Homogenized tissue phantoms for quantitative evaluation of subsurface fluorescence contrast

The use of phantoms comprising diluted tissue homogenates with a buried capillary containing quantum dots is demonstrated as a method to investigate the optical and biophysical factors influencing the imaging of subsurface fluorescence contrast agents. Validation of the method is demonstrated using both liquid phantoms of known optical absorption and reduced scattering and Monte Carlo computer simulations of photon transport. Conclusions regarding the optimal excitation wavelength are given and quantified with respect to the tissue optical properties. The tissue homogenate method should be of value for quantitative optimization studies relevant to, for example, endoscopic imaging.     

X-ray imaging optimization using virtual phantoms and computerized observer modelling

This study develops and demonstrates a realistic x-ray imaging simulator with computerized observers to maximize lesion detectability and minimize patient exposure. A software package, ViPRIS, incorporating two computational patient phantoms, has been developed for simulating x-ray radiographic images. A tomographic phantom, VIP-Man, constructed from Visible Human anatomical colour images is used to simulate the scattered portion using the ESGnrc Monte Carlo code. The primary portion of an x-ray image is simulated using the projection ray-tracing method through the Visible Human CT data set. To produce a realistic image, the software simulates quantum noise, blurring effects, lesions, detector absorption efficiency and other imaging artefacts. The primary and scattered portions of an x-ray chest image are combined to form a final image for computerized observer studies and image quality analysis. Absorbed doses in organs and tissues of the segmented VIP-Man phantom were also obtained from the Monte Carlo simulations. Approximately 25,000 simulated images and 2,500,000 data files were analysed using computerized observers. Hotelling and Laguerre-Gauss Hotelling observers are used to perform various lesion detection tasks. Several model observer tasks were used including SKE/BKE, MAFC and SKEV. The energy levels and fluence at the minimum dose required to detect a small lesion were determined with respect to lesion size, location and system parameters.     

Phantom material for quantitative evaluation of MR images

Reference material for quantitative Magnetic Resonance Imaging (MRI) has been developed by combining heavy and light water (D2O, H2O), gelling agent agar, and paramagnetic transition metal ions (Gd3+). The process of preparation is described. By in vitro measurement of relaxation times, T1 and T2, it can be shown that tissue relevant values are achievable. The influence of different relaxation times, as well as the effect of different proton spin densities, on MRI signal intensities is determined. Some similarities existing between the magnetic resonance behaviour of tissue water and phantom substance water are discussed.     

Aliasing effects in digital images of line-pair phantoms

Line-pair phantoms are commonly used for evaluating screen-film systems. When imaged digitally, aliasing effects give rise to additional periodic patterns. This paper examines one such effect that medical physicists are likely to encounter, and which can be used as an indicator of super-resolution.     

Fluorescence-enhanced optical imaging of large phantoms using single and simultaneous dual point illumination geometries

Fluorescence-enhanced optical tomography is typically performed using single point illumination and multiple point collection measurement geometry. Single point illumination is often insufficient to illuminate greater volumes of large phantoms and results in an inadequate fluorescent signal to noise ratio (SNR) for the majority of measurements. In this work, the use of simultaneous multiple point illumination geometry is proposed for acquiring a large number of fluorescent measurements with a sufficiently high SNR. As a feasibility study, dual point excitation sources, which are in-phase, were used in order to acquire surface measurements and perform three-dimensional reconstructions on phantoms of large volume and/or significant penetration depth. Measurements were acquired in the frequency-domain using a modulated intensified CCD imaging system under different experimental conditions of target depth (1.4-2.8 cm deep) with a perfect uptake optical contrast. Three-dimensional reconstructions of the fluorescence absorption from the dual point illumination geometry compare well with the reconstructions from the single point illumination geometry. Targets located up to 2 cm deep were located successfully, establishing the feasibility of reconstructions from simultaneous multiple point excitation sources. With improved excitation light rejection, multiple point illumination geometry may prove useful in reconstructing more challenging domains containing deeply embedded targets. Image quality assessment tools are required to determine the optimal measurement geometry for the largest set off imaging tasks.     

A language for generating tomographic images of mathematical phantoms

A computer language is presented that can be used to generate image files, as if the images are created with a CT or a MR scanner. The language defines objects in the "scanner's" coordinate system, as sets of quadratic inequalities. Each of these objects, e.g., an ellipsoid or a half-plane or a cylinder, has its own density. Objects can be superimposed and collections of objects are allowed to translate and rotate. The language allows for a concise way of describing complex objects with precisely defined geometries and densities. An implementation of the language can be used for testing, developing, and analyzing diagnostic software, treatment planning systems, etc. A software module that is based on the language can be made available. The utility of the module for acceptance testing of radiation therapy treatment planning systems is described.     

The use of quantitative ultrasound to monitor fracture healing: a feasibility study using phantoms

Fracture healing has traditionally been monitored subjectively using manual manipulation of the fracture site and evaluation of radiographic images. A more objective method of monitoring would provide obvious advantages, allowing healing progress to be quantitatively assessed and so providing the opportunity for early detection of problems. A tibia phantom was used to investigate whether the longitudinal propagation velocity of ultrasound across a fracture site could be used quantitatively to assess fracture healing. The characteristic of fracture healing simulated by the phantom was the changing gap between the bone ends at the fracture site. The ultrasound velocity was measured using a recently developed machine, the SoundScan 2000 (Myriad Ultrasound Systems Ltd, Israel). The precision of the SoundScan 2000 was found to be 0.4% in vitro. Ultrasound velocity predicted the simulated fracture gap with a high degree of accuracy (R2 = 0.994). The measured and the theoretically calculated velocity for different widths between the simulated bone ends was found to be highly correlated with a coefficient of determination of 0.998. This result shows that the use of quantitative ultrasound to monitor fracture healing warrants further investigation in vivo.     

The use of quantitative ultrasound to monitor fracture healing: a feasibility study using phantoms

Fracture healing has traditionally been monitored subjectively using manual manipulation of the fracture site and evaluation of radiographic images. A more objective method of monitoring would provide obvious advantages, allowing healing progress to be quantitatively assessed and so providing the opportunity for early detection of problems. A tibia phantom was used to investigate whether the longitudinal propagation velocity of ultrasound across a fracture site could be used quantitatively to assess fracture healing. The characteristic of fracture healing simulated by the phantom was the changing gap between the bone ends at the fracture site. The ultrasound velocity was measured using a recently developed machine, the SoundScan 2000 (Myriad Ultrasound Systems Ltd, Israel). The precision of the SoundScan 2000 was found to be 0.4% in vitro. Ultrasound velocity predicted the simulated fracture gap with a high degree of accuracy (R²=0.994). The measured and the theoretically calculated velocity for different widths between the simulated bone ends was found to be highly correlated with a coefficient of determination of 0.998. This result shows that the use of quantitative ultrasound to monitor fracture healing warrants further investigation in vivo.     

Fiberglass limb phantoms: fabrication and use for quantitative scintigraphy

Quantitative radionuclide scintigraphy often requires empirical calibration factors derived from phantoms which simulate the radioactivity distribution, tissue geometry and tissue composition of the region of interest. This paper describes a method in which casts made with fiberglass tape of the region of interest. This paper describes a method in which casts made with fiberglass tape are used to form realistic, water-fillable phantoms of the limbs. Phantoms were constructed for the hind legs of the dog and rabbit, species frequently used in developing new radioscintigraphic techniques. Leg bones removed from euthanized animals were mounted anatomically within the casts. The dimensions of the phantom cavities were determined by x-ray computed tomography. A procedure was developed for orienting the phantoms to match the hind leg geometry of a given experimental setup. Use of the phantoms for image activity calibration is illustrated for a geometric-mean counting technique used to determine 99mTc activity densities in soft-tissue regions of the dog thigh. Generalization of the calibration technique to planar and tomographic imaging is straightforward. In situ measurements of 99mTc activity density obtained by external counting were compared with in vitro radioassays of excised tissue. For 22 tissue samples obtained from four dogs, the in situ and in vitro data were linearly correlated (r = 0.98, p much less than or equal to 0.001) over a 50-fold range of activity density. The mean and standard deviation of the observed percent discrepancies [% discrepancy = 100 (in situ - in vitro)/in vitro] were (7.8 +/- 2.9) and (13.7 +/- 2.1), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

A quantitative objective method for the evaluation of anti-sperm cell-mediated immunity in humans.

Anti-sperm cell-mediated immunity (CMI) is considered as a crucial facet of infertility in patients of both sexes. A precise and objective method is designed, based on a one-step agarose leukocyte migration inhibition factor (LMIF) assay. The migration areas are evaluated by a computer-assisted image analysis system. Optimal concentrations of leukocytes and sperm, as well as technical conditions are described. The radial migration indexes (RMI) and area migration indexes (AMI) are computed and expressed as a migration index (MI) percentage for each patient or control. Preliminary clinical results indicate a highly significant association between migration inhibition and cases of 'immunopathological infertility'. The method described is considered a promising tool for a rapid and quantitative evaluation of a suspected anti-sperm CMI in infertile and recurrently aborting patients.     

Laser reflectance imaging of human forearms and their tissue-equivalent phantoms

Laser back-scattered radiation from a human forearm is affected by the compositional variation in tissues and was imaged by a reflectance imaging system. The measurement probe consisted of one input fibre and one output fibre, separated by a distance of 0.3 cm. The diffuse reflectance data were collected by placing the probe on the forearm. By interpolation and median filtering of these data, the colourcoded reflectance images of the forearms of ten subjects were reconstructed. For comparative analysis of the mean reflectance, the forearm area was divided into ten regions. The mean normalised back-scattered intensity (NBI) near the ulnar region of the wrist was 4.76±0.24% and was significantly higher (p<0.0005) compared with that at other regions, which varied from 3.49±0.17% to 4.43±0.14%. Tissue-equivalent phantoms of these, required for the clinical assessment of optical techniques, were constructed using various combinations of paraffin wax and dyes. The matching of the NBI images of these stable and inexpensive phantoms with those of the forearms of the respective subjects showed the similarity of their optical parameters.     

Spherical aberration correction in multiphoton fluorescence imaging using objective correction collar

Multiphoton microscopy has evolved into a powerful bioimaging tool in three dimensions. However, the ability to image biological specimens in-depth can be hindered by sample spherical aberration and scattering. These two phenomena can result in the degradation of image resolution and the loss of detected multiphoton signal. In this work, we use the correction collar (for cover glass thickness) associated with a water immersion objective in an attempt to improve multiphoton imaging. In the two samples we examined (human skin and rat tail tendon), we found that while the improvement in image resolution was not visible qualitatively, the measured axial fluorescence or second harmonic generation signal profiles indicate that the use of the correction collar can help to improve the detected multiphoton signals. The maximum increases are 36% and 57% for the skin (sulforhodamine B fluorescence) and tendon (second harmonic generation) specimens, respectively. Our result shows that for in-depth multiphoton imaging, the correction collar may be used to correct for spherical aberration. However, each tissue type needs to be examined to determine the optimal correction collar setting to be used.     

Anniversary paper: evaluation of medical imaging systems

Medical imaging used to be primarily within the domain of radiology, but with the advent of virtual pathology slides and telemedicine, imaging technology is expanding in the healthcare enterprise. As new imaging technologies are developed, they must be evaluated to assess the impact and benefit on patient care. The authors review the hierarchical model of the efficacy of diagnostic imaging systems by Fryback and Thornbury [Med. Decis. Making 11, 88-94 (1991)] as a guiding principle for system evaluation. Evaluation of medical imaging systems encompasses everything from the hardware and software used to acquire, store, and transmit images to the presentation of images to the interpreting clinician. Evaluation of medical imaging systems can take many forms, from the purely technical (e.g., patient dose measurement) to the increasingly complex (e.g., determining whether a new imaging method saves lives and benefits society). Evaluation methodologies cover a broad range, from receiver operating characteristic (ROC) techniques that measure diagnostic accuracy to timing studies that measure image-interpretation workflow efficiency. The authors review briefly the history of the development of evaluation methodologies and review ROC methodology as well as other types of evaluation methods. They discuss unique challenges in system evaluation that face the imaging community today and opportunities for future advances.     

Evaluations of magnetic resonance imaging parameters with simple phantoms

Imaging parameters associated with a clinical magnetic resonance imaging (MRI) system, evaluated with the use of simple and inexpensive phantoms, are described in evaluation of a clinical MRI system. Images, obtained with a Diasonics 0.35-T MRI system using an elliptical whole-body radio frequency coil, are presented which demonstrate geometric distortion, inaccuracy of image dimensions, and artifacts. Measurements of reproducibility and uniformity of both signal intensity and spin-lattice relaxation times are presented for uniform phantoms. Replicate measurements are analyzed by two-way analyses of variance to determine the significance of variations as a function of position and slice. Apparent T1's are not significantly different among the slices for the images analyzed, but there is a significant effect due to position in the field. Direct measurement of the radio frequency field for the center slice follows a pattern which is similar. Spin-lattice relaxation times are compared among two-point calculations and nonlinear four-point calculations, and the effects of pooling data are found to increase the precision of T1 measurements.