Multi-Energy SPECT Calibration Source for Detector Sensitivity

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Solution Overview

Problem

Existing SPECT imaging technologies face errors due to detector-specific sensitivity and uniformity differences when using class standards, which can introduce uncertainty, especially when the energy of the calibration source differs from the patient scan radioisotope energy.

Innovation Solution

A multiple energy emission source is used for calibration to determine system-specific planar sensitivities and uniformities at different emission energies, allowing for more accurate activity concentration estimation by measuring sensitivities and uniformities at various energy levels, and optionally calibrating a dose calibrator using a long-lived point source with emissions between 50 keV and 400 keV.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a class standard sensitivity or uniformity is used for calibration, then the calibration process is simplified, but the detector-specific sensitivity or uniformity may differ, introducing error in quantitative SPECT imaging

Engineering Contradiction:

Improvecalibration process simplicityVSAvoidquantitative imaging accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the calibration approach from using class standard parameters to measuring system-specific parameters at multiple energy levels. By measuring sensitivity and uniformity at different energies (e.g., 140 keV for Tc-99m and 511 keV for F-18), the system adapts to detector-specific characteristics, resolving the contradiction between calibration simplicity and quantitative accuracy.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If system-specific sensitivity is measured using a dose calibrator with a source at one energy, then the sensitivity measurement is obtained, but uncertainty increases when the radioisotope energy differs from the calibration source energy

Engineering Contradiction:

Improvesensitivity measurement capabilityVSAvoidenergy mismatch uncertainty

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent makes the calibration system universal by measuring sensitivity and uniformity at multiple energy levels. This multi-energy calibration approach allows the same system to accurately measure different radioisotopes (Tc-99m at 140 keV, F-18 at 511 keV, I-123 at 159 keV) without introducing energy mismatch uncertainty, as the detector's response is characterized at each relevant energy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent changes the calibration parameter from single-energy sensitivity to multi-energy sensitivity and uniformity measurements. By characterizing the detector's response at multiple energy levels, the system can interpolate or select the appropriate calibration parameters for any given radioisotope, eliminating uncertainty from energy differences between calibration sources and patient scans.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If a sheet source for measuring uniformity corrections is used at a different energy than the patient scan radioisotope, then uniformity measurement is achieved, but energy-dependent uniformity differences introduce uncertainty

Engineering Contradiction:

Improveuniformity measurement capabilityVSAvoidenergy-dependent uniformity accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the uniformity calibration from single-energy to multi-energy measurements. By measuring uniformity corrections at different energy levels using the same sheet source, the system captures the energy-dependent behavior of the detector. This allows selection or interpolation of the appropriate uniformity correction for the specific radioisotope being scanned, eliminating uncertainty from energy mismatches.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach provides more accurate and system-specific calibration, reducing variability in SPECT imaging by matching calibration energies to clinically relevant isotope energies, thereby improving the accuracy of activity concentration measurements and dose calibration.

Implementation Method 1

Counts of emissions from the radiotracer are detected. The activity concentration of the radiotracer from different locations is reconstructed from the detected emissions.

Methodology Applied

Scientific EffectGamma radiation detection: Photoelectric Effect

Implementation Method 2

A first system-specific planar sensitivity or a first system-specific uniformity of a gamma camera to a calibration source is measured for a first energy. The calibration source has multiple emission energy peaks including the first energy and a second energy.

Methodology Applied

Scientific EffectRadioactive decay: Radioactive Decay

Data Source

PatentUS9910162B2Calibrating in single photon emission computed tomography with multi-emission energies

Publication Date: 2018.03.06 SIEMENS MEDICAL SOLUTIONS USA INC

AI summary

For calibration (24) for quantitative SPECT, a multiple energy emission source (11) is used for calibration. The planar sensitivities and/or uniformities are determined at different emission energies based on detections from the multiple energy emission source. For estimating (32) the activity concentration, sensitivities and/or uniformities based on measures (26) at different emission energies increase accuracy. The multiple energy emission source (11) may alternatively or additionally be used to calibrate (40) a dose calibrator (15).