Evaluation of Adjoint Methods in Photoacoustic Tomography with Under-Sampled Sensors

Photo-Acoustic Tomography (PAT) can reconstruct a distribution of optical absorbers acting as instantaneous sound sources in subcutaneous microvasculature of a human breast. Adjoint methods for PAT, typically Time-Reversal (TR) and Back-Projection (BP), are ways to refocus time-reversed acoustic signals on sources by wave propagation from the position of sensors. TR and BP have different treatments for received signals, but they are equivalent under continuously sampling on a closed circular sensor array in two dimensions. Here, we analyze image quality with discrete under-sampled sensors in the sense of the Shannon sampling theorem. We investigate resolution and contrast of TR and BP, respectively in one source-sensor pair configuration and the frequency domain. With Hankel's asymptotic expansion to the integrands of imaging functions, our main contribution is to demonstrate that TR and BP have better performance on contrast and resolution, respectively. We also show that the integrand of TR includes additional side lobes which degrade axial resolution whereas that of BP conversely has relatively small amplitudes. Moreover, omnidirectional resolution is improved if more sensors are employed to collect the received signals. Nevertheless, for the under-sampled sensors, we propose the Truncated Back-Projection (TBP) method to enhance the contrast of BP using removing higher frequency components in the received signals. We conduct numerical experiments on the two-dimensional projected phantom model extracted from OA-Breast Database. The experiments verify our theories and show that the proposed TBP possesses better omnidirectional resolution as well as contrast compared with TR and BP with under-sampled sensors

Presentations and word problem for strong semilattices of semigroups

Let I be a semilattice, and Si (i ∈ I) be a family of disjoint semigroups. Then we prove that the strong semilattice S = S[I, Si , φj,i] of semigroups Si with homomorphisms φj,i : Sj → Si (j ≥ i) is finitely presented if and only if I is finite and each Si (i ∈ I) is finitely presented. Moreover, for a finite semilattice I, S has a soluble word problem if and only if each Si (i ∈ I) has a soluble word problem. Finally, we give an example of nonautomatic semigroup which has a soluble word problem

High-Speed High Effiency Large Area Resonant Cavity Enhanced p-I-n Photodiodes for Multimode Fiber Communications

Cataloged from PDF version of article.In this letter, we report AlGaAs–GaAs p-i-n photodiodes with a 3-dB bandwidth in excess of 10 GHz for devices as large as 60- m diameter. Resonant cavity enhanced photodetection is employed to improve quantum efficiency, resulting in more than 90% peak quantum efficiency at 850 nm

Comparing Venous Reconstructions and Antimicrobial Graft Reconstructions in Mycotic Abdominal Aortic Aneurysms and Aortic Graft Infections

Background: The perioperative mortality and morbidity rates of surgical repair of mycotic abdominal aortic aneurysms and aortic graft infections are high, and the appropriate treatment is debated. This retrospective study compared venous and antimicrobial prosthetic aortic graft reconstructions. Methods: All patients of the Northwest Clinics and St. Antonius Hospital who were treated for mycotic abdominal aortic aneurysms or aortic graft infections between January 1, 2008, and January 1, 2018, were analyzed. Exclusion criterion was treatment other than venous or antimicrobial reconstructions. Primary end points were 30-day complications and mortality rates and 3-year overall survival. Secondary end points were reintervention-free survival, persistent infection and reinfection rates, and hospital length of stay. Results: Fifty-one patients met the inclusion criteria, of whom 32 underwent venous reconstructions and 19 antimicrobial prosthetic aortic graft reconstructions. Baseline characteristics did not differ significantly between these groups, except for duration of surgical repair, which was longer in the venous group. The 30-day and 1-year mortality rates, reinfection rates, complication rates, and hospital length of stay did not significantly differ between the groups. The 3-year overall survival was 77% for venous reconstruction compared with 66% for antimicrobial reconstruction (P = 0.781). The 30-day reintervention rate was 19% for the venous group compared with 42% for the prosthetic group (P = 0.071). Reintervention-free survival at 3 years was 46% for the venous group compared with 52% for the prosthetic group (P = 0.615). Conclusions: Venous reconstruction tends to have better 3-year overall survival and lower 30-day reintervention rates compared with antimicrobial prosthetic graft reconstruction in patients with mycotic abdominal aortic aneurysms or abdominal aortic graft infections. In the acute setting, antimicrobial prosthetic graft reconstruction is a valuable solution due to the shorter operation time and similar 30-day mortality and complication rates

Deformable Model for 3D Intramodal Nonrigid Breast Image Registration with Fiducial Skin Markers

We implemented a new approach to intramodal non-rigid 3D breast image registration. Our method uses fiducial skin markers (FSM) placed on the breast surface. After determining the displacements of FSM, finite element method (FEM) is used to distribute the markers’ displacements linearly over the entire breast volume using the analogy between the orthogonal components of the displacement field and a steady state heat transfer (SSHT). It is valid because the displacement field in x, y and z direction and a SSHT problem can both be modeled using LaPlace’s equation and the displacements are analogous to temperature differences in SSHT. It can be solved via standard heat conduction FEM software with arbitrary conductivity of surface elements significantly higher than that of volume elements. After determining the displacements of the mesh nodes over the entire breast volume, moving breast volume is registered to target breast volume using an image warping algorithm. Very good quality of the registration was obtained. Following similarity measurements were estimated: Normalized Mutual Information (NMI), Normalized Correlation Coefficient (NCC) and Sum of Absolute Valued Differences (SAVD). We also compared our method with rigid registration technique

Repeatability, and Intra-Observer and Interobserver Agreement of Two Dimensional Perfusion Angiography in Patients with Chronic Limb Threatening Ischaemia

Objective. Two dimensional (2D) perfusion angiography is a method that provides quantitative foot perfusion information from standard digital subtraction angiography acquisitions. The aim of this study was to test the reliability of this method in patients with chronic limb threatening ischaemia (CLTI) by investigating repeatability, and intra-observer and interobserver agreement. Methods: Twenty patients with CLTI and a below the knee endovascular revascularisation were included in a prospective clinical study. Prior to treatment two perfusion angiography runs were acquired with a five minute interval without performing an intervention. In these recordings, regions of interest were selected and time density curves and perfusion parameters were determined. To investigate intra-observer agreement one observer performed five measurements on the same acquisition for each patient. To investigate interobserver agreement three observers performed measurements on the same acquisition for each patient. Results were presented in Bland-Altman plots and as the intraclass correlation coefficient per parameter. Results: Two patients were excluded from repeatability analyses because of major motion artefacts. Repeatability analyses of the 18 remaining patients showed excellent correlation for every parameter (> .96). Intra-observer and interobserver agreement for all 20 patients were excellent for all parameters (1.00). Conclusion: Repeatability and intra-observer and interobserver agreement of 2D perfusion angiography in patients with CLTI were found to be excellent. It is therefore a reliable tool when used according to the standardised methods described in this study

High bandwidth-efficiency resonant cavity enhanced Schottky photodiodes for 800-850 nm wavelength operation

Cataloged from PDF version of article.High-speed resonant cavity enhanced Schottky photodiodes operating in 800-850 nm wavelength region are demonstrated. The devices are fabricated in the AlGaAs/GaAs material system. The Schottky contact is a semitransparent Au film which also serves as the top reflector of the Fabry-Perot cavity. The detectors exhibit a peak quantum efficiency of eta = 0.5 at lambda = 827 nm wavelength and a 3 dB bandwidth of more than 50 GHz resulting in a bandwidth-efficiency product of more than 25 GHz. (C) 1998 American Institute of Physic

High-speed >90% quantum-efficiency p–i–n photodiodes with a resonance wavelength adjustable in the 795–835 nm range

Cataloged from PDF version of article.We report GaAs/AlGaAs-based high-speed, high-efficiency, resonant cavity enhanced p–i–nphotodiodes. The devices were fabricated by using a microwave-compatible fabrication process. By using a postprocess recess etch, we tuned the resonance wavelength from 835 to 795 nm while keeping the peak efficiencies above 90%. The maximum quantum efficiency was 92% at a resonance wavelength of 823 nm. The photodiode had an experimental setup-limited temporal response of 12 ps. When the system response is deconvolved, the 3 dB bandwidth corresponds to 50 GHz, which is in good agreement with our theoretical calculations. © 1999 American Institute of Physic

Injury to the lacrimal apparatus after endoscopic sinus surgery: Surgical implications from active transport dacryocystography

In order to evaluate the lacrimal drainage system injury after functional endoscopic sinus surgery, surgical records and postoperative active transport dacryocystography imaging of 31 patients were analyzed. Presence of the lacrimal bone dehiscence and no passage of the contrast material into the inferior meatus were noted as the signs of injury to the lacrimal canal on active transport dacryocystography. Bony dehiscence was detected in 53.2% of the operated sides but 20% of the nonoperated sides. No passage of the contrast material into the inferior meatus was observed in 14.9% of the operated sides. There were no cases of epiphora postoperatively. The lacrimal drainage system injury was more frequently observed on the left sides operated. We conclude that lacrimal drainage system injury might occur in various extents during functional endoscopic sinus surgery. However, it does not necessarily result in postoperative epiphora. Performing the middle meatal antrostomy in posteroinferior direction, and uncinectomy with backbiting forceps or a shaver might help in reducing the lacrimal injury. Active transport dacryocystography can be adopted as an alternative diagnostic tool in detection of the lacrimal injury. (Otolaryngol Head Neck Surg 2001;124:308-12.) Functional endoscopic sinus surgery (FESS) has gained popularity among otorhinolaryngologists since its first introduction in mid-70s. The primary reason is probably that it enables direct visualization of intranasal anatomic structures and pathologies. Although the procedure seems to be easy to perform, it is indeed a delicate operation, and surgical injury to the neighboring structures does still occur. Various important complications such as cerebrospinal fluid leak and blindness have been reported following FESS. 1 Nevertheless, lacrimal injury is frequently overlooked. Lacrimal drainage system (LDS) is one of the most vulnerable structures to the surgical trauma in the course of FESS due to its intimate anatomic localization. Epiphora after LDS injury has been reported to range from 0.3 to 1.7%. 2-4 However, LDS injury does not necessarily result in epiphora. Asymptomatic cases, which had the intraoperative occult damage, have also been reported in 15% of the patients undergoing endoscopic ethmoidectomies. 3 Therefore, assessing the anatomic integrity and function of the LDS is important. Several methods have been used for evaluation of the LDS. METHODS AND MATERIALS In order to examine the degree and type of possible injury to the LDS, 31 patients who underwent FESS at the otorhinolaryngology department of Celal Bayar University School of Medicine in Manisa, Turkey, were postoperatively evaluated with ATD. Clinical records regarding the age and gender of the patients, diagnosis, type of operation, and surgical findings as well as the period between the operation and ATD evaluation were retrospectively analyzed. Patients who had preoperative epiphora or previous dacryocystorhinostomy operation were excluded from the study. The parameters studied on ATD examination for the evaluation of the LDS injury were the integrity of the bony lacrimal canal and its patency, which was indicated by observation of the nonionic contrast material in the inferior meatus. Operative and ATD findings were analyzed separately on the left and right sides in each patient. In unilateral cases, ATD findings on the nonoperated side were also recorded as a control group. The side differences in all surgical interventions and differences in findings between the operated and the nonoperated sides in unilateral cases were statistically analyzed. A t test was used in statistical analysis for the comparison of the percentages. All patients were operated on using the technique of FESS described by Stammberger 1 and Kennedy et a

Robust Entanglement in Atomic Systems via Lambda-Type Processes

It is shown that the system of two three-level atoms in $\Lambda$ configuration in a cavity can evolve to a long-lived maximum entangled state if the Stokes photons vanish from the cavity by means of either leakage or damping. The difference in evolution picture corresponding to the general model and effective model with two-photon process in two-level system is discussed.Comment: 10 pages, 3 figure