Changes In T2 Values Research Articles

TH-C-L100J-06: Monitoring Myocardial Infarction Induced Calcium Homeostasis Alteration by MRI in a Small Murine Model

Purpose: Alterations in myocyte calcium regulation for both the mechanical dysfunction and the arrhythmogenesis associated with congestive heart failure. In spite of the established importance calcium regulation in the heart both prior to, and following, myocardial injury, monitoring strategies to assess calcium homeostasis in affected cardiac tissues are extremely limited. We propose to characterize the dynamic and temporal features of calcium responses due to myocardial injury in a small murine model using as a contrast agent. Method and Materials: There are 3 groups of mice (6–10 weeks) namely control, sham-operated, and myocardial infarction (MI). In the MI studies, permanent myocardial infarcts were produced by ligating the left anterior descending coronary artery. Images were acquired on a horizontal 7.0 T Bruker BioSpec MRI spectrometer equipped with a micro imaging gradient. A series of short-axis T1-weighted cardiac images were acquired as well as pre- and post- infusion T1 maps using an ECG-gated, flow-compensated Lock-Locker MRI pulse sequence. Results: ECG gated cardiac MRI provided high quality images for left-ventricle, and the infusion of clearly showed a large change in T1 values. The left-ventricular post- relaxivity, ΔR1 (=1/ΔT1), thus far for control, sham-operated, and MI groups are 3.54±0.94, 2.63±1.37, and 1.91 sec−1, respectively. The post-MI group showed potentially lower ΔR1 values. Increased sample size for each animal group is warranted. Further investigation is necessary to determine if could provide insights into the temporal myocardial remodeling process where influx might be altered. Conclusion: One motivation for this study is that myocardial injury causes physiological remodeling leading to potential handling alteration. This process can be potentially monitored with a cardiac manganese-enhanced T1 mapping technique. Furthermore, changes in ΔR1 could potentially be calibrated to the absolute manganese content for left-ventricular myocardium.

What causes diminished corticomedullary differentiation in renal insufficiency?

To investigate whether the loss of corticomedullary differentiation (CMD) on T1-weighted MR images due to renal insufficiency can be attributed to changes in T1 values of the cortex, medulla, or both. Study subjects included 10 patients (serum creatinine range 0.6-3.0 mg/dL) referred for suspected renovascular disease who underwent 99mTc-diethylene triamine pentaacetic acid (DTPA) renography to determine single kidney glomerular filtration rate (SKGFR) and same-day MRI, which included T1 measurements and unenhanced T1-weighted gradient echo imaging. Corticomedullary differentiation on T1-weighted images was assessed qualitatively and quantitatively. SKGFR values ranged from 3.5 to 89.4 mL/minute based on radionuclide studies. T1 relaxation times of the medulla exceeded those of renal cortex by 147.9+/-176.0 msec (mean+/-standard deviation [SD]). Regression analysis showed a negative correlation between cortex T1 and SKGFR (r=-0.5; P=0.03), whereas there was no significant correlation between medullary T1 and SKGFR. The difference between medullary and cortical T1s correlated significantly with SKGFR (r=0.58; P<0.01). In all five kidneys with a corticomedullary contrast-to-noise ratio (CNR)<5.0 on T1-weighted images, SKGFR was less than 20 mL/minute. In our subject population, loss of CMD with decreasing SKGFR can be attributed primarily to an increased T1 relaxation time of the cortex. Medullary T1 values vary but do not appear to correlate with degree of renal insufficiency.

Advances in magnetic resonance imaging

The major advances in clinical MRI relate to the widespread introduction of high field (3.0 Tesla) imaging systems and the development of parallel imaging techniques. The increased signal to noise ratio of high field imaging systems is compromised by the need to compensate for susceptibility, chemical shift and energy deposition. Changes in T1 values at high field strength are tissue specific but in general produce a reduction in contrast. Paramagnetic contrast materials show little change in longitudinal relaxation times at high field strength. The use of frequency specific fat suppression techniques to reduce chemical shift artefacts is of particular value at high field strength. The use of parallel imaging techniques complements increases in field strength by allowing reduction of susceptibility artefacts and reduced blurring in fast spin echo or HASTE acquisitions and reduction in specific absorption rate (SAR).

Is Magnetic Resonance Image Guidance the Key to Opening Chronic Total Occlusions?

Through progressive plaque growth or fibrotic organization of occlusive thrombus, atherosclerosis may result in chronic total occlusion (CTO) of a major arterial conduit. If CTO develops slowly, collateral pathways may supply sufficient perfusion to retain tissue viability despite occlusion of the major inflow conduit. However, such collateral-mediated perfusion rarely matches that provided by an open main conduit, particularly during the peak demand of regional muscular activity. Although strategies to limit regional oxygen demand (eg, β-blockers for the treatment of angina pectoris) or to enhance collateral function (eg, a walking program for superficial femoral occlusion, experimental angiogenesis) may be of some benefit, these approaches generally offer less complete return of normal physiology and relief of ischemic symptoms than does direct revascularization of the occluded vessel. With surgical bypass, the nature of the occlusion (its length, duration, tortuosity, calcification) is less important than the presence of a suitable distal anastomotic target. On the other hand, with catheter-based techniques, success depends heavily on these lesion characteristics. In fact, crossing such occluded segments with a guidewire remains the dominant barrier to catheter-based treatments of occluded arterial segments. Once the guidewire has been passed successfully into the distal true lumen, the process of dilating and stenting the segment is usually straightforward and durable, at least with the use of drug-eluting stents in coronary CTOs.1,2 Article p 1101 Devices designed to cross CTOs should have 3 key features: an ability to distinguish a true luminal path from one created within (dissection) or through (perforation) the vessel wall of the occluded segment, an ability to change direction (steer) to correct deviations from the desired path through the occlusion, and an ability to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, …

MR-guided Percutaneous Intramyocardial Injection with an MR-compatible Catheter: Feasibility and Changes in T1 Values after Injection of Extracellular Contrast Medium in Pigs

To assess the feasibility of percutaneous magnetic resonance (MR)-guided intramyocardial injection of gadodiamide by using real-time imaging and to quantify T1 values and the size of the enhanced region for different concentrations of contrast agent for 30 minutes after injection. Animal care committee approval was obtained. A catheter with a needle tip was advanced into the left ventricle in seven pigs by using real-time imaging with radial steady-state free precession. After intramyocardial injection of 2 mL of solution at concentrations of 0.05 or 0.10 mmol/mL gadodiamide, local changes in T1 values and size of the contrast material-enhanced region were sequentially measured at 3, 15, and 30 minutes after injection by using the Look-Locker sequence. Two-tailed paired Student t tests were used for statistical analysis. Catheter guidance and visualization of contrast agent distribution were feasible in all animals. Regional changes in T1 values were significantly different for different contrast agent concentrations (for 0.05 mmol/mL, 456 msec +/- 5 [+/- standard error of the mean]; for 0.10 mmol/mL, 228 msec +/- 4; P < .001) measured 3 minutes after injection. T1 values increased significantly (P < .05) to 720 msec +/- 7 for 0.05 mmol/mL gadodiamide and 445 msec +/- 6 for 0.10 mmol/mL gadodiamide 30 minutes after injection but remained significantly lower than those of remote myocardium (879 msec +/- 8). The size of the contrast-enhanced region increased from 13 mm(2) +/- 2 at 3 minutes to 30 mm(2) +/- 3 at 30 minutes (P < .05). Catheter MR-guided percutaneous intramyocardial injection is feasible; after intramyocardial injection of gadodiamide at concentrations of 0.05 and 0.10 mmol/mL, T1 values decreased over the observation time.

Neuromuscular Activation of Triceps Surae Using Muscle Functional MRI and EMG

The aim of the present study was to clarify the neuromuscular activation patterns among individual triceps surae (TS) muscles during a repetitive plantarflexion using muscle functional magnetic resonance imaging (MRI) (mfMRI) and electromyography (EMG). Six healthy men participated in this study, performing 5 sets of 10 repetitions of a calf-raise exercise bilaterally, unilaterally, and unilaterally with an additional 15% of body-weight load. The transverse relaxation times (T2) in the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles were measured from mfMR images obtained with the subject at rest and immediately after exercise; integrated EMG (iEMG) activity was recorded from the same muscles during exercise using surface electrodes. There was remarkable correspondence between the changes in T2 values and iEMG activity under the three different workloads for individual TS muscles. In addition, changes in T2 value that occurred as a function of increasing exercise loads were linearly correlated with iEMG activity in the MG (r=0.58, P<0.05) and SOL (r=0.63, P<0.01), but not in the LG. These results suggest that 1) mfMRI signals and iEMG activity correlate with workload in individual TS muscles, 2) mfMRI signals are associated with neuromuscular activity reflected in iEMG in the MG and SOL but not in the LG, and 3) these relationships are associated with neuromuscular and metabolic factors during exercise.

High resolution MRI relaxation measurements of water in the articular cartilage of the meniscectomized rat knee at 4.7 T.

Measurements by magnetic resonance imaging (MRI) of the spin-spin (T2), spin-lattice (T1) and spin-density (M0) parameters of water protons, optimized by using the Cramér-Rao Lower Bound (CRLB) theory, were made to quantify the effect of surgically induced osteoarthritis on rat knee cartilage at 4.7 T. Partial meniscectomy was performed on the right medial condyle of four Sprague Dawley rats, leaving the left medial condyle as a control. The animals were euthanized 3 weeks after the operation; the entire limbs were removed and T2 and T1 relaxation measurements and M0 measurements of the protons of water were obtained using conventional Carr-Purcell-Meiboom-Gill (CPMG) and saturation recovery methods. M0 was normalized with respect to a water phantom, to obtain the relative spin-density M0%. Weight-bearing cartilage areas on the meniscectomized medial condyles exhibited a significant increase of T2 relaxation time (p < 0.001) and of M0% (p < 0.01) with respect to the control; T1 relaxation times did not show any statistically significant changes. CRLB-based sampling optimization offered an insight to improved measurement precision and a reduction of scanning time against conventional sampling methods methods. Quantitative MRI assessment of the meniscectomized rat knee shows that cartilage exhibits changes in T2 and M0 values 3 weeks after operation.

Diurnal T2 Value Changes in the Lumbar Intervertebral Discs

AIM: To investigate if there is any in vivo diurnal T2 value changes in the nucleus pulposus in normal and degenerated lumbar intervertebral discs. MATERIALS AND METHODS: Eighteen volunteers (16 men, two women) with no symptoms related to lumbar disease were imaged in the morning before beginning daily work and in the evening after finishing work. Sagittal fast spin-echo T2-weighted images were obtained, following spin-echo transverse imaging for T2 analysis. RESULTS: The normal disc group ( n=71) showed statistically significant diurnal T2 value changes ( p<0.001), whilst the degenerating disc group ( n=19) showed no significant diurnal changes. The normal disc group up to age 34 years showed statistically significant diurnal T2 value changes. However no significant changes were demonstrated after the age 35 years. CONCLUSION: Statistically significant diurnal T2 value changes in the normal lumbar intervertebral discs were demonstrated. Disappearance of the diurnal T2 value changes in the normal discs after the age 35 years was revealed for the first time and thought to be an aspect of aging, not caused by degeneration.

Effect of peripheral nerve injury on nuclear magnetic resonance relaxation times of rat skeletal muscle.

The authors evaluate the changes in magnetic resonance (MR) relaxation times of rat skeletal muscles in vivo after nerve injury and during neural recovery, and determine the major determinants of relaxation times. Magnetic resonance relaxation times, blood volume, and water and fat content were examined after nerve injury and during recovery with time course. Nerve injury led to longer T2 values compared with controls, but there were no significant changes in T1 values. After the initial prolongation of T2 after nerve injury, no changes were observed. Neural recovery resulted in a return of T2 values to normal. The time course of changes in blood volume was similar to that of changes in T2, and T2 values were correlated strongly with 19-fluorine-MR spectroscopy estimates of blood volume (r2 = 0.94). T2 values may be useful to monitor recovery after nerve injury and may be related to the blood volume in skeletal muscle.

Multivariate quality assessment of aged RP-HPLC columns

The inner structure of RP-HPLC columns can change (‘age’) during routine use. The columns may be monitored to check the magnitude and type of the changes. One approach is to investigate, besides the chromatograms, the retention behaviour of a few selected solutes at different mobile phases (markers) during routine use. A distinction can be made between a general shift in retention and changes in selectivity. The changes in retention of selected solutes on aged columns in comparison with fresh columns are collected in one multivariate statistic, Hotelling's T2-statistic, instead of separate univariate statistics. The T2-values are denoted on a control chart to visualize the changes in retention and to compare them with a control limit. Changes of T2-values above this limit cannot be considered negligible. An alternative approach is to select underlying variables or principal components of a larger set of solutes. These underlying variables can be treated just like the selected original variables. Examples are given of control charts for artificially aged columns. The results corroborate a global categorization made of the artificially aged columns based on the retention times of a large number of solutes at different mobile phases. © 1996 by John Wiley & Sons Ltd.

Non-invasive monitoring of tissue response to radiotherapy by localised proton spin-lattice relaxation time in mice

Proton spin-lattice relaxation time T1 of the localised tumour portion and its neighbouring portion of tumour-bearing mice legs is successively observed before and after radiotherapy by applying the previously proposed magnetic focusing method. Changes in T1 values are also compared with the histological radiation effects. For un-irradiated tumours, T1 increases gradually with tumour growth. T1 of the tumour portion shows significant decrease after radiotherapy. The decrease in the T1 values of the tumour clearly depends on the single radiation dose of 30, 45 and 60 Gy, respectively. A rapid decrease in the T1 values of the tumour occurs prior to the decrease in tumour volume. These decreases in the T1 values of the tumour after radiotherapy correspond positively to the increase of the histological radiation effects. After the reduction in the T1 values of the irradiated tumour portion, a successive increase in T1 values is observed and suggests local recurrence of the tumour. These results show that localised T1 relaxation time is a good reflection of the tissue response to radiotherapy.

MRI of primary amyloidosis

In a patient with primary amyloidosis, we compared T2 values and relative signal intensity ratios of involved organs to those of normal patients. T2 was significantly decreased in the spleen and adrenals, while significantly increased in the pancreas. T2 values were insignificantly changed in the liver, subcutaneous fat, bone marrow, or kidney. Ratios may facilitate detection of relative changes in T2 values.

New Applications of Crown Ethers. X. 13C NMR Relaxation Times Study of Cation-Binding Behavior of Monoazacrown Ethers and Bis(monoazacrown ether)s

Abstract 13C NMR relaxation times (T1s) have been determined for monoazacrown ethers (CA15C5 and CA18C6) and bis(monoazacrown ether)s (BCA15C5, BCA18C6, BOA15C5, and BOA18C6) in the absence and presence of Na+and K+ ions. For the monoazacrown ethers with heptyl side chain and the bis(monoazacrown ether)s with pentamethylene bridge chain marked changes in T1 values are observed upon the complexation, and the changes are dependent on the cation and on the structure of the ligands. The complexation with Na+ ion can give a larger effect on the T1 values for the bis(monoazacrown ether)s of 15- and 18-membered rings, especially on the mobility of the bridging chain carbons, which is indicative of the formation of an intramolecular sandwich complex. On the other hand, the present T1 study again shows the prominent effect of the oxygen in the bridging chain on the complexation of BOA15C5 and BOA18C6. Small differences in T1 values obtained between Na+ complexes and K+ complexes of these two bis(crown ether)s suggest that the complexes take an analogous partial structure for the two cations.

Residual mediastinal masses in Hodgkin disease: prediction of size with MR imaging.

Eighteen patients with mediastinal involvement of Hodgkin disease were examined with magnetic resonance (MR) imaging before and during therapy to find out if size of residual masses could be predicted from the MR characteristics of the tumor at diagnosis. After the first treatment, a significant decrease in T2 values and signal intensity ratios of tumor to fat and tumor to muscle was found in all patients. There was no significant change in T1 values. The relative decrease in tumor size correlated well with signal intensity ratios and poorly with T2 values of the original tumor. No correlation with T1 values was found. The authors conclude that size of the residual mass can be predicted from the initial size of the tumor and the signal intensity ratios at diagnosis. Since the degree of low signal intensity in the tumor before treatment probably reflects the amount of fibrotic tissue, these results support the hypothesis that residual masses after treatment are remnants of the fibrotic stroma of the original tumor.

Proton nuclear magnetic resonance studies on brain edema.

The water in normal and edematous brain tissues of rats was studied by the pulse nuclear magnetic resonance (NMR) technique, measuring the longitudinal relaxation time (T1) and the transverse relaxation time (T2). In the normal brain, T1 and T2 were single components, both shorter than in pure water. Prolongation and separation of T2 into two components, one fast and one slow, were the characteristic findings in brain edema induced by both cold injury and triethyl tin (TET), although some differences between the two types of edema existed in the content of the lesion and in the degree of changes in T1 and T2 values. Quantitative analysis of T1 and T2 values in their time course relating to water content demonstrated that prolongation of T1 referred to the volume of increased water in tissues examined, and that two phases of T2 reflected the distribution and the content of the edema fluid. From the analysis of the slow component of T2 versus water content during edema formation, it was demonstrated that the increase in edema fluid was steady, and its content was constant during formation of TET-induced edema. On the contrary, during the formation of cold-injury edema, water-rich edema fluid increased during the initial few hours, and protein-rich edema fluid increased thereafter. It was concluded that proton NMR relaxation time measurements may provide new understanding in the field of brain edema research.

Studies of the interaction of bovine neurophysin-II with [1-hemi-D-(3-13C)cystine] oxytocin and [1-hemi-(3-13C)cystine] oxytocin.

The interactions of [1‐hemi‐(3‐13C)cystine]oxytocin and [1‐hemi‐D‐(3‐13C) cystine]oxytocin with bovine neurophysin‐II have been studied in aqueous solution under various conditions of pH using carbon‐13 (13C) nuclear magnetic resonance spectroscopy (n.m.r.). We have monitored changes in 13C chemical shifts (δ), spin‐lattice relaxation times (T1) and linewidths (πT2*)‐1 of the [1‐hemi‐(3‐13C)cystine] oxytocin as a function of the concentration of added neurophysin. [1‐Hemi‐d‐(3‐13C)cystine]oxytocin does not interact with neurophysin and shows no changes in the above spectral parameters as a function of increasing protein concentrations. The 13C chemical shifts have been monitored as a function of pH for both 13C‐enriched, diastereoisomeric oxytocin analogs in the presence and absence of neurophysin. The midpoints of the pH‐titration curves for [1‐hemi‐(3‐13C)cystine]oxytocin and [1‐hemi‐d‐(3‐13C) cystine]oxytocin in the absence or presence of neurophysin are 6.2 and 5.5, respectively. T1 values are independent of pH for both peptides in free solution, and the rotational correlation times (tc) obtained for the peptides are of the order of magnitude expected from the Stokes‐Einstein relation (5.0 times 10‐10 sec rad‐1). T1 values decrease and linewidths increase for [1‐hemi‐(3‐13C)cystine]oxytocin in the presence of neurophysin. Fast‐exchange on the n.m.r. time scale occurs at low pH. Only broad lines can be detected at neutral pH rendering 13C T1 measurements difficult. It appears that increasing the concentration of neurophysin in the presence of [1‐hemi‐(3‐13C)cystine]oxytocin leads to aggregation of the system as judged by the 13C T1 results and corresponding rotational correlation times. In light of the significant changes in T1 values and small changes in δ values, it would seem that T1 measurements are more accurate monitors of peptide‐protein interactions than are 13C chemical shifts when the interaction of the peptide with the protein does not involve any changes in steric constraints of the peptide being monitored.

Biphasic change of proton magnetic relaxation times during azo-dye hepatocarcinogenesis.

For the first time, change in the proton longitudinal relaxation times (T1) of rat tissues has been examined throughout the whole process of azo-dye hepatocarcinogenesis. Two maxima of the T1 values were observed for liver, on Day 60 and after Day 120, and these changes correlated well with the changes in water content. The first peak was ascribed to the immature hepatocytes of hyperplastic nodules, and the second peak to the developed hepatoma cells. The significance of the change in T1 values as a preneoplastic change is discussed.