided by the manufacturer for individual machine

c) Each technologist performs the required studies for the precision study and all the data is averaged for the departmental error rate

d) Each technologist has their own precision error rate that is applied when the tech performs a study

c) Each technologist performs the required studies for the precision study and all the data is averaged for the departmental error rate

Multiple techs each participate in the data gathering phase of the precision study. The final precision error is arrived from averaging all the technologists.

What is the definition of calibration?

a) A standard expression of the relationship between BMD and reference data

b) The act of calibrating an instrument

c) Calibration quantifies and improves the performance of an instrument

d) 2 and 3 only

d) 2 and 3 only

The definition of calibration is the act of calibrating an instrument. Calibration also improves and quantifies the performance of an instrument, which applies to bone density testing.