Gamna-Gandy bodies of the spleen detected with MR imaging: a case report.

We report a case of a female patient with portal hypertension due to liver cirrhosis. In this case, MR imaging revealed small siderotic nodules of the spleen, called Gamna-Gandy bodies. These lesions are found in patients with portal vein or splenic vein thrombosis, hemolytic anemia, leukemia, or lymphoma, patients receiving blood transfusions, acquired hemochromatosis, or paroxysmal nocturnal hemoglobinuria. There are only few reports in the literature about these siderotic nodules which are not very familiar. MR imaging seems to be the superior imaging method for detection of these lesions. It is important to consider Gamna-Gandy bodies in the differential diagnosis of portal hypertension and the other diseases mentioned above.     

Magnetic resonance imaging in hemophilic children: value of gradient echo and contrast-enhanced imaging

The purpose of this study was to determine the value of Gradient Echo imaging for the evaluation of cartilage (3D fatsat) and blood products (2D Hemoflash), and the use of contrast enhanced SE imaging for the evaluation of synovial changes, in comparison to the clinical evaluation of children with hemophilia A. We investigated 21 joints in 16 patients with evidence of hemophilia A (mean age 11.3+/-2.1 years). In all patients, clinical examination, plain film radiographs, and MR evaluation were performed magnetic resonance imaging (MRI) was performed by using sagittal T1 SE and T2 SE images, as well as 3D fatsat GE and 2D GE images. Axial and sagittal T1 weighted SE images were obtained before and after contrast application. Findings from the clinical examination and MR imaging, regarding the evaluation of blood, synovia, and cartilage were compared. Clinical examination revealed evidence of a bleeding episode in 12 joints (57.1%), whereas MRI revealed evidence of blood or blood products in 15 joints (71.4%). Clinical investigations, including bleeding scores, pain scores, and physical examination scores did not correlate with MR findings. Due to the MR findings in 6 of 16 patients, therapeutic management was changed from on demand to prophylactic therapy. MR imaging with gradient echo and contrast-enhanced sequences is more sensitive than clinical examination for the detection of blood products in children with hemophilia. Its ability to demonstrate potentially early stages of cartilage or synovial alterations might assist in therapy planning. Clinical scores might underestimate effects of hemophilia.     

Contrast-enhanced magnetic resonance tomoangiography: A new imaging technique for studying thoracic great vessels

The authors propose a new imaging approach for studying thoracic great vessels, using high-speed MR imaging combined with intravenous rapid bolus injection of a paramagnetic contrast media. The decrease of the T₁ relaxation time of flowing blood induced by the contrast agent (Gd-DOTA) caused an increased signal intensity within the vessel lumen for a time period allowing multiplanar imaging of various vascular structures. The intraluminal signal enhancement is mainly related to the blood concentration of the contrast agent as in conventional X-ray angiography. Information on the aorta and pulmonary arteries obtained by the so-called contrast-enhanced magnetic resonance tomoangiography appears complementary to that obtained with other vascular MR imaging procedures such as cine-MRI and magnetic resonance angiography (MRA).     

Reliability of mean transit time obtained using perfusion-weighted MR imaging; comparison with positron emission tomography

The purpose of this project was to assess the reliability of the cerebral mean transit time (MTT) obtained using perfusion-weighted MR imaging by comparing it with the MTT obtained when performing positron emission tomography (PET). Ten patients with chronic occlusive cerebrovascular disease were investigated. They had either unilateral internal carotid artery occlusion or middle cerebral artery occlusion. The regions-of-interest were placed in non-infarcted areas within the territory of the middle cerebral artery on the affected side. Control regions-of-interest were placed in mirrored regions of the contralateral side. Linear regression analyses were performed using the parameters of the MTT obtained with perfusion-weighted MR imaging and the MTT, cerebral blood flow, vascular reactivity, and oxygen extraction fraction obtained with PET. The respective MTTs of the affected and non-affected sides obtained with perfusion-weighted MR imaging versus those with PET were 7.3 +/- 2.2 s and 6.0 +/- 1.2 s versus 8.2 +/- 3.0 s and 6.4 +/- 1.7 s. The MTT obtained using perfusion-weighted MR imaging and PET demonstrated statistically significant correlation (r = 0.87, p < 0.0001). The MTT obtained with perfusion-weighted MR imaging correlated statistically with cerebral blood flow (r = -0.74, p < 0.001), vascular reactivity (r = -0.73, p < 0.001) and oxygen extraction fraction (r = 0.61, p < 0.01). Similarly, the MTT obtained using PET statistically correlated with cerebral blood flow (r = -0.78, p < 0.0001), vascular reactivity (r = -0.51, p < 0.05) and oxygen extraction fraction (r = 0.68, p < 0.01). The reliability of the MTT obtained using perfusion-weighted MR imaging appears to be approximately equal to that obtained with positron emission tomography.     

Study of cerebrovascular reserve capacity by magnetic resonance perfusion weighted imaging and photoacoustic imaging

The aim of this work was to assess the feasibility of photoacoustic imaging (PAI) and MR imaging for evaluating the cerebrovascular reserve capacity (CVRC) in animal models. Wistar-Kyoto (WKY) rats and spontaneous hypertensive rats (SHR) were used for MRI. BALB/c mice were used for PAI. MR perfusion weighted imaging (PWI) was performed on a 1.5-T whole-body MR system before and after oral administration of acetazolamide (ACZ). The region of interest (ROI) was chosen in the bilateral frontal lobe for measuring regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and mean transit time (MTT). The vessel diameters of the superficial layer of the cortex were measured by PAI in the resting and ACZ-activated mice. The results showed that there was a statistical difference between the resting and ACZ-activated animals in vessel diameter, rCBV and rCBF values. The increments in rCBV and rCBF of WKY rats between resting and ACZ test states were significantly higher than that of SHR. The pathological findings of small arterial walls and lumen of the brain were also different between WKY and SHR rats. The diameters of blood vessels in the superficial layer of the brain measured by PAI were enlarged after the ACZ tolerance test. This result was also observed in the MRI CBV map, where the signal of the vessel in the superficial layer of the cortex became redder after the ACZ stimulation, suggesting the increase of blood flow. It can be concluded that MR PWI and PAI combined with the ACZ test might be useful in evaluating the CVRC and revealing the pathologic changes in cerebral vessels.     

Magnetic resonance imaging of the uterus in vivo and in vitro at an ultra low magnetic field (0.02 T): Assessment of its normal structure and of leiomyomas

The purpose of this investigation was to analyze the normal anatomy and leiomyomas of the uterus with an ultra low field (0.02 T) magnetic resonance imaging (MRI) device. MR imaging was performed on 18 uteri, 11 of which were imaged both preoperatively (in vivo) and as an operative specimen (in vitro), 6 only as an operative specimen, and 1 only preoperatively. All uteri were examined histologically after imaging. The junctional zone was much better delineated in vivo than in vitro, indicating that its appearance on MR is partly due to blood flow. No structures contributing to its visibility in vitro could be demonstrated histologically. Twenty leiomyomas (size range 7–79 mm) in 12 uteri were found with MRI. They were slightly better discerned in vivo than in vitro. The leiomyomas, having no degenerative changes, had a signal intensity which was the same or lower than that of the myometrium. On images obtained in vitro the signal intensity of these leiomyomas relative to that of myometrium correlated directly with their muscular content (R = 0.74, p = .002). The authors conclude that the junctional zone is a sum of physiological and structural factors, the latter being responsible for its in vitro delineation. MR imaging of the uterus in vitro did not give more information than MR imaging in vivo. All leiomyomas larger than 10 mm could be detected, indicating that MR imaging at 0.02 T is an accurate method for the imaging of the uterine leiomyomas.     

Reproducibility of MRI-derived measurements of right ventricular volumes and myocardial mass

Magnetic resonance (MR) imaging has been shown to provide accurate measurements of right ventricular (RV) volumes and myocardial mass. The purpose of this study was to evaluate the reproducibility of MR imaging, which in clinical practice may be as important as its absolute accuracy. The reproducibility of MR imaging measurements of the right ventricle was assessed by analyzing 40 serial functional MR imaging examinations of the right ventricle with variance component analysis. Standard deviations and 95% ranges for change were: for RV myocardial mass, 5.9 and 16 g; and for RV ejection fraction, 6.0% and 16%, respectively. Reproducibility was similar for cine and spin-echo MR imaging. The intraobserver and interobserver errors were especially large, indicating that observer subjectivity is the limiting factor in the interpretation of the MR images. This study suggests that the reproducibility of RV measurements is adequate to detect RV hypertrophy and a low ejection fraction in the individual patient. For accurate follow-up examinations, whereby smaller changes are to be detected, the reproducibility of MR imaging measurements may not be sufficient. More effort is needed to improve the reproducibility of MR imaging measurements.     

Intravascular delivery of hyperpolarized129Xenon forin vivo MRI

The nuclear polarization of¹²⁹Xe and³He can be enhanced by several orders of magnitude by using optical pumping techniques, thus allowing NMR detection of xenon and helium in very low concentrations. The benefits of optically enhanced magnetic resonance (MR) are already exploited in MR imaging of the lungs using optically polarized³He. The high solubility of xenon in blood and lipids suggests a variety ofin vivo MR applications, for instance perfusion measurements or functional MR studies. This article reviews some current work directed towards delivery of optically polarized xenon forin vivo MR applications.     

Oxygen-sensitive 19F NMR imaging of the vascular system in vivo

The fluorine nuclear magnetic resonance spin-lattice relaxation rate (1/T1) of the perfluorochemical blood substitute perfluorotripropylamine (FTPA) is very sensitive to oxygen tension. This presents the possibility of measuring blood oxygen tension by 19F MR imaging. We obtained oxygen-sensitive 19F NMR images of the circulatory system of rats infused with emulsified FTPA. Blood oxygenation was assessed under conditions of both air- and 100% O2-breathing. T1 relaxation times were derived from MR images using a partial saturation pulse sequence. The T1 times were compared with a phantom calibration curve to calculate average blood pO2 values in the lung, liver, and spleen. The results showed marked, organ-specific increases in blood oxygen tension when the rat breathed 100% O2 instead of air.     

Determining uterine blood flow in pregnancy with magnetic resonance imaging

Objective

The purpose of this study is to determine the feasibility of measuring total uterine blood flow in pregnancy using magnetic resonance imaging (MRI) technique.

Methods

Uterine blood flow was determined in pregnant women in whom MRI was being carried out to assess a fetal anomaly. A two-dimensional time-of-flight magnetic resonance (MR) angiogram sequence was performed. Scout images and a peripherally gated phase contrast MR sequence were planned to study simultaneous blood flow in the uterine and ovarian arteries.

Results

The MR pelvic angiogram sequence was completed in 13 women. The uterine arteries were visualized and their cross-sectional area determined. The complexity of the pelvic blood supply prevented the calculation of blood flow velocity and, thus, total uterine blood flow.

Conclusion

The measurement of total uterine blood flow during pregnancy was not possible using our MR technique. The ovarian vessels were not consistently visualized. Doppler ultrasonography remains the best modality by which to estimate total uterine blood flow in pregnancy.     

A comparison of T2*-weighted magnitude and phase imaging for measuring the arterial input function in the rat aorta following intravenous injection of gadolinium contrast agent

The arterial input function (AIF) is important for quantitative MR imaging perfusion experiments employing Gd contrast agents. This study compared the accuracy of T(2)*-weighted magnitude and phase imaging for noninvasive measurement of the AIF in the rat aorta. Twenty-eight in vivo experiments were performed involving simultaneous arterial blood sampling and MR imaging following Gd injection. In vitro experiments were also performed to confirm the in vivo results. At 1.89 T and TE=3 ms, the relationship between changes in 1/T(2)* in blood (estimated from MR signal magnitude) and Gd concentration ([Gd]) was measured to be approximately 19 s(-1) mM(-1), while that between phase and [Gd] was approximately 0.19 rad mM(-1). Both of these values are consistent with previously published results. The in vivo phase data had approximately half as much scatter with respect to [Gd] than the in vivo magnitude data (r(2)=.34 vs. r(2)=.17, respectively). This is likely due to the fact that the estimated change in 1/T(2)* is more sensitive than the phase to a variety of factors such as partial volume effects and T(1) weighting. Therefore, this study indicates that phase imaging may be a preferred method for measuring the AIF in the rat aorta compared to T(2)*-weighted magnitude imaging.     

MR safety and compatibility of a noninvasively expandable total-joint endoprosthesis

A noninvasively expandable total-joint endoprosthesis is now available for pediatric patients; the prosthesis can be lengthened by external application of a magnetic field. We investigated the risks of unintentional heating or lengthening of the prosthesis during MR imaging and evaluated the effect of the device on the diagnostic efficacy of MR imaging of surrounding tissues. We performed MR imaging at 1.5 T by using standard pulse sequences and pulse sequences with high-gradient and high-radiofrequency duty cycle. MR imaging caused no measurable change in prosthesis length, and the temperature of the prosthesis increased by less than 1 degrees C during repeated 14-min exposures. Despite significant signal loss and image distortion around the prosthetic joint, clinically useful images were obtained as close as 12 cm from the ends of the prosthetic stems, measured toward the body of the device. Thus, the prosthesis can be safely exposed to MR imaging pulse sequences at 1.5 T, and the visualization of some tissue surrounding the device is clinically useful.     

Methods for the systematic investigation of gastrointestinal contrast media for MRI: evaluation of intestinal distribution by radiographic monitoring

Comparison of the effectiveness of various gastrointestinal (GI) contrast agents for magnetic resonance (MR) imaging is often complicated by varying amounts intraluminal filling with the orally administered agents. To achieve more uniform and reproducible imaging results with GI contrast agents for MR imaging (GICMR), we evaluated a radiographic method for monitoring intraluminal filling and distribution. Solutions of Mn-DPDP (2 mM), to which a small amount of barium sulfate (6 wt/vol%) was added, were administered orally to dogs. Gastric emptying and small bowel transit were monitored fluoroscopically. MR imaging was performed either 1) at a fixed time after administration of the contrast agent or 2) at a variable interval when the contrast agent was observed fluoroscopically to be in the terminal ileum. When initiation of MR imaging was guided by fluoroscopic monitoring of intestinal contrast distribution, uniform and reproducible intestinal contrast enhancement by GICMR was achieved. However, when MR imaging was performed at a fixed time interval after oral administration, non-uniform and variable GI visualization was obtained, and this corresponded to the variable intestinal distribution observed fluoroscopically. We conclude that reproducible intestinal filling with orally administered contrast agents can be accomplished with a radiographic monitoring technique, and this promotes more consistent GI visualization on MR images. Such standardized and reproducible methods are necessary for studies in which the effectiveness of GI contrast media for MR imaging is evaluated and compared.     

Noninvasive quantification of fluid mechanical energy losses in the total cavopulmonary connection with magnetic resonance phase velocity mapping

A major determinant of the success of surgical vascular modifications, such as the total cavopulmonary connection (TCPC), is the energetic efficiency that is assessed by calculating the mechanical energy loss of blood flow through the new connection. Currently, however, to determine the energy loss, invasive pressure measurements are necessary. Therefore, this study evaluated the feasibility of the viscous dissipation (VD) method, which has the potential to provide the energy loss without the need for invasive pressure measurements. Two experimental phantoms, a U-shaped tube and a glass TCPC, were scanned in a magnetic resonance (MR) imaging scanner and the images were used to construct computational models of both geometries. MR phase velocity mapping (PVM) acquisitions of all three spatial components of the fluid velocity were made in both phantoms and the VD was calculated. VD results from MR PVM experiments were compared with VD results from computational fluid dynamics (CFD) simulations on the image-based computational models. The results showed an overall agreement between MR PVM and CFD. There was a similar ascending tendency in the VD values as the image spatial resolution increased. The most accurate computations of the energy loss were achieved for a CFD grid density that was too high for MR to achieve under current MR system capabilities (in-plane pixel size of less than 0.4 mm). Nevertheless, the agreement between the MR PVM and the CFD VD results under the same resolution settings suggests that the VD method implemented with a clinical imaging modality such as MR has good potential to quantify the energy loss in vascular geometries such as the TCPC.     

MR imaging of excessively obese patients: the use of an open permanent magnet

Excessive obesity can pose a limitation to both clinical and radiographic evaluation. Although CT and MR have revolutionized head and body imaging, patients with weights above 300 lb present a restriction of these imaging modalities. Magnetic resonance imaging (MRI) is well suited for imaging excessively obese patients, because the RF used does not have difficulty in penetrating large amounts of adipose tissue as ionizing radiation or sound waves does. The limitations of conventional MR imaging in these obese patients are the gantry size and the table weight limit. The recent development of a new low field MR imager with a larger gantry size and greater weight capacity, has the potential for imaging obese patients that cannot be evaluated by standard CT or MR. In this paper, we report our experience in imaging nine excessively obese patients with weights between 350 and 490 lb using a permanent magnet operating at 0.064 T.     

Acute and subacute liver-related hemorrhage: MRI findings

We retrospectively reviewed the MR studies on all patients with liver-related fluid collections compatible with acute or early subacute hemorrhage, who underwent MR imaging at our center between June 1994 and January 1998. All patients had a clinical history of an underlying liver lesion or injury with a duration of symptomatology of less than 5 days. In three patients with only 2-3 days of symptoms, the liver-related hemorrhagic fluid was hypointense on T1-weighted images and markedly hypointense on T2-weighted images relative to liver, consistent with intracellular deoxyhemoglobin. The fluid was relatively homogeneous in signal intensity. In three patients with 3-5 days of symptoms, the majority of liver-related fluid was hyperintense on T1-weighted images and hypointense on T2-weighted images relative to liver, consistent with intracellular methemoglobin. Three of these latter four patients also had fluid collections of varying T1-and T2-weighted signal intensity consistent with blood breakdown products of varying ages. Clinical findings matched the MR findings of acute/early subacute blood in all cases. Our results describe the findings of acute and early subacute liver hemorrhage. The most helpful MR feature of bleeding of recent origin is very low signal intensity of the fluid on T2-weighted imaging.     

Research and progress in magnetic resonance imaging of triple-negative breast cancer

Triple-negative breast cancer (TNBC), which characterized by distinct biological and clinical pathological features, has a worse prognosis because the lack of effective therapeutic targets. Breast MR is the most accurate imaging modality for diagnosis of breast cancer currently. MR imaging recognition could assist in diagnosis, pretreatment planning and prognosis evaluation of TNBC. MR findings of a larger solitary lesion, mass with smooth mass margin, high signal intensity on T₂-weighted images and rim enhancement are typical MRI features associated with TNBC. Further work is necessary about the clinical application of dynamic contrast-enhanced MR imaging (DCE-MRI), DWI and MRS.     

Diagnosis of peripheral pulmonary emboli by MR imaging: an experimental study in dogs

The peripheral pulmonary arteries of 5 dogs were embolized with boiled autologous clots via the external right jugular vein. Angiography determined the location and approximate size of the emboli in the peripheral pulmonary arteries. With spin echo techniques, transverse axial magnetic resonance (MR) images (0.3 T, 12.77 MHz) were obtained in each animal from apex to thorax base, on a permanent magnet scanner. The sensitivity of MR imaging was assessed to detect these clots and to determine their size and location. In 2 dogs, scans were also obtained before embolization in order to exclude possible artifactual areas of increased signal. Fourteen out of 19 emboli were identified on the MR scans as areas of increased signal. Their diameter measured a minimum of 2.7 mm matching the filling defects seen on the angiograms. There were three false positive emboli on MR probably related to slow blood flow in the inferior vena cava. There were 9 false negative emboli on MR. The increased MR signal seen in dogs with pulmonary emboli results from the embolus itself and from slow blood flow distal to the obstructive embolus.     

A four-element phased array coil for high resolution and parallel MR imaging of the knee

A four-element phased array coil for MR imaging of the knee was designed, built and tested for clinical use at 1.5 Tesla. In routine imaging, it provides over twofold increase in signal-to-noise (SNR) compared to two commercially available knee coils, and supports higher spatial image resolution. The phased array knee coil was also tested for its compatibility with parallel MR imaging that reduces imaging time by several folds over conventional MR technique. Results obtained using SiMultaneous Acquisition of Spatial Harmonics (SMASH) technique shows that our phased array knee coil can be used with parallel MR imaging. These improvements may enhance knee diagnosis with higher image quality and reduced scan time.     

Labelling of cultured macrophages with novel magnetic nanoparticles

Magnetic resonance (MR) imaging is capable of demonstrating human anatomy and pathological conditions. Iron oxide magnetic nanoparticles (MNPs) have been used in MR imaging as liver-specific contrast medium, cellular and molecular imaging probes. Because few studies focused on the MNPs other than iron oxides, we developed FeNi alloy MNPs coated with polyethylenimine (PEI). In this study, we demonstrated PEI-coated FeNi MNPs are able to label the cells, which could be detected in MR imaging. For labelling purpose, MNPs were incubated with mouse macrophage cell line (Raw 264.7) for 24 h and these PEI-labelled FeNi alloy MNPs can be uptaken by macrophages efficiently compared with Ferucarbotran, a commercialized superparamagnetic iron oxide (SPIO) under flow cytometry measurement. Besides, these cells labelled with MNPs could be imaged in MR with the identical potency as Ferucarbotran. Further investigation of the cells using Prussian blue staining revealed that FeNi alloy MNPs inside the cells is not oxidized. This phenomenon alleviated the consideration of potential risk of nickel toxicity. We conclude that PEI-coated FeNi MNPs could be candidate for MR contrast medium.