Agnese Lucesoli

A Nonrigid Registration of MR Breast Images Using Complex-valued Wavelet Transform

In this paper, a fast, slice-by-slice, nonrigid registration algorithm of dynamic magnetic resonance breast images is presented. The method is based on a multiresolution motion estimation of the breast using complex discrete wavelet transform (CDWT): the pyramid of oriented complex subimages is used to implement a hierarchical phase-matching-based motion estimation algorithm. The resulting motion estimate is nonrigid and pixel-independent. To assess the method performance, we computed the correlation coefficient and the normalized mutual information between pre- and postcontrast images with and without realignment. The indices increased after using our approach and the improvement was superior to rigid or affine registration. A set of clinical scores was also evaluated. The clinical validation demonstrated an increased readability in the subtraction images. In particular, CDWT registration allowed a best definition of breast and lesion borders and greater detail detectability.

A method for dynamic subtraction MR imaging of the liver

BackgroundSubtraction of Dynamic Contrast-Enhanced 3D Magnetic Resonance (DCE-MR) volumes can result in images that depict and accurately characterize a variety of liver lesions. However, the diagnostic utility of subtraction images depends on the extent of co-registration between non-enhanced and enhanced volumes. Movement of liver structures during acquisition must be corrected prior to subtraction. Currently available methods are computer intensive. We report a new method for the dynamic subtraction of MR liver images that does not require excessive computer time.MethodsNineteen consecutive patients (median age 45 years; range 37–67) were evaluated by VIBE T1-weighted sequences (TR 5.2 ms, TE 2.6 ms, flip angle 20°, slice thickness 1.5 mm) acquired before and 45s after contrast injection. Acquisition parameters were optimized for best portal system enhancement. Pre and post-contrast liver volumes were realigned using our 3D registration method which combines: (a) rigid 3D translation using maximization of normalized mutual information (NMI), and (b) fast 2D non-rigid registration which employs a complex discrete wavelet transform algorithm to maximize pixel phase correlation and perform multiresolution analysis. Registration performance was assessed quantitatively by NMI.ResultsThe new registration procedure was able to realign liver structures in all 19 patients. NMI increased by about 8% after rigid registration (native vs. rigid registration 0.073 ± 0.031 vs. 0.078 ± 0.031, n.s., paired t-test) and by a further 23% (0.096 ± 0.035 vs. 0.078 ± 0.031, p < 0.001, paired t-test) after non-rigid realignment. The overall average NMI increase was 31%.ConclusionThis new method for realigning dynamic contrast-enhanced 3D MR volumes of liver leads to subtraction images that enhance diagnostic possibilities for liver lesions.

Stationary Mode Distribution and Sidewall Roughness Effects in Overmoded Optical Waveguides

In this paper, the authors investigate analytically the transformation from the initial guided mode distribution to the stationary state and the effects of the bidimensional roughness profile, in multimode polymeric buried waveguides. In these structures, due to the geometrical dimensions and the operating wavelength, about a thousands of guided modes can propagate, even for weak core/cladding dielectric contrast. The coupling coefficients are computed by exploiting the geometrical features of the optical channels, such as the waveguide dimensions and the roughness surface statistics. The analysis gives insight on the guided/guided and guided/radiated mode interaction, and higher order solution is proposed, in the case of a great number of modes interacting over distances that are extremely long as compared to the signal wavelength and the roughness correlation length. Experimental results are valuated by means of semicontact atomic force microscopy as well as compared with existing numerical models.

Distance optical sensor for quantitative endoscopy

We present a novel optical sensor able to measure the distance between the tip of an endoscopic probe and the anatomical object under examination. In medical endoscopy, knowledge of the real distance from the endoscope to the anatomical wall provides the actual dimensions and areas of the anatomical objects. Currently, endoscopic examination is limited to a direct and qualitative observation of anatomical cavities. The major obstacle to quantitative imaging is the inability to calibrate the acquired images because of the magnification system. However, the possibility of monitoring the actual size of anatomical objects is a powerful tool both in research and in clinical investigation. To solve this problem in a satisfactory way we study and realize an absolute distance sensor based on fiber optic low-coherence interferometry (FOLCI). Until now the sensor has been tested on pig trachea, simulating the real humidity and temperature (37 degrees C) conditions. It showed high sensitivity, providing correct and repeatable distance measurements on biological samples even in case of very low reflected power (down to 2 to 3 nW), with an error lower than 0.1 mm.

Size measurement in endoscopic images by low coherence interferometry

We present a novel optical sensor that is able to measure the real dimensions and areas of anatomical objects in endoscopic images by taking advantage of the knowledge of the real distance from the endoscope tip to the anatomical wall under examination. At present the major obstacle to quantitative endoscopy is the inability of calibrating the acquired images because of the magnification system. In order to solve this problem in a satisfactory way we have studied and realized a new system combining an imaging system, applied to a clinical endoscope, with an absolute distance sensor based on fiber optic low coherence interferometry (FOLCI). Up to now the sensor has been tested on pig trachea, simulating the real humidity and temperature (37 °C) conditions. The sensor show high sensitivity, providing correct measurements of the size of biological samples even in the case of very low reflected power (down to 2–3 nW).

Quantitative endoscopy by FOLCI-based distance sensor

In medical endoscopy, quantifying anatomical dimensions would be of great help, but the appropriate tools are not yet available. We present a novel method for the calibration and size measurement of endoscopic images. We realized an optical sensor, based on Fiber Optic Low Coherence Interferometry (FOLCI), capable of measuring the absolute distance between the tip of an endoscopic probe and an anatomical object under inspection. We showed that this sensor provides very sensitive and accurate (error lower than 0.1 mm) measurements of biological samples. The sensing fiber of the sensor was introduced in the operative channel of an Olympus rhinoscope. After calibrating the endoscope magnification system as a function of the distance, our system was capable of providing the size of any object included in the field of view of the endoscope. Tests performed on planar targets and pig trachea showed the accuracy of the system to be adequate for allowing quantitative dimensional information.

Low-Coherence Interferometry Optical Sensor for the Characterization of Deposited Thin Film

Non-destructive sensor for the measurement of thickness and refractive index of polymeric layers deposit on glass bases. The sensor is oriented to the manufacture of polymers for O-PCB interconnects. Michelson FOLCI configuration has been applied. Article not available.

Optical Ranging in Endoscopy: Towards Quantitative Imaging

Nowadays endoscopic analysis is limited to a direct and qualitative view of internal anatomy. On the other hand, the measurement of the actual size of anatomical objects could be a powerful instrument both in research and in clinical survey. For instance, an important application could be monitoring lesion size, both during diagnosis and in follow-up. The foremost obstacle to quantitative imaging is the incapability of measuring the distance between the endoscopic probe and the anatomical object under examination, since the dimension of the object in the image depends on that distance. This problem has not been solved yet in a satisfactory way.

Parasitic Coupling Effects in Multimode Buried Channel Waveguides Arrays for O-PCB Interconnects

The use of buried channel waveguides in optical printed circuits boards (O-PCB) offers the possibility of overcoming some problems and limitations encountered in high-frequency electrical interconnects. Although the use of optical waveguides reduces significantly crosstalk and electromagnetic interferences, parasitic coupling effects between the buried channels may appear when waveguide arrays are realized. In this paper, we analyze theoretically and experimentally the conditions inducing crosstalk effects in a multimode array, realized by means of a conventional photolithographic patterning technique. In particular, the results show how the common configuration used to pattern an array of optical waveguides produces a parasitic slab waveguide close to the core channels, accounting for a substantial increase of the coupling effects.

Characterization of Optical PCB Interconnects by Means of Low-Coherence Interferometry

Thanks to the low-coherence interferometry it is possible to characterize the transmission of highly dense multimode polymeric waveguides for the O-PCB. In particular the attenuation and the multi-modal dispersion are directly deduced by interferometry patterns.