PRaVDA: The first solid-state system for proton computed tomography.

PURPOSE: Proton CT is widely recognised as a beneficial alternative to conventional X-ray CT for treatment planning in proton beam radiotherapy. A novel proton CT imaging system, based entirely on solid-state detector technology, is presented. Compared to conventional scintillator-based calorimeters, positional sensitive detectors allow for multiple protons to be tracked per read out cycle, leading to a potential reduction in proton CT scan time. Design and characterisation of its components are discussed. An early proton CT image obtained with a fully solid-state imaging system is shown and accuracy (as defined in Section IV) in Relative Stopping Power to water (RSP) quantified. METHOD: A solid-state imaging system for proton CT, based on silicon strip detectors, has been developed by the PRaVDA collaboration. The system comprises a tracking system that infers individual proton trajectories through an imaging phantom, and a Range Telescope (RT) which records the corresponding residual energy (range) for each proton. A back-projection-then-filtering algorithm is used for CT reconstruction of an experimentally acquired proton CT scan. RESULTS: An initial experimental result for proton CT imaging with a fully solid-state system is shown for an imaging phantom, namely a 75 mm diameter PMMA sphere containing tissue substitute inserts, imaged with a passively-scattered 125 MeV beam. Accuracy in RSP is measured to be ⩽1.6% for all the inserts shown. CONCLUSIONS: A fully solid-state imaging system for proton CT has been shown capable of imaging a phantom with protons and successfully improving RSP accuracy. These promising results, together with system the capability to cope with high proton fluences (2×108 protons/s), suggests that this research platform could improve current standards in treatment planning for proton beam radiotherapy.

An acoustical study of the qin.

The qin (guqin, chi'in) is a seven-string zither of ancient lineage that is prominent in Chinese musical culture. The qin's history is intertwined with philosophy and folklore and its construction is replete with symbolism. The qin was associated with the Imperial aristocracy, and it remains an instrument of high culture. The qin is played with strings horizontal, and the soundbox is made in two halves; the front is usually carved out of paulownia and the back is a flat plate of catalpa. There are two sound holes in the back. It appears that no acoustical study of the qin has been published hitherto. This paper describes vibroacoustic measurements on five examples, the analysis of which reveals the qin's basic sound radiation mechanisms. At low frequencies the qin shows beam bending and torsional modes with some coupling to air in the cavity. At higher frequencies the radiation is dominated by a dense spectrum of mixed cavity and wood modes; the cavity modes are described by a one-dimensional transmission matrix model.

Vibrational behavior of a soundbox in an atmosphere with a variable speed of sound.

This paper describes a semi-quantitative method, suitable for a student laboratory exercise that shows that the acoustic properties of the soundbox of a musical instrument depend on the sound speed of the atmosphere surrounding and filling the instrument. A gas tent was constructed and used to enclose instruments in helium, carbon dioxide and mixtures thereof, allowing the sound speed to be varied from 250 to 1000 m/s. Soundboard admittance data were taken using a guitar and a violin as examples. The data, expressed as contour plots, show clearly the qualitative relationship between air and wood modes, and the guitar data are compared with a simple mechanical model. Experimental details of the construction and operation of gas tent are given, with attention paid to safety issues.

Vibroacoustic characteristics of a gothic harp.

The "gothic" style of harp was popular across most of Europe from the late medieval period to the Renaissance. These harps have a one-piece, longitudinally oriented hardwood soundboard, as opposed to the transverse-oriented bonded softwood structure on a modern instrument. In addition, the one-piece back is flexible, whereas the back of a modern instrument is a rigid molded shell. To study the gothic harp, one was constructed from plans created by the Boston Museum of Fine Arts from a late German model in their collection. The vibrational behaviors of the soundboard and soundbox were measured at various stages of construction. The completed instrument was subjected to modal analysis and radiativity measurements. The sound radiation is dominated by two breathing modes at 188 and 273 Hz, each with strong motion of the back, and modes around 350 Hz. Taken together, these modes function like the A0/T1 resonance pairs seen in the soundboxes of other instruments, and a comparison is made with the guitar. Also observed is that as the frequency increases, radiation is emitted from higher up the soundboard, and from higher soundholes. This feature has been observed in other harps, and is a consequence of the harp family's unique geometry.

Vibro-acoustic characteristics of an Aoyama Amphion concert harp.

The mechanical admittance of the soundboards of four full-size concert harps from three manufacturers was measured, and the results show that there is little variation between them. More detailed vibro-acoustic data were then obtained for an Aoyama Amphion harp. Analysis of these data show that the individual soundholes amplify the radiated sound in successive frequency bands associated with the modal frequencies of the soundboard. The lower holes tend to contribute at the lower end of the frequency scale, and the higher holes at the higher end of the scale.

Vibrational characteristics of harp soundboards.

Harps exist in different forms, from large factory-made concert harps to small hand-made folk harps. This variety presents both a challenge and an opportunity for acousticians. The musical quality of a harp depends on many factors, but key among these is the soundboard. This work sets out to define some general desirable qualities of a harp soundboard. First, in order to understand the relationship between the vibrational behavior of a bare soundboard and that of a completed instrument, a 36-string harp was built from scratch. Measurements were made at each stage of construction, and the results showed how the bare soundboard properties affect those of the finished harp. Second, the soundboards of several harps of different sizes were assessed by measuring the admittances along the string bar. These data showed that one relationship crucial to the quality of the soundboard is that between the modal shapes and modal frequencies of the soundboard, and the position and fundamental frequencies of the strings attached to it. A general statement is made about this relationship, one which should be of use to harp makers.