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At least 19 recordsLinked to original sources
PubMed1976

T2 lipopolysaccharide antigen of Salmonella: genetic determination of T2 and properties of the T2, T2,S, and T2,SR Forms.

The T2 antigenic form of Salmonella bareilly was examined. The absence of O specificity in this strain was shown to be due to its nonfunctional rfb genes; when the rfb gene cluster was replaced by the rfb cluster derived from smooth donor strains, T2,S and T2,SR recombinants were produced that expressed both T2 and either 0-6,7 or 0-4,12 specificity, depending on O antigen of the donor strain. The T2, T2,S, and T2,SR forms were all unstable on culture and segregated T2-negative forms (R, S, and SR, respectively) at a high rate. In all these respects the T2 antigen closely resembled the other T-form antigen, T1. The genes responsible for the T2 antigen, rfu, were not close to rfb, but their precise location and relation to rft (which determines T1 antigen) could not be discovered because of the instability to the T2 form and low recombination frequency in the necessary interspecies crosses.

Genes↗
PubMed1978

Correlation of reverse-T3 and 3,3'-T2 (T2') plasma concentrations under physiological and experimental conditions in man.

T2' plasma levels are measured under different conditions and correlated to the repective rT3 concentrations. Specific RIAs for T2' and rT3 are used. Pharmacological doses of T3 cause an increase of plasma T2'; if T3 or T4 doses are administered to an athyroid patient which cause a similar level of plasma T3 the increase of T2' is much larger during T4 treatment. Cord blood levels of T2' are 2--3-fold higher than in normal adults whereas rT3 concentrations are about 10 times higher than normal. After birth rT3 and T2' levels decrease in about a parallel manner. After a bolus iv injection of 500 microgram rT3, T2' starts to increase as early as 2 min after injection. PTU in therapeutic doses causes a rapid increase of plasma rT3 with a maximum 4 h after ingestion. A dose of 150 mg PTU causes a maximum of about 100% above baseline. T2' also increases but to a lesser degree (about 50% above baseline). We conclude that rT3 is a most important precursor of T2' whereas T3 contributes only to a minor degree to the total T2' production under physiological conditions.

Adult↗
PubMed1989

Does signal-attenuation on high-field T2-weighted MRI of the brain reflect regional cerebral iron deposition? Observations on the relationship between regional cerebral water proton T2 values and iron levels.

T2-weighted MRI shows attenuated signals from the basal ganglia, such signal attenuation being more evident at high magnetic field strengths of 1.5 tesla (T). The basal ganglia contain high levels of iron, and it has been suggested that these iron deposits lead to shortening of bulk water T2 protons via a mechanism involving diffusion of water through local magnetic field gradients generated by the iron. This mechanism generates a relaxation contribution that is proportional to the square of the applied static field B0, and if it is significant the relaxation rate 1/T2 should be strongly dependent on Bo. T2-weighted MRI would then provide a potential means of imaging regional cerebral iron levels at field strengths that are high enough for this mechanism to be important. The bulk water proton spin-spin relaxation times (T2) of samples from caudate nucleus, frontal cortex, and white matter, taken from fresh cerebral necropsy material of four subjects dying of non-neurological conditions, and one subject with Parkinson's disease have been measured. T2 values were compared with regional cerebral iron content. At high field strengths (2.35 T and 8.5 T) no significant variation in regional cerebral water proton T2 values was found; caudate, cortex and white matter had similar water proton spin-spin relaxation times in spite of the variation in their iron content. Increasing the field strength from 2.35 T to 8.5 T resulted in a generalised 50% decrease in mean regional cerebral T2 values, as opposed to the 13-fold decrease expected if T2 relaxation was dominated by a mechanism that is dependent on B02. It was thus not possible to provide evidence that iron deposition per se is responsible for the attenuated signal obtained from the basal ganglia in T2-weighted MRI.

Body Water↗
PubMed1978

[A simple method for the simultaneous analysis of r-T3 and 33'-T2 by mass fragmentography using GC-MS. (Part II. Mass fragmentographic identification of 33'-T2 and r-T3 in biological fluids) (author's transl)].

In view of the previous report of the possibility of 33'-T2 and r-T3 measurements, the identification of these iodinated compounds was performed by mass fragmentography. The peaks at m/e 218, 624 (33'-T2) and m/e 218, 750 (r-T3) were applied to establish the precise qualitative evaluation of unknown peaks. The base peak at m/e 218 (thyroid analogues) was applied to avail itself of simultaneous multiple ion analyses by GC-MS. The following results were obtained. 1) Mass fragmentography makes possible the simultaneous measurements of 33'-T2, r-T3 and other thyroid analogues with 1 ml of serum and urine samples obtained from rats or human beings. 2) This method is very convenient for extracting the compounds from biological fluids, and the procedure can be carried out easily in a short time. The specificity of this method surpasses and cannot be compared to any other existing quantitative methods.

Animals↗
PubMed1976

T2 lipopolysaccharide antigen of Salmonella: comparison of the properties of T2 and mucoid forms.

The T2 form of Salmonella was found to resemble mucoid mutants to some extent by growing as rather slimy colonies, especially at low temperatures. Its sensitivity to rough-specific phages was greatly reduced at low temperature. However, the T2 form did not produce colanic acid. The mucoid mutants of Salmonella studies corresponded to previously described mucoid mutants of Escherichia coli culturally, chemically,and genetically.

Escherichia coli↗
PubMed1992

Breath-hold T2-weighted sequences of the liver: a comparison of four techniques at 1.0 and 1.5 T.

T2-weighted images are considered the most sensitive for lesion detection at high field; however, long imaging time is problematic. Accordingly, the authors compared four breath-hold T2 or T2* weighted sequences comprising T2*-weighted FLASH, T2*-weighted PSIF, T2-weighted rapid spin echo (RASE), and T2-weighted Turbo-FLASH (Turbo) in 20 different healthy volunteers, 10 at 1.0 T and 10 at 1.5 T with reference to regular T2-weighted spin echo. Images were evaluated quantitatively by liver signal to noise (S/N) and spleen-liver signal difference to noise (SD/N) ratios and qualitatively for presence of artifacts and image quality. Data were evaluated for 1.0 T and 1.5 T separately and combined. In the combined evaluation, T2*-FLASH had good S/N (23.1 + 5.1) but low SD/N (2.9 + 1.7) and suffered from susceptibility artifacts. T2* PSIF had good S/N (28.1 + 10.0) and moderate SD/N (6.0 + 2.4), but occasionally had heterogeneous signal intensity. Flow signal void was an attractive feature. T2 RASE had very low S/N (4.4 + 1.9) and low SD/N (2.3 + 1.1) and suffered from flow artifacts. T2-Turbo had good S/N (24.6 + 8.6) and SD/N (8.9 + 2.5). Flow signal void was present, but small matrix size decreased image quality. The results of our study suggest that T2*-PSIF and T2-Turbo have good S/N and SD/N and fair image quality which may be clinically useful for breath-hold T2-weighted sequences of the liver.

Adult↗
PubMedDate not supplied

Interventricular differences in myocardial T2 measurements: experimental and clinical studies.

The goal of this study was to determine the accuracy, the reproducibility, and some of the tissue determinants of image-based myocardial T2 measurements. Image-based T2 calculations for the free walls of the right ventricle (RV) and left ventricle (LV), in vitro T2 determination (at 0.47 T), and water, fat, and collagen content analyses were performed in ex vivo hog hearts. T2 values of the RV and LV free walls were also determined from spin-echo images of 14 healthy human subjects. Preliminary reproducibility studies were performed with 10 sets of images acquired from a single subject. For both in vitro and image-based T2 values of hog hearts, RV T2 was significantly longer than LV T2. Water content was the only tissue factor to significantly correlate with in vitro and image-based T2 values. For the 14 human subjects studied, image-based T2 values calculated from the first- and third-echo images demonstrated a significant difference between LV and RV. The difference was not significant when the first- and second-echo images were used. Image-based T2 measurements of a single subject showed a coefficient of variation of 6.8% for the LV and 9.1% for the RV. The authors conclude that image-based T2 measurements of normal myocardium can be made with sufficient precision to identify differences of the magnitude of those found between RV and LV T2 values. Image-based T2 values of myocardium may provide useful data to aid in patient treatment.

Adult↗
PubMed1991

In vivo determination of multiexponential T2 relaxation in the brain of patients with multiple sclerosis.

In vivo measurement of T2 relaxation times in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) is potentially useful for the evaluation of the disease activity. Seven patients with definite MS were investigated over a period of three years (19 examinations), using a whole-body MRI scanner operating at 0.15 T with a specially designed high-power radio-frequency head coil. A modified CPMG sequence with a 180 degree pulse interval of TE = 6 msec and 128 echoes was used for the T2 relaxation measurement of the areas of increased signal (AIS) and white matter (WM). A biexponential T2 analysis of each pixel of the spin-echo images was computed. The T2 relaxation processes were found to be a monoexponential function in WM. The T2 relaxation times of apparently normal white matter in MS patients was significantly longer than in control subjects. The T2 relaxation curves of the AIS were found in most cases to fit a biexponential function characterized by a short and a long T2. T2 long relaxation times of AIS were spread out over a wide range (150-560 msec). The study of T2 long histograms shows that some AIS can be divided into two or three parts depending on the T2 long values. Each of these parts may correspond to a pathological process such as edema, demyelination and gliosis. Evolution of T2 relaxation times over a period of time cannot as yet be correlated with modifications in the clinical state.

Adult↗
PubMed1990

Direct relationship between proton T2 and exercise intensity in skeletal muscle MR images.

Exercise selectively increases the signal intensities (SI) of active muscles in T2-weighted magnetic resonance (MR) images. If these SI increases are graded with exercise intensity, the identification of muscle recruitment patterns may be possible using MR imaging. The purpose of this study was to determine the effect of force generation during exercise on muscle T2 values. Also, we examined the effects of extracellular fluid volume (ECV) expansion on muscle T2 values. Transaxial midcalf images were collected before and after exercise on eight volunteers in a 1.5T GE magnet using a standard spin echo sequence. Exercise consisted of three consecutive bouts of ankle dorsiflexion against graded loads. Three subjects also underwent brief bouts of lower leg venous occlusion (ECV expansion) during and in addition to the exercise protocol. T2 values for the dorsiflexors significantly increased after exercise. Greater mean force produced during exercise caused greater increases in T2 after exercise (T2 = 29.6 +/- 0.9 X Force). Exercise and venous occlusion caused equivalent increases in muscle cross-sectional area. These equivalent increases in ECV were not accompanied by equivalent increases in muscle T2; venous occlusion alone caused less than a 5% increase in T2 while exercise caused a 14% to 25% increase. Consequently, a direct relationship between increases in T2 and in ECV after exercise was not established. Venous occlusion during exercise, however, did significantly augment the increase in T2 and ECV of the anterior compartment muscles. Contrast enhancement among muscles after exercise in T2-weighted MR images is dependent on generated force during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Multiple short-echo (2.5-ms) quantitation of in vivo sodium T2 relaxation.

The MR behavior of the sodium-23 nucleus in vivo is a complex problem which has generated considerable interest over the last 20 years. Early studies on excised tissue samples revealed that the sodium nucleus exhibited a two-component T2 relaxation. This biexponential T2 relaxation was characterized by a short component with a T2 = 0.7-4.8 ms, and a long component with a T2 = 7.0-26.0 ms. We have developed a 3D pulse sequence capable of performing multiple Hahn echo in vivo sodium-23 imaging at echo times as short as 2.5 ms. This sequence obtains the shorter spin echo times by presaturating the spins outside of the desired imaging region, allowing the use of nonselective rf pulses. Using this sequence we have been able to quantify the long and short T2 components of normal brain tissue, vitreous humor of the eye, and a rabbit VX-2 carcinoma. We found that gray matter and white matter of normal brain have a monoexponential T2 relaxation with T2 = 17.6 +/- 2.4 ms. The vitreous humor T2 relaxation is also monoexponential with T2 = 56.8 +/- 2.1 ms. However, we find that some of the rabbit VX2 carcinomas exhibit a biexponential T2 decay with a short component of 3.3 +/- 4.6 ms and a long component of 22.0 +/- 9.0 ms.

Absorption↗
PubMedDate not supplied

Follow-up of regional myocardial T2 relaxation times in patients with myocardial infarction evaluated with magnetic resonance imaging.

Multi-echo spin-echo cardiac magnetic resonance imaging studies (echo times 30, 60, 90 and 120 ms) were performed in 19 patients with a 7-14-day (mean 10) old myocardial infarction and were repeated in 13 patients 4-7 months (mean 6) later. Also, 10 normal subjects were studied with magnetic resonance imaging. T2 relaxation times of certain left ventricular segments were calculated from the signal intensities at echo times of 30 and 90 ms. Compared to normal individuals, the mean T2 values on the early magnetic resonance images of the patients with inferior infarction showed significantly prolonged T2 times in the inferiorly localized segments, while on the follow-up magnetic resonance images the T2 times had almost returned to the normal range. Also the patients with anterior infarction showed significantly prolonged T2 times in the anteriorly localized segments on the early nuclear magnetic resonance images, but the T2 times remained prolonged at the follow-up magnetic resonance images. For every patient a myocardial damage score was determined, which was defined as the sum of the segmental T2 values in the patients minus the upper limit of normal T2 values obtained from the normal volunteers (= mean normal + 2SD). The damage score on both the early and late magnetic resonance imaging study correlated well with infarct size determined by myocardial enzyme release. Only the patients with an inferior infarction showed a significant decrease in damage score at follow-up magnetic resonance imaging. It is concluded that the regional T2 relaxation times are increased in infarcted myocardial regions and may remain prolonged for at least up to 7 months after the acute event, particularly in patients with an anterior infarction. These findings demonstrate the clinical potential of T2-weighted magnetic resonance imaging studies for detecting myocardial infarction, and estimating infarct size for an extended period after acute myocardial infarction.

Adult↗
PubMed1991

[MR imaging of adrenal masses smaller than 5 cm. Characterization with T2 relaxation time at 1.5 T].

The T2 relaxation times of 28 adrenal masses smaller than 5 cm obtained using a 1.5 Tesla MR imaging system were analysed to evaluate the ability of this parameter to characterize the tissue masses. The adrenal masses included 13 nonhyperfunctioning adenomas, five hyperfunctioning adenomas, five metastatic tumors, two pheochromocytomas, one nodular hyperplasia, one ganglioneuroma, and one cyst. The mean T2 value of nonhyperfunctioning adenomas was almost the same as that of hyperfunctioning adenomas. A significant difference was found in T2 (p less than 0.01) between nonhyperfunctioning adenoma (50 msec +/- 7 msec; mean +/- S.D.) and metastatic tumor (63 msec +/- 11 msec), whereas there was no significant difference in mass size between them. The two pheochromocytomas and the ganglioneuroma, which were derived from adrenal medulla, had relatively long T2 of over 70 msec. The T2 values of nodular hyperplasia and adrenal cyst were 58 msec and 123 msec, respectively. Although the T2 values of metastatic tumors tended to be longer than those of nonhyperfunctioning adenomas, differentiation between them with a T2 of 60 msec was not necessarily possible, especially in smaller masses. The T2 values of two metastatic tumors of less than 2 cm indicated 50 msec levels. There seemed to be a correlation between mass size and T2 in metastatic tumors. In adenomas, however, no significant correlation was demonstrated. We conclude that the characterization of small adrenal masses by T2 at 1.5 Tesla is unsatisfactory in differentiating metastatic tumors from nonhyperfunctioning adenomas.

Adrenal Gland Diseases↗
PubMed1991

Muscle activity localization with 31P spectroscopy and calculated T2-weighted 1H images.

Using 31P spectroscopy and magnetic resonance imaging (MRI), the authors studied changes in muscle phosphorous metabolites and T2 with isometric knee extension to evaluate the potential role of T2 images in coil placement for exercise spectroscopy studies. Increased signal intensity was visible in active muscles on T2 images after exercise. Calculated T2-weighted values were elevated immediately after exercise in the quadriceps (P less than .01). T2 increases for individual quadricep muscles varied, with the largest changes in the rectus femoris and the least in the vastus lateralis. 31P spectroscopy studies demonstrated similar findings: percent change in T2 correlated positively with inorganic phosphorus to phosphocreatine ratio (Pi/PCr) (r = 0.89, P less than .01) and negatively with pH (r = -0.88, P less than .01). The correlations between imaging and spectroscopy suggest that T2 images may allow more precise placement of phosphorous coils in exercise studies. The heterogeneity of T2 changes within the quadriceps with exercise suggests that assumptions about muscle activity may be misleading. T2 images may provide muscle activity verification for exercise studies.

Adult↗
PubMed2026

Changes in ACL T2* Metrics Over the Course of the Female Menstrual Cycle: A New Biomarker for the ACL Injury Risk?

BACKGROUND: Sex-based disparities in the anterior cruciate ligament (ACL) injury risk may be partly explained by cyclic variations in sex hormones that drive systemic shifts in tissue osmoregulation. Ultrashort echo time (UTE) T2* magnetic resonance imaging provides a noninvasive, quantitative means of evaluating the water content and collagen orientation in tissue. HYPOTHESIS: Eumenorrheic female participants will exhibit significant ACL T2* changes across the cycle, while anovulatory control participants will demonstrate no significant changes over time. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 25 women with no prior knee injuries were enrolled: 10 premenopausal, eumenorrheic participants and 15 anovulatory control participants (6 postmenopausal and 9 premenopausal using oral contraceptives). Bilateral knee magnetic resonance imaging was performed at 4 time points evenly spaced over 1 month, with the first visit within 24 hours of menses onset. Ovulation status was confirmed using commercially available ovulation predictor kits. Three-dimensional UTE sequences (11 echoes; 0.03-25 ms) were acquired to evaluate bicomponent ACL T2* metrics. Linear mixed-effects models assessed temporal differences in long and short T2* values, and the Cohen d quantified effect size. RESULTS: Eumenorrheic participants demonstrated significantly shorter preovulatory long T2* values compared with postovulatory values (mean difference, 1.0 ms [95% CI, 0.2-1.9 ms]; P = .015; Cohen d = 0.51). No significant temporal differences were observed for any T2* metric in anovulatory controls. CONCLUSION: Eumenorrheic female participants exhibited significant preovulatory to postovulatory changes in ACL T2* metrics, while anovulatory controls demonstrated no significant changes over time. These findings suggest that ACL T2* metrics are sensitive to cyclic fluctuations in female sex hormones across the menstrual cycle.

Humans↗
PubMed1992

T1 and T2 carcinoma of the urinary bladder: long term results with external, preoperative, or interstitial radiotherapy.

Between January 1974 and December 1984, 273 consecutive patients with cancer of the urinary bladder, Stages T1 or T2, any N, M0, were referred to the radiotherapy department of the Catharina Hospital at Eindhoven, The Netherlands and 265 were treated in a non-randomized fashion according to one of the three following schedules: 137 patients (67 T1, 70 T2) received radiotherapy only; 96 (44 T1, 52 T2) had preoperative radiotherapy followed by cystectomy and diversion according to the Bricker technique in 94/96; 32 patients (13 T1, 19 T2) had low total dose (12 Gy median) external radiotherapy followed by an interstitial cesium implant. The external radiotherapy fields included the pelvic structures. Total dose was 64 Gy median in the radiotherapy-only group and 40 Gy median in the preoperative irradiated group. The median follow-up in survivors was 81 months (range: 15-203). Locoregional relapse was observed in 50% in the group treated by external radiotherapy alone versus 17% in the group treated by preoperative radiation plus surgery and 28% of the patients who received cesium implant. During follow-up, 106/137 (77%), 67/96 (70%) and 13/32 (41%) patients died. In the radiotherapy-alone group, 38 died from intercurrent diseases, 36 from bladder cancer, two from therapy-related complications and cause of death was unknown in 30 patients. In the preoperative radiation group, the figures were 17 for intercurrent deaths, 26 related to progressive bladder cancer, 14 died due to perioperative complications and cause of death was unknown in 10. Cause of death was intercurrent in six and due to bladder cancer in seven patients treated by cesium implant. Probability of survival (calculated from the date of histological diagnosis) for the whole group, with censoring death to intercurrent disease was 53% at 5 years (56% for T1; 51% for T2) and 41% (40% for T1; 43% for T2) at 10 years. No significant difference was observed between T1 and T2 (p = 0.76). Survival in the treatment subgroups was, for patients treated by external radiotherapy only: 50% at 5 years and 33% at 10 years; for patients treated by external radiotherapy and surgery: 49% at 5 years and 42% at 10 years; for patients treated by cesium implant: 76% at 5 years and 76% at 10 years. Survival of patients in the cesium implant group was significantly better than in the other groups (p = 0.0001). Following variables were analyzed using the Cox proportional hazards model: age, gender, T1 or T2 stage, grade, cesium implant or not, and surgery or not.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗