Reliable assessment of perfusivity and diffusivity from diffusion imaging of the body.

Diffusion-weighted MRI of the body has the potential to provide important new insights into physiological and microstructural properties. The intra-voxel incoherent motion (IVIM) model relates the observed DW-MRI signal decay to parameters that reflect perfusivity (D*) and its volume fraction (f), and diffusivity (D). However, the commonly used voxel-wise fitting of the IVIM model leads to parameter estimates with poor precision, which has hampered their practical usage. In this work, we increase the estimates' precision by introducing a model of spatial homogeneity, through which we obtain estimates of model parameters for all of the voxels at once, instead of solving for each voxel independently. Furthermore, we introduce an efficient iterative solver which utilizes a model-based bootstrap estimate of the distribution of residuals and a binary graph cut to generate optimal model parameter updates. Simulation experiments show that our approach reduces the relative root mean square error of the estimated parameters by 80% for the D* parameter and by 50% for the f and D parameters. We demonstrated the clinical impact of our model in distinguishing between enhancing and nonenhancing ileum segments in 24 Crohn's disease patients. Our model detected the enhanced segments with 91%/92% sensitivity/specificity which is better than the 81%/85% obtained by the voxel-independent approach.

Quantitative body DW-MRI biomarkers uncertainty estimation using unscented wild-bootstrap.

We present a new method for the uncertainty estimation of diffusion parameters for quantitative body DW-MRI assessment. Diffusion parameters uncertainty estimation from DW-MRI is necessary for clinical applications that use these parameters to assess pathology. However, uncertainty estimation using traditional techniques requires repeated acquisitions, which is undesirable in routine clinical use. Model-based bootstrap techniques, for example, assume an underlying linear model for residuals rescaling and cannot be utilized directly for body diffusion parameters uncertainty estimation due to the non-linearity of the body diffusion model. To offset this limitation, our method uses the Unscented transform to compute the residuals rescaling parameters from the non-linear body diffusion model, and then applies the wild-bootstrap method to infer the body diffusion parameters uncertainty. Validation through phantom and human subject experiments shows that our method identify the regions with higher uncertainty in body DWI-MRI model parameters correctly with realtive error of -36% in the uncertainty values.

Is there a role for abdominal computed tomographic scans in appendicitis?

OBJECTIVE: To better define the effectiveness of abdominal computed tomographic scanning (ACTS) in adult patients with suspected appendicitis. DESIGN: Retrospective analysis. SETTING: A community teaching hospital. PATIENTS: Ninety-seven patients with appendicitis in the differential diagnosis, whose clinical findings were insufficient to perform surgery or to discharge from the hospital, during a 14-month period. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Accuracy of ACTS, rate of appendectomies that show no appendicitis (negative appendectomy rate), and frequency of ACTS as a definitive diagnostic test. RESULTS: Forty-nine of the 50 patients with appendicitis were correctly diagnosed by ACTS. Forty-three of the 47 patients without appendicitis were correctly diagnosed by ACTS. Positive predictive value was 92%, negative predictive value was 98%, and accuracy was 96%. The ACTS group had a negative appendectomy rate of 5.8% (3/52), lower than the hospital rate of 14% for the preceding 3 years. The ACTS established an alternative diagnosis in 16 patients, allowed 10 other patients to be discharged early or not admitted, and was the critical diagnostic test in 30 of the patients with appendicitis. Therefore, the ACTS played a definitive role in the treatment of 56 (57.7%) of the 97 patients. CONCLUSIONS: The ACTS was an accurate test in the diagnosis of appendicitis and was of significant benefit in 57.7% of the patients studied. However, it was difficult to predict which patients were most likely to benefit. Expanded selective use of ACTS for patients with clinically indeterminate appendicitis may result in a lower negative appendectomy rate and fewer patient admissions for observation.