Optical phantom materials for near infrared laser photocoagulation studies.

BACKGROUND AND OBJECTIVE: Phantoms were developed that simulate tissue with dynamic and static optical properties with which to study the effects of laser irradiation. STUDY DESIGN/MATERIALS AND METHODS: Albumen, agar, and an absorbing dye (Naphthol Green) were combined to form a phantom with heat sensitive optical properties to mimic tissue response. The optical properties of this phantom were measured by using the added absorber technique. A polyacrylamide phantom with static optical properties was designed with the equivalent values of micro(a) and micro'(s) by combining appropriate concentrations of Naphthol Green and Intralipid-10%. RESULTS: The absorption and reduced scattering coefficient of the phantoms were 0. 50 +/- 0.04 cm(-1) and 2.67 +/- 0.07 cm(-1) respectively, in the native state at 805 nm. In the coagulated state, the absorption and scattering coefficient were 0.7 +/- 0.1 cm(-1) and 13.1 +/- 0.5 cm(-1) respectively. CONCLUSION: Two phantoms with dynamic or static optical properties were developed with properties similar to tissue. They may be used in future studies of opto-thermal effects in tissues.     

Understanding why contrast enhancement in dynamic MRI is not reproducible: illustration with a simple phantom

Abstract: The goal of this work was to verify in a phantom study the necessity of a calibration method for comparison in dynamic contrast-enhanced magnetic resonance imaging (MRI) examinations. A perspex phantom with a dilution series of Gd-DTPA was used to measure the dynamic signal enhancement of a sequence. With nine MRI scanners from Bruker (0.23, 0.5, and 2 Tesla), Philips [0.5 and 1.5 Tesla (ACS-NT and S15)], and Siemens (0.2, 1.0, and 1.5 Tesla) one 2D FLASH and two 3D FLASH experiments were performed under identical measurement conditions. Under different measurement conditions (2D and 3D FLASH, TR, TE, FA) different characteristics in signal enhancement exist on a scanner. The same measurement conditions at different scanners (same magnetic field strength) also result in different signal enhancement. Dynamic contrast enhanced MRI examinations from different measurement conditions or scanners cannot be compared. To solve this problem a calibration is needed.     

Design and Characterisation of a Tissue Phantom System for Optical Diagnostics

We present an optical phantom system especially suited to investigating the generation and transport of laser-induced fluorescence in biological tissues. The phantom system consists of micrometre-sized particles of aluminium oxide, iron and coloured resin dispersed in a solid, transparent host (polyorganosiloxane), from which mechanically stable samples can be made. Mie theory is applied to predict the radiation transport parameters from the optical properties of the isolated components. The predictions are in good agreement with the results of integrating sphere measurements. The radiation transport parameters of the samples are reproducible and temporally stable. Received for publication 4 June 1997; accepted following revision 8 November 1997.     

The propagation of optical radiation in tissue. II: Optical properties of tissues and resulting fluence distributions

This paper is the second of two reviewing the propagation of electromagnetic radiation of wavelength 0.25–10m in tissue. This part begins with a discussion of how the fundamental optical interaction coefficients of tissue may be measured. Both direct methods, in which the coefficients are measured for optically thin samples, and indirect methods, in which the coefficients are inferred from measurements on bulk samples are described. The difficulties inherent in both types of measurement are outlined. Next the wavelength dependence of the scattering and absorption coefficient is discussed, both from a heuristic point of view and by illustration from current literature. We illustrate how the optical spectrum can be divided into regions where the propagation of light is dominated by absorption or scattering effects. Finally we show how the distribution of light fluence in these spectral regions is dramatically different and illustrate the important features of these distributions.     

Virtual reality hand therapy: A new tool for nonopioid analgesia for acute procedural pain,hand rehabilitation,and VR embodiment therapy for phantom limb pain

IntroductionAffordable virtual reality (VR) technology is now widely available. Billions of dollars are currently being invested into improving and mass producing VR and augmented reality products.Purpose of the StudyThe purpose of the present study is to explore the potential of immersive VR to make physical therapy/occupational therapy less painful, more fun, and to help motivate patients to cooperate with their hand therapist.DiscussionThe following topics are covered: a) psychological influences on pain perception, b) the logic of how VR analgesia works, c) evidence for reduction of acute procedural pain during hand therapy, d) recent major advances in VR technology, and e) future directions—immersive VR embodiment therapy for phantom limb (chronic) pain.ConclusionVR hand therapy has potential for a wide range of patient populations needing hand therapy, including acute pain and potentially chronic pain patients. Being in VR helps reduce the patients’ pain, making it less painful for patients to move their hand/fingers during hand therapy, and gamified VR can help motivate the patient to perform therapeutic hand exercises, and make hand therapy more fun. In addition, VR camera–based hand tracking technology may be used to help therapists monitor how well patients are doing their hand therapy exercises, and to quantify whether adherence to treatment increases long-term functionality. Additional research and development into using VR as a tool for hand therapist is recommended for both acute pain and persistent pain patient populations.     

Performance of a dedicated light delivery and dosimetry device for photodynamic therapy of nasopharyngeal carcinoma: phantom and volunteer experiments

The objective of this study was to develop a light delivery and measurement device for photodynamic therapy (PDT) in the nasopharyngeal cavity, which achieves a homogeneous and reproducible fluence rate distribution to a target area and provides proper shielding of predefined risk areas.MATERIALS AND METHODS: A flexible silicone applicator was developed, incorporating light delivery and dosimetry fibers. The applicator can be inserted through the mouth and fixed in the nasopharyngeal cavity. Tissue optical phantoms were prepared on the basis of optical properties measured in vivo using diffuse reflectance spectroscopy (DRS). The fluence rate over the length of the applicator surface was measured in air, in tissue optical phantoms and in five healthy volunteers. RESULTS: The fluence rate distribution over the applicator surface in air and tissue optical phantom was found to be more homogeneous (SD/mean 3.8% and 18.3%, respectively) than the fluence rate distribution in five volunteers (SD/mean ranging from 19% up to 52%). The maximum observed fluence rate build-up in the nasopharynx varied between subjects and ranged from a factor of 4.1-6.9. Shielding of the risk area such as the soft palate and tongue was effective. CONCLUSIONS: In air and in tissue optical phantoms the fluence rate distribution of the device was highly homogeneous. The observed inter-subject and intra-subject variations in fluence rate in healthy volunteers originated from differences in optical properties and nasopharyngeal geometry. Light delivery based on a single tissue surface measurement will not be adequate. In situ dosimetric measurements are required to determine the light fluence delivered to a geometrically complex site such as the nasopharynx. These observations should be taken in consideration when developing light applicators for PDT of the nasopharynx and other non-uniform surfaces.     

Three-dimensional image registration of phantom vertebrae for image-guided surgery: a preliminary study.

OBJECTIVE: Applications of three-dimensional ultrasound (3D US) are emerging throughout the field of medicine. In this study, tracked, free-hand 3D phantom US images were mapped to computed tomograms (CT) as a development for image-guided surgery (IGS) of the spine. In the operating room, the registration of tracked 3D US images to other imaging modalities, such as CT, could allow the surgeon to identify more precisely the surgical target area prior to the incision. An independent quantitative measure of registration accuracy using a fiducial marker system was provided. METHODS: Three-dimensional free-hand US images of a phantom spine were created by tracking the transducer with an optical sensing system. Two sets of images were acquired from three lumbar vertebrae using 4.5- and 7.5-MHz transducers. These images were then segmented for the extraction of the posterior vertebral surface. Next, a surface-based registration of US to the corresponding segmented CT images was performed. Registration errors were computed as the distance between a set of target points transformed using the experimental transformation and the same set of target points transformed using fiducial markers as a gold standard. RESULTS: Results indicated that alignment of these image sets is feasible using only part of the vertebral surface. In particular, the regions of the spinous process and laminae were used for registration. Target registration errors (TREs) were found to be lowest using the highest resolution CT images. Using the CT scans with 2-mm slice thickness, the TRE was calculated to be 1.33 +/- 0.30 mm for the 7.5-MHz US data set and 2.81 +/- 0.10 mm for the 4.5-MHz US data set. Moreover, residual errors in these surface alignments were 0.69 +/- 0.18 mm and 0.61 +/- 0.20 mm for the 4.5- and 7.5-MHz sets, respectively. CONCLUSION: A rigid, surface-based registration of CT images to phantom spinal US images, acquired with a free-hand, tracked transducer, is achievable with a limited, easily obtainable portion of the vertebral surface.     

A chemically defined medium for the propagation of rat prostate adenocarcinoma cells

A chemically defined medium (MB-DF) has been developed for the propagation of the rat prostate adenocarcinoma cell line (PA-III). The medium (MB-DF) was supplemented with fetuin, insulin, transferrin, dexamethasone, and 5α-dihydrotestosterone, but require no serum supplement. The adapted line, PA-III,. has been grown in this serum-free medium for 30 passages over a period of 12 months without losing the malignant or other characteristics of the parent line. When transplanted into syngeneic rats, the PA-III, cells reconstituted the adenocarcinoma and metastasized spontaneously via ipsilateral lymphatic channels to the lungs. This cell line will be of use in further analyses of enzymes associated with biological properties of the tumor cells.     

Enhancement of light propagation depth in skin: cross-validation of mathematical modeling methods

Various techniques to enhance light propagation in skin have been studied in low-level laser therapy. In this study, three mathematical modeling methods for five selected techniques were implemented so that we could understand the mechanisms that enhance light propagation in skin. The five techniques included the increasing of the power and diameter of a laser beam, the application of a hyperosmotic chemical agent (HCA), and the whole and partial compression of the skin surface. The photon density profile of the five techniques was solved with three mathematical modeling methods: the finite element method (FEM), the Monte Carlo method (MCM), and the analytic solution method (ASM). We cross-validated the three mathematical modeling results by comparing photon density profiles and analyzing modeling error. The mathematical modeling results verified that the penetration depth of light can be enhanced if incident beam power and diameter, amount of HCA, or whole and partial skin compression is increased. In this study, light with wavelengths of 377 nm, 577 nm, and 633 nm was used.     

Fluid management and strength postsimulated use of primary and secondary dressings for treating diabetic foot ulcers: Robotic phantom studies

Non‐offloaded diabetic heel ulcers and the wound dressings used to treat them may be subjected to considerable bodyweight forces. A novel robotic foot phantom with a diabetic heel ulcer was designed and constructed to test the combined performances of applied primary and secondary dressings, in simulated non‐offloaded (standing) and offloaded (supine) postures. We specifically compared the performances of the primary Exufiber dressing (Mölnlycke Health Care) combined with the secondary Mepilex Border Flex dressing (Mölnlycke) against a corresponding pair from an alternative manufacturer. Fluid retention and distribution between the primary and secondary dressings of each pair were determined using weight tests, and mechanical strength of the primary dressings was further measured postsimulated use through tensile testing. The Exufiber and Mepilex Border Flex pair performed similarly in the two simulated postures (retention = ~97%), whereas the comparator pair exhibited a 13%‐decrease in retention for a supine to standing transition. Furthermore, the Exufiber dressing delivered up to 2‐times more fluid to its paired secondary dressing and endured 1.7‐times greater strain energy than the corresponding primary dressing before failure occurred. The present robotic foot phantom and associated methods are versatile and suitable for testing any dressing, in consideration of the relevant clinical factors and practice.     

Surgery in Afghanistan: a light model for field surgery during war.

Owing to a poor capability for evacuation, mobile medical teams were sent to the area of Gazni in Afghanistan to work with local paramedics as part of a medical programme for the area. The teams were equipped to perform major surgery. During 1 month a surgical team inside Afghanistan performed 53 operations. The operations were performed in the patients' homes at night. The team had to move frequently so as not to be spotted by the Soviet and government surveillance. Equipment equivalent to a light field hospital was stored in a safe place and the team carried supplies for 1 or 2 days on their bicycles. One postoperative death and one wound infection were recorded. It is concluded that adequate surgery can be performed inside territories where enemy forces have air control and under primitive conditions with an acceptable rate of complications. However, due to the nature of the guerrilla warfare with scattered military confrontations over vast areas, the average time between injury and treatment for war casualties was 36 h.     

Stokes polarimetry imaging of rat-tail tissue in a turbid medium using incident circularly polarized light

BACKGROUND AND OBJECTIVES: We describe a Stokes polarimetry imaging technique that quantifies the polarization properties of remitted light backscattered from a sample. STUDY DESIGN/MATERIALS AND METHODS: Right- and left-circularly polarized near-infrared light was used to illuminate rat-tail tissue embedded in turbid gelatin. RESULTS: The degree of linear polarization (DoLP) and degree of circular polarization (DoCP) image-maps indicate that increasing the depth of the rat tail within the turbid medium and varying the rat-tail geometry and orientation relative to the light source affected the contrast between structures and adjacent tissue layers. CONCLUSION: Stokes polarimetry imaging shows that the intervertebral discs and soft tissue regions of rat tails strongly depolarize incident circularly polarized light. Tendon regions remit light with a more linear form due to birefringence. Both DoLP and DoCP image-maps provide contrast between tissue structures. When differentiating between unpolarized light and light with low DoCP or DoLP, the polarization of backscattered light from the turbid medium must to be taken into consideration.     

Molecular genetic studies of gene identification for osteoporosis: a 2004 update.

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.     

Elastolytic and collagenolytic studies of arteries. Implications for the mechanical properties of aneurysms

Studies were performed in vitro on cylindrical segments of 56 canine common carotid arteries, 32 human external iliac arteries, nine internal iliac arteries, and ten common iliac arteries, using purified elastase and purified collagenase. Treatment with elastase caused the canine vessels to dilate but to remain intact. Similar results were obtained with the human vessels, except that treatment with elastase caused only slight dilation. All canine and human vessels treated with collagenase ruptured. We concluded that wall integrity depends on intact collagen rather than elastin. Comparison between external iliac arteries and internal and common iliac arteries showed that the latter vessels exhibited dramatically greater dilatation and compliance changes after treatment with collagenase. This finding corresponds to the greater tendency of aneurysms to develop in internal and common iliac arteries.