Beam-on imaging of short-lived positron emitters during proton therapy.

In vivo dose delivery verification in proton therapy can be performed by positron emission tomography (PET) of the positron-emitting nuclei produced by the proton beam in the patient. A PET scanner installed in the treatment position of a proton therapy facility that takes data with the beam on will see very short-lived nuclides as well as longer-lived nuclides. The most important short-lived nuclide for proton therapy is 12N (Dendooven et al 2015 Phys. Med. Biol. 60 8923-47), which has a half-life of 11 ms. The results of a proof-of-principle experiment of beam-on PET imaging of short-lived 12N nuclei are presented. The Philips Digital Photon Counting Module TEK PET system was used, which is based on LYSO scintillators mounted on digital SiPM photosensors. A 90 MeV proton beam from the cyclotron at KVI-CART was used to investigate the energy and time spectra of PET coincidences during beam-on. Events coinciding with proton bunches, such as prompt gamma rays, were removed from the data via an anti-coincidence filter with the cyclotron RF. The resulting energy spectrum allowed good identification of the 511 keV PET counts during beam-on. A method was developed to subtract the long-lived background from the 12N image by introducing a beam-off period into the cyclotron beam time structure. We measured 2D images and 1D profiles of the 12N distribution. A range shift of 5 mm was measured as 6 ± 3 mm using the 12N profile. A larger, more efficient, PET system with a higher data throughput capability will allow beam-on 12N PET imaging of single spots in the distal layer of an irradiation with an increased signal-to-background ratio and thus better accuracy. A simulation shows that a large dual panel scanner, which images a single spot directly after it is delivered, can measure a 5 mm range shift with millimeter accuracy: 5.5 ± 1.1 mm for 1 × 108 protons and 5.2 ± 0.5 mm for 5 × 108 protons. This makes fast and accurate feedback on the dose delivery during treatment possible.

Experimental evaluation of the resolution improvement provided by a silicon PET probe.

A high-resolution PET system, which incorporates a silicon detector probe into a conventional PET scanner, has been proposed to obtain increased image quality in a limited region of interest. Detailed simulation studies have previously shown that the additional probe information improves the spatial resolution of the reconstructed image and increases lesion detectability, with no cost to other image quality measures. The current study expands on the previous work by using a laboratory prototype of the silicon PET-probe system to examine the resolution improvement in an experimental setting. Two different versions of the probe prototype were assessed, both consisting of a back-to-back pair of 1-mm thick silicon pad detectors, one arranged in 32 × 16 arrays of 1.4 mm × 1.4 mm pixels and the other in 40 × 26 arrays of 1.0 mm × 1.0 mm pixels. Each detector was read out by a set of VATAGP7 ASICs and a custom-designed data acquisition board which allowed trigger and data interfacing with the PET scanner, itself consisting of BGO block detectors segmented into 8 × 6 arrays of 6 mm × 12 mm × 30 mm crystals. Limited-angle probe data was acquired from a group of Na-22 point-like sources in order to observe the maximum resolution achievable using the probe system. Data from a Derenzo-like resolution phantom was acquired, then scaled to obtain similar statistical quality as that of previous simulation studies. In this case, images were reconstructed using measurements of the PET ring alone and with the inclusion of the probe data. Images of the Na-22 source demonstrated a resolution of 1.5 mm FWHM in the probe data, the PET ring resolution being approximately 6 mm. Profiles taken through the image of the Derenzo-like phantom showed a clear increase in spatial resolution. Improvements in peak-to-valley ratios of 50% and 38%, in the 4.8 mm and 4.0 mm phantom features respectively, were observed, while previously unresolvable 3.2 mm features were brought to light by the addition of the probe. These results support the possibility of improving the image resolution of a clinical PET scanner using the silicon PET-probe.

Study of a high-resolution PET system using a silicon detector probe.

A high-resolution silicon detector probe, in coincidence with a conventional PET scanner, is expected to provide images of higher quality than those achievable using the scanner alone. Spatial resolution should improve due to the finer pixelization of the probe detector, while increased sensitivity in the probe vicinity is expected to decrease noise. A PET-probe prototype is being developed utilizing this principle. The system includes a probe consisting of ten layers of silicon detectors, each a 80 × 52 array of 1 × 1 × 1 mm(3) pixels, to be operated in coincidence with a modern clinical PET scanner. Detailed simulation studies of this system have been performed to assess the effect of the additional probe information on the quality of the reconstructed images. A grid of point sources was simulated to study the contribution of the probe to the system resolution at different locations over the field of view (FOV). A resolution phantom was used to demonstrate the effect on image resolution for two probe positions. A homogeneous source distribution with hot and cold regions was used to demonstrate that the localized improvement in resolution does not come at the expense of the overall quality of the image. Since the improvement is constrained to an area close to the probe, breast imaging is proposed as a potential application for the novel geometry. In this sense, a simplified breast phantom, adjacent to heart and torso compartments, was simulated and the effect of the probe on lesion detectability, through measurements of the local contrast recovery coefficient-to-noise ratio (CNR), was observed. The list-mode ML-EM algorithm was used for image reconstruction in all cases. As expected, the point spread function of the PET-probe system was found to be non-isotropic and vary with position, offering improvement in specific regions. Increase in resolution, of factors of up to 2, was observed in the region close to the probe. Images of the resolution phantom showed visible improvement in resolution when including the probe in the simulations. The image quality study demonstrated that contrast and spill-over ratio in other areas of the FOV were not sacrificed for this enhancement. The CNR study performed on the breast phantom indicates increased lesion detectability provided by the probe.

Silicon as an Unconventional Detector in Positron Emission Tomography.

Positron emission tomography (PET) is a widely used technique in medical imaging and in studying small animal models of human disease. In the conventional approach, the 511 keV annihilation photons emitted from a patient or small animal are detected by a ring of scintillators such as LYSO read out by arrays of photodetectors. Although this has been a successful in achieving ~5mm FWHM spatial resolution in human studies and ~1mm resolution in dedicated small animal instruments, there is interest in significantly improving these figures. Silicon, although its stopping power is modest for 511 keV photons, offers a number of potential advantages over more conventional approaches. Foremost is its high spatial resolution in 3D: our past studies show that there is little diffculty in localizing 511 keV photon interactions to ~0.3mm. Since spatial resolution and reconstructed image noise trade off in a highly non-linear manner that depends on the PET instrument response, if high spatial resolution is the goal, silicon may outperform standard PET detectors even though it has lower sensitivity to 511 keV photons. To evaluate silicon in a variety of PET "magnifying glass" configurations, an instrument has been constructed that consists of an outer partial-ring of PET scintillation detectors into which various arrangements of silicon detectors can be inserted to emulate dual-ring or imaging probe geometries. Recent results have demonstrated 0.7 mm FWHM resolution using pad detectors having 16×32 arrays of 1.4mm square pads and setups have shown promising results in both small animal and PET imaging probe configurations. Although many challenges remain, silicon has potential to become the PET detector of choice when spatial resolution is the primary consideration.

Sequence determination and analysis of S-adenosyl-L-homocysteine hydrolase from yellow lupine (Lupinus luteus).

The coding sequences of two S-adenosyl-L-homocysteine hydrolases (SAHases) were identified in yellow lupine by screenig of a cDNA library. One of them, corresponding to the complete protein, was sequenced and compared with 52 other SAHase sequences. Phylogenetic analysis of these proteins identified three groups of the enzymes. Group A comprises only bacterial sequences. Group B is subdivided into two subgroups, one of which (B1) is formed by animal sequences. Subgroup B2 consist of two distinct clusters, B2a and B2b. Cluster B2b comprises all known plant sequences, including the yellow lupine enzyme, which are distinguished by a 50-residue insert. Group C is heterogeneous and contains SAHases from Archaea as well as a new class of animal enzymes, distinctly different from those in group B1.

[Evaluation of illicit drug use among students from universities in Gdansk]. / Ocena uzywania srodków uzalezniajacych przez studentów wyzszych uczelni Gdanska.

Anonymous questionnaire examinations were performed among 1585 students from eight universities in Gdansk, including 664 men and 921 woman from 17 to 48 (mean 21.4 +/- 2.26) years old. Illicit drugs were used by 45.9% of them, including 33.7% applying sporadically. Since a large group of respondents (approx. 24%) used from two to seven narcotics, frequency of students' contacts with different narcotics, given below, was altogether higher than 45.9%. Women significantly less frequently than men were taken two or more illicit drugs (chi 2 = 69.4; p < 0.0001). Cannabis was used by approx. 41% respondents (including about 29.8% applying sporadically), amphetamine by about 11% (including about 7.4% applying sporadically), LSD and magic mushrooms approx. 3.7% each, cocaine 1.1%. A few students took opium alkaloids, ecstasy, jimson-weed, and peyote. Men applied illicit drugs significantly more often than women did (chi 2 = 65.16; p < 0.0001). Drug addicted students (approx. 1.4%) smoked more cigarettes and drunk more alcohol. The frequency of illicit drugs use was the highest among students from Academy of Fine Arts (about 70%), University School of Physical Education (about 58%) and Gdansk University (about 49%). Respondents of Priest Seminary have had no contacts with narcotics.

Filling mechanics of obstructed and de-obstructed rat urinary bladders.

Chronic bladder distension occurs after partial outlet obstruction and can lead to decompensation and impaired function. To quantify the degree of chronic bladder distension, we previously defined the zero pressure volume (ZPV), the largest contained volume at zero transmural pressure. In the current study, we investigated the short- and long-term effects of outlet obstruction and de-obstruction on chronic distension and passive bladder filling mechanics. Voiding patterns were measured 10 days (short term) or 6 weeks (long term) after partial bladder outlet obstruction and the bladders were tested in vitro at that time. De-obstructed bladders were obstructed for 6 weeks, and voiding patterns were measured 10 days or 6 weeks after de-obstruction, followed by in vitro testing. Mean voided volume was increased in de-obstructed bladders but not obstructed bladders. The volume of urine in the bladder at euthanasia was greater than mean voided volume in obstructed bladders and less than mean voided volume in de-obstructed bladders, indicating large residual urine in the obstructed bladders. ZPV was significantly increased only after long-term obstruction or de-obstruction. Similarly, intravesical pressure and mean bladder wall stress were increased only after long-term obstruction or de-obstruction. We conclude that tissue remodeling occurs in the bladder wall after long-term obstruction, possibly both as a result of and leading to chronic overdistension and high residual urine. Tissue remodeling occurs in the bladder wall after long-term de-obstruction, possibly due to large voided volumes. Neurourol. Urodynam. 18:659-671, 1999.

Estimating detrusor pressure at home in pediatric patients with myelomeningocele.

PURPOSE: We evaluated a method of estimating detrusor pressure at home in patients with myelomeningocele who perform clean intermittent catheterization to empty the bladder. MATERIALS AND METHODS: Patients with myelomeningocele who perform clean intermittent catheterization underwent cystometry. At home they determined bladder pressure before draining a full bladder and after partial draining with the bladder almost empty. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure. RESULTS: A total of 4 boys and 5 girls with a mean age plus or minus standard deviation of 9.6+/-7.9 years who were enrolled in our study made 16.9+/-15.2 home bladder pressure and volume recordings weekly each during a mean of 5.8+/-4.3 months. Mean bladder capacity determined at home was significantly greater than cystometric capacity (354+/-185 versus 250+/-146 ml.). At a mean home and cystometric volume of 190+/-110 ml. full bladder pressure at home was not significantly different from cystometric vesical pressure (31.0+/-8.8 versus 27.5+/-7.5 cm. water). At a mean volume of 23+/-15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure at full and almost empty volumes (14.1+/-5.5 versus 17.0+/-7.4 and 15.5+/-5.8 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0+/-6.3 versus 10.2+/-9.2 cm. water). CONCLUSIONS: Estimation of detrusor pressure at home is reliable and accurate in patients who perform clean intermittent catheterization. These pressure determinations may be used as a baseline for rapid identification of changes in bladder function.