Logi Vidarsson | PubMed Health

PubMed2005

Echo time optimization for linear combination myelin imaging.

A 3-echo linear combination myelin imaging method is presented. The echo times and weights are chosen such that the signal-to-noise ratio (SNR) of myelin-water is maximized, and signals from other white matter components are sufficiently suppressed. Interfering tissue water and cerebrospinal fluid (CSF) signals are much stronger than myelin due to their longer T2 and abundance. By carefully optimizing the echo times a 50-fold tissue water suppression is achieved along with a 10-fold CSF suppression. For comparison 4, 5, and 32 echo filters are also designed using the same method. The SNR efficiency of these filters is very similar. The 3-echo filter design was validated by phantom scans. In addition, multislice in vivo myelin images were acquired from both a healthy volunteer and a multiple sclerosis patient. Total scan time was 5 min. A uniform T2 filter is also designed to pass all white matter species with uniform gain. The myelin-water fraction of the in vivo 3-echo data set is then measured by dividing the myelin image by the uniformly filtered image. Obtained myelin-water fractions compare well with previous work.

Algorithms↗

PubMed2005

The lactating breast: contrast-enhanced MR imaging of normal tissue and cancer.

PURPOSE: To retrospectively describe the magnetic resonance (MR) imaging characteristics of normal breast tissue and breast cancer in the setting of lactation. MATERIALS AND METHODS: The HIPAA-compliant study was exempt from institutional approval, and informed consent was not required. Unilateral MR imaging of 10 breasts was performed in seven lactating patients aged 27-42 years. For the three patients in whom both breasts were imaged, each breast was imaged on a separate day. Nonenhanced T1-weighted and fat-saturated T2-weighted images and contrast material-enhanced dynamic three-dimensional (3D) T1-weighted spiral gradient-echo images interleaved with T1-weighted high-spatial-resolution 3D gradient-echo images (2.0 x 1.0 x 0.4-mm voxels) were obtained. Three readers in consensus assessed the glandular density, T2-weighted signal intensity, milk duct appearance, and contrast enhancement in normal and tumor-containing breast regions. The pharmacokinetic contrast enhancement parameters of tumors were compared with those of normal tissue by using Student t and Mann-Whitney tests. RESULTS: MR findings of normal breast tissue in the seven women included increased glandular density in six women, high T2-weighted signal intensity in six, dilated central ducts in seven, and rapid initial glandular contrast enhancement in seven. MR findings of invasive ductal carcinoma in five women, compared with findings of the normal glandular tissue, included lower T2-weighted signal intensity in five women, more avid and rapid contrast enhancement in five, and early contrast enhancement washout in four. One minute after contrast agent injection, tumor signal intensity increased significantly more than normal lactating tissue signal intensity (153% vs 60% from baseline, P = .016). The median two-compartment model K(21) exchange rate in the tumors, 0.078 sec(-1), was significantly faster than the K(21) exchange rate in normal tissue, 0.011 sec(-1) (P = .03). CONCLUSION: Normal lactating glands have increased density, high T2-weighted signal intensity, and rapid moderate contrast enhancement. Breast cancers are visible during lactation owing to their lower signal intensity and more intense initial contrast enhancement with early washout compared with normal breast tissue.

Adult↗