T1 measurements with clinical MR units

Development and practical evaluation of a saturation effect learning simulator for inflow magnetic resonance angiography

The quality of visualization in inflow magnetic resonance angiography (MRA) depends highly on the excitation state of the longitudinal magnetization obtained using specified imaging parameters. In addition, signal intensity changes controlled by the preparation pulse-such as inversion recovery (IR) and saturation recovery (SR)-can potentially be used as quantitative physiological values. Although having practitioners understand these relationships both qualitatively and quantitatively is important, handling clinical equipment in practical learning or experiments involves limited opportunities. The simulator corresponds to a three-dimensional spoiled gradient echo sequence and allows users to freely input multiple virtual excitation effects in space and time. The purpose of this study was to quantitatively evaluate the agreement between the measured MRAs obtained in flow phantom tests and virtual MRAs simulated under similar conditions. We imaged two vascular flow phantoms on a 3.0 T MR system using three-dimensional (3D) time-of-flight (TOF) MRA and 3D inversion recovery tissue signal suppression (IR-suppression) MRA protocols. We evaluated quantitative values for consistency between the measured and virtual MRAs images with matched spatial resolution. Then we assessed the coincidence by reformatting maximum-intensity projection images with 1 mm isotropic pixels, with it ranging from 89.6 to 92.0% and 89.1 to 92.9% for TOF MRA and IR-suppression MRA, respectively. These results may be useful as a reference index for the theoretical study of MRA images by practitioners, for complementary validation by phantom testing, or for the development of MRI-related simulators.

Using ELP Repeats as a Scaffold for De Novo Construction of Gadolinium-Binding Domains within Multifunctional Recombinant Proteins for Targeted Delivery of Gadolinium to Tumour Cells

Three artificial proteins that bind the gadolinium ion (Gd3+) with tumour-specific ligands were de novo engineered and tested as candidate drugs for binary radiotherapy (BRT) and contrast agents for magnetic resonance imaging (MRI). Gd3+-binding modules were derived from calmodulin. They were joined with elastin-like polypeptide (ELP) repeats from human elastin to form the four-centre Gd3+-binding domain (4MBS-domain) that further was combined with F3 peptide (a ligand of nucleolin, a tumour marker) to form the F3-W4 block. The F3-W4 block was taken alone (E2-13W4 protein), as two repeats (E1-W8) and as three repeats (E1-W12). Each protein was supplemented with three copies of the RGD motif (a ligand of integrin αvβ3) and green fluorescent protein (GFP). In contrast to Magnevist (a Gd-containing contrast agent), the proteins exhibited three to four times higher accumulation in U87MG glioma and A375 melanoma cell lines than in normal fibroblasts. The proteins remained for >24 h in tumours induced by Ca755 adenocarcinoma in C57BL/6 mice. They exhibited stability towards blood proteases and only accumulated in the liver and kidney. The technological advantages of using the engineered proteins as a basis for developing efficient and non-toxic agents for early diagnosis of tumours by MRI as well as part of BRT were demonstrated.

Connexin 43-targeted T1 contrast agent for MRI diagnosis of glioma

Glioblastoma multiforme is the most aggressive form of brain tumor. Early and accurate diagnosis of glioma and its borders is an important step for its successful treatment. One of the promising targets for selective visualization of glioma and its margins is connexin 43 (Cx43), which is highly expressed in reactive astrocytes and migrating glioma cells. The purpose of this study was to synthesize a Gd-based contrast agent conjugated with specific antibodies to Cx43 for efficient visualization of glioma C6 in vivo. We have prepared stable nontoxic conjugates of monoclonal antibody to Cx43 and polylysine-DTPA ligands complexed with Gd(III), which are characterized by higher T1 relaxivity (6.5 mM(-1) s(-1) at 7 T) than the commercial agent Magnevist® (3.4 mM(-1) s(-1)). Cellular uptake of Cx43-specific T1 contrast agent in glioma C6 cells was more than four times higher than the nonspecific IgG-contrast agent, as detected by flow cytometry and confocal analysis. MRI experiments showed that the obtained agents could markedly enhance visualization of glioma C6 in vivo after their intravenous administration. Significant accumulation of Cx43-targeted contrast agents in glioma and the peritumoral zone led not only to enhanced contrast but also to improved detection of the tumor periphery. Fluorescence imaging confirmed notable accumulation of Cx43-specific conjugates in the peritumoral zone compared with nonspecific IgG conjugates at 24 h after intravenous injection. All these features of Cx43-targeted contrast agents might be useful for more precise diagnosis of glioma and its borders by MRI.

Multislice T1 relaxation time measurements in the brain using IR-EPI: Reproducibility, normal values, and histogram analysis in patients with multiple sclerosis

PURPOSE

To perform T(1) measurements using inversion recovery (IR) echoplanar imaging (EPI) to evaluate reproducibility, normal values, and T(1) histogram analysis as a measure of disease progression in multiple sclerosis (MS) patients.

MATERIALS AND METHODS

Multislice IR-EPI was performed in 10 controls and 36 MS patients. Region-of-interest (ROI) and T(1) histogram analysis were performed on T(1) maps and compared to hypointense T(1) lesions and brain atrophy in MS patients.

RESULTS

Coefficient of variation (COV) varied from 1.6% to 4.9%. Callosal normal (appearing) white matter (N(A)WM) showed the lowest and cortical gray matter the highest T(1) values. T(1) histogram analysis in controls showed a sharp WM peak centered on a T(1) value of 729 msec (range = 679-765) with extension into a shoulder of higher T(1) values. In MS patients, a shift toward higher T(1) values (mean = 788 msec, range = 700-957) with a lower relative peak amplitude was present, predominantly resulting from T(1) prolongation in NAWM. T(1) histogram parameters strongly related to hypointense T(1) lesion volume and brain atrophy in MS patients.

CONCLUSIONS

IR-EPI provides a reproducible method to obtain T(1) values in the brain. Regional variation in T(1) values is present in N(A)WM of volunteers and MS patients. Since T(1) histogram parameters reflect changes in NAWM and correlate with conventional measures of disease burden in MS patients, T(1) histogram analysis may provide a global measure of disease progression in MS.

Detection of deoxygenation-related signal change in acute ischemic stroke patients by T2*-weighted magnetic resonance imaging

BACKGROUND AND PURPOSE

Acute decreases in the MR T2*-weighted signal have been reported in experimental models of middle cerebral artery occlusion. This has been attributed to blood deoxygenation in association with an increased brain oxygen extraction fraction. The aim of this study was to detect this signal by susceptibility-weighted MR imaging in acute ischemic stroke patients.

METHODS

Dynamic susceptibility contrast-enhanced MR (DSC-MR) imaging was performed within 4 hours of stroke onset in 6 patients with unilateral cerebral artery occlusion (middle cerebral artery, n=5; internal carotid artery, n=1). Cerebral blood volume was estimated on a pixel-by-pixel basis. DSC-MR images taken before arrival of the contrast medium were examined visually to identify hypointense areas. Bilateral regions of interest were set in the middle cerebral artery territory for comparison of the mean signal intensity. A semilogarithmic plot of signal intensity versus cerebral blood volume for every pixel in the region of interest was also analyzed.

RESULTS

The side on which the hypointense area was seen was significantly correlated with the side of arterial occlusion. The mean signal intensity was significantly smaller on the affected side than on the contralateral side. The semilogarithmic plot of signal intensity versus cerebral blood volume indicated greater deoxyhemoglobin concentrations for the ipsilateral than for the contralateral region of interest.

CONCLUSIONS

DSC-MR images allow detection of hypointensity in the affected cerebral hemisphere in acute ischemic stroke patients. Such hypointensity may indicate increased oxygen extraction fraction (misery perfusion) and may provide information valuable to patient care.