In this article, we discuss the fundamental modes, time-skew error, and Dual-ended readout of monolithic crystals. Then, we discuss what each of these modes means. After that, we'll talk about some important features to watch out for. Moreover, you'll be given an idea of how the crystals perform when combined with monolithic blocks. To help you, we will also discuss the difference between dual-ended and single-ended readouts.
Time-skew error
To obtain a reasonable time-skew error estimate, it is necessary to know the exact time of the gamma event. To calculate the time-skew error, we used a model involving a symmetric LYSO detector and a 22Na point source. The model assumes that the energy of the source remains constant during the experiment. The result is the time-skew error estimates are based on the average number of channels crossing the threshold.
We calculated the time-skew error for two monolithic crystals. Each of them was independently calibrated and measured in coincidence, with the source and detector placed between the blocks. This method yielded CTR values when averaging up to eight timestamps. The best timing resolution was attained at 660 p.f.w.h.m. with the sixth earliest timestamp weighted by energy. This method considered all impacts of the scintillation volume.
Fundamental mode
A basic property of crystals is the ability to generate fundamental modes. Monolithic crystals exhibit these modes in different ways. For example, the fundamental mode (M1) has a wavelength of 10 MHz, while the anharmonic mode (M2) has a wavelength of 12.5 MHz. There are various geometrical configurations of monolithic crystals, each with a fundamental mode. The basic properties of monolithic crystals are discussed in this article.
One common type of monolithic crystal filter is a two-pole cascaded structure. This configuration offers better out-of-band rejection, with an insertion loss of less than 10 dB. In a cascaded configuration, two or more monolithic crystals are fabricated into a single filter, with the output produced by amplification and acoustic coupling. Monolithic crystal filters can also be used in high-frequency RF applications. They can provide extremely high out-of-band rejection.
Anharmonic overtones
Anharmonic overtones are vibrational modes that are higher than the fundamental frequency of the material. In this way, they help to describe all of a material's properties. However, this is not enough to describe the properties of a monolithic crystal. Anharmonic effects need to be considered when describing a crystal's properties. The following section examines the nature of these modes.
The fundamental mode of the crystal constitutes the desired resonances in the pass band. On the other hand, anharmonic overtones are unwanted resonances. The resonator vibrates in series of harmonic overtones of its fundamental mode, each of which corresponds to an anharmonic overtone. The fundamental mode of a monolithic crystal may be designed with a harmonic frequency as its center frequency.
Dual-ended readout
To achieve high spatial and temporal resolution, the Dual-ended readout for monolithic polyhedral crystals requires two detectors coupled to opposite ends of the array. The DOI, or difference in intensity, is then calculated by comparing the signal amplitudes from the two detectors. This method is particularly useful in the measurement of small-scale structure changes, such as crystals of lutetium-yttrium ox orthosilicate, where the DOI is 2mm. The disadvantage of this method is that the array size and the number of detectors required are doubled. This, in turn, increases the costs.
With a Dual-ended readout for monolithic LYSO crystals, high-resolution PET imaging is now a reality. The system's unique design combines eight detector modules with a monolithic LYSO crystal array. Each module contains eight detectors, forming a ring. The Dual-ended readout for monolithic crystals provides summed signals of pixels on each row and column. The design also allows for accurate centroid measurement and 1.6 mm full width at half-maximum resolution. For one-millimeter resolution, a 1 mm source correction is required.
Position decoding of gamma ray impacts
To estimate the DOI of gamma ray impacts on a monolithic crystal, one must strike a balance between computational cost and DOI resolution. In this paper, we present a simple and accurate method to reconstruct DOI from two side readouts of a monolithic scintillator. This method only requires one dimensional look-up tables, which is suitable for monolithic crystals.
The DOI response was calculated for two different Y positions, Y = 1.8 mm and Y = 0 mm. This approach allows us to determine the point of interaction within the monolithic crystal array and improve its sensitivity. We also investigated the timing resolution using the spatial distribution of the photons at the detector array. Moreover, the DOI capability was evaluated in various regions of the monolithic crystal.
LYSO crystals
The LYSO monolithic crystals are characterized by an eight-fold array of SiPM elements. The more SiPM elements are present in the crystal, the more distinct the scintillation light distribution will be. The energy spectra of different LYSO crystals are compared.
The two major types of LYSO crystals are monolithic and multilith. The latter are ideal for clinical PET applications, enabling decoding of 3D photon impact position. Both types of crystals are suited for both TOF and conventional PET scanners. Monolithic crystals can be used with a wide range of sensitivity. They can also be used in a typical ring configuration.