Basic Digital Imaging Concepts

Question 1

What is the difference between a pixel and a voxel

Answer 1

A pixel represents the smallest sampled 2D element in an image. It has dimensions given along two axes in mm

A voxel is the volume element, defined in three dimensions.

Question 2

What is an image matrix

Answer 2

An array of square pixels (picture elements) arranged in columns and rows.

Question 3

What is a bit

Answer 3

A unit that represents 2 tones within a pixel

typically black and white), using the values 0 for black and 1 for white or vice versa. A grayscale image is composed of pixels represented by multiple bits of information, typically ranging from 2 to 8 bits or more.

Bit depth (k bit)

The k bit is the number of bits per pixel, the grey scale of an image is equal to 2k-bit, for example:

k bit of 2 = 4 shades of grey
k bit of 8 = 256 shades of grey

The higher the bit depth, the more grey scale and therefore the higher the contrast resolution.

Question 4

What is a gray scale

Answer 4

The NUMBER of gray shades or brightness levels visible on an image (monitor)

Question 5

What is data compression and name the 2 data compression techniques used in radiology

Answer 5

Data Compression is a technique in which the size of data is reduced without loss of information.

Lossy compression :

The lossy compression technique does not restored the data in its original form, after decompression (Irreversible)

Lossless compression: lossless compression restores and rebuilt the data in its original form, after decompression
(Reversible)

Question 6

What is teleradiology

Answer 6

Teleradiology is the electronic transmission of diagnostic imaging studies from one location to another for the purposes of interpretation and/or consultation.

Question 7

What are the key elements of the picture archiving and communication system (PACS)

Answer 7

1. Image acquisition device - device used to can patient and computer gateway computer to produce images

• Digital Imaging and Communications in Medicine (DICOM) is the universal PACS format that enables image resizing and orientation calibration of medical data

2. Secure networks for transmission - LAN within a department , LAN that connects to various departments, teleradiology

3.Workstations/ viewing stations - allows radiologists to review images - high res LCD in radiology department vs medium resolution on wards

modern display workstation has communication hardware, processing software, a display monitor system, a local database and resource management.

4. Servers and storage

• Storage area network (SAN) - corporate - independent server storage
• Network-attached storage (NAS) - sits on network - also an i ndependent server storage
• Direct attached storage (DAS) - hard drives on server that run PAC can also store data