Flashcards Image Digitization and Display

What is analog imaging?

An imaging method that records radioactive decay events using continuous (X,Y) coordinates directly onto film.

What are the disadvantages of analog imaging?

No post-acquisition manipulation, no quantitative analysis, and incorrect settings require image reacquisition.

What is digital imaging?

An imaging method that converts radioactive decay events into discrete pixel locations for storage, processing, and quantitative analysis.

What is an analog-to-digital converter (ADC)?

A device that converts continuous analog signals into discrete digital values and assigns events to pixels.

What is a pixel?

The smallest discrete picture element in a digital image, identified by (X,Y) coordinates.

What is an image matrix?

A grid of pixels used to construct a digital image.

What are common matrix sizes in nuclear medicine?

64 × 64, 128 × 128, and 256 × 256.

How is pixel size calculated?

Pixel size = FOV (mm) ÷ matrix dimension.

What determines pixel size?

Field of view (FOV), matrix size, and zoom factor.

What happens to pixel size when matrix size increases?

Pixel size decreases, potentially improving spatial resolution.

What happens to pixel size when FOV increases?

Pixel size increases if matrix size remains constant.

What is pixel depth?

The maximum number of counts or gray levels a pixel can represent, determined by the number of bits.

What is byte mode?

8-bit pixel depth allowing 256 values (0-255 counts).

What is word mode?

16-bit pixel depth allowing 65,536 values (0-65,535 counts).

What is the main advantage of word mode over byte mode?

Higher count capacity and reduced risk of pixel saturation.

What is the disadvantage of word mode?

Requires twice as much memory as byte mode.

What is pixel saturation?

When a pixel receives more counts than its bit depth can represent.

What can happen when a pixel saturates in byte mode?

Acquisition may stop, the pixel may reset, or the image may be affected by count overflow.

Why is word mode preferred for high-count studies?

It accommodates significantly more counts per pixel without saturation.

What is the Nyquist sampling theorem in nuclear medicine imaging?

Pixel size should be no greater than half the camera's spatial FWHM to avoid undersampling.

What is the recommended maximum pixel size relative to FWHM?

One-half of the camera's FWHM.

What happens when pixels are too large?

Spatial resolution decreases, edges become less distinct, and small structures may be lost.

What happens when pixels are too small?

Counts per pixel decrease, increasing statistical noise.

Why should pixel size generally not be much smaller than one-third FWHM?

Excessively small pixels increase image noise without providing meaningful additional spatial information.

What is the trade-off when selecting matrix size?

Spatial resolution versus count density, image noise, and acquisition time.

When is a 64 × 64 matrix preferred?

Low-count studies or situations where high spatial resolution is less important.

When is a 128 × 128 matrix preferred?

Studies requiring a balance between spatial resolution and count statistics.

When is a 256 × 256 matrix preferred?

High-count studies requiring greater spatial detail.

How does increasing matrix size affect counts per pixel?

Counts per pixel decrease when total counts and FOV remain constant.

How does increasing matrix size affect image noise?

Statistical noise per pixel increases because fewer counts are collected in each pixel.

What is digital zoom?

A method that multiplies event coordinates by a zoom factor to magnify a selected portion of the image.

How does digital zoom affect FOV?

Increasing zoom decreases the effective field of view.

How does digital zoom affect pixel size?

Increasing zoom decreases effective pixel size.

What is the formula for pixel size with digital zoom?

Pixel size = FOV ÷ (matrix dimension × zoom factor).

Can digital zoom improve resolution beyond the camera's hardware limitations?

No; it can improve sampling but cannot create new spatial information beyond the system's intrinsic resolution.

What is frame mode acquisition?

An acquisition method that accumulates event counts directly into corresponding pixels of an image matrix.

How are static images acquired in frame mode?

Counts accumulate in a single memory buffer before the completed image is transferred to storage.

What is double buffering?

Using two memory buffers so one frame can be stored while the next frame is acquired.

Why is double buffering important in dynamic imaging?

It prevents data loss between consecutive frames.

What is gated frame mode?

An acquisition method that synchronizes image collection with a physiologic signal, such as an ECG.

What ECG signal is commonly used for cardiac gating?

The R-wave.

How many frames are commonly acquired during gated cardiac imaging?

16 frames per cardiac cycle.

What is the purpose of gated cardiac imaging?

To evaluate changes in cardiac function throughout the cardiac cycle.

Why are irregular heartbeats rejected during gated acquisition?

To reduce errors caused by inconsistent cardiac cycle timing.

What is list mode acquisition?

An acquisition method that stores each detected event individually with its coordinates, timing, and applicable physiologic markers.

What information is stored in list mode?

Individual event coordinates (X,Y), timing information, and physiologic markers when available.

What is the main advantage of list mode?

Flexible retrospective processing, including changing frame timing after acquisition.

What is the main disadvantage of list mode?

It requires significantly more memory than frame mode.

What is the difference between frame mode and list mode?

Frame mode bins counts into pixels during acquisition; list mode stores individual events for later processing.

What is image smoothing?

A processing technique that reduces statistical noise by averaging or adjusting neighboring pixel values.

What is a smoothing kernel?

A mathematical filter that determines how neighboring pixel values contribute to a new pixel value.

What is the main benefit of smoothing?

Reduces image noise and improves visual uniformity.

What is the disadvantage of excessive smoothing?

It reduces spatial detail and may obscure small lesions or important diagnostic features.

What is a look-up table (LUT)?

A table that maps pixel count values to grayscale or color intensities for image display.

In the standard grayscale display described in these notes, what does black represent?

The highest pixel count or greatest activity.

In the standard grayscale display described in these notes, what does white represent?

Zero counts or the lowest activity.

What is the purpose of a grayscale display?

To represent differences in detected activity using shades from black to white.

What is a color scale?

A display method that assigns different colors to pixel count values.

What are RGB colors?

Red, green, and blue components combined to create colors in digital displays.

What is the advantage of color scales?

They can make differences in count density or activity easier to distinguish.

What is a disadvantage of color scales?

Color perception varies between observers and may influence interpretation.

What is the purpose of a color bar?

To show how displayed colors correspond to relative count densities.

What is LUT normalization in dynamic imaging?

Applying a consistent count-to-display scale across frames so activity changes can be compared over time.

What is contrast adjustment?

Changing the mapping of pixel counts to displayed intensities to emphasize selected activity ranges.

What are examples of nonlinear display scaling?

Logarithmic, exponential, and gamma scaling.

Why is nonlinear scaling used?

To emphasize selected low-count or high-count regions that may be difficult to distinguish with linear scaling.

What is screen capture in digital imaging?

Saving the displayed image, including its processing appearance and annotations.

What factors can affect nuclear medicine image interpretation?

Radiopharmaceutical biodistribution, patient physiology, image quality, and observer perception.

What are mental reality maps in image interpretation?

Internal expectations shaped by experience that influence how clinicians recognize and interpret image patterns.

Why is clinical context important when interpreting nuclear medicine images?

Because image findings must be correlated with patient physiology, radiopharmaceutical distribution, and clinical information.