João Alfredo Santos

Stereo reconstruction of a submerged scene

This article presents work dedicated to the study of refraction effects between two media in stereo reconstruction of a tridimensional scene. This refraction induces nonlinear effects making the stereo processing highly complex. We propose a linear approximation which maps this problem into a new problem with a conventional solution. We present results taken both from synthetic images generated by a raytracer and results from real life scenes.

Preliminary assessment of the dose to the interventional radiologist in fluoro-CT-guided procedures.

A preliminary assessment of the occupational dose to the intervention radiologist received in fluoroscopy computerised tomography (CT) used to guide the collection of lung and bone biopsies is presented. The main aim of this work was to evaluate the capability of the reading system as well as of the available whole-body (WB) and extremity dosemeters used in routine monthly monitoring periods to measure per procedure dose values. The intervention radiologist was allocated 10 WB detectors (LiF: Mg, Ti, TLD-100) placed at chest and abdomen levels above and below the lead apron, and at both right and left arms, knees and feet. A special glove was developed with casings for the insertion of 11 extremity detectors (LiF:Mg, Cu, P, TLD-100H) for the identification of the most highly exposed fingers. The H(p)(10) dose values received above the lead apron (ranged 0.20-0.02 mSv) depend mainly on the duration of the examination and on the placement of physician relative to the beam, while values below the apron are relatively low. The left arm seems to receive a higher dose value. H(p)(0.07) values to the hand (ranged 36.30-0.06 mSv) show that the index, middle and ring fingers are the most highly exposed. In this study, the wrist dose was negligible compared with the finger dose. These results are preliminary and further studies are needed to better characterise the dose assessment in CT fluoroscopy.

Impact of tumor contrast in orthogonal ray imaging: A prostate irradiation study

A new very-low-dose imaging technology to assist external-beam radiotherapy treatments has been proposed. This technique, called orthogonal ray imaging, does not require X-ray source rotation around the target. It is based on the detection of photons escaping the target at almost right angles with respect to the incoming photon flux. Modern image-guided radiation therapy techniques allow an accurate positioning of the patient, consequently improving the treatment accuracy. However, some of these techniques, such as electronic portal imaging and mega-voltage cone-beam computed tomography provide poor resolution in soft tissues. Other techniques like kilovoltage cone-beam computed tomography, allow a good visualization of these type of tissues but at the cost of an increase of the dose delivered to the patient, consequently increasing the risk of possible side-effects on the surrounding healthy tissues. One way to enhance the contrast of the lesion region is by injecting a contrast agent. The aim of this study was to evaluate through simulation the benefit of iodinated-contrast agent (Ultravist 370) administration in cases of prostate cancer in OrthoCT using the Geant4 simulation toolkit and the anthropomorphic phantom NCAT. We conclude that (1) in all studied scenarios it was possible to obtain OrthoCT images with good visual agreement with the simulated dose as well as the phantom pelvic structures with a maximum dose of the order of 2mGy and (2) the administration of 100mL of Ultravist 370 is not enough to allow the visualization of the tumor or the normal prostate tissue.

Gafchromic XR-QA2 film as a complementary dosimeter for hand-monitoring in CTF-guided biopsies

Computed tomography fluoroscopy (CTF) is a useful imaging technique to guide biopsies, particularly lung biopsies, but it also has the potential for very high hand exposures, despite use of quick-check method and needle holders whenever feasible. Therefore, reliable monitoring is crucial to ensure the safe use of CTF. This is a challenge, because ring dosimeters monitor exposure only at the base of one finger, while the fingertips may be exposed to the highly collimated CT beam. In this work we have explored the possibility of using Gafchromic XR-QA2 self-developing film as a complementary dosimeter to quantify hand exposure during CTF-guided biopsies. A glove used in a previous study and designed to contain 11 TLDs was adapted to include Gafchromic strips 7 mm wide, covering the fingers. A total of 22 biopsies were successfully performed wearing this GafTLD glove under sterile gloves, and the IR reported no difficulty or reduction of dexterity while wearing it. Comparison of dose distributions obtained from digitization of the Gafchromic film strips and absolute Hp(0.07) readings from TLDs showed good agreement, despite some positional uncertainty due to relative movement. Per procedure, doses at the base of the ring finger can be as low as 3%-8% of hand dose maximum. Accumulated dose at the base of the ring finger was four times lower than the dose maximum. PACS numbers: 07.57.Kp, 29.40.-n, 85.25.Pb, 87.57.qp.Computed tomography fluoroscopy (CTF) is a useful imaging technique to guide biopsies, particularly lung biopsies, but it also has the potential for very high hand exposures, despite use of quick‐check method and needle holders whenever feasible. Therefore, reliable monitoring is crucial to ensure the safe use of CTF. This is a challenge, because ring dosimeters monitor exposure only at the base of one finger, while the fingertips may be exposed to the highly collimated CT beam. In this work we have explored the possibility of using Gafchromic XR‐QA2 self‐developing film as a complementary dosimeter to quantify hand exposure during CTF‐guided biopsies. A glove used in a previous study and designed to contain 11 TLDs was adapted to include Gafchromic strips 7 mm wide, covering the fingers. A total of 22 biopsies were successfully performed wearing this GafTLD glove under sterile gloves, and the IR reported no difficulty or reduction of dexterity while wearing it. Comparison of dose distributions obtained from digitization of the Gafchromic film strips and absolute Hp(0.07) readings from TLDs showed good agreement, despite some positional uncertainty due to relative movement. Per procedure, doses at the base of the ring finger can be as low as 3%–8% of hand dose maximum. Accumulated dose at the base of the ring finger was four times lower than the dose maximum. PACS numbers: 07.57.Kp, 29.40.‐n, 85.25.Pb, 87.57.qp

Monitoring Tumor Lung Irradiation With Megavoltage Patient-Scattered Radiation: A Full System Simulation Study

We analyze by simulation a fully-3-D, low-dose imaging system aiming at assisting external-beam radiotherapy, either for on-board patient imaging, or for real-time radiotherapy monitoring. The system consists in detecting megavoltage patient-scattered radiation that is emitted at right angles with respect to the beam axis. Since photon scattering in the patient occurs with higher intensity in tissues of higher density, a multislice photon detection system positioned perpendicularly to the beam axis yields a signal correlated with patient morphology, including the tumor. We thus report on GEANT4 simulations carried out with an anthropomorphic phantom in order to analyze the capability of the system to detect pertinent and clinically relevant scenarios, e.g., lung tumor deviation and tumor regression/progression. The signal distribution obtained with a realistic full system (including the multislice collimator, the scintillator crystals, and the charge electronic readout mode) show a very high visual agreement both with the simulated, prescribed dose, and with the tumor location/size, as well as with the phantom structures. The capability of this system to obtain morphological images without X-ray source rotation potentially allows to highly reduce dose in healthy tissues and organs at risk in respect to other existing image-guided radiation therapy techniques, thus complementing them.

Observation of tumor morphological changes in lung irradiation with orthogonal ray imaging: RTmonitoring - A simulation study

Orthogonal ray imaging is a new potential technique that consists in detecting radiation dispersed in the patient and emitted perpendicularly to the beam axis. RTmonitoring aims at real time radiotherapy (RT) monitoring. OrthoCT addresses low-dose patient morphologic imaging, mainly on-board for assisting RT (not studied here). We report Geant4 simulations analyzing the capability of RTmonitoring to detect (1) a lung tumor deviation of 9.36mm, (2) a tumor shrinkage of 9.36mm, and (3) a tumor growth of 30mm. The original spherical tumor has the density of water and a diameter of ca 30mm. In RT treatment planning security margins are added around the tumor to be irradiated in order to account for these and other RT disturbing mechanisms. Here, despite not addressing a real treatment plan, we simulate the aforementioned tumor morphological changes to investigate whether an RTmonitoring system can be useful in detecting such changes. Indeed, tumor dislocation/modification in the lung represents a topic of strong research and development worldwide for all forms of RT. A beam missing the dislocated tumor will represent an underdosage that may be strongly correlated with tumor relapse. On the other hand, the detection of tumor shrinkage in lung RT may allow for a reduction of the dose field, which represents an important relief of the dose burden to the surrounding healthy lung. It is known that healthy lung tissue subjected to RT doses result at times in fibrosis which impairs respiratory function. Finally, detection of tumor growth represents equally an important asset in RT due to the evident tumor underdosage if such scenario is missed. We show that the counts distributions obtained with RTmonitoring result in a very high visual correlation both with the simulated, original dose distribution, and with the tumor location. Therefore, this technique is likely to represent a high potential asset for image-guided RT, adaptive RT, and real-time RT dose verification.

Application to the Port of Sines of a new tool for risk assessment in port navigation

This paper describes a first approach on the risk assessment in port navigation using GUIOMAR, an integrated system for port and coastal engineering modelling developed at the National Civil Engineering Laboratory (LNEC), Portugal, using a GIS software environment. A set of automatic procedures was designed to include a new methodology based on the amplitude of the wave-induced vertical movement of a ship along its trajectory. In this methodology, the risk in port navigation is assessed on the basis of a combination of the probability of exceedance of a pre-set threshold for the ship’s vertical movements and its consequences. To test the new procedures, a set of sea wave records obtained at the Sines wave-buoy from 1988 to 2002 was transferred into Sines Port using two numerical models of sea wave propagation and deformation (SWAN and DREAMS), included in the GUIOMAR system. The numerical model WAMIT was used for estimating the wave-induced ship’s vertical movements inside the port. By applying the new procedures, automatic generation of risk maps was carried out for navigation in the vicinity of the West breakwater of the Port of Sines. The recent developments contribute towards a more versatile and efficient GUIOMAR system, which results in a more adequate tool to support decision-making processes in port and coastal management.

Low Cost Alternative to Lead Glass Shielding in PET/CT Control/Scanner Room Window

The aim of this work is to propose a reasonably priced alternative to expensive lead glass used in PET/CT windows connecting the control room and the scanner room. These windows can be extremely useful to detect if the patient needs quickly to be assisted, for anesthesia surveillance when needed, among several other purposes and is mandatory to exist in these facilities. The window must provide also radiation protection to the worker inside the control room. One way to accomplish this task is to use lead glass. However, lead glass is expensive and is usually manufactured as predetermined lead equivalent thicknesses (frequently 2 mm or more). It is also designed to be lead equivalent with nominal thicknesses specified for radiology energy ranges. Depending on the distances involved and on the workload, since the photon energy irradiating from PET patients is significantly higher (511 keV) than other nuclear medicine and radiology procedures, it is usually necessary to protect the professionally exposed worker with a high thickness of lead or lead equivalent glass. For a big area window, a lead glass plate can be quite expensive. In this work it is presented a less expensive solution using common glass with thickness higher than 15 cm. Calculations are presented for typical situations and workloads, assuring protection both from PET and CT.

Wave Effects on Ships Moored at Figueira Da Foz Harbour

The Figueira da Foz harbour is located at the mouth of the Mondego River in the West coast of Portugal. Two shore-connected breakwaters that, due to their layout, have a quite poor performance shelter it. In fact, some of the incident waves cause large movements in the ships moored at the general cargo quay. The breakage of mooring lines is a quite common accident there. This paper presents the methodology employed and summarizes the results obtained in both the wave penetration study when the harbour basin is dredged up to -7.00 m C.D. and the study of the wave effects on the behaviour of a ship moored at the general cargo quay. INTRODUCTION The Figneira da Foz harbour, Fig. 1, is located at the mouth of the Mondego River on the West coast of Portugal. It is protected by two shore-connected breakwaters: the so-called North (776 m long, crest level +6.00 m C.D.) and South (980 m long, crest level +6.00 m C.D.) breakwaters. The harbour entrance is 250 m wide and faces west. The port facilities are distributed on both margins of the Mondego River and include a general cargo quay, a marina and a fishing dock. Nowadays, the seabed depth at the outer-harbour and at the harbour channel is around -5.00 m C.D.. Close to North breakwater head the seabed depth reaches -14.00 m C.D.. The wave regime at the harbour entrance, Fortes et al. (2000), is characterized by wave directions ranging from SW (225 ~ to W-60~ (330~ the most frequent wave directions being those of the sector W to NW. The values of the zero crossing period, Tz, range from 6 to 14 s. The significant wave heights vary between 0.16 and 8.4 m, the most common values being in the interval 0.5 to 3.0 m. Records from the Port Authority Research Officer, jasantos@tnec.pt, 2 Research Officer, gneves@lnec.pt, 3 Research Assistant, jfortes@lnec.pt Hydraulics Department, L.N.E.C., 1700-066 Lisboa, Portugal