We propose a method for estimating membrane permeability and the intracellular diffusion coefficient using pulsed-gradient spin-echo measurement in combination with numerical simulation. The diffusion signal attenuation of leukocytes was measured with 4π2q2(Δ−δ/3) values up to 6000 s/mm2. For numerical simulations, the cell was modeled as a 15×15 μm2 square with various membrane permeabilities and intracellular diffusion coefficients. Minimization of the difference in signal attenuations between the measurement and the simulation enabled estimations of these unknown parameters for the leukocytes. A cell sample of 2.17×108 cells/mL had a membrane permeability and an intracellular diffusion coefficient of 23 μm/s and 8.9×10-4 mm2/s, respectively.
Purpose: The purposes of this study were to evaluate the positive and negative predictive values of the BI-RADS®-MR descriptors of focal masses and to develop an interpretation model based on the kinetic and morphologic parameters. Methods: Retrospective review was performed of 171 consecutive focal breast masses. MR imaging was performed on a 1.5T system using the volumetric interpolated breath-hold examination sequence (mean partition thickness, 1.2 mm; time of acquisition, 35 s). Kinetic enhancement patterns were assessed by visually comparing signal intensity on the dynamic images acquired at 60 s and 4 min (washout, plateau, and persistent). Results: There were 126 malignant and 45 benign lesions. The most frequent morphological finding among the malignant lesions was heterogeneous internal enhancement in the delayed phase (96%; P<0.001); the most frequent finding in benign lesions was smooth margin or smooth shape/margin (80 to 82%; P<0.001). The features with the highest positive predictive value for carcinoma were spiculated margin (100%), delayed central enhancement (100%), delayed enhancing internal septations (97%), and irregular shape (97%). The characteristics with the highest diagnostic accuracy for malignancy were spiculated margin (100%) and heterogeneous enhancement following washout in the smooth shape/margin group (100%). The sensitivity, specificity, and positive and negative predictive values of an interpretation model based on a combination of the morphologic characteristics and kinetic information were 99%, 89%, 96%, and 98%, respectively. Conclusion: A combination of morphologic criteria, particularly lesion shape/margin and internal heterogeneity, and kinetic information is useful for differentiating benign and malignant lesions.
A system combining electron spin resonance imaging (ESRI) with another imaging modality capable of enabling visualization of the distribution of bioradicals on an anatomical map of the specimens would be a superior biomedical imaging system. We describe the development of an ESR/MR dual-imaging system with one permanent magnet and the biomedical applications of this system. The magnetic circuit developed for the ESR/MR dual-imaging system consisted of the permanent magnet made of Fe-Nd-B, pole pieces, and poke. The permanent magnet was installed on the MR side only, and the ESR side was made of pole pieces only. The magnetic field was adjusted to 0.5T at MR and to 0.042T at ESR. The overall dimensions of the magnet developed for the ESR/MR imaging system were 460 (W)×440 (D)×460 (H) mm, and it weighed 220 kg. The distance of each center for the magnet for ESR and MR imaging could be set as close as 200 mm. The entire ESR/MR imaging system can be installed in a common laboratory without magnetic shielding. MR images of plants (myoga) and small animals (mice and rats) were successfully acquired with or without ESR operation. ESR spectra of nitroxyl spin probes were also measured, even with MRI operation. ESR signals of triarylmethyl derivatives with narrow line-width (0.026 mT) were observed in living mice while MRI was operating. The ESR/MR imaging dual functions work properly with no electric or magnetic interference. The ESR/MR dual images demonstrate that this system enables visualization of the distribution of bioradicals on the anatomical map of the object.
Purpose: To assess MRI in diagnosing ectopic pregnancy (EP), emphasizing T2*-weighted imaging (WI) efficacy. Methods and Materials: This is a prospective study of 24 female patients (16 to 41 years, average 29.9) clinically suspected of EP from April 1999 to June 2001. Eighteen had minimal vaginal bleeding and slight abdominal pain. All had positive pregnancy tests, and sonography showed no intrauterine pregnancy despite estimated gestational age of embryos and/or high concentrations of human chorionic gonadotrophin. MRI was performed with a 1.5T imager (Siemens, Vision VB33A) with a body-array coil. T2-WI (HASTE), T1-WI (2D FLASH), and T2*-WI (2D FLASH) were obtained without contrast. T2-WI was routinely obtained in 3 directions. T2*-WI orientation was determined based on the T2-WI. One of 4 radiologists with experience interpreting abdominal MR images interpreted images based on transvaginal ultrasonography (TVUS) and laboratory results. Abnormal adnexal mass with remarkable low signal area on T2*-WI was diagnosed as EP. Results: We diagnosed 19 cases as EP. Tubectomy in eighteen and abdominal total hysterectomy in one confirmed diagnosis. In one undergoing diagnostic laparoscopy, EP was denied. In 5 cases diagnosed negative based on the above criterion, no mass was detected in three, and no area of low signal was recognized on T2*-WI in the masses in two. EP was denied in four of five, and in one of the five, who underwent tubectomy, EP without bleeding was diagnosed. All EP were tubal pregnancies at final diagnosis, 19 were ampullar pregnancies and one, interstitial. Using MRI to diagnose EP, with T2*-WI as a key diagnostic factor, sensitivity was 95%, specificity 100%, and accuracy 96%. Conclusions: MRI using T2*-WI is a sensitive, specific, and accurate method to evaluate EP. T2*-WI is highly accurate for detecting and diagnosing EP because of its sensitivity to fresh hematoma.
With the development of fast scan techniques and technical advances in software, cardiac MRI can now be used for morphological and functional evaluation of the heart with good reliability and high spatial and temporal resolution. Cardiac MRI is employed at many institutions, mainly for assessing ischemic heart disease. Cardiac MRI can be used to identify coronary artery stenosis, evaluate myocardial viability, assess left ventricular wall motion and function, measure coronary blood flow and flow reserve, and obtain other useful information for the diagnosis of ischemic heart disease in a single examination, serving as a true comprehensive cardiac study. With regard to the evaluation of coronary artery stenosis, new techniques, such as whole-heart coronary MRA, permit visualization of the coronary arteries to their peripheral branches without contrast agent. Good results have been reported for whole-heart MRA as compared with X-ray coronary angiography (CAG). Attempts to evaluate plaque characteristics by visualizing the walls of the coronary arteries have also been reported recently. Technical improvements have been made in myocardial perfusion MRI to detect myocardial ischemia and in delayed contrast-enhanced MRI to assess myocardial viability, and some researchers have recently reported that the diagnostic capabilities of these techniques match or surpass those of cardiac nuclear medicine studies. We outline the features of the latest MR imaging techniques for the diagnosis of ischemic heart disease, discuss their practical applications, and compare them with other imaging modalities.
The characteristic magnetic resonance (MR) findings of Cockayne syndrome have been reported; however, the corresponding characteristics on diffusion-weighted and fluid-attenuated inversion recovery (FLAIR) imaging are yet to be documented. In this adult case with Cockayne syndrome, we identified small patchy subcortical lesions visualized as areas of high intensity on diffusion-weighted images and low intensity on FLAIR images. It is possible that these findings reflect active demyelinating lesions.
We report a case of mesoblastic nephroma detected prenatally by magnetic resonance (MR) imaging. MR imaging could provide valuable information about the origin and nature of a fetal abdominal mass and help define the relationship of the mass to adjacent structures.
Unlike fenestration of the posterior cerebral arterial circulation, fenestration of the anterior cerebral arterial circulation has not been well described. We investigated the location and configuration of fenestration of the middle cerebral artery (MCA) detected by magnetic resonance (MR) angiography. We found 6 fenestrations of the MCA among cranial MR angiography images obtained from about 2,000 patients during the past 9 years at our institution using either of two 1.5T imagers. All images were obtained by the three-dimensional time-of-flight technique. Maximum-intensity projection images in the horizontal rotation view were displayed stereoscopically. All 6 fenestrations had small slit-like configurations, five located at the proximal M1 segment, the other, at the middle M1 segment. No associated aneurysm was found. Although MCA fenestration is extremely rare and cerebral artery fenestration usually has no clinical significance, an aneurysm can arise at the proximal end of the fenestration. Thus, recognizing MCA fenestration is important when interpreting cranial MR angiograms.