Lecture 4

Question 1

Digitizing exposures at either extreme will result in _____ tissue-density resolution.

An algorithm is needed to process the specific body part based on the optimal exposure range. What is this done by?

Answer 1

Low

Exposure data recognition

Question 2

What are 3 things the edr (exposure data recognition) does?

Answer 2

1. Searches for the anatomy
2. Identifies collimated borders
3. Eliminates scatter outside the FOV

Question 3

What is the image histogram?

Answer 3

This is the data that the system records within the collimated area & produces a graphical representation of the densities.

Question 4

Black areas indicate a ________ acquired signal.

The middle area of the histogram represent _______ tones.

The extreme opposite end represent _____ to ____ acquired signal.

Answer 4

greater; medium; weak to no

Question 5

In plotting a histogram, what goes on the x and y axis?

Answer 5

X-axis: receptor exposure
Y-axis: no of pixels in each exposure

Question 6

Low kvp = lower energy = ______ histogram

High kvp = higher energy = ________ histogram

When we say the histogram is “anatomy specific”, what does that mean?

Answer 6

broader/wider ; narrow

The raw data used to plot the histogram is compared against a normal histogram of the same anatomy and image correction takes place.

Question 7

Give an example of when histogram analysis error may occur.

Answer 7

If at least three collimated field edges are unidentified, all data (including raw exposure or scatter outside the field) may be included in the histogram.

Question 8

Histogram analysis errors are less likely to occur with? Why?
A. DR IR
B. CR IR

Answer 8

A. DR IR ; because the image data are extracted from the exposed detectors only.

Question 9

What is automatic rescaling?

Answer 9

This is the process by which the grayscale is mapped to the VOI (value of interest) to present a specific display of brightness.

Question 10

If exposure is too low, causes ______ ______. If exposure is too high, causes _______ and _______.

Answer 10

quantum mottle; loss of contrast and edge detail.

Question 11

What is used as a reference to evaluate the raw information and correct luminance values?

Answer 11

Look-Up Table (LUT)

Question 12

What is histogram equalization?

Answer 12

A digital imaging processing technique used in a variety of modalities in radiology to enhance contrast.

Question 13

What is segmentation?

Answer 13

Delineation of areas of interest in imaging in terms of pixels or voxels

Question 14

1. What is the region of interest?
2. Give one purpose of a ROI

Answer 14

1. Keyboard controlled identification of a given area of an image for numerical analysis and the area of anatomy being scanned that is of particular importance in the image.
2. Calculation of pixel statistics.