MODIFIED TEST STATISTICS BY INTER-VOXEL VARIANCE SHRINKAGE WITH AN APPLICATION TO fMRI

Functional Magnetic Resonance Imaging (fMRI) is a non-invasive technique which is commonly used to quantify changes in blood oxygenation and flow coupled to neuronal activation. One of the primary goals of fMRI studies is to identify localized brain regions where neuronal activation levels vary between groups. Single voxel t-tests have been commonly used to determine whether activation related to the protocol differs across groups. Due to the generally limited number of subjects within each study, accurate estimation of variance at each voxel is difficult. Thus, combining information across voxels in the statistical analysis of fMRI data is desirable in order to improve efficiency. Here we construct a hierarchical model and apply an Empirical Bayes framework on the analysis of group fMRI data, employing techniques used in high throughput genomic studies. The key idea is to shrink residual variances by combining information across voxels, and subsequently to construct an improved test statistic in lieu of the classical t-statistic. This hierarchical model results in a shrinkage of voxel-wise residual sample variances towards a common value. The shrunken estimator for voxelspecific variance components on the group analyses outperforms the classical residual error estimator in terms of mean squared error. Moreover, the shrunken test-statistic decreases false positive rate when testing differences in brain contrast maps across a wide range of simulation studies. This methodology was also applied to experimental data regarding a cognitive activation task.

Added value of coronary artery calcium score as an adjunct to gated SPECT for the evaluation of coronary artery disease in an intermediate-risk population

The coronary artery calcium (CAC) score is a readily and widely available tool for the noninvasive diagnosis of atherosclerotic coronary artery disease (CAD). The aim of this study was to investigate the added value of the CAC score as an adjunct to gated SPECT for the assessment of CAD in an intermediate-risk population. METHODS: Seventy-seven prospectively recruited patients with intermediate risk (as determined by the Framingham Heart Study 10-y CAD risk score) and referred for coronary angiography because of suspected CAD underwent stress (99m)Tc-tetrofosmin SPECT myocardial perfusion imaging (MPI) and CT CAC scoring within 2 wk before coronary angiography. The sensitivity and specificity of SPECT alone and of the combination of the 2 methods (SPECT plus CAC score) in demonstrating significant CAD (>/=50% stenosis on coronary angiography) were compared. RESULTS: Forty-two (55%) of the 77 patients had CAD on coronary angiography, and 35 (45%) had abnormal SPECT results. The CAC score was significantly higher in subjects with perfusion abnormalities than in those who had normal SPECT results (889 +/- 836 [mean +/- SD] vs. 286 +/- 335; P < 0.0001). Similarly, with rising CAC scores, a larger percentage of patients had CAD. Receiver-operating-characteristic analysis showed that a CAC score of greater than or equal to 709 was the optimal cutoff for detecting CAD missed by SPECT. SPECT alone had a sensitivity and a specificity for the detection of significant CAD of 76% and 91%, respectively. Combining SPECT with the CAC score (at a cutoff of 709) improved the sensitivity of SPECT (from 76% to 86%) for the detection of CAD, in association with a nonsignificant decrease in specificity (from 91% to 86%). CONCLUSION: The CAC score may offer incremental diagnostic information over SPECT data for identifying patients with significant CAD and negative MPI results.

An Active Learning Module for an Introduction to Software Engineering Course

Many schools do not begin to introduce college students to software engineering until they have had at least one semester of programming. Since software engineering is a large, complex, and abstract subject it is difficult to construct active learning exercises that build on the students’ elementary knowledge of programming and still teach basic software engineering principles. It is also the case that beginning students typically know how to construct small programs, but they have little experience with the techniques necessary to produce reliable and long-term maintainable modules. I have addressed these two concerns by defining a local standard (Montana Tech Method (MTM) Software Development Standard for Small Modules Template) that step-by-step directs students toward the construction of highly reliable small modules using well known, best-practices software engineering techniques. “Small module” is here defined as a coherent development task that can be unit tested, and can be car ried out by a single (or a pair of) software engineer(s) in at most a few weeks. The standard describes the process to be used and also provides a template for the top-level documentation. The instructional module’s sequence of mini-lectures and exercises associated with the use of this (and other) local standards are used throughout the course, which perforce covers more abstract software engineering material using traditional reading and writing assignments. The sequence of mini-lectures and hands-on assignments (many of which are done in small groups) constitutes an instructional module that can be used in any similar software engineering course.

An Attempt to Increase the Permeability and Porosity of the Cut Bank Oil Sand By Treatment with Various Reagents

The purpose of this investigation was to attempt to find some means of increasing the effective porosity and permeabil­ity of the producing sands of the Cut Bank Oil Field, with the hope that thereby the ultimate recovery of petroleum from this field may be increased. Although the percentage increase in production thus effected would undoubtedly be small, it would represent a substantial volume of petroleum in view of the great quantity of oil and gas present in this field.

Reliability of intraoperative high-resolution 2D ultrasound as an alternative to high-field strength MR imaging for tumor resection control: a prospective comparative study

OBJECT: Ultrasound may be a reliable but simpler alternative to intraoperative MR imaging (iMR imaging) for tumor resection control. However, its reliability in the detection of tumor remnants has not been definitely proven. The aim of the study was to compare high-field iMR imaging (1.5 T) and high-resolution 2D ultrasound in terms of tumor resection control. METHODS: A prospective comparative study of 26 consecutive patients was performed. The following parameters were compared: the existence of tumor remnants after presumed radical removal and the quality of the images. Tumor remnants were categorized as: detectable with both imaging modalities or visible only with 1 modality. RESULTS: Tumor remnants were detected in 21 cases (80.8%) with iMR imaging. All large remnants were demonstrated with both modalities, and their image quality was good. Two-dimensional ultrasound was not as effective in detecting remnants<1 cm. Two remnants detected with iMR imaging were missed by ultrasound. In 2 cases suspicious signals visible only on ultrasound images were misinterpreted as remnants but turned out to be a blood clot and peritumoral parenchyma. The average time for acquisition of an ultrasound image was 2 minutes, whereas that for an iMR image was approximately 10 minutes. Neither modality resulted in any procedure-related complications or morbidity. CONCLUSIONS: Intraoperative MR imaging is more precise in detecting small tumor remnants than 2D ultrasound. Nevertheless, the latter may be used as a less expensive and less time-consuming alternative that provides almost real-time feedback information. Its accuracy is highest in case of more confined, deeply located remnants. In cases of more superficially located remnants, its role is more limited.