Futuristic PET scanner with brain scan overlay, symbolizing precision in medical imaging.

Unlock Precision: A Guide to Reliable Timing in PET Scanners

Beau Callahan in Health & Wellness December 2025 • 4 min read.

"Discover how to optimize coincidence resolving time (CRT) measurements in PET detectors using advanced waveform digitizers for enhanced medical imaging."

In the realm of medical imaging, precision is paramount. Positron Emission Tomography (PET) stands as a powerful tool, offering insights into the body's functions at a molecular level. However, the clarity and accuracy of PET scans hinge on a critical factor: timing. Specifically, the coincidence resolving time (CRT) - the ability to precisely measure when two gamma photons strike the detectors simultaneously - plays a vital role in producing high-quality images.

Imagine trying to capture a photo of a hummingbird in flight with a camera that has a slow shutter speed. The result would be a blurry image, lacking the detail needed to truly appreciate the bird's intricate movements. Similarly, in PET imaging, a poor CRT can lead to blurred images, making it difficult to detect small lesions or subtle changes within the body. This is where advanced technology comes into play.

Recent advancements have focused on developing PET detectors and readout circuits with enhanced timing performance. Multichannel waveform digitizers, sophisticated pieces of equipment that analyze the output signals from detectors, have emerged as key tools. These digitizers, particularly those based on the Domino Ring Sampler 4 (DRS4) chip, offer the potential for incredibly precise timing measurements. But, as with any advanced technology, there are nuances to consider to ensure optimal performance.

The DRS4 Chip: A Double-Edged Sword

Futuristic PET scanner with brain scan overlay, symbolizing precision in medical imaging.

The DRS4 chip is a sophisticated piece of technology designed to capture and analyze the signals from PET detectors with remarkable speed and precision. It acts like a high-speed camera, recording the shape and timing of electrical pulses generated when gamma photons interact with the detector. However, researchers have discovered that using the DRS4 chip effectively requires careful attention to data acquisition (DAQ) techniques.

The key issue lies in how the input channels of the waveform digitizer are configured. Think of the DRS4 chip as having multiple lanes for data to flow through. The way these lanes are used can significantly impact the accuracy of CRT measurements. There are two main approaches:

Intra-chip sampling: Using input channels that are located within the same DRS4 chip.
Inter-chip sampling: Using input channels that are located on different DRS4 chips.

A recent study highlighted a potential pitfall with intra-chip sampling. Researchers found that this method can lead to unusual streak patterns in CRT maps, essentially creating an artificial distortion of the timing data. This distortion can result in an artificially low CRT value, giving the impression of better timing resolution than is actually being achieved. The culprit? Signal crosstalk – a phenomenon where signals from one channel interfere with those of another.

Best Practices for Reliable CRT Measurement

The study emphasizes the importance of using inter-chip sampling when measuring CRT with DRS4-based digitizers. By using channels from different chips, the risk of signal crosstalk is minimized, leading to more reliable and accurate timing measurements. This approach provides a more realistic assessment of the PET detector's timing resolution, ensuring that the resulting images are as clear and precise as possible. Ultimately, this translates to better diagnoses and improved patient care.

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Everything You Need To Know

What is coincidence resolving time (CRT), and why is it important in PET scans?

Coincidence resolving time (CRT) is a critical factor in Positron Emission Tomography (PET) scans. It measures the ability to precisely measure when two gamma photons strike the detectors simultaneously. Accurate CRT is vital because it directly impacts the clarity and accuracy of PET images. A poor CRT can lead to blurred images, making it difficult to detect small lesions or subtle changes within the body, which can affect diagnosis and treatment planning. The impact of improved CRT means that subtle changes in the body can be observed, which would lead to more accurate diagnoses.

How are advanced waveform digitizers used in PET scanners to improve medical imaging?

Advanced waveform digitizers, especially those using the Domino Ring Sampler 4 (DRS4) chip, are used to analyze signals from PET detectors. The DRS4 chip captures the shape and timing of electrical pulses generated when gamma photons interact with the detector. This allows for incredibly precise timing measurements, helping to improve the overall quality and reliability of PET scans. These digitizers enhance medical imaging by providing detailed information about the timing of photon detection, contributing to clearer and more accurate images.

What are intra-chip and inter-chip sampling, and why is inter-chip sampling preferred for measuring CRT?

Intra-chip sampling refers to using input channels located within the same DRS4 chip for data acquisition. Inter-chip sampling involves using input channels located on different DRS4 chips. When measuring CRT with DRS4-based digitizers, inter-chip sampling is preferred because intra-chip sampling can lead to signal crosstalk, causing distortions in the timing data and artificially low CRT values. Therefore, inter-chip sampling provides more reliable and accurate timing measurements, as it minimizes the risk of signal interference.

What is signal crosstalk, and how does it affect CRT measurements in PET scanners?

Signal crosstalk is the interference of signals from one channel with those of another. In the context of DRS4 chips, signal crosstalk can occur during intra-chip sampling, where channels within the same chip interfere with each other. This interference can distort timing data and lead to inaccurate CRT measurements. Minimizing signal crosstalk is crucial for obtaining reliable timing information and ensuring the accuracy of PET images. This is why inter-chip sampling is preferred because the channels are far enough away from each other to minimize the impact.

What are the best practices for ensuring reliable CRT measurement when using DRS4-based digitizers?

To ensure reliable CRT measurement with DRS4-based digitizers, it is important to use inter-chip sampling to minimize signal crosstalk. This approach provides a more realistic assessment of the PET detector's timing resolution, leading to clearer and more precise images. Attention to data acquisition (DAQ) techniques is also essential to optimize performance and avoid distortions in timing data. By adhering to these best practices, medical professionals can enhance the accuracy of PET scans, improving diagnoses and patient care.