Induced Signal Intensity Research Articles

Manganese kinetics demonstrated a double contrast in acute but not in chronic infarction in a mouse model of myocardial ischemia reperfusion

In this study we investigated whether Manganese (Mn2+) wash-in kinetics can add new information regarding a myocardial infarct characterization in particular if it can differentiate an acute infarct from a chronic scar. Manganese (Mn2+) is considered as a specific MRI contrast agent that enters viable cardiomyocytes through calcium pathways. Compared to extracellular Gadolinium based contrast agents, it has the potential to assess cell viability and has already shown its ability to accurately measure infarct size with late enhancement imaging. So far, only information from the wash out phase after recirculation has been used for the detection and characterization of myocardial infarct. In this study, we used a model of 60min ischemia followed by reperfusion on C57/BL6 mice. MRI exam was performed on a clinical 3T scanner, either 24 hours (n = 10) or 8 days (n =12) after reperfusion (acute and chronic infarct respectively). Mn2+-induced signal intensity (SI) kinetics were measured into three distinct areas, remote, infarction and left ventricular blood pool and compared to ex vivo TTC and Masson’s trichrome. For both infarction types (acute and chronic) the SI kinetics showed a fast entry of the contrast agent into the blood pool followed by a slower wash-out corresponding to the recirculation phase of Mn2+. The SI into the remote area increased slowly from the start of the Mn2+ infusion to still 45 minutes later when a plateau was reached. We observed fast entry of Mn2+ into acute infarction followed by a recirculation phase that lead to a double contrast between infarction and “remote”, whereas the entry of Mn2+ into chronic infarction was slow and SI stayed lower than in “remote” (see figure ​figure1).1). As a main hypothesis, extracellular space is largely enhanced in acute infarction due to cell membrane rupture (necrosis) and interstitial edema, whereas scar tissue is densely composed of collagen fibers that reduce the distribution volume of free Mn2+ ions. Figure 1 Time course of normalized SI after MnCl2 infusion in different areas of the myocardium (remote, infarct and left ventricular blood pool), for mice with acute (left) or chronic (right) infarction. Bold lines are mean SI and thin lines are SEM. In addition to its ability to depict accurately the infarcted area at late enhancement, Mn2+ is also able to discriminate acute versus chronic injury by the observation of double-contrast wash-in kinetics in a mouse model of ischemia reperfusion.

Neuronal projections from ventral tegmental area to forebrain structures in rat studied by manganese-enhanced magnetic resonance imaging

Manganese-enhanced magnetic resonance imaging (MEMRI) has been widely applied to trace neuronal tracts and to monitor morphological and functional responses of specific brain circuits to changes in physiological and/or environmental conditions. In this study, we traced the efferent axonal projections from ventral tegmental area (VTA) to forebrain structures, an integrating part of the reward circuit implicated in drug addiction, in rats using MEMRI. Urethane- and chloral hydrate-anesthetized rats received injection of 100 nl of 200 mM MnCl(2) solution into the right VTA. Mn(2+)-induced signal enhancements were monitored 24 h after injection. The dose of MnCl(2) injection was shown, by histological evaluation, to have minor toxic effects to the neurons in/near the injection site. Dynamic Mn(2+)-induced signal intensity changes in urethane-anesthetized rats during a 24-h period were fit to a sigmoidal function to obtain parameters slope and t(50), which describe the dynamics of apparent Mn(2+)accumulation. The results showed that most of the forebrain structures known to receive neuronal projections from the VTA, including prefrontal cortex, nucleus accumbens, globus pallidus and caudate putaman, were enhanced at 24 h after injection of MnCl(2) into the ipsilateral VTA, and anesthesia seemed have little effects on the amount of Mn(2+)being transported from the VTA to these structures.

The change of photo-induced resistivity properties in La2/3Ca1/3MnO3 thin films

Photo-induced resistivity change p has been studied in perovskite manganite La2/3Ca1/3MnO3 thin films with a continous wave laser and modulated laser pulses in this paper. Experimental results show that in the sample films, the maximum of photo-induced resistivity change（ΔR/R）max can reach 43.5%,which is a very exciting figure in this research field. Modulated laser pulse induced signal intensity has a highly nonlinear relation with the applied current and temperature. The maximum of photo-induced resistivity increase is a second power function of the applied current, while the temperature at which the maximum appears is proportional to the bias current. There exist an optimal bias current and a temperature for optical response in this film. These results are attributed to the optical excited eg↓ carriers and polarons.

MR Lymphangiography for Detection of Minimal Nodal Disease in Patients with Prostate Cancer

As prostate cancer is the second leading cause of cancer death in men in the USA, the clinical challenge is to develop methods that allow early diagnosis, accurate staging and precise treatment. Metastases to local and distant lymph nodes play a major role in the choice of therapy and in predicting outcome of these patients ( 1 Wilkinson BA Hamdy FC State-of-the-art staging in prostate cancer. BJU International. 2001; 87: 423-430 Crossref PubMed Google Scholar ). Clinical examination to detect lymph node metastases alone is inadequate and surgical dissection and serial histologic examinations are currently accepted “yardsticks”. In the past years, there has been debate about the pros and cons of total lymph node resection, particularly because of its morbidity, lengthiness of the surgical procedure and the resources necessary for complete pathologic evaluation of harvested nodes ( 2 Paul DB Loening SA Narayana AS Culp DA Morbidity from pelvic lymphadenectomy in staging carcinoma of the prostate. J Urol. 1983; 129: 1141-1144 Abstract Full Text PDF PubMed Scopus (71) Google Scholar ). Non-invasive imaging techniques for the detection of lymph node metastases would be of great help and a potential cost savings (imaging study vs. surgical lymphadenectomy) in the evaluation and re-staging of cancer patients. All current cross sectional imaging techniques (US, CT and MRI) have a relatively low sensitivity in detecting nodal metastases primarily because detection relies on insensitive size criteria (>10 mm short axis) ( 3 Rorvik J Halvorsen O Espeland A Haukaas S Inability of refined CT to assess local extent of prostatic cancer. Acta Radiol. 1993; : 39-42 Crossref PubMed Google Scholar ). Ultrasmall superparamagnetic iron oxide (USPIO) is a relatively new RES targeted MR contrast agent that is known for lymph node uptake ( 4 Anzai Y McLachlan S Morris M Saxton R Lufkin R Dextran-coated superparamagnetic iron oxide, an MR contrast agent for assessing lymph nodes in the head and neck. AJNR Am J Neuroradiol. 1994; 15: 87-94 PubMed Google Scholar , 5 Anzai Y Prince M Iron oxide-enhanced MR lymphography: the evaluation of cervical lymph node metastases in head and neck cancer. J Magn Reson Imaging. 1997; 7: 75-81 Crossref PubMed Scopus (86) Google Scholar , 6 Harisinghani M Saini S Slater G Schnall M Rifkin M MR imaging of pelvic lymph nodes in primary pelvic cancer with USPIO (Combidex). 1997 Contrast Medical Research Conference. Acad Radiol, Kyoto, Japan1997 Google Scholar , 7 Harisinghani MG Saini S Weissleder R et al. MR lymphangiography using ultrasmall superparamagnetic iron oxide in patients with primary abdominal and pelvic malignancies: radiographic-pathologic correlation. AJR Am J Roentgenol. 1999; 172: 1347-1351 Crossref PubMed Scopus (154) Google Scholar , 8 Harisinghani MG Saini S Hahn PF Weissleder R Mueller PR MR imaging of lymph nodes in patients with primary abdominal and pelvic malignancies using ultrasmall superparamagnetic iron oxide (Combidex). Acad Radiol. 1998; 5 (discussion S183–164): S167-169 Abstract Full Text PDF PubMed Google Scholar , 9 Bellin MF Roy C Kinkel K et al. Lymph node metastases: safety and effectiveness of MR imaging with ultrasmall superparamagnetic iron oxide particles—initial clinical experience. Radiology. 1998; 207: 799-808 PubMed Google Scholar , 10 Bellin R, Kinkel K, Challier E, et al. MR lymphography with ultrasmall iron oxide particles in patients with urologic and pelvic cancer. European Congress of Radiology. Vienna, 1997 Google Scholar , 11 Weissleder R Elizondo G Wittenberg J Lee A Josephson L Brady T Ultrasmall superparamagnetic iron oxide: an intravenous contrast agent for assesing lymph nodes with MR imaging. Radiology. 1990; 175: 494-498 PubMed Google Scholar , 12 Weissleder R Heautot J Schaefer B et al. MR lymphography: Study of a high-efficiency lymphotrophic agent. Radiology. 1994; 191: 225-230 PubMed Google Scholar , 13 Weissleder R Elizondo G Wittenberg J Rabito C Bengele H Josephson L Ultrasmall superparamagnetic iron oxide: Characterization of a new class of contrast agents for MR imaging. Radiology. 1990; 175: 489-493 PubMed Google Scholar ). The purpose of this study was to evaluate the utility of USPIO (Combidex™ Sinerem®) induced signal intensity changes in lymph nodes for staging patients with prostate cancer. Also assessed was the utility of postcontrast images alone in characterizing lymph nodes.

High Precision Measurement of Mean Transit Time for Pharmacological MRI

P36 Introduction Pharmacological MRI based on BOLD contrast is difficult since drug induced signal intensity changes are small. An alternative is bolus track MRI using a paramagnetic contrast agent which, however, has limitations regarding quantitation, one reason is the poor definition of the arterial input curve (AIC). Although AIC in principle can be determined from contrast agent induced signal intensity changes in larger arteries, the conversion into concentration time courses is inprecise. In this study a new approach was employed correcting the AIC before deconvolution. For evaluation cerebral perfusion was assessed before and after application of L-Arginine (L-Arg). Methods Bolus Track MRI (TE 54 ms; TR 0.8 s; 128x128x8) was performed after i.v. administration of 0.2 mmol/kg GdDTPA in four volunteers before and after L-Arg (500 mg/kg, i.v.). In one slice a white matter ROI was selected and AIC was taken from 6 different groups of arterial pixels and averaged. Concentrations were calculated and part of first passage in AIC was replaced with a fitting function that has been varied in an optimization procedure. The goal was to find the best prediction of time courses in tissue by model-dependent convolution in a transport-diffusion-model. ”Improved“ AIC determined in this way were used as most probable AIC at high concentrations for MTT determination. Results For the ”standard“ AIC, the MTT values were 2.7 ± 0.6 s before and 2.3 ± 0.5 s after L-Arg, the ratio of MTT in the same tissue regions after/before L-Arg was 0.8 ± 0.2. The MTT shortening indicated a CBF increase but not significantly. Using model-dependent deconvolution, the ”improved“ MTT values were similar, but less noisy. MTT values were 3.0 ± 0.5 s before and 2.5 ± 0.5 s after L-Arg. The improvement in SNR was particularly evident when assessing the after/before ratios of MTT which were 0.83 ± 0.02. Conclusion The improved definition of the input function significantly reduced the noise in our data as indicated by smaller standard deviations. As illustrated by the measurement of L-Arg-induced CBF increase, this improvement should make the assessment of rather small pharmacologically induced perfusion changes more precise.

MR imaging of gene delivery to the central nervous system with an artificial vector.

To determine whether gene delivery by means of a synthetic no viral DNA delivery system that is capable of gene transfer can be mapped with magnetic resonance (MR) imaging. The DNA delivery system consisted of aminated (poly-L-lysine-conjugated) dextran chains anchored together with a central superparamagnetic core. Three different types of constructs were synthesized that differed in their amino content and, thus, DNA-loading capacity. The model plasmid consisted of complementary DNA encoding for humanized green fluorescent protein. Constructs were tested in cell culture and in vivo in a rat model. All three constructs were capable of transfecting human cells in culture with transfection efficiencies ranging from 0.3% to 4.1%, which is similar to that of diethylaminoethyl-dextran. MR imaging experiments showed that DNA constructs induced signal intensity changes that co-localized with phosphorus-33-labeled plasmid distribution at autoradiography. After injection of the constructs into the corpus callosum of rats, weak green fluorescent protein expression of neuronal and glial cells could be detected at immunohistologic examination. Dextran-based nonviral DNA delivery systems are capable of transfecting cells and can be visualized with MR imaging.

Dy-DTPA-BMA as an Indicator of Tissue Viability in MR Imaging

The aim of this study was to investigate whether dysprosium (Dy) induced signal intensity (SI) loss in infarcted tissue in MR imaging. Myocardial infarction was induced in 12 pigs and Dy-DTPA-BMA (1.0 mmol/kg b.w.) was administered i.v. to 6 pigs 4 hours after occlusion and allowed to accumulate in the infarctions for 2 hours. Dy was analysed by inductively coupled plasma atomic emission spectrometry in infarcted and non-ischaemic tissue samples. The remaining 6 pigs, not administered contrast medium, served as controls. The infarctions demonstrated a high SI in the proton density- and T2-weighted sequences in both groups (ex vivo), although the Dy-DTPA-BMA group demonstrated a 3-fold greater concentration of Dy in infarcted compared with non-ischaemic myocardium. The lack of SI loss after Dy accumulation indicates that susceptibility effects are minor or absent in infarcted myocardium.

Dy-DTPA-BMA as an Indicator of Tissue Viability in MR Imaging

The aim of this study was to investigate whether dysprosium (Dy) induced signal intensity (SI) loss in infarcted tissue in MR imaging. Myocardial infarction was induced in 12 pigs and Dy-DTPA-BMA (1.0 mmol/kg b.w.) was administered i.v. to 6 pigs 4 hours after occlusion and allowed to accumulate in the infarctions for 2 hours. Dy was analysed by inductively coupled plasma atomic emission spectrometry in infarcted and non-ischaemic tissue samples. The remaining 6 pigs, not administered contrast medium, served as controls. The infarctions demonstrated a high SI in the proton density- and T2-weighted sequences in both groups (ex vivo), although the Dy-DTPA-BMA group demonstrated a 3-fold greater concentration of Dy in infarcted compared with non-ischaemic myocardium. The lack of SI loss after Dy accumulation indicates that susceptibility effects are minor or absent in infarcted myocardium.

MR angiography of congenital heart disease: value of segmented two-dimensional inflow technique and maximum-intensity-projection display.

Magnetic resonance (MR) angiography of the cardiovascular system was evaluated in 41 patients with congenital heart disease by using a two-dimensional (2D) inflow technique based on a magnetization-prepared gradient-echo pulse sequence with segmented k-space data acquisition and electrocardiographic gating at 0.5 T. Inversion and saturation prepulses were used to suppress stationary tissue and enhance intravascular signal. Presaturation slabs were applied where certain vascular structures had to be suppressed. Sequence parameters were optimized by evaluating signal intensity and contrast characteristics for various flip angles and inversion and saturation delay times. The heart and intrathoracic vasculature were encompassed with 40-50 overlapping sections. Both 2D angiograms and maximum-intensity-projection images were evaluated. Combining data sets acquired in the sagittal and transverse orientations provided the most satisfactory information about the pulmonary arteries. The highest signal-to-noise ratios were obtained with a flip angle of 65 degrees and short prepulse delay times. Two-dimensional MR angiography can provide useful diagnostic information but requires a thorough understanding of in-plane and hemodynamically induced signal intensity changes.

Matrix-effect observations in inductively coupled plasma mass spectrometry

Matrix effects in inductively Coupled plasma mass spectrometry (ICP-MS) may be divided into two basic categories: matrix induced spectral overlap problems and matrix induced signal intensity changes. In this work, matrix induced signal intensity changes are studied in some detail. In general, a high concentration of a matrix element results in the suppression of analyte signals. The degree of the matrix effect is strongly dependent on the nebuliser flow-rate and tends to be less severe at low nebuliser flow-rates than at high nebuliser flow-rates. While suppression effects seem most general, it is possible to observe enhancements, particularly at high nebuliser flow-rates. Plasma power and sampling depth do not appear to have a major influence on matrix effects. Definite mass trends are observed for the matrix effect. Heavy matrix elements cause the most severe matrix effects and light analytes are more seriously affected than heavier ones. Also, more severe matrix effects occur in the presence of matrix elements that have low ionisation potentials. Finally, the matrix effect depends more on the absolute concentration of the matrix element rather than on the relative concentration of matrix to analyte and thus matrix effects can be minimised by dilution. The main cause of the observed matrix effects appears to be a disturbance of the ion beam path through the ion optics and the mass spectrometer by the high concentration of the matrix element.