Topic 6 Nuclear Medicine Acquisition Methods

• Methods of Data Acquisition

• Frame Mode and List Mode Acquisitions

• Dynamic and Gated Acquisitions

• Static and Whole Body Acquisitions

• Sampling and Information Density

Frame Mode

Camera FOV vs Image Matrix

List Mode

Multi Energies and Isotopes

• Multi Energies: – Single isotope: 111-In, 67-Ga.

– Photopeaks add together and form a single image

• Dual Isotopes– Separate frames.

Dual Isotope Imaging

Pixel Size

• Pixel size determination:– system spatial resolution– size of object interested– time for processing

– storage

Pixel Size

Image Quality - Pixel Size

Information Density

• Spatial precision depends on count density

• For circular object and uniform background:– n>k2/(c2*d2) – where k~3-5, – c: image contrast, – d: object diameter

Information Density - Noise

Detection of Information - Count Density

Noise vs Matrix Size

Zoom Mode - Same Resolution

Byte vs Word AcquisitionPixel Depth

Types of Studies

• Static Studies– Matrix size, pixel size (<3 mm/pixel)

• Whole Body Imaging– Relative motion of patient & detector with

synchronised collection– Acquisition time (and count density) is

determined by the scan speed (~10-15cm/min)

Types of Studies

• Dynamic Studies – uptake or clearance over an extended period

– acquire a sequence of images

– fixed time frame or phase acquisition (different time frame)

– Frame rate depends on radiotracer kinetics.– Matrix size: 64x64 or 128x128

• Gated Acquisition– A pre-determined number of frames in memory

– Gate signal triggers first frame for a fixed time

– A list mode could be used for checking irregular heart beat

Whole Body Imaging -Different Intensity

Gated Acquisition

SPECT Acquisition

• Parameters that affect the SPECT acquisition: pixel size, arc selection, number of angular samples, acquisition time at each angle, rotation mode.

• Pixel size - system’s spatial resolution (FWHM/3)

• Arc selection - 360, 180 for heart, no less than 180.

• Angular samples: n=2πR/d (d: pixel size, R: radial distance)

• Acquisition time: Total acquisition time /n (~10-30 min).

• Rotation mode: step-and-shot (good resolution); Continues (more efficient)

• Gated SPECT: A gated study instead of each simple projection.

• Whole body SPECT: Several SPECT acquisition re-assembled

SPECT Image QualityPixel Size

SPECT Image Quality-Number of Projections