Measurement of the vascular input function in mice for DCE-MRI

DCE-MRI is an important technique in the study of small animal cancer models because its sensitivity to vascular changes opens the possibility of quantitative assessment of early therapeutic response. However, extraction of physiologically descriptive parameters from DCE-MRI data relies upon measurement of the vascular input function (VIF), which represents the contrast agent concentration time course in the blood plasma. This is difficult in small animal models due to artifacts associated with partial volume, inflow enhancement, and the limited temporal resolution achievable with MR imaging. In this work, the development of a suite of techniques for high temporal resolution, artifact resistant measurement of the VIF in mice is described. One obstacle in VIF measurement is inflow enhancement, which decreases the sensitivity of the MR signal to the presence of contrast agent. Because the traditional techniques used to suppress inflow enhancement degrade the achievable spatiotemporal resolution of the pulse sequence, improvements can be achieved by reducing the time required for the suppression. Thus, a novel RF pulse which provides spatial presaturation contemporaneously with the RF excitation was implemented and evaluated. This maximizes the achievable temporal resolution by removing the additional RF and gradient pulses typically required for suppression of inflow enhancement. A second challenge is achieving the temporal resolution required for accurate characterization of the VIF, which exceeds what can be achieved with conventional imaging techniques while maintaining adequate spatial resolution and tumor coverage. Thus, an anatomically constrained reconstruction strategy was developed that allows for sampling of the VIF at extremely high acceleration factors, permitting capture of the initial pass of the contrast agent in mice. Simulation, phantom, and in vivo validation of all components were performed. Finally, the two components were used to perform VIF measurement in the murine heart. An in vivo study of the VIF reproducibility was performed, and an improvement in the measured injection-to-injection variation was observed. This will lead to improvements in the reliability of quantitative DCE-MRI measurements and increase their sensitivity

Thickness dependence of the magnetic hysteresis of NiFe-31% films as a function of an applied isotropic in-plane stress

The magnetic hysteresis of dc magnetron-sputtered Ni69Fe31 films that were sandwiched between titanium layers was investigated as a function of an externally applied isotropic in-plane strain. The hysteresis curves were measured with a Kerr magnetometer that monitored the longitudinal Kerr ellipticity as a function of the in-plane magnetic field. The strain was created by bending the samples in two dimensions using a pressure cell. Measurements were performed on films with different thicknesses. The magnetoelastic properties appeared to be much smaller for films with a thickness of 100 nm than for films with a thickness of 288 or 500 nm. This might be due to a change of the domain wall pinning, or a change of the domain wall density as a function of the film thickness. Measurements under compressive isotropic in-plane stress were shown to be possible by flipping the sample in the pressure holder and measuring through the glass substrate. The Faraday effect and stress-induced birefringence in the glass substrate did not hinder the accumulation of noiseless hysteresis data. The magnetoelastic effects appeared to be different for positive and negative values of the applied stress

Abnormal structural connectivity in the brain networks of children with hydrocephalus

Increased intracranial pressure and ventriculomegaly in children with hydrocephalus are known to have adverse effects on white matter structure. This study seeks to investigate the impact of hydrocephalus on topological features of brain networks in children. The goal was to investigate structural network connectivity, at both global and regional levels, in the brains in children with hydrocephalus using graph theory analysis and diffusion tensor tractography. Three groups of children were included in the study (29 normally developing controls, 9 preoperative hydrocephalus patients, and 17 postoperative hydrocephalus patients). Graph theory analysis was applied to calculate the global network measures including small-worldness, normalized clustering coefficients, normalized characteristic path length, global efficiency, and modularity. Abnormalities in regional network parameters, including nodal degree, local efficiency, clustering coefficient, and betweenness centrality, were also compared between the two patients groups (separately) and the controls using two tailed t-test at significance level of p < 0.05 (corrected for multiple comparison). Children with hydrocephalus in both the preoperative and postoperative groups were found to have significantly lower small-worldness and lower normalized clustering coefficient than controls. Children with hydrocephalus in the postoperative group were also found to have significantly lower normalized characteristic path length and lower modularity. At regional level, significant group differences (or differences at trend level) in regional network measures were found between hydrocephalus patients and the controls in a series of brain regions including the medial occipital gyrus, medial frontal gyrus, thalamus, cingulate gyrus, lingual gyrus, rectal gyrus, caudate, cuneus, and insular. Our data showed that structural connectivity analysis using graph theory and diffusion tensor tractography is sensitive to detect abnormalities of brain network connectivity associated with hydrocephalus at both global and regional levels, thus providing a new avenue for potential diagnosis and prognosis tool for children with hydrocephalus

Visualizing the prostate gland by MR imaging in young and old mice.

Prostate imaging requires optimization in young and old mouse models. We tested which MR sequences and field strengths best depict the prostate gland in young and old mice; and, whether prostate MR signal, size, and architecture change with age.Magnetic resonance imaging (MRI) of the prostate of young (2 months) and old (18 months) male nude mice (n = 6) was performed at 4.7 and 7 T and SCID mice (n = 6) at 7 T field strengths, using T1, fat suppressed T1, DWI, T2, fat suppressed T2, as well as T2-based- and proton density-based Dixon "water only" sequences. Images were ranked for best overall sequence for prostate visualization, prostate delineation, and quality of fat suppression. Prostate volume and signal characteristics were compared and histology was performed.T2-based-Dixon "water only" images ranked best overall for prostate visualization and delineation as well as fat suppression (n = 6, P<0.001) at both 4.7 T and 7 T in nude and 7T in SCID mice. Evaluated in nude mice, T2-based Dixon "water only" had greater prostate CNR and lower fat SNR at 7 T than 4.7 T (P<0.001). Prostate volume was less in older than younger mice (n = 6, P<0.02 nude mice; n = 6, P<0.002 SCID mice). Prostate T2 FSE as well as proton density-based and T2-based-Dixon "water only" signal intensity was higher in younger than older mice (P<0.001 nude mice; P<0.01 SCID mice) both at 4.7 and 7 T. This corresponded to an increase in glandular hyperplasia in older mice by histology (P<0.01, n = 6).T2-based Dixon "water only" images best depict the mouse prostate in young and old nude mice at 4.7 and 7 T. The mouse prostate decreases in size with age. The decrease in T2 and T2-based Dixon "water only" signal with age corresponds with glandular hyperplasia. Findings suggest age should be an important determinant when choosing models of prostate biology and disease

Representative MR images of the prostate gland of nude (4.7T, A), SCID (7T, B) young (top) and old (bottom) mice with different MR sequences.

<p>Arrow indicates the prostate gland.</p

Prostate gland histology of young and old mice, H&E stain, ×400.

<p>A) Nude young mice, minimal hyperplasia, grade 1; B) Nude old mice, mild hyperplasia, grade 2; C) SCID young mice, minimal hyperplasia, grade 1; D) SCID old mice, moderate hyperplasia, grade 3.</p

Prostate visualization, prostate border delineation, and fat suppression of young and old SCID and nude mice ranked significantly higher on T2-Dixon “water only” overall and generally better than T2 FS images using either 4.7 T or 7T scanners.

<p>A) 7T magnet, young vs old mice (*, P<0.01, T2-Dixon vs T2 FS; #, P<0.001, T2-Dixon “water only” young vs old); B) 4.7 T vs 7T (*, P<0.01, T2-Dixon vs T2 FS; #, P<.05, T2-Dixon “water only” 4.7T vs 7T). Reader 1 data presented.</p

7T vs 4.7T T2-Dixon “water only” Fat SNR and Prostate CNR.

<p>7T vs 4.7T T2-Dixon “water only” Fat SNR and Prostate CNR.</p

Comparison of visualization, border delineation, and fat suppression at 4.7T and 7T (P-values).

*<p>Overall P-values.</p

T2-Dixon “water only” vs T2-FS Fat SNR and Prostate CNR.

<p>T2-Dixon “water only” vs T2-FS Fat SNR and Prostate CNR.</p