Determining disk hydration status with a MnCl2-based MR model

PURPOSE: An extensive body of literature demonstrates a strong correlation between intervertebral disk (IVD) hydration status (HS) and functional spinal integrity. However, to date, in vivo IVD HS assessment has relied largely on subjective and nonrepeatable measures. The aim of this study was to establish the consistency of signal homogeneity of a novel semisolid-state manganese chloride (MnCl2)-based phantom for HS correlation using conventional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Sixteen MnCl2 phantoms, of increasing relative molar concentration (range 0.01 to 2.9 mM), underwent axial MR imaging. Phantom signal-to-noise ratio measures were recorded for each concentration on several sequence types. Coefficient of variance data were calculated to determine the degree of MR signal variation at each concentration. RESULTS: Analysis of variance testing suggested no significant difference in coefficient of variance data derived from phantom signal intensities using either T1- (P = .13) or T2-weighted sequence types (P = .96), suggesting a high degree of relative signal homogeneity. CONCLUSIONS: The findings of this study suggest that a MnCl2 phantom combined with a nonfield reactive, semirigid, gelatin suspension media can produce a predictable, concentration-related, homogeneous MR signal response. This may be an appropriate base material for a noninvasive model to allow accurate quantification of the hydration status of the in vivo human IVD.     

A MnCl2-based phantom for IVD hydration status determination using MRI: Pre-clinical reliability analyses

Introduction

Non-biological, yet signal-responsive, MR phantom materials are becoming increasingly commonplace. One such novel agent, semi-solid manganese chloride (MnCl₂), has recently been described as a potential calibration standard for direct assessment of in vivo cartilage fluid content. Given the established correlation between intervertebral disc (IVD) hydration state and physiologic spinal functioning, such a tool, allowing calibration for ‘quantitative’ appraisal of disc fluid content, has many potential applications. The purpose of this study was to demonstrate MR signal-to-noise ratio (SNR) measurement reliability of a novel MnCl₂-based signal calibration phantom for in vivo disc hydration analysis, using a 10 × 10 inter- and intra-observer reliability analysis in the pre-clinical setting.

Materials and methods

A series of novel MnCl₂ calibration phantoms were imaged to assess intra-/inter-observer reliability during measurement of signal intensity. The phantoms were imaged under ten different MR sequences, generating 75 signal regions from which SNR values were measured. Inter-observer reliability was tested by inviting ten individuals to obtain signal measurements from each image, on a single occasion. To test intra-observer reliability, a single participant was asked to record measurements of the same features on ten separate occasions.

Results

1425 Discrete measurement points were available for combined reliability analyses. Single-measure intraclass correlation coefficients showed high measurement agreement, with both intra- and inter-observer values approaching 1.00.

Conclusion

This study demonstrates that signal measurements can be obtained using MnCl₂ disc phantoms, with a high degree of observer reliability, supporting their use as a signal calibration standard during orthopaedic MR-based cartilage imaging.     

BaSO4-loaded agarose: a construction material for multimodality imaging phantoms

RATIONALE AND OBJECTIVES: Phantom studies are an important part of the evaluation of imaging techniques; however, presently available phantom construction materials are not adequate for studies involving both magnetic resonance (MR) imaging and computed tomography (CT). The purpose of this study was to design a phantom construction material useful for multimodality imaging experiments. MATERIALS AND METHODS: Iodinated contrast agent or BaSO4 was added during the formation of agarose gels. Both CT and MR imaging were performed, and T1 and T2 values and CT numbers (in Hounsfield units) were obtained for multiple combinations of contrast material and agarose. Results. The T2 values of agarose gels span the range of those values found in biologic tissues. Phantoms containing iodinated contrast agent were not stable; contrast agent diffused across concentration gradients. BaSO4-loaded agarose phantoms were stable, however, and varying barium concentrations produced phantoms that spanned the range of CT numbers found in biologic tissues. Addition of BaSO4 did not substantially alter T1 or T2 values of agarose gels. Agarose concentration had only a small effect on the CT numbers of BaSO4 suspensions. CONCLUSION: BaSO4-loaded agarose is an effective material for construction of multimodality imaging phantoms. It provides adequate signal intensity for MR imaging and attenuation for CT, with independently variable contrast in both modalities.     

MR pulse sequence selection for optimal display of acrylic polymer phantoms

PurposeAcrylic phantoms are being increasingly used as an alternative to cadaveric and animal derived tissue samples in pre-clinical magnetic resonance (MR) imaging research studies. Such phantoms have been imaged using a variety of MR sequences but little effort has been devoted to determining the most appropriate MR pulse sequence. In order to address this question, a prospective comparative study was performed to determine which MR sequence optimally demonstrates acrylic polymer phantoms.MethodsNine MR imaging sequences were selected and used to image an acrylic phantom placed in a water bath. The mid-sagittal slice of each sequence was used to determine signal-to-noise (S/N) and contrast-to-noise (C/N) ratios. The signal intensity maximum gradient at the phantom/fluid interface was used as a measure of edge delineation.ResultsOf the nine sequences reviewed the T2 driven equilibrium pulse sequence (DRIVE), a 3D turbo spin echo (TSE) sequence, provided the highest S/N (72.88) and C/N (69.62) ratios, while the proton density (PD) TSE or intermediate T2 TSE sequences provided the best edge delineation (definition of the acrylic-fluid interface).ConclusionThis study suggests that selection of MR pulse sequences when evaluating a submersed acrylic phantom is dependent on which information is most important to the researcher. If S/N and C/N are considered most important, of the nine MR sequences tested, the T2 DRIVE sequence may be best employed. If edge delineation is considered most important, then PD or intermediate T2 TSE sequences may be best employed.     

Fast inversion-recovery MR: the effect of hybrid RARE readout on the null points of fat and cerebrospinal fluid.

PURPOSETo evaluate the effect of the hybrid RARE (rapid acquisition with relaxation enhancement) readout, commonly coupled to inversion-recovery pulse sequences, on the null inversiton time (TI) of fluid and fat using both phantoms and human volunteers.METHODSTwo phantoms, simulating fat (phantom A) and cerebrospinal fluid (phantom B), respectively, were imaged using a fast inversion-recovery sequence that coupled an inversion-recovery preparation pulse to a hybrid RARE readout. At repetition times (TRs) ranging from 700 to 20,000, the TI necessary to null the signal from each phantom (null TI) was determined for an echo train length of 4, 6, 8, 10, 12, 14, 16, 18, and 20, respectively. Plots of null TI versus echo train length at different TRs were generated for both phantoms. Fast inversion-recovery MR imaging of the cervical spine and brain was performed in healthy volunteers. At a fixed TR and TI, the adequacy of signal suppression from bone marrow and cerebrospinal fluid was assessed as a function of echo train length.RESULTSThere was a gradual decrease of null TI for both phantoms with echo train length. This decrease persisted at longer TRs for phantom B (T1 = 3175 +/- 70 milliseconds) than for phantom A (T1 = 218 +/- 5 milliseconds). In the human volunteers, there was a gradual loss of suppression of signal from bone marrow and cerebrospinal fluid, with changes in the hybrid RARE readout.CONCLUSIONTo optimize specific tissue suppression, radiologists implementing fast inversion-recovery MR imaging should be aware of the effects of the hybrid RARE readout on null TI.     

Quantitative analysis of sodium fast and slow component in in vivo human brain tissue using MR Na image]

In vivo sodium concentrations in the normal brain tissue and a tumorous tissue were analyzed using MR Na image. The nuclear magnetic resonance enabled us to divide the signal from sodium in the living tissue into 2 parts based on the differences of T2 value. Those are fast component having the T2 value of less than 5 msec and slow component of 15-40 msec. We investigated the effect of macromolecules on T2 value of sodium image using polyvinyl alcohol (PVA) powder. MR Na image was taken with the parameters of TR/TD, 110 ms/1.9 ms (FID image) and TR/TE, 110 ms/20 ms (SE image). Saline solution showed high intensity on both FID image and SE image. Saline solution added PVA (PVA phantom) also showed high intensity on FID image, whereas the signal intensity of PVA phantom in SE image extinguished. To know the relation between the signal intensity and sodium concentration, sodium concentration--signal intensity curve was obtained using phantoms with various sodium concentrations (0.05-1.0%). This curve showed a direct proportion between sodium concentration and signal intensity on Na image. We measured further the sodium concentrations of the human brain tissue. Sodium phantoms were arranged around the heads and the MR Na images of the normal brains from 3 volunteers and a patient with a brain tumor (meningioma) were taken. The sodium concentrations of occipital lobe, basal ganglia and the tumorous tissue were calculated using the sodium concentration--signal intensity curve obtained from the phantoms arranged around the heads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic contrast-enhanced T2-weighted MR imaging of recurrent malignant gliomas treated with thalidomide and carboplatin

BACKGROUND AND PURPOSE: Dynamic, contrast-enhanced MR imaging has allowed quantitative assessment of cerebral blood volume (CBV) in brain tumors. The purpose of our study was to compare postcontrast T1-weighted imaging with dynamic, contrast-enhanced T2*-weighted echo-planar imaging in the evaluation of the response of recurrent malignant gliomas to thalidomide and carboplatin. METHODS: Serial MR imaging was performed in 18 consecutive patients with recurrent malignant gliomas receiving both thalidomide and carboplatin for 12-month periods. Six patients undergoing carboplatin therapy alone were chosen as control subjects. Conventional postcontrast T1-weighted images were compared with relative CBV (rCBV) maps calculated on a pixel-by-pixel basis from dynamic echo-planar imaging data. Tumor progression was evaluated clinically using established criteria for malignant gliomas. Studies were performed at 2- to 3-month intervals, and imaging and clinical findings were compared. RESULTS: Tumor response to treatment, based on clinical findings, did not correlate well with conventional imaging findings. The rCBV values decreased significantly in all patients between the start of therapy and the first follow-up in the study group, but not in the control group. The difference in rCBV values between the clinically stable and the progressive group at 12-month follow-up was statistically significant, with the progressive group having higher values. CONCLUSION: Dynamic, contrast-enhanced MR imaging is a valuable adjunct to conventional imaging in assessing tumor activity during antiangiogenic therapy, and correlates better than conventional studies with clinical status and response to therapy.     

Adrenal masses: quantification of fat content with double-echo chemical shift in-phase and opposed-phase FLASH MR images for differentiation of adrenal adenomas

PURPOSE: To quantify fat content in adrenal lesions with double-echo chemical shift magnetic resonance (MR) imaging in a phantom study and to differentiate adrenal adenomas from other adrenal masses by assessing fat content in a clinical study. MATERIALS AND METHODS: The study consisted of two parts: a phantom study and a clinical study. To explore the effect of the T1 value on in- and opposed-phase MR images of fat-containing tissues, phantom models with various proportions of fat and gadopentetate dimeglumine concentrations were implemented. Signal intensity (SI) indexes ([SI in-phase - SI opposed-phase]/SI in-phase) were calculated with double-echo fast low-angle shot (FLASH) MR imaging. In the clinical study, 23 patients with 28 adrenal masses (16 adrenal adenomas, nine adrenal metastases, and three pheochromocytomas) underwent double-echo FLASH MR imaging, and SI indexes were calculated. RESULTS: SI index reached a maximum of 0.87 at 53% fat fraction for gadopentetate dimeglumine concentration at 0.5 mmol/L as the simulated T1 of the adrenal mass. The SI indexes of the adrenal adenomas, adrenal metastases, and pheochromocytomas, respectively, were 0.36, -0.15, and -0.07, and estimated fat fraction from the phantom study was 26.5%, 0%, and 0%. All adrenal adenomas contained fat on double-echo FLASH images. There was no overlap in SI index between adenomas and other tumors. CONCLUSION: Preliminary experience indicates that quantitative measurement of the fat fraction of adrenal masses is possible with the double-echo chemical shift FLASH technique and allows for differentiating adrenal adenomas from other adrenal masses.     

Investigation of a logistic model for T2* dynamic susceptibility contrast magnetic resonance imaging (dscMRI) perfusion studies

There are a number of T1- and T2-based dynamic contrast-enhanced magnetic resonance imaging pharmacokinetic modeling approaches to study cancer microvasculature. Alternatively, model-free approaches offer an easy, quantitative assessment of microcirculation. In this work, we investigate a 6-parameter model-free approach applied to a T2*-weighted echo-planar imaging bolus response curve. We tested this new approach on a small cohort of patients with clinically diagnosed primary rectal carcinoma before adjuvant chemoradiotherapy and surgical excision. Comparison with healthy muscle tissue shows that logistic parameters P1/P2, P4, and P5 offer good discrimination between tumor and healthy tissue. Bolus response logistic parameters P4 and P5 have been implicated in previous T1-based works as being important in the assessment of cancer malignancy. Further comparison of T2* parameters with signal attenuation amplitude (maximum signal drop) and percentage baseline signal loss also corroborates the models' ability to quantify the microenvironment.     

强直性脊柱炎骶髂关节影像学分析(附24例骶髂关节平片、CT和MR影像对比观察)

目的：旨在评估强直性脊柱炎（ＡＳ）患者骶髂关节炎的ＭＲ影像特征，并比较Ｘ线平片、ＣＴ和ＭＲ影像在诊断骶髂关节炎中的作用。材料与方法：搜集２４例ＡＳ患者，分别行Ｘ线平片、ＣＴ和ＭＲＩ检查。增强前ＭＲ扫描序列包括ＳＥＴ１ＷＩ、ＦＳＥＴ２ＷＩ和梯度回波的准Ｔ２ＷＩ（ＧＲＴ２＊ＷＩ）。增强后ＭＲ扫描序列参数与增强前ＳＥＴ１ＷＩ相同。另选９例志愿者，行ＭＲ平扫检查。结果：８例志愿者１６个骶髂关节的Ｔ１ＷＩ和Ｔ２ＷＩ可直接显示正常骶髂关节软骨，表现为线形或点样的中等信号影。９例志愿者１１个骶髂关节的骨髓内可见局灶性脂肪沉积。２４例ＡＳ患者的４２个骶髂关节可见软骨异常，表现为Ｔ１ＷＩ和Ｔ２ＷＩ上正常线形中等信号的软骨影像消失，代之以不规则增粗或扭曲样中等信号。分析表明：在骶髂关节炎的诊断方面，ＭＲ和ＣＴ明显优于Ｘ线平片（Ｐ＜０．００１）。结论：同Ｘ线片比较，虽ＣＴ和ＭＲＩ均有助于ＡＳ骶髂关节炎的诊断，但ＭＲ影像可显示ＣＴ和Ｘ线所不能显示的软骨异常和骨髓内水肿改变；骨髓内脂肪沉积可属正常变异；扭曲样中等强度信号应视为软骨的异常征象。     

Nickel-doped agarose gel phantoms in MR imaging

A method for the production of a tissue-mimicking phantom material for MR imaging is described. The material consists of a nickel-doped agarose gel. The T1 and T2 values of the gel can be varied independently by changing the relative amounts of nickel and agarose. Practically any T1 and T2 combination of clinical interest can be obtained. The long-term stability was studied and found to be good. The relaxation times were estimated using an MR analyzer. The accuracy and the reproducibility of these measurements were evaluated and found to be reassuring. Gel phantoms were also scanned in an MR unit. The signal strength of an inversion recovery sequence was evaluated using the gel phantoms in order to verify their usefulness. These measurements were compared to theory with good agreement. Furthermore, tissue-equivalent phantoms were made. Gels resembling gray matter, white matter, and CSF were scanned. Comparisons with clinical in vivo scans, as well as calculated levels were made. It is anticipated that the gel phantoms described here will be useful in quality assurance as well as in pulse sequence optimization.     

Iron oxide nanoparticle-labeled rat smooth muscle cells: cardiac MR imaging for cell graft monitoring and quantitation

PURPOSE: To perform a quantitative analysis of anionic maghemite nanoparticle-labeled cells in vitro and determine the effect of labeling on signal intensity at magnetic resonance (MR) imaging. MATERIALS AND METHODS: The study was approved by the institutional animal care and use committee at H?pital Bichat. In vitro cell proliferation, iron content per cell, and MR signal intensity of cells were measured in agarose phantoms for 0-14 days of culture after labeling of rat smooth muscle cells with anionic maghemite nanoparticles. Next, iron oxide-labeled smooth muscle cells were injected into healthy hearts and hearts with ischemic injury in seven live Fisher rats. Ex vivo MR imaging experiments in excised hearts 2 and 48 hours after injection were performed with a 1.5-T medical imaging system by using T2-weighted gradient-echo and spin-echo sequences. Histologic sections were obtained after MR imaging. Correlation analyses between division factor of iron load and cell amplification factor and between 1/T2 and number of labeled cells or number of days in culture were performed by using linear regression. RESULTS: Viability of smooth muscle cells was not affected by magnetic labeling. Transmission electron micrographs of cells revealed the presence of iron oxide nanoparticles in vesicles up to day 14 of culture. Intracellular iron concentration decreased in parallel with cell division (r2 = 0.99) and was correlated with MR signal intensity (r2 = 0.95). T2*-weighted MR images of excised rat hearts showed hypointense signal in myocardium at 2 and 48 hours after local injection of labeled cells. Subsequent histologic staining evidenced iron oxide nanoparticles within cells and confirmed the presence of the original cells at 2 and 48 hours after implantation. CONCLUSION: Magnetic labeling of smooth muscle cells with anionic maghemite nanoparticles allows detection of cells with MR imaging after local transplantation in the heart.     

Production of a human-tissue-equivalent MRI phantom: optimization of material heating

PURPOSE: We conceived a 2-stage heating method to dissolve the ingredients of magnetic resonance (MR) imaging phantoms to overcome issues of uneven quality in conventional MR imaging phantoms, and we evaluated uniformity and the reproducibility of our method. METHODS: We used a 3-liter capacity, column-shaped, enamel-coated porcelain container to produce a muscle-equivalent phantom (diameter, 160 mm; height, 100 mm; volume, 2 liters). The phantom contained: 1) carrageenan as a gelling agent; 2) agarose as a T2 modifier; 3) GdCl3 as a T1 modifier; 4) NaN3 as an antiseptic; and 5) distilled water. We applied both direct heating and 2-stage heating of pre-soaked materials. We placed powdered materials directly into hot water for direct heating but soaked them in water one day before use (post-swelling) in 2-stage heating. The materials in the container were melted in a silicone oil bath of 120 or 140 degrees C under various conditions, then allowed to gel by natural cooling. We observed the resulting gel phantoms macroscopically using a CCD camera and evaluated their uniformity by microscopy and MR imaging. RESULTS: We found it necessary to raise the temperature inside the phantom to 100.0 degrees C, to produce a uniform gel with stable homogeneity and few bubbles. Use of an enamel-coated porcelain container required setting the temperature of the oil bath at 140 degrees C. CONCLUSION: A uniform and reproducible human tissue-equivalent phantom with few bubbles can be manufactured using our 2-stage heating method, which employs pre-soaking in a silicone oil bath at 140 degrees C for 30 min. We then added the swollen carrageenan to the agarose solution, which heating the temperature to 140 degrees C for 30 min while continuously stirring at 120 rpm, following with natural cooling.     

Ultra‐short echo time (UTE) MR imaging of the lung: Comparison between normal and emphysematous lungs in mutant mice

Purpose:

To investigate the utility of ultra‐short echo time (UTE) sequence as pulmonary MRI to detect non‐uniform disruption of lung architecture that is typical of emphysema.

Materials and Methods:

MRI of the lungs was conducted with a three‐dimensional UTE sequence in transgenic mice with severe emphysema and their wild‐type littermates in a 3 Tesla clinical MR system. Measurements of the signal intensity (SI) and transverse relaxation time (T2*) of the lung parenchyma were performed with various echo times (TEs) ranging from 100 μs to 2 ms.

Results:

Much higher SI of the lung parenchyma was observed at an UTE of 100 μs compared with longer TEs. The emphysematous lungs had reduced SIs and T2* than the controls, in particular at end‐expiratory phase. The results suggested that both SI and T2* in lung parenchyma measured with the method represent fractional volume of lung tissue.

Conclusion:

The UTE imaging provided MR signal from the lung parenchyma. Moreover, the UTE sequence was sensitive to emphysematous changes and may provide a direct assessment of lung parenchyma. UTE imaging has the potential to assist detection of localized pathological destruction of lung tissue architecture in emphysema. J. Magn. Reson. Imaging 2010;32:326–333. © 2010 Wiley‐Liss, Inc.     

Mucinous versus nonmucinous rectal carcinomas: differentiation with MR imaging.

PURPOSE: To determine if quantitative and qualitative magnetic resonance (MR) imaging measures can help differentiation of mucinous from nonmucinous rectal tumors. MATERIALS AND METHODS: In 26 patients with pathologically proved mucinous (n = 9) and nonmucinous (n = 17) rectal tumors, MR imaging was performed with T1-weighted spin-echo (SE) and T2-weighted fast SE sequences in all patients and with a gadolinium-enhanced T1-weighted sequence in 18. With use of the signal intensity (SI) measurements in the tumors and reference tissues, tumor-to-muscle, tumor-to-fat, and tumor-to-urine SI ratios were calculated. In addition, the SI and contrast-enhancement patterns in the tumors were assessed qualitatively by three blinded readers. RESULTS: Mucinous tumors had a much higher SI on the T2-weighted fast SE images. Tumor-to-muscle, tumor-to-fat, and tumor-to-urine SI ratios were significantly higher in the mucinous compared with the nonmucinous tumors (P = .0004, P = .0008, and P = .00002, respectively). Qualitative evaluation of the SI correlated well between readers 1 and 2 (r = 0.93), readers 1 and 3 (r = 0.94), and readers 2 and 3 (r = 0.91). Agreement for the contrast-enhancement patterns was 67%, 72%, and 67%, respectively, with most mucinous tumors having predominantly high SI and a peripheral contrast-enhancement pattern. CONCLUSION: Mucinous and nonmucinous rectal tumors can be differentiated with MR imaging because mucinous tumors show high SI on T2-weighted fast SE images.     

Functional MR imaging during hypercapnia and hyperoxia: noninvasive tool for monitoring changes in liver perfusion and hemodynamics in a rat model

PURPOSE: To prospectively assess functional magnetic resonance (MR) imaging during hypercapnia and hyperoxia for monitoring changes in liver perfusion and hemodynamics in rats. MATERIALS AND METHODS: All experiments were performed with approval of an animal care and use committee. Functional T2*-weighted gradient-echo MR images of the rat liver were acquired during hyperoxia and graded hypercapnia (n=24). Additional images were acquired during portal vein ligation (n=4), induced hypovolemia (n=5), and 70% hepatectomy (n=5). Hypercapnic effects were confirmed with Doppler ultrasonography and with gadopentetate dimeglumine. Differences between groups were analyzed by using Wilcoxon rank sum test, except for the graded hypercapnia, for which one-way analysis of variance was used. RESULTS: Liver signal intensity (SI) increased due to hyperoxia; the percentage change in SI was seven times greater than that in muscle tissue; this reflects higher vascularity of the liver. Liver SI decreased due to hypercapnia; the percentage change in SI was negative in the liver but positive in the muscle (P<.001). Induced hypovolemia resulted in considerable decreases in functional MR imaging response; this reflects lower liver perfusion. Clinical applicability of the functional MR imaging method was proved by monitoring changes in liver perfusion that resulted from liver resection. CONCLUSION: In the liver, the magnitude of the percentage change in SI induced by hypercapnia and hyperoxia reflects changes in total blood volume; whereas percentage change in SI values induced by hypercapnia from a negative to a positive value reflects relative changes in portal-to-arterial blood flow ratio.     

Using a phantom to compare MR techniques for determining the ratio of intraabdominal to subcutaneous adipose tissue

OBJECTIVE: Patients who have a greater distribution of intraabdominal adipose tissue as compared with subcutaneous adipose tissue and an increased ratio of intraabdominal adipose tissue to subcutaneous adipose tissue are at greater risk for developing cardiovascular disease and type 2 diabetes mellitus. In previous MR investigations, researchers have used conventional T1-weighted spin-echo images to determine the ratio of intraabdominal adipose tissue to subcutaneous adipose tissue. However, no investigation, to our knowledge, has been performed to determine the accuracy of using different MR sequences to estimate adipose distribution. The purpose of our investigation was to compare MR imaging and segmentation techniques in calculating the ratio of intraabdominal to subcutaneous adipose tissue using an adiposity phantom. MATERIALS AND METHODS: A phantom was created to simulate the distribution of subcutaneous and intraabdominal fat (with known volumes). Axial MR images were obtained twice through the phantom using a 5-mm slice thickness and zero gap for the following T1-weighted sequences: spin-echo, fast Dixon, and three-dimensional (3D) spoiled gradient-echo. An in-house computer software program was then used to segment the volumes of fat and calculate the volume of intraabdominal adipose tissue and subcutaneous adipose tissue and the ratio of intraabdominal to subcutaneous adipose tissue. Each imaging data set was segmented three times, so six sets of data were yielded for each imaging technique. The percentage predicted of the true volume was calculated for each MR imaging technique for each fat variable. The mean percentages for each variable were then compared using one-factor analysis of variance to determine whether differences exist among the three MR techniques. RESULTS: The three MR imaging techniques had statistically significant different means for the predicted true volume of two variables: volume of subcutaneous adipose tissue (p < 0.001) and volume of intraabdominal adipose tissue (p = 0.0426). Estimates based on fast Dixon images were closest to the true volumes for all the variables. All MR imaging techniques performed similarly in estimating the ratio of intraabdominal adipose tissue to subcutaneous adipose tissue (p = 0.9117). The acquisition time for the 3D spoiled gradient-echo images was 10-22 times faster than for the other sequences. CONCLUSION: Conventional T1-weighted spin-echo MR imaging, the current sequence used in practice for measuring visceral adiposity, may not be the optimal MR sequence for this purpose. We found that the T1-weighted fast Dixon sequence was the most accurate at estimating all fat volumes. The T1-weighted 3D spoiled gradient-echo sequence generated similar ratios of intraabdominal to subcutaneous adipose tissue in a fraction of the acquisition time.     

Technical considerations for injection of a mixture of iodinated contrast material and Artirem for combined CT and MR arthrography

PURPOSE: To determine the influence of 4 independent parameters on signal intensity and density measurements after injection of an arthrography-specific form of gadoterate meglumine and an iodinated contrast material for combined MR and CT arthrography. The parameters included: 1) variations of gadolinium and iodinated contrast agents within the mixture, 2) variations of concentration of the iodinated contrast agent, 3) variation of temperature of the mixture, 4) the type of MR pulse sequence acquired. MATERIALS AND METHODS: The study was performed on a CT using a phantom containing 47 different syringes. Ten separate mixtures of gadolinium and iodinated contrast agents were obtained, each with a 10% change in the respective proportion of each contrast agent. This was repeated 4 times for 4 iodinated contrast agents of different iodine concentration. Two control syringes, 4 mixtures containing 50% normal saline and 50% iodinated contrast material (one for each of the 4 concentrations of iodinated contrast material) and one with a mixture of 50% of normal saline and gadolinium contrast agent. For the MR acquisition, the syringes were separated into 4 groups for 4 phantoms. On a 1.5 T MR unit, SE T1W, FSE T2W, PD and 3D FIESTA sequences were acquired. All acquisitions were repeated 2 times, and a 3 different temperatures. RESULTS: The progressive increase in the proportion of gadolinium contrast in the solution was associated with a non-linear increase of signal on T1W, 3D FIESTA, and PD images. The signal intensity reached a plateau at concentrations between 40-60%. Signal variations on the 3D FIESTA sequence were significant. On T2W images, there was an increase of measured signal intensity at low gadolinium concentrations. On CT, there was a linear relationship between density measurements and dilution of gadolinium. The progressive increase of the concentration of the iodinated contrast was associated with increased signal loss on MR and progressive increase of density values on CT. Temperature variations were associated with signal intensity changes on T2W and FIESTA images, but not on T1W images. CONCLUSION: At 1.5 T, a mixture of 50% iodinated contrast and 50% gadolinium contrast corresponded to an acceptable compromise for combined acquisition of MR and CT arthrography.     

Phyllodes tumor of the breast: correlation between MR findings and histologic grade

PURPOSE: To retrospectively evaluate the magnetic resonance (MR) imaging findings of phyllodes tumor of the breast and to compare these findings with the histologic grade. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. The authors reviewed the MR findings in 30 female patients aged 16-73 years (mean, 40.2 years) with surgically confirmed phyllodes tumors. Analyzed MR findings included tumor shape, margin, internal enhancement, and size; signal intensity (SI) of tumor higher than that of normal breast tissue on T1-weighted images; SI of tumor lower than or equal to that of normal tissue on T2-weighted images; cyst wall appearance; kinetic curve assessment; and apparent diffusion coefficient (ADC). The MR findings and histologic grade were statistically analyzed to determine whether any correlations existed. Significant MR findings were compared with histopathologic findings. RESULTS: Nineteen benign, six intermediate (characterized by five to nine cell reproductions at 10 high-power fields, pushing or infiltrative margins, moderate stromal cellularity, and atypia and overgrowth), and five malignant phyllodes tumors were assessed. Irregular cyst wall (P = .003), tumor SI lower than or equal to normal tissue SI on T2-weighted images (P = .005), and low ADC (P = .001) correlated significantly with histologic grade. Tumor SI higher than normal tissue SI on T1-weighted images was more frequent in the malignant (in three of five tumors) and intermediate (in three of six tumors) groups than in the benign group (in two of 19 tumors); however, it was not a significant finding (P = .024). Tumor SI higher than normal tissue SI on T1-weighted images and irregular cyst wall corresponded histopathologically to hemorrhagic infarction and necrosis, respectively. Tumor SI lower than or equal to normal tissue SI on T2-weighted images and low ADC corresponded histopathologically to stromal hypercellularity. Other findings were not significant. CONCLUSION: Several MR findings can be used to help determine the histologic grade of phyllodes breast tumors.     

Basal cell adenoma of the parotid gland: MR imaging findings with pathologic correlation

BACKGROUND AND PURPOSE: Basal cell adenomas (BCAs) are rare tumors of the parotid gland. Only a few case reports describing MR imaging features of BCA have been published. The aim of this study was to describe and characterize the MR findings of BCAs of the parotid gland. MATERIALS AND METHODS: We retrospectively reviewed MR images of BCA with pathologic correlation in 8 cases (2 men and 6 women; age range, 52-82 years) collected between January 1992 and August 2004 from our pathologic data base. All MR images were retrospectively evaluated with respect to the marginal morphology, signal intensity (SI), and enhancement behavior by 2 experienced radiologists. RESULTS: On pathologic examination, 5 tumors were solid type, 2 were trabecular type, and 1 was membranous type. All of the tumors were well circumscribed with smooth contours. Cystic changes were seen in 4 cases. On T1-weighted images (T1WI), 7 tumors showed homogeneously low SI equal to muscle and one showed heterogeneously low SI. On T2-weighted images (T2WI), all of them showed slightly lower SI than that of surrounding parotid tissue. On gadolinium-enhanced T1WI, 6 tumors demonstrated moderate enhancement and one demonstrated strong enhancement (membranous type). Dynamic studies were performed in 4 cases. All showed rapid and prolonged enhancement. CONCLUSION: MR imaging findings of BCA were well-defined and smooth marginal morphologies, relatively low SI on both T11W and T2WI, and rapid and prolonged enhancement on dynamic study. Although BCAs are rare, they should be suspected when a tumor shows all of the characteristics noted here.