Assessment of cardiac iron by MRI susceptometry and R2* in patients with thalassemia

A magnetic resonance imaging cardiac magnetic susceptometry (MRI-CS) technique for assessing cardiac tissue iron concentration based on phase mapping was developed. Normal control subjects (n=9) and thalassemia patients (n=13) receiving long-term blood transfusion therapy underwent MRI-CS and MRI measurements of the cardiac relaxation rate R2*. Using MRI-CS, subepicardium and subendocardium iron concentrations were quantified exploiting the hemosiderin/ferritin iron specific magnetic susceptibility. The average of subepicardium and subendocardium iron concentrations and R2* of the septum were found to be strongly correlated (r=0.96, P<.0001), and linear regression analysis yielded CIC (μg Fe/g_{wet tissue})=(6.4±0.4)·R2* _septum (s⁻¹) − (120±40). The results demonstrated that septal R2* indeed measures cardiac iron level.     

Hyperpolarized He diffusion MRI and histology of secreted frizzled related protein-1 (SFRP1) deficient lungs in a Murine model

Secreted frizzled related protein-1 (SFRP1) plays a key role in many diverse processes, including embryogenesis, tissue repair, bone formation, and tumor genesis. Previous studies have shown the effects of the SFRP1 gene on lung development using the SFRP1 knockout mouse model via histological and physiological studies. In this study, the feasibility of ADC (acquired via HP ³He) to detect altered lung structure in the SFRP1 knockout (SFRP1^−/−) mice was investigated, and compared to analysis by histology. This study consisted of two groups, the wild-type (WT) mice and the knockout (KO) mice with n = 6 mice for each group. ³He ADC MRI and histology were performed on all of the animals. The global L_m values of WT and KO mice were 35.0 ± 0.8 μm and 38.4 ± 3.8 μm, respectively, which translated to an increase of 9.58% in the L_m of KO mice. The mean global ADCs for the WT and KO mice were 0.12 ± 0.01 cm²/s and 0.13 ± 0.01 cm²/s, respectively, which equated to a relative increase of 8.0% in the KO mice compared to the WT mice. In the sub-analysis of the anterior, medial and posterior lung regions, L_m increased by 10.50%, 6.66% and 11.84% in the KO mice, respectively, whereas the differences in ADC between the two groups in the anterior, medial, and posterior regions were 7.3%, 8.3%, and 4.6%, respectively. These results suggest that HP MRI measurements can be used as a suitable substitute for histology to obtain valuable information about lung geometry non-invasively. This technique is also advantageous as regional measurements can be performed, which can identify lung destruction more precisely. Most importantly, this approach extends far beyond the specific pathology analyzed in this study, as it can be applied to many other pathological conditions in the lung tissue, as well to many other embryonic studies.     

Assessment of MRI issues for the Argus II retinal prosthesis

Objective

The objective was to evaluate magnetic resonance imaging (MRI) issues (magnetic field interactions, heating, artifacts and functional alterations) at 1.5 T and 3 T for the Argus II Retinal Prosthesis (Second Sight Medical Products, Sylmar, CA, USA).

Materials and Methods

Standardized protocols were used to assess magnetic field interactions (translational attraction and torque; 3 T, worst case), MRI-related heating (1.5 and 3 T), artifacts (3 T; worst case) and functional changes (1.5 and 3 T) associated with MRI.

Results

The magnetic field interactions were acceptable. MRI-related heating, which was studied at a relatively high, MR system-reported whole body averaged specific absorption rates, will not pose a hazard to the patient under the conditions used for testing. While artifacts were “moderate” in relation to the dimensions of the Argus II Retinal Prosthesis, optimization of MRI parameters can reduce the size of the artifacts. Exposures to MRI conditions at 1.5 and 3 T did not damage or alter the functional aspects of the Argus II Retinal Prosthesis.

Conclusions

In consideration of the test results, a patient with the Argus II Retinal Prosthesis may undergo MRI at 1.5 T or 3 T when specific guidelines and MRI conditions are followed, including those advised by the manufacturer.     

Monitoring chemotherapeutic response in RIF-1 tumors by single-quantum and triple-quantum-filtered (23)Na MRI, (1)H diffusion-weighted MRI and PET imaging

The effects of 5-fluorouracil (5FU, 150 mg/kg, ip) on subcutaneously implanted radiation-induced fibrosarcoma (RIF-1) tumors were monitored by in vivo (1)H MRI to evaluate the water apparent diffusion coefficient (ADC), by single-quantum (SQ) and triple-quantum-filtered (TQF) (23)Na MRI to evaluate compartmental Na(+) content and by positron emission tomography (PET) to evaluate 2-[(18)F]fluoro-2-deoxy-d-glucose (FDG) uptake in the tumor. The MRI experiments were performed on untreated control and treated mice once before and then daily for 3 days after treatment. The PET experiments were performed on separate groups of age- and tumor-volume-matched animals once before and then 3 days after treatment. Tumor volumes significantly decreased in treated animals 2 and 3 days posttreatment. At the same time points, in vivo MRI measurements showed an increase in both total tissue SQ (23)Na signal intensity (SI) and water ADC in treated tumors while control tumors showed no change in these parameters. TQF (23)Na SI and FDG uptake were significantly lower in treated tumors compared with control tumors 3 days after 5FU treatment. The correlated increases in total tissue (23)Na SI and water ADC following chemotherapy reflect an increase in extracellular space, while the lower TQF (23)Na SI and FDG uptake in treated tumors compared with control tumors suggest a shift in tumor metabolism from glycolysis to oxidation and/or a decrease in cell density.     

Assessment by MRI of local porosity in dough during proving. theoretical considerations and experimental validation using a spin-echo sequence

Proving is a key stage in the development of the final structure of bread, as invasive measurements may provoke dough collapse. Therefore, better understanding and better control of the nucleation and the growth of bubbles require the development of non-invasive methods of measurement. In the present work, a non-invasive method is presented for the measurement of local dough porosity from MR image analysis. For this, a direct relation between the gray level of a voxel and its gas fraction was established in the absence of heat and mass transfer. At whole dough scale for a one-dimensional expansion, the porosity estimated from the gray level was compared with the porosity estimated from total dough volume measurements in a range of [0.10, 0.74 m(3) of gas/m(3) of dough]. For short proving times (<30 min), MR image analysis underestimated porosity by a maximum of 0.03 m(3) of gas/m(3) of dough, but otherwise the difference between the two means of measurement was within the standard error of total dough measurements (+/-0.01 m(3) of gas/m(3) of dough). Maps of local porosity in dough during proving are also presented and discussed.     

NMR Water Proton T1 Mechanism in Blood Diluted by its Own Plasma

The water proton T1 in human blood diluted by its own plasma was measured with a FT-NMR spectrometer operating at 60MHz for protons. A linear relationship (with a correlation of 0.99) was found between the 1/T1 and hemoglobin content(Hb) in the blood. The exchange of water between the extracellular plasma and the intracellular Hb in blood is known to satisfy the fast chemical exchange conditions, and the decay of magnetization in blood is reported to have a single exponential. Therefore, the obtained relationship should represent fast chemfcal intracellular Hb and the extrace exchange between the lular plasma.     

Assessment of pulmonary air trapping and obstruction in expiration: an experimental MRI study

PURPOSE: The aim of this experimental study was to evaluate the potential of a simple expiration technique by means of magnetic resonance imaging (MRI) in an animal model to detect pulmonary air-trapping areas after artificial bronchial obstruction. MATERIAL AND METHODS: Sixteen pigs were evaluated by means of a modified T1-weighted FLASH with fat saturation in respiratory arrest (TR=4.6 ms, TE=1.8 ms, alpha=10 degrees, S.D.=3-5 mm). A measurement of the signal intensity (SI) in the peripheral lung tissue was made in both inspiration and expiration before and after inhalation of 2 ml of 0.5% acetylcholine to simulate a bronchial obstruction. A final measurement of the lung SI was also made after bronchospasmolytic induction through salbutamol (beta2-mimetic bronchodilator). RESULTS: In expiration, a mean SI increase in peripheral lung tissue of about 183% was seen in comparison to inspiration (mean SI increase of 11-32). After inhalation of 0.5% acetylcholine, the expirational signal increase in peripheral lung tissue was only 114% of the original SI. The expirational signal homogeneity decreased after inhalation of acetylcholine. After inhalation of salbutamol, the lung tissue signal elevation in expiration was 193%. CONCLUSION: We interpret the low expiratory signal elevation after acetylcholine inhalation as a result of an air-trapped bronchial constriction in certain areas. The simple expiratory technique in an animal model showed that it is suitable to demonstrate obstructive air trapping using MRI.     

Assessment of pulmonary artery pulse wave velocity in children: An MRI pilot study

Purpose

To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.

Methods

Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.

Results

PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).

Conclusion

PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children.     

Assessment of peripheral tissue perfusion disorder in streptozotocin-induced diabetic rats using dynamic contrast-enhanced MRI

Purpose

To assess peripheral tissue perfusion disorder in streptozotocin (STZ)-induced diabetic rats by using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

Materials and Methods

A rat diabetes model was produced by intravenous injection of STZ. Diabetic rats were sustainably treated with either saline or insulin using an Alzet osmotic pump. Hind paw tissue perfusion was measured by signal intensity (SI) enhancement after gadolinium diethylenetriaminepentaacetic acid injection in DCE-MRI study and quantified using the initial area under the SI-time curve (IAUC). Peripheral tissue uptake of [¹⁴C]iodoantipyrine (IAP) was also determined as a marker of tissue blood flow for comparison with the IAUC value indicating tissue perfusion.

Results

STZ caused hyperglycemia at 1 and 2 weeks after injection. Treatment with insulin significantly alleviated hyperglycemia. At 2 weeks after STZ injection, peripheral tissue perfusion was clearly reduced in the diabetic rats and its reduction was significantly improved in the insulin-treated diabetic rats. Tissue perfusion evaluated by DCE-MRI was similar to the tissue blood flow measured by [¹⁴C]IAP uptake.

Conclusion

Our findings demonstrated that DCE-MRI can assess peripheral tissue perfusion disorder in diabetes. DCE-MRI could be suitable for noninvasive evaluation of peripheral tissue perfusion in both preclinical and clinical studies. It may also be useful for developing novel drugs to protect against diabetic vascular complications.     

Changes in MRI signal intensity during hypercapnic challenge under conscious and anesthetized conditions

Most functional magnetic resonance imaging (fMRI) studies in animals are conducted under anesthesia to minimize motion artifacts. However, methods and techniques have been developed recently for imaging fully conscious rats. Functional MRI studies on conscious animals report enhanced BOLD signal changes as compared to the anesthetized condition. In this study, rats were exposed to different concentrations of carbon dioxide (CO(2)) while conscious and anesthetized to test whether cerebrovascular reactivity may be contributing to these enhanced BOLD signal changes. Hypercapnia produced significantly greater increases in MRI signal intensity in fully conscious animals (6.7-13.3% changes) as when anesthetized with 1% isoflurane (3.2-4.9% changes). In addition, the response to hypercapnia was more immediate in the conscious condition (< 30s) with signal risetimes twice as fast as in the anesthetized state (60s). Both cortical and subcortical brain regions showed a robust, dose- dependent increase in MRI signal intensity with hypercapnic challenge while the animals were conscious but little or no change when anesthetized. Baseline variations in MRI signal were higher while animals were conscious but this was off set by greater signal intensity changes leading to a greater contrast-to-noise ratio, 13.1 in conscious animals, as compared to 8.0 in the anesthetized condition. In summary, cerebral vasculature appears to be more sensitive to hypercapnic challenge in the conscious condition resulting in enhanced T2* MRI signal intensity and the potential for better BOLD signal changes during functional imaging.     

热作用下蛋白及全血光学特性变化的实验研究

利用自行研制的双积分球系统 ,对不同温度 (37℃～ 80℃ )加热后的蛋白及人全血的光学特性参数 (对波长为 6 32 8nm的光而言 )进行了实验研究。结果表明 :热作用下生物样品生理特性的改变可用光学特性参数的变化来描述。不同的热剂量作用下 ,样品形态及结构的改变是不同的 ,相应的光学特性参数 (吸收系数与散射系数 )变化也不同 ;相同热作用下 ,样品成分的不同 ,导致样品光学特性参数的改变也存在差别。光学检测技术可望为热疗的实时无损监测提供一种新的手段。     

Blood oxygen level-dependent MRI for the monitoring of neoadjuvant chemotherapy in breast carcinoma: initial experience

Purpose

To determine the feasibility of using R2? map MRI for pretreatment diagnosis and monitoring of tumor response to neoadjuvant chemotherapy (NAC) in patients with breast cancer.

Material and Methods

Twenty-eight women with breast cancer, as evidenced by pathology, underwent MR imaging prior to and after chemotherapy. All patients were examined by conventional MRI and R2? map imaging. Subjects were divided into major histological response (MHR) and non-major histological response (NMHR) groups. Mean R2? values of cancerous and normal glandular tissues were measured before and following NAC. Differences in R2? and ΔR2?% values between these two groups were compared with paired or independent t tests. The relationship between ΔR2?% and histological response was examined using Spearman's correlation test.

Results

Before NAC, the average R2? values in carcinoma were lower than in normal glandular tissue (P<.05). After two to four cycles of NAC, the R2? values in carcinoma were increased (P<.05 ), but this change was not significant in normal glandular tissue. After NAC, ΔR2?% was significantly higher in MHR as compared to NMHR (P<.05). The ΔR2?% correlated with the histological response (r=0.581, P<.01).

Conclusion

In women undergoing NAC for breast cancer treatment, R2? and ΔR2?% appear to provide predictive information of tumor response which is probably associated with changes in tumor angiogenesis and tissue oxygenation. R2? map imaging of breasts may therefore be useful in monitoring tumor response to NAC.     

B 1 inhomogeneity effects on spin density andT 1 contrast in MRI

Summary An analysis of the effect ofB ₁ inhomogeneity on spin density andT ₁ contrasted images is here given. Distortions both in saturation recovery and inversion recovery sequences are found. The impact of these distortions onin vivo spectroscopy, where quantitative data are required, is also discussed. In general, these aspects are found to be reduced at shortertime parameters of the pulse sequences. Work partially supported by Progetto Finalizzato Tecnologie Biomediche of CNR and by Esacontrol, Genova.     

A new vascular coupling device: Assessment of MRI issues at 3-tesla

Objective

Vascular grafting frequently involves a time-consuming operation. A new vascular coupling device (VCD) made from metallic material was recently developed that may be advantageous because of the reduced operative time and decreased patient risks. Because of the metal, there are safety concerns related to MRI. Therefore, the purpose of this investigation was to use standardized testing techniques to evaluate MRI issues for this VCD in association with a 3-Tesla MR system.

Methods

The VCD (corlife oHG, Hannover, Germany) was evaluated for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts at 3-Tesla. MRI-related heating was assessed with the VCD in a gelled-saline-filled phantom with MRI performed at a whole body averaged SAR of 2.9-W/kg for 15-min. Artifacts were assessed using T1-weighted, spin echo, and gradient echo pulse sequences.

Results

The VCD exhibited minor magnetic field interactions and minimal heating (maximum temperature elevation, 1.8 °C). Artifacts were relatively small in relation to the size and shape of this implant. The lumen of the VCD could not be visualized using the gradient echo pulse sequence.

Conclusions

The metallic VCD that underwent evaluation is MR conditional for a patient undergoing an MRI procedure at 3-Tesla or less.     

荧光光谱法测定血中的三氟拉嗪

利用固相萃取技术分离血中三氟拉嗪 ,荧光法进行了测定。方法的线性范围为 0 .1— 30μg/m L ,回收率为 75 %— 86 % ,相对标准偏差为 2 .7%— 5 .2 % ,检出限为 0 .1μg/m L。     

Optimal region-of-interest MRI R2* measurements for the assessment of hepatic iron content in thalassaemia major

Objectives

To evaluate the performance of region-of-interest (ROI)-based MRI R2* measurements by using the first-moment noise-corrected model (M¹NCM) to correct the non-central Chi noise in magnitude images from phased arrays for hepatic iron content (HIC) assessment.

Methods

R2* values were quantified using the M¹NCM model. Three approaches were employed to determine the representative R2*: fitting of the ROI-averaged signal (average-then-fit, ATF); outputting the median and mean of R2*s from the pixel-wise fitting of decay signals within the ROI (denoted as PWFmed and PWFmea, respectively). The accuracy and precision of the three approaches were evaluated on synthesized data. The agreement among these approaches and their intra- and inter-observer reproducibility were assessed on 105 thalassaemia major patients.

Results

Simulations showed that ATF consistently yielded the highest accuracy and precision at varying noise levels. By contrast, PWFmed and PWFmea slightly and significantly overestimated high R2* at poor signal-to-noise ratios, respectively. Patient study showed that ATF agreed well with PWFmed, whereas PWFmea produced high R2* measurements for patients with severe HIC. No significant difference was observed in the reproducibility of the three approaches.

Conclusions

PWFmea tends to overestimate high R2*, whereas ATF and PWFmed can produce more accurate R2* measurements for HIC assessment.     

Paramagnetic contribution of serum iron to the spin-lattice relaxation rate (1/T 1) determined by MRI

T ₁ maps of phantoms containing the samples of pure serum or Mn(II)-doped serum at pH=2 were imaged by 1.5 T and 1 T MR Imagers. TheT ₁ measurements made for the determination of the paramagnetic increase were carried out before and after adding ascorbic acid. The difference of the 1/T ₁ in samples with and without ascorbic acid was evaluated as the paramagnetic contribution (PMC) of serum iron. As iron content of serum varied from iron deficient to iron overload, the PMC values increased from 0.93 to 0.565 s^?1 at 1.5 T and from 0.103 to 0.609 s^?1 at 1 T. For confirmative purposes, serum iron of each sample was determined from the paramagnetic contribution and also by an autoanalyzer. The contents of serum iron determined from PMC were in good agreement with those by the autoanalyzer and also with the literature. The data suggest that the paramagnetic contribution of serum iron can be measured by MRI.