Computers in Medicine

bytes in a bit

8

bytes in a kilobit

in a megabit

in a gigabyte

in a terabyte

1 kilobyte (kb) = 1024 bytes = 2¹⁰ bytes

1 megabyte (Mb) = 1024 kb = 2²⁰ bytes

1 gigabyte (GB) = 1024 MB=2³⁰ bytes

1 terabyte (TB) = 1024 GB = 2⁴⁰ bytes

where is hexadecimal relevant

In service mode on Varian Clinacs, voltage value readouts are displayed in hexadecimal for many sensors.

what base system is hexadecimal

hexadecimal is a base 16 number system.

generally how does hexadecimal work

1. Hexadecimal uses the numbers 0-9 to represent 0-9, but then it gets a little weirder as A-F are used to represent 10-15.

   1. So converting hexadecimal to decimal F is 15, E is 14, D is 13 and so on and so forth.

2. Every hexadecimal digit is termed a “nibble” and is composed of 4 bits, 2 hexadecimal digits make up a full byte.

translate to decimal from hexadecimal: 8AA0

1. In binary: 1000101010100000

2. In decimal: 35,488

1. If we decompose our sample binary value of 1000101010100000 into nibbles then we have:

   1. (1000)(1010)(1010)(0000) and then convert each nibble to hexadecimal.

   2. We have (2³=8)(2³+2¹=10)(2³+2¹=10)(0=0) or (8)(10)(10)(0).

   3. So, in hexadecimal: 8AA0.

CPU

the functions of the CPU are to address memory and logical functions as well as decoding instructions.

memory types and function on computer

short term, high speed electronic storage for data and instructions.

1. RAM (Random Access Memory) is read/write.

2. ROM (Read Only Memory) is read only.

motherboard and computer bus functions

1. the motherboard allows all of the various components listed above to link together through communication pathways (the bus, think of it as a central nervous system for a computer).  The computer bus is responsible for communicating the memory addresses where information is to be stored/retrieved as well as the moving specific data itself.

operating system function

the operating system is a program that sits between the user and the computer hardware allowing the two to communicate. The operating system must host drivers (which are sets of instructions for how to control hardware) and is responsible for the wonderful graphical user interfaces (GUI) we have all come to love (in contrast remember DOS)

steps to convert analog to digital

1. Sampling - finding the value of the signal at a point in time.

2. Quantization - assign the signal a binary value.

what important consideration must be made with monitors in radiology

monitors are the link between us and images in the digital world cheaper monitors may be incapable of displaying 16 bit grayscale images or may do so inaccurately as the electronics involved in the DAC may limit this. This is why in any field where monitors are used for viewing medical images it is critical the monitor display be accurate. In radiology a poor monitor could result in misdiagnosis or in radiotherapy it could result in incorrect contouring.

explain bit depth

1. when performing an ADC or DAC the most important aspect to consider is the associated bit depth.

2. True analog data has unlimited bit depth and when converting it to digital a suitable range of values must be available to adequately represent the incoming data. Let say we are dealing with a radiograph we are scanning into the computer.

   1. if we scan it into the computer using equipment capable of 16 bit scanning, (every pixel has 16 bit of memory assigned) that means every pixel can have a numerical value up to  65,536. So when displaying this on a monitor (assuming the monitor has 16 bit DAC) there can be 65,536 grey scale values displayed. This will result in a nice image closely resembling the original.

   2. if we scan it into the computer using equipment capable of 8 bit scanning, (every pixel has 8 bit of memory assigned) that means every pixel can have a numerical value up to 256. So when displaying this on a monitor there can be 256 grey scale values displayed

typical N values for CR, DSA, CT/MRI Nuc med scans where NxN is pixel

1. Computed Radiographic Image, N = 2048.

2. Digital Subtraction Angiographic Image, N = 1024.

3. CT/MRI Scans, N = 512.

4. Nuclear Medicine Scan, N = 128.

explain how to determine bits for a single pixel needed by grayscale

1. If we let the number of gray scale values available in the digitization of an image be represented by the variable, G, then we can further note that G is dependent on binary.

   1. That is, G is generally a value of two raised by some integer (let’s call this m).  The power in this expression represents the number of bits that are required to store this pixel.

      1. For example, let’s say that we want 256 shades of gray for a pixel.  This means that G is equal to 256.  Or,

         1. G = 256 = 2^m.

      2. Solving for m, yields:

         1. m = 8.

      3. This means that this pixel will require 8 bits for storage (and, therefore, each other pixel in this image will require 8 bits).

what does DICOM stand for

Digital Image and Communication in Medicine

what does PACs stand for

Picture Archival and Communication System.

what is PACs for

1. The function of PACS, for digital media, is to act as:

   1. image reading station,

   2. file room,

   3. image transferer,

   4. image duplicator,

   5. image processing and editor.

image smoothing

effectively a method used to simplify an image while retaining possible useful information.  In words, this is done by reducing noise or eliminating useless detail while not introducing distortions to the image set.

• each pixel is analyzed individually and compared with the average of its neighboring pixels.  If the analyzed pixel is determined to fluctuate to a certain degree established in the algorithm compared to its neighbors, then the pixel is given a new value that is more closely related to its adjacent and nearby pixels.

edge enhancement

as opposed to image smoothing, edge enhancement is a mathematically derived method in which more statistical noise is introduced into the image as a side-effect of emphasizing edges found within image sets.  There is an inherent trade-off between smoothing algorithms and edge enhancement algorithms.

flat field correction

is a technique often used in digital imaging as a means of improving global quality of a 2D digital image.  The goal of the technique is to remove pixel-to-pixel variations and artifacts so that the entire image has a more uniform response.  The method by which this is achieved is conceptually very simple but requires the prior acquisition of both dark (an image acquired when there is no signal present) and flood field (an image with an even signal incident upon the detector) images. This calibration is frequently recommended for both the OBI and portal dosimetry imaging panels on LINACs.