wk6 Imaging acquisitions

Comprehensive vocabulary flashcards covering nuclear medicine image acquisition terminology, matrix parameters, acquisition modes, and hybrid imaging principles.

$$99mTc$$

A commonly used radionuclide in nuclear medicine with a peak energy of $140\,keV$ and a typical energy window of $20\%$.

LEHR

An abbreviation for Low Energy High Resolution, a type of collimator used in image acquisition.

Matrix

A square grid created in computer memory where gamma camera events are accumulated to generate a digital image; common sizes include $64 \times 64$, $128 \times 128$, and $256 \times 256$.

Pixel

Short for picture element, it refers to an individual location within a matrix where counts are recorded based on digitized $x$ and $y$ positions.

Pixel Depth

The maximum number of counts or events that can be recorded per pixel, determined by the number of bits allocated ($8$ bits or $16$ bits).

$$1\,\text{Byte}$$

A pixel depth of $8$ bits, which allows for a count range of $0-255$ per pixel.

$$1\,\text{Word}$$

A pixel depth of $16$ bits, allowing for a count range of $0-65,535$ per pixel; this is the standard for Nuclear Medicine imaging.

Spatial Resolution

The ability of the gamma camera to resolve small objects or the minimum distance between two points such that they can be pictured separately.

List Mode

An acquisition mode where $x$ and $y$ coordinates for individual events are stored with periodic markers; it allows flexible data analysis but uses a huge amount of memory.

Frame Mode

The most common acquisition mode where individual events are sorted into specific $x-y$ locations in the matrix immediately after digitization.

Zoom

A function that magnifies an object by modifying pixel size while keeping the number of pixels in the matrix constant.

Dynamic Acquisition

A series of images acquired sequentially to evaluate the rate of accumulation or excretion of a radiopharmaceutical from organs or tissues.

Static Acquisition

A single $2D$ image of a specific body area acquired for either a set number of counts or a fixed timeframe.

Whole Body Acquisition

A $2D$ image of the entire body where the patient bed moves continuously through the detectors, typically using a $512 \times 1024$ matrix.

SPECT

Single Photon Emission Computed Tomography; it produces $3D$ images by collecting multiple planar projections around the patient using a step-and-shoot or continuous method.

MIP

Maximum Intensity Projection; a way of viewing reconstructed $3D$ SPECT data.

Gated Acquisition

An imaging method for heart chambers using the $R$ wave of a patient's ECG ($R-R$ interval) to divide the cardiac cycle into frames.

DICOM

Digital Imaging and Communications in Medicine; a standardized format for medical images that allows integration and interchange between different imaging devices.

PACS

Picture Archiving and Communication System; a network used to store and display DICOM images, connecting to the Radiological Information System (RIS).

Hybrid Imaging

The combination of functional imaging (like SPECT or PET) with anatomical imaging (like CT or MRI) to improve localization and diagnostic accuracy.

Helical CT

A type of CT scanning where the x-ray tube rotates continuously as the bed moves, reducing patient movement artifacts and scanning larger areas faster.

Attenuation Correction

A process used to compensate for the loss of counts caused by photons being absorbed in overlying tissue, often using a low-dose CT to create an attenuation map.

CTAC

CT Attenuation Correction; provides advantages over radionuclide sources including less noise, faster acquisition, and no need for decay calculations or source replacement.