Data Processing for Dosimetry: Dead-time Correction & SPECT Processing in Medical Imaging, Schemes and Mind Maps of Management of Health Service

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Data processing for dosimetry

Matt Aldridge, Clinical Scientist, UCLH

Imaging-based dose estimation

A A   t dt

Activity

Time

Dead-time correction

System-specific dead-time model and dead-time

constant determined by phantom experiments

using same window setting as used for patient

studies, as well as similar scattering conditions.

Dead-time correction at high counting rates

(131I imaging) – significant number of events

with energies outside the energy of the

photopeak window – contribute to camera

dead-time

Dead-time correction

SPECT processing – Attenuation correction

SPECT processing – scatter correction

Scatter in 131I – high-energy photons (637 and 723 keV)

Use TEW scatter correction (accounts for downscatter of high energy emissions)#

Patient imaging studies – scatter events in the photopeak window estimated by TEW are 40% - 50% of the total events

Ci,scat = (Ci,lower/Wlower + Ci,upper/Wupper) X Wmain/

Applying reconstructions

AC only ACSC (^) ACSCRR

Partial volume correction

Segmentation

Segmentation process starts at the seed point. All neighbours within a specified square/cube are checked.

Seed point

Voxels that comply with threshold criterion are included in the organ/lesion VOI.

Segmentation

Automatic organ segmentation for:

Lungs

Liver

All bone cavities (bone marrow + spinal cord)

e.g. lung segmentation – click on point inside the lung in a CT slice –

will look for all points below -400HU (default lung threshold)

Multi SPECT-CT

Processing

Reconstruction

Registration

Segmentation

Quantitation

SPECT/CT (1) SPECT/CT (2) SPECT/CT (t)

Injection parameters (^) System sensitivity (^) Residence timeActivity curves