Adrenal adenomas: characteristic postgadolinium capillary blush on dynamic MR imaging

We sought to evaluate dynamic post-gadolinium contrast enhanced magnetic resonance (MR) imaging characteristics of adrenal adenomas with comparison to those of malignant adrenal tumors. MR images, including in- and out-of-phase spoiled gradient echo (SGE) and dynamic gadolinium enhancement, of 35 adrenal adenomas in 34 patients, and 12 malignant adrenal tumors in 12 patients, were reviewed retrospectively. MR images were assessed for the presence of a capillary blush on immediate postgadolinium SGE images, and for rapid washout of contrast on 45-second postgadolinium SGE images. Thirty-five adrenal adenomas (mean size, 3.1 cm) and 12 malignant adrenal tumors (mean size, 7.4 cm) were assessed. Of 35 adrenal adenomas, 25 (71%) showed a homogeneous capillary blush on immediate postgadolinium images. Thirty-three (94%) adrenal adenomas demonstrated rapid washout on 45-second postgadolinium images (P < 0.001). Of 35 adrenal adenomas, 30 (86%) showed diminished signal intensity (SI) on out-of-phase images. Of 12 malignant adrenal tumors, none showed a homogeneous capillary blush on immediate postgadolinium images. Six (50%) malignant tumors showed negligible enhancement, four (33%) showed irregular patchy enhancement, and two (17%) showed peripheral enhancement (P < 0.001). On 45-second postgadolinium images, 11 (92%) of 12 malignant adrenal tumors showed irregular enhancement. In the majority of adrenal adenomas, an initial homogeneous capillary blush and rapid washout are demonstrated on gadolinium-enhanced dynamic MR imaging. Our preliminary results suggest that this may provide useful complementary information to the appearance of adrenal masses on in- and out-of-phase images.     

Genitourinary MR: Kidneys and adrenal glands

Due to its high tissue contrast and multiplanar imaging capabilites, MRI provides a detailed display of renal and adrenal anatomy. Recent technical developments overcoming the problem of respiration induced motion artifacts and the use of paramagnetic contrast agents have further improved the performance of MRI which has now evolved as an alternative or complementary imaging modality to ultrasound, excretory urography and computed tomography. Dynamic contrast-enhanced studies will usually allow to detect even small enhancing solid areas within the cyst wall. Use of a fast (turbo) spoiled gradient echo sequence allows for assessment of contrast enhancement dynamics in renal and adrenal masses. For tumor staging, the multiplanar imaging capabilities of MRI are advantageous. Perinephric extent is best detected using opposed-phase GRE images resulting in an artifical accentuation of renal contours. Extension into venous structures is best diagnosed by using a GRE sequence allowing for distinction between flowing blood and tumor thrombus. Noninvasive differentiation of adrenal lesions can be performed with an unprecedented accuracy using chemical-shift imaging.     

Characterization of adrenal lesions using chemical shift MRI: comparison between 1.5 Tesla and two echo time pair selection at 3.0 Tesla MRI

Purpose:

To compare chemical shift MRI obtained at 1.5 Tesla (T) and two pairs of echo time (TE) in‐phase and opposed‐phase 3.0T MRI to assess their usefulness for the differentiation between adrenal adenomas and non‐adenomas.

Materials and Methods:

We evaluated 91 adrenal masses (75 adenomas, 16 non‐adenomas) in 85 patients. The MR imaging parameters were: T1‐dual‐gradient‐echo(GRE) [echo times (TEs) = 1.1/2.3 ms (first‐echo‐pair) or 3.5/4.6 ms (second‐echo‐pair)] at 3.0T, and T1‐dual‐GRE (TEs = 2.4/4.8 ms) at 1.5T. Scans were quantitatively assessed for the signal intensity (SI) index, calculated as [(SIin‐phase‐SIopposed‐phase)/(SIin‐phase)] × 100(%). To test for differences between adenomas and non‐adenomas, we performed quantitative analysis and analysis of variance.

Results:

For all images, the SI index differed significantly between adenomas and non‐adenomas. The sensitivity /specificity of SI index at the first‐echo‐pair of 3.0T was 100%/ 100%, that of 95.6%/ 100% at the second‐echo‐pair of 3.0T, and 91.7%/ 88.9% at 1.5T, respectively. At intra‐individual comparisons, the SI indices obtained with the second‐echo‐pair at 3.0T were significantly lower than on the first‐echo‐pair at 3.0T and 1.5T.

Conclusion:

Chemical shift MRI at 3.0T provides more accurate differentiation between adenomas and non‐adenomas than at 1.5T. The SI index of the first‐echo‐pair at 3.0T is the most reliable evaluation method for differentiating adrenal adenomas from non‐adenomas. J. Magn. Reson. Imaging 2012;35:95‐102. © 2011 Wiley Periodicals, Inc.     

Ultrafast MR imaging of the pelvis.

MR gradient systems with higher slew rates and gradient amplitude enable certain forms of imaging that are not practical with older gradient systems. These newer pulse sequences include single shot half-Fourier T2-weighted images and echo planar imaging. More important in MR imaging of the pelvis, these gradient systems benefit more conventional imaging methods such as gadolinium-enhanced 3D MR angiography, dynamic gradient echo contrast-enhanced images, and T2-weighted fast spin echo images, by shortening echo times. For most MR imaging of the pelvis, spatial resolution is paramount, and therefore sequences such as half-Fourier acquisition Turbo spin echo (HASTE) and 3D gadolinium-enhanced dynamic imaging play a less important role than in the upper abdomen. The potential of these techniques for diffusion or perfusion studies in the pelvis has not been explored.     

Evaluation of adrenal masses in oncologic patients: dynamic contrast-enhanced MR vs CT

The CT examinations, precontrast gradient echo MR images, and fast contrast enhanced dynamic MR studies were evaluated in 44 patients with 52 adrenal masses and known malignant disease of different origin. Morphologic features (size, shape, attenuation, contour, and enhancement) on CT scans, signal intensity on T2-weighted MR images, and patterns of enhancement on Gd-DTPA enhanced dynamic MR studies were analyzed in all patients. With dynamic contrast enhanced studies with prolonged imaging up to 15 min after Gd-DTPA, masses with moderate enhancement and complete washout after 10 min were considered as adenomas. Computed tomography and plain MR had a sensitivity of 0.71 and 0.96, a specificity of 0.75 and 0.88, and overall accuracy of 0.56 and 0.71, respectively. Simultaneous use of precontrast MR and dynamic contrast enhanced studies led to an accurate diagnosis in 88% (sensitivity = 1.0, specificity = 0.91) and thus should be considered in oncologic patients with undetermined adrenal masses.     

Direct imaging of magnetic field gradients by group spin-echo selection.

A new image processing method for single-echo gradient echo imaging is presented which extracts local phase gradient information by k-space filtering instead of by phased reconstruction and spatial differentiation. It is shown that local phase gradient directions and semiquantitative local phase gradient magnitudes can be directly measured, even in regions where phased image reconstruction suffers from multiple phase foldovers due to strong phase modulations. The directional information thus obtained can be used as a reference to identify and correct phase modulation foldovers in phase maps which may be computed from the same raw data. The method is applied here to measure static magnetic field gradients and illustrates fundamental k-space signal properties of gradient echo imaging. Based on this concept, image artifacts caused by conventional strong k-space filtering in gradient echo imaging are discussed.     

Differentiation of calcification from chronic hemorrhage with corrected gradient echo phase imaging

PURPOSE: The purpose of the current study was to prospectively evaluate the role of corrected gradient echo phase imaging in differentiation of calcified granuloma from chronic hemorrhage. METHOD: Eighty-five patients with single/multiple calcifications and hemorrhages irrespective of their location were studied with corrected gradient echo phase imaging. In all the cases, CT was used as the gold standard for the presence/absence of calcification. RESULTS: All calcified lesions showed positive phase, whereas chronic hemorrhages showed negative phase in all cases. Five calcified lesions showed no phase shift at TE =15 ms and positive shift at TE = 35 ms. Heterogeneous phase shift was observed in three calcified lesions at TE = 35 ms; all three lesions showed positive phase shift at TE = 15 ms. There was no site-specific problem in differentiation of calcification from chronic hemorrhage including in the basal ganglia. CONCLUSION: We conclude that calcified granuloma can be easily differentiated from chronic hemorrhage with corrected gradient echo phase imaging, which may obviate the need for CT for its confirmation.     

How accurate is MR imaging in characterisation of adrenal masses: update of a long-term study.

OBJECTIVE: The purpose of this study was to update a long-term study that evaluates the accuracy of MR imaging in the characterisation of adrenal tumours. In all patients, MR imaging findings were correlated with histopathologic results. PATIENTS: In 204/560 patients who underwent MR imaging for characterisation of an adrenal mass, histopathologic results were available. The final study group consisted of 229 adrenal masses in 204 patients. MR imaging was performed using T2-weighted fast spin-echo imaging and unenhanced and gadolinium-enhanced T1-weighted spin-echo imaging in all patients. In addition, chemical shift imaging was performed in 182 patients and dynamic gadolinium-enhanced studies in 198 patients. Chemical shift images and dynamic studies were qualitatively assessed. All images were reviewed by an experienced investigator (Gertraud Heinz-Peer) who was blinded to the clinical history and the results of prior imaging studies. RESULTS: The sensitivity of MR imaging for the differentiation of benign and malignant adrenal masses was 89%, the specificity 99%, and the accuracy was 93.9%. This results in a positive predictive value (PPV) of 90.9% and a negative predictive value (NPV) of 94.2%. These results are comparable to the data published previously by our study group with a lower number of cases. CONCLUSION: Large study numbers show that MR imaging is a reliable method in characterisation of benign and malignant adrenal masses. Since laparoscopic adrenalectomy has become the new gold standard in the surgical treatment of benign adrenal lesions, the high accuracy of MR imaging in characterisation of those lesions offers even patients with large adrenal masses (>5 cm) the advantages of the minimally invasive technique.     

Hyperfunctioning and nonhyperfunctioning benign adrenal cortical lesions: characterization and comparison with MR imaging

The authors evaluated the potential of magnetic resonance (MR) imaging at 0.35 T to permit differentiation of nine hyperfunctioning adrenal cortical lesions from 21 nonhyperfunctioning adrenal cortical adenomas. Both qualitative data (visual assessment) and quantitative data (signal intensity ratios, T1, and T2) were used for tissue characterization. With a 2,000/56-100 sequence (repetition time msec/echo time msec), the majority of lesions were visually isointense to liver. Of 34 quantitative measures, only lesion-liver and lesion-kidney intensity ratios at 2,000/150 showed statistically significant differences among nonhyperfunctioning adenomas, aldosterone-producing lesions, and corticosteroid-producing lesions; however, the authors question the significance of these differences because of the abundant noise associated with the 2,000/150 sequence. The results suggest that nonhyperfunctioning adrenal cortical adenomas cannot be distinguished from benign hyperfunctioning cortical lesions with use of MR imaging at 0.35 T.     

Distinguishing hepatic metastases from hemangiomas: qualitative and quantitative diagnostic performance through dual echo respiratory-triggered fast spin echo magnetic resonance imaging

OBJECTIVE: To determine the relative value of qualitative (reader opinion) and quantitative (values derived from dual echo T2 fast spin echo [FSE]) measures in distinguishing hepatic metastases from hemangiomas. METHODS: Forty-nine patients with hemangiomas and 23 with metastases were studied with dual echo respiratory-triggered FSE and dynamic 2-dimensional spoiled gradient echo (GRE) imaging. Lesion T2 was estimated from signal intensity ratios on the first and second echoes. Two experienced radiologists independently evaluated groups of images based on 5 separate qualitative measures: first echo FSE, second echo FSE, first and second echo FSE, dynamic GRE, and all images together. RESULTS: The mean calculated T2s were 226 +/- 74 milliseconds for hemangiomas and 105 +/- 22 milliseconds for metastases (P < 0.001). A T2 cutoff of 130 milliseconds distinguished metastases from hemangiomas with a sensitivity of 94%, specificity of 91%, and accuracy of nearly 94%. There was no significant difference between the best quantitative measure and the best qualitative measure for either reader. CONCLUSION: Liver lesion T2 relaxation times calculated from dual echo FSE images provide information useful in discriminating metastases from hemangiomas, as does reader opinion.     

Vascular staging of renal and adrenal malignancies with a noncontrast enhanced steady state free precession technique

Purpose:

To compare a noncontrast enhanced balanced steady state free precession (bSSFP) MRI technique with a conventional dynamic contrast‐enhanced (DCE) three‐dimensional (3D) spoiled gradient recalled echo (SPGR) imaging in the vascular staging of renal and adrenal malignancies.

Materials and Methods:

Sixty‐three MRIs with both bSSFP and DCE acquisitions performed for initial staging of renal and adrenal malignancies were retrospectively evaluated for presence and extent of thrombus in the renal veins and inferior vena cava (IVC). Thrombus characterization was also evaluated. DCE imaging was used as the standard‐of‐reference. Histopathology was available in 46 of 63 cases as an additional external standard.

Results:

There is very good agreement between bSSFP and DCE imaging for determining the presence or absence of thrombus in the renal veins (r = 0.95; P < 0.0001) and IVC (r = 0.91; P < 0.0001). BSSFP is less successful at distinguishing bland from tumor thrombus.

Conclusion:

Noncontrast enhanced bSSFP is an acceptable alternative to DCE imaging for vascular staging of locally advanced renal/adrenal malignancies, with somewhat limited ability to distinguish bland from tumor thrombus. J. Magn. Reson. Imaging 2011;33:1406–1413. © 2011 Wiley‐Liss, Inc.     

Vascular interventions guided by ultrafast MR imaging: Evaluation of different materials

The ability of MRI to acquire not only anatomical but also functional information makes MRI guided vascular interventions an interesting goal. Recent developments in ultrafast MR imaging sequences such as fast gradient echo or echo planar (EPI) mean that not only real time MRI but also MRI guided vascular interventions are real possibilities for the not too distant future. However, currently available guide wires and catheters are potentially unusable in MRI because they are either ferromagnetic or MRI invisible. In order to find different materials suitable for real time MRI, various devices were examined with fast gradient echo and interleaved EPI pulse sequences. The measurements were performed using a continuously running, pseudo real time MRI system to investigate the dynamic imaging behavior under guide wire insertion. Suggestions are made as how to construct guide wires and catheters, which can be visualized with ultrafast imaging sequences, while not causing prohibitive artifacts or image distortions.     

急性胰腺炎的并发症:胰周血管疾病的MRI表现

目的探讨急性胰腺炎(AP)并发各类胰周血管疾病的MRI表现。资料与方法回顾性分析本院2009年6月至2010年9月期间122例AP患者资料,男73例,女49例,平均年龄(45±16)岁。所有病例均签署知情同意书。采用GE1.5TMR扫描:梯度回波T1加权,快速恢复快速自旋回波T2加权,单次激发快速自旋回波T2加权,MR胰胆管成像,动态增强扫描。观察:(1)动脉侵犯/动脉炎;(2)假性动脉瘤;(3)静脉炎、静脉血栓形成/静脉栓塞;(4)胰源性门静脉高压症/门静脉海绵样变。结果本组AP并发胰周血管病变的发生率为17.2%(21/122)。21例AP并发胰周血管病变患者中,动脉侵犯/动脉炎占16/21(脾动脉、肝总动脉、肠系膜上动脉、腹腔干受累率分别为16/16、13/16、12/16、7/16)。脾动脉假性动脉瘤占1/21。静脉炎占19/21(脾静脉、门静脉、肠系膜上静脉受累率分别为19/19、13/19、9/19),静脉血栓形成/静脉栓塞占2/21(1例脾静脉部分性栓塞,另1例门静脉、脾静脉、肠系膜上静脉广泛性栓塞)。胰源性门静脉高压症/门静脉海绵样变占2/21。结论 AP能并发多种胰周血管病变,每种血管病变都...     

Dynamic range compression in MRI by means of a nonlinear gradient pulse

In current magnetic resonance imaging (MRI), valuable information must often be discarded because the NMR signal has greater dynamic range than the analog-to-digital converter (ADC) hardware. Typically, a small set of high-intensity data points near the center of the spin echo is responsible for most of the MRI data dynamic range. We predict that it is possible to reduce the dynamic range of the MRI spin echo by incorporating an identical nonlinear gradient pulse into each repetition of the imaging pulse sequence, prior to data sampling. This pulse converts the phase distribution of the subject, ordinarily a linear function of image coordinates, into a nonlinear function. A nonlinear phase distribution can have a negligible impact on image magnitude and yet a profound impact on spin-echo magnitude. Given a nonlinear phase distribution, there will no longer be a single data point at which all of the protons have an identical phase (the echo center). Instead, the protons become phase coherent on a piecemeal basis, the echo peak is smoothed out, and its maximum amplitude and dynamic range are greatly diminished. Using gradient pulses of quadratic spatial variation, we estimate that maximum echo amplitude and dynamic range can be reduced in most cases by an order of magnitude. © 1988 Academic Press, Inc.     

Differentiation of recurrent rectal cancer and scarring with dynamic MR imaging

The accuracy of dynamic contrast enhanced magnetic resonance (MR) imaging in the differentiation of malignant and benign pelvic lesions during follow-up of patients with treated colorectal tumours was evaluated prospectively. 19 patients (11 men, 8 women; age range 35-70 years; mean 57 years) with suspected local recurrence of colorectal malignancy were evaluated with MR imaging. Dynamic MR imaging with axial Turbo-FLASH gradient echo imaging and bolus injection of contrast medium was performed. Dynamic images, each consisting of one slice in the same location, were acquired at 5, 10, 15, 20 and 30 s, and at 1, 2, 3, 4, 5 and 10 min. The maximum change in signal intensity (Emax), the acceleration rate of the time-intensity curve (TIC) and the ratio of the signal intensity of the lesions to the signal intensity of the iliac artery (SIL/SIA) were used as the enhancement parameters. The TIC and SIL/SIA ratio at 60 s were found to be valuable in the differential diagnosis; Emax had no significance in differentiating benign and malignant lesions. Sensitivity was 83% for each calculated parameter. SIL/SIA has the highest specificity and accuracy among the parameters.     

Effects of inflow and radiofrequency spoiling on the arterial input function in dynamic contrast‐enhanced MRI: A combined phantom and simulation study

The arterial input function is crucial in pharmacokinetic analysis of dynamic contrast‐enhanced MRI data. Among other artifacts in arterial input function quantification, the blood inflow effect and nonideal radiofrequency spoiling can induce large measurement errors with subsequent reduction of accuracy in the pharmacokinetic parameters. These errors were investigated for a 3D spoiled gradient‐echo sequence using a pulsatile flow phantom and a total of 144 typical imaging settings. In the presence of large inflow effects, results showed poor average accuracy and large spread between imaging settings, when the standard spoiled gradient‐echo signal equation was used in the analysis. For example, one of the investigated inflow conditions resulted in a mean error of about 40% and a spread, given by the coefficient of variation, of 20% for K^trans. Minimizing inflow effects by appropriate slice placement, combined with compensation for nonideal radiofrequency spoiling, significantly improved the results, but they remained poorer than without flow (e.g., 3–4 times larger coefficient of variation for K^trans). It was concluded that the 3D spoiled gradient‐echo sequence is not optimal for accurate arterial input function quantification and that correction for nonideal radiofrequency spoiling in combination with inflow minimizing slice placement should be used to reduce the errors. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

MR化学位移成像诊断肾上腺腺瘤的研究

目的：研究MRI对肾上腺肿瘤的定性诊断价值。方法：对23个肾上腺腺瘤和35个其他肾上腺占位性病变的患者行SE序列T1WI、快速自旋回波（TSE）序列T2WI和化学位移成像（CSI）序列扫描。肿物直径8-92mm。计算并比较肿物与肝脏、脾脏和水模在反相位和同相位上的信号比值变化。结果：腺瘤组有20/23的病例肿物-脾脏信号比（ASR）＜0.59,而基人他占位性病变ASR均大于0.73。MR CSI序列诊断肾上腺腺瘤的敏感性为87%,特异性为100%。结论：MR化学位移成像对肾上腺腺瘤的定性诊断具有重要价值。     

New reconstruction technique for echo-planar imaging to allow combined use of odd and even numbered echoes

An image reconstruction technique for echo-planar imaging is proposed. This technique combines odd and even numbered echo signals. It is thus possible to reduce the frequency of the time-modulated gradient used in echo-planar imaging by 50%, and to reduce its amplitude by almost 50% for sinusoidal gradient modulation.     

Initial experience with dynamic MR imaging in evaluation of normal bone marrow versus malignant bone marrow infiltrations in humans

The purpose of this study was (a) evaluation of dynamic contrast-enhanced MR imaging of normal bone marrow versus malignant bone marrow infiltrations in patients with proven B-cell-type chronic lymphocytic leukemia (B-CLL) and (b) correlation with the clinical stage according to Binet (stages A, B, C) and response to therapy. Bone marrow imaging of the lumbar spine, pelvis, and proximal femurs was performed at 1.5 T in 45 patients without known malignancy and in 30 patients with B-CLL. The differences between opposed-phase and in-phase dynamic gradient-echo sequences before and up to 10 minutes after intravenous application of .1 mmol/kg body weight of gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) were evaluated in normal bone marrow. The contrast-enhancement patterns of normal and malignant bone marrow were compared using the opposed-phase dynamic gradient-echo sequence. Ten of the patients with bone marrow infiltrations (Binet stage C) additionally underwent MR imaging follow-up during therapy. Opposed-phase gradient echo sequences demonstrated a signal decrease of normal bone marrow, and in-phase gradient echo sequences demonstrated a signal increase of normal bone marrow after administration of Gd-DTPA. The dynamic signal intensity time courses differed significantly (P < .05) between Binet stages B and C and controls as well as among the three Binet stages of B-CLL. In the 10 patients followed during therapy, MR imaging sensitively demonstrated response (n = 6), nonresponse (n = 2), or relapse after initial response (n = 2). In out-of-phase imaging, both normal bone marrow and initial bone marrow infiltration in CLL stage Binet A show signal decrease after administration of contrast agent, whereas there is increase in signal intensity in higher-grade bone marrow infiltration in Binet stage B or C disease. The signal loss of normal bone marrow in out-of-phase imaging is a phase effect rather than a T2* effect. The differentiation of initial from higher-grade bone marrow infiltration on out-of-phase images relies solely on a shift in the fat/water ratio.     

Breast imaging. Preoperative breast cancer staging: comparison of USPIO-enhanced MR imaging and 18F-fluorodeoxyglucose (FDC) positron emission tomography (PET) imaging for axillary lymph node staging—initial findings

Magnetic resonance (MR) imaging after ultra-small super paramagnetic iron oxide (USPIO) injection and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) for preoperative axillary lymph node staging in patients with breast cancer were evaluated using histopathologic findings as the reference standard. USPIO-enhanced MR and FDG-PET were performed in ten patients with breast cancer who were scheduled for surgery and axillary node resection. T2-weighted fast spin echo, T1-weighted three-dimensional (3D) gradient echo, T2*-weighted gradient echo and gadolinium-enhanced T1-weighted 3D gradient echo with spectral fat saturation were evaluated. MR imaging before USPIO infusion was not performed. The results were correlated with FDG-PET (acquired with dedicated PET camera, visual analysis) and histological findings. The histopathologic axillary staging was negative for nodal malignancy in five patients and positive in the remaining five patients. There was one false positive finding for USPIO-enhanced MR and one false negative finding for FDG-PET. A sensitivity (true positive rate) of 100%, specificity (true negative rate) of 80%, positive predictive value of 80%, and negative predictive value of 100% were achieved for USPIO-enhanced MR and of 80%, 100%, 100%, 80% for FDG-PET, respectively. The most useful sequences in the detection of invaded lymph nodes were in the decreasing order: gadolinium-enhanced T1-weighted 3D gradient echo with fat saturation, T2*-weighted 2D gradient echo, T1-weighted 3D gradient echo and T2-weighted 2D spin echo. In our study, USPIO-enhanced T1 gradient echo after gadolinium injection and fat saturation emerged as a very useful sequence in the staging of lymph nodes. The combination of USPIO-enhanced MR and FDG-PET achieved 100% sensitivity, specificity, PPV and NPV. If these results are confirmed, the combination of USPIO MR with FDG-PET has the potential to identify the patient candidates for axillary dissection versus sentinel node lymphadenectomy.