Fundamentals of Imaging

RAD 206

Digital Imaging, Artifacts & Errors

The advantages of CR are its large dynamic range, digital format, portability, and post-processing capability

But not PERFECT –Imaging Errors can still occur

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What is Digital Radiography?

• Historically, digital radiography referred to specialized modalities that produced digital images.

• Examples would include:– CT– MRI– Nuclear Medicine– Ultrasound

Digital Radiography Today

• Since the early 1990s, Digital Radiography has grown to include Computed Radiography(CR) and ‘true’ Digital Radiography(DR) or Direct Radiography.

Computer Language

• Computer Letters are on offor 1 0

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That is binary digits ( numbers)

Example of Computer words

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Illustration of the exposure, readout and erasure stages involved in generating a computed radiography image

Image Matrixx

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Y

(X7-Y5-11)

• Pixels Pixels are individual picture elements in a two-dimensional image.

• matrix matrix is the total number of pixels in an image ( from vertical and horizontal dimensions).( If there are 1,024 (1 k) pixels in both the horizontal and vertical dimensions, then the image contains 1 k x 1 k = 1 M, or 1,0242 pixels.)

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Matrix , Pixel , Voxel

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Types of Digital Radiographyin convectional Radiography

• Detectors in Digital Imaging• Gas and solid state detectors (CT scan and BMD)• Scintillators Detectors & Photoconductors

(Nuclear Med)• Photo-stimulable phosphors for CRCR ( computed

Radiography)• DDRDDR or DRDR (Direct Digital Radiography)

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• Bit– 0 or 1– ( see also KB, MB, GB)

• Byte– The amount of gray scale in the image. The bit is the exponent

to two, ie, a 2 bit image is two to the second (or four), So the image would have 4 shades of gray possible. Today, images are 10 or 12 bit.

Common Digital Terms

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Common Digital Terms• Pixel– Picture element. This is the basic component of

the digital image, it is what we see. 2 dimensional• Voxel– Volume element. This is a 3 dimensional element

that includes depth. The pixel is essentially the end of the voxel.

• Matrix– The actual image we see is made up of a series of pixels in rows

and columns called a matrix. Generally, the larger the matrix the better the spatial resolution of the image. (512 x 512)

• FoV– Field of view. This is how much anatomy is displayed. A

12 cm FoV will display 12 cm of anatomy on the screen. The smaller the FoV the more magnified the anatomy is.

Common Digital Terms

Common Digital Terms• Window width– The gray scale of the digital image. The larger

the width the more grays demonstrated the lower the contrast of the image.

• Window level– The density or brightness of the image. The

higher the number the brighter the image.