Browsing by Subject "Image Processing, Computer-Assisted"

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Open Access
Accelerated phase-cycled SSFP imaging with compressed sensing
(Institute of Electrical and Electronics Engineers Inc., 2015) Çukur, T.
Balanced steady-state free precession (SSFP) imaging suffers from irrecoverable signal losses, known as banding artifacts, in regions of large B0 field inhomogeneity. A common solution is to acquire multiple phase-cycled images each with a different frequency sensitivity, such that the location of banding artifacts are shifted in space. These images are then combined to alleviate signal loss across the entire field-of-view. Although high levels of artifact suppression are viable using a large number of images, this is a time costly process that limits clinical utility. Here, we propose to accelerate individual acquisitions such that the overall scan time is equal to that of a single SSFP acquisition. Aliasing artifacts and noise are minimized by using a variable-density random sampling pattern in k-space, and by generating disjoint sampling patterns for separate acquisitions. A sparsity-enforcing method is then used for image reconstruction. Demonstrations on realistic brain phantom images, and in vivo brain and knee images are provided. In all cases, the proposed technique enables robust SSFP imaging in the presence of field inhomogeneities without prolonging scan times. © 2014 IEEE.
Open Access
Functional subdomains within human FFA
(Society for Neuroscience, 2013) Çukur, T.; Huth, A. G.; Nishimoto, S.; Gallant, J. L.
The fusiform face area (FFA) is a well-studied human brain region that shows strong activation for faces. In functional MRI studies, FFA is often assumed to be a homogeneous collection of voxels with similar visual tuning. To test this assumption, we used natural movies and a quantitative voxelwise modeling and decoding framework to estimate category tuning profiles for individual voxels within FFA. We find that the responses in most FFA voxels are strongly enhanced by faces, as reported in previous studies. However, we also find that responses of individual voxels are selectively enhanced or suppressed by a wide variety of other categories and that these broader tuning profiles differ across FFA voxels. Cluster analysis of category tuning profiles across voxels reveals three spatially segregated functional subdomains within FFA. These subdomains differ primarily in their responses for nonface categories, such as animals, vehicles, and communication verbs. Furthermore, this segregation does not depend on the statistical threshold used to define FFA from responses to functional localizers. These results suggest that voxels within FFA represent more diverse information about object and action categories than generally assumed. © 2013 the authors.
Open Access
Malignant-lesion segmentation using 4D co-occurrence texture analysis applied to dynamic contrast-enhanced magnetic resonance breast image data
(2007) Woods, B.J.; Clymer, B.D.; Kurc, T.; Heverhagen J.T.; Stevens, R.; Orsdemir, A.; Bulan O.; Knopp, M.V.
Purpose: To investigate the use of four-dimensional (4D) co-occurrence-based texture analysis to distinguish between nonmalignant and malignant tissues in dynamic contrast-enhanced (DCE) MR images. Materials and Methods: 4D texture analysis was performedon DCE-MRI data sets of breast lesions. A model-free neural network-based classification system assigned each voxel a "nonmalignant" or "malignant" label based on the textural features. The classification results were compared via receiver operating characteristic (ROC) curve analysis with the manual lesion segmentation produced by two radiologists (observers 1 and 2). Results: The mean sensitivity and specificity of the classifier agreed with the mean observer 2 performance when compared with segmentations by observer 1 for a 95% confidence interval, using a two-sided t-test with α = 0.05. The results show that an area under the ROC curve (Az) of 0.99948, 0.99867, and 0.99957 can be achieved by comparing the classifier vs. observer 1, classifier vs. union of both observers, and classifier vs. intersection of both observers, respectively. Conclusion: This study shows that a neural network classifier based on 4D texture analysis inputs can achieve a performance comparable to that achieved by human observers, and that further research in this area is warranted. © 2007 Wiley-Liss, Inc.
Open Access
Polymorphism of spermatocytic seminoma. A morphometric study
(Hindawi Publishing Corporation, 1994) Frasik, W.; Okoń, K.; Sokołowski, A.
Spermatocytic seminoma (SS) is one of the testicular tumours. It is distinguished from other germ cell neoplasms by a special type of polymorphism. The aim of the present study was a morphometric analysis (Microplane II image system) of this phenomenon. In histological slides we measured the profile area of nuclei in about 500 adjacent cells. The basic material consisted of 12 cases (c.) of infiltrating SS, and the comparative material included intracanalicular SS (IcSS-1c.), other types of seminoma - typical (TS-2 c.), anaplastic (AS-2c.) and spermatogenesis in an elderly man (Sg-1 c.). We carried out a statistical analysis of the populations of cellular nuclei: we determined nuclear population similarities and differences, as well as their relation to various types of standard distributions such as Erlang, gamma, lognormal, normal and Weibull. Part of the SS histograms including IcSS showed similarities. The mean value of the profile area range from 32.5 to 56.5 μm2. In other types of seminomas this value was much higher. The Kolmogorov-Smirnov two-sample test showed differences between the compared nuclear populations. Lack of the differences was found only between certain SS (including IcSS). The results of comparisons of the populations studied with standard distributions showed that the analysed nuclear populations can be successfully described by more than one theoretical distribution. However, among the spermatocytic seminomas analysed, in contrast to TS and AS, we found distributions not corresponding to any of the standard distributions. The results of our findings argue also against the occurrence of haploid nuclei in SS cells. In slides from SS there were forms much larger than the nuclei of spermatocytes in Sg. In combination with the data concerning ploidy of the neoplasm we postulate that SS nuclear polymorphism is dependent both on maturation and atypia.
Open Access
Tracking the position and rotational orientation of a catheter using a transmit array system
(IEEE, 2013) Celik, H.; Mahcicek, D. I.; Senel, O.; Wright, G. A.; Atalar, Ergin
A new method for detecting the rotational orientation and tracking the position of an inductively coupled radio frequency (ICRF) coil using a transmit array system is proposed. The method employs a conventional body birdcage coil, but the quadrature hybrid is eliminated so that the two excitation channels can be used separately. The transmit array system provides RF excitations such that the body birdcage coil creates linearly polarized and changing RF pulses instead of a conventional rotational forward-polarized excitation. The receive coils and their operations are not modified. Inductively coupled RF coils are constructed on catheters for detecting rotational orientation and for tracking purposes. Signals from the anatomy and from tissue close to the ICRF coil are different due to the new RF excitation scheme: the ICRF coil can be separated from the anatomy in real time, and after doing so, a color-coded image is reconstructed. More importantly, this novel method enables a real-time calculation of the absolute rotational orientation of an ICRF coil constructed on a catheter. © 1982-2012 IEEE.