Arterial input functions determined from MR signal magnitude and phase for quantitative dynamic contrast‐enhanced MRI in the human pelvis

Dynamic contrast‐enhanced (DCE) MRI is often used to measure the transfer constant (K^trans) and distribution volume (v_e) in pelvic tumors. For optimal accuracy and reproducibility, one must quantify the arterial input function (AIF). Unfortunately, this is challenging due to inflow and signal saturation. A potential solution is to use MR signal phase (?), which is relatively unaffected by these factors. We hypothesized that phase‐derived AIFs (AIF_?) would provide more reproducible K^trans and v_e values than magnitude‐derived AIFs (AIF_|S|). We tested this in 27 prostate dynamic contrast‐enhanced MRI studies (echo time = 2.56 ms, temporal resolution = 13.5 s), using muscle as a standard. AIF_? peak amplitude varied much less as a function of measurement location (inferior–superior) than AIF_|S| (5.6 ± 0.6 mM vs. 2.6 ± 1.5 mM), likely as a result of ? inflow insensitivity. However, our main hypothesis was not confirmed. The best AIF_|S| provided similar reproducibility versus AIF_? (interpatient muscle K^trans = 0.039 ± 0.021 min^?1 vs. 0.037 ± 0.025 min^?1, v_e = 0.090 ± 0.041 vs. 0.062 ± 0.022, respectively). Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Enhanced mass on contrast-enhanced breast MR imaging: Lesion characterization using combination of dynamic contrast-enhanced and diffusion-weighted MR images

Purpose

To evaluate the diagnostic accuracy of a combination of dynamic contrast‐enhanced MR imaging (DCE‐MRI) and diffusion‐weighted MR imaging (DWI) in characterization of enhanced mass on breast MR imaging and to find the strongest discriminators between carcinoma and benignancy.

Materials and Methods

We analyzed consecutive breast MR images in 270 patients; however, 13 lesions in 93 patients were excluded based on our criteria. We analyzed tumor size, shape, margin, internal mass enhancement, kinetic curve pattern, and apparent diffusion coefficient (ADC) values. We applied univariate and multivariate analyses to find the strongest indicators of malignancy and calculate a predictive probability for malignancy. We added the corresponding categories to these prediction probabilities for malignancy and calculated diagnostic accuracy when we consider category 4b, 4c, and 5 lesions as malignant and category 4a, 3, and 2 lesions as benign. In a validation study, 75 enhancing lesions in 71 patients were examined consecutively.

Results

Irregular margin, heterogeneous internal enhancement, rim enhancement, plateau time–intensity curve (TIC) pattern, and washout TIC pattern were the strongest indicators of malignancy as well as past studies, and ADC values less than 1.1 × 10^?3 mm²/s were also the strongest indicators of malignancy. In a validation study, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 92% (56/61), 86% (12/14), 97% (56/58), 71% (12/17), and 91% (68/75), respectively.

Conclusion

The combination of DWI and DCE‐MRI could produce high diagnostic accuracy in the characterization of enhanced mass on breast MR imaging. J. Magn. Reson. Imaging 2008;28:1157–1165. © 2008 Wiley‐Liss, Inc.

     

Combined quantitative dynamic contrast-enhanced MR imaging and (1)H MR spectroscopic imaging of human prostate cancer

PURPOSE: To differentiate prostate carcinoma from healthy peripheral zone and central gland using quantitative dynamic contrast-enhanced (DCE) magnetic resonance (MR) imaging and two-dimensional (1)H MR spectroscopic imaging (MRSI) combined into one clinical protocol. MATERIALS AND METHODS: Twenty-three prostate cancer patients were studied with a combined DCE-MRI and MRSI protocol. Cancer regions were localized by histopathology of whole mount sections after radical prostatectomy. Pharmacokinetic modeling parameters, K(trans) and k(ep), as well as the relative levels of the prostate metabolites citrate, choline, and creatine, were determined in cancer, healthy peripheral zone (PZ), and in central gland (CG). RESULTS: K(trans) and k(ep) were higher (P < 0.05) in cancer and in CG than in normal PZ. The (choline + creatine)/citrate ratio was elevated in cancer compared to the PZ and CG (P < 0.05). While a (choline + creatine)/citrate ratio above 0.68 was found to be a reliable indicator of cancer, elevated K(trans) was only a reliable cancer indicator in the diagnosis of individual patients. K(trans) and (choline + creatine)/citrate ratios in cancer were poorly correlated (Pearson r(2) = 0.07), and thus microvascular and metabolic abnormalities may have complementary value in cancer diagnosis. CONCLUSION: The combination of high-resolution spatio-vascular information from dynamic MRI and metabolic information from MRSI has excellent potential for improved localization and characterization of prostate cancer in a clinical setting. J. Magn. Reson. Imaging 2004;20:279-287. Copyright 2004 Wiley-Liss, Inc.     

Single breath-hold multiarterial dynamic MRI of the liver at 3T using a 3D fat-suppressed keyhole technique

PURPOSE: To evaluate the feasibility of single breath-hold, multiarterial MRI of the liver using the THRIVE-CENTRA-keyhole technique. MATERIALS AND METHODS: Twenty-eight patients with 63 focal hepatic lesions underwent liver MR examinations that included the three-dimensional THRIVE-CENTRA-keyhole sequence. Three or six phases were obtained for arterial phase scanning during a single breath-hold. Central k-space data were collected for each phase but the remaining peripheral k-space data were collected only once. The enhancement pattern of each hepatic lesion was analyzed according to the specific diagnosis. RESULTS: Hepatocellular carcinomas (n = 24) enhancement patterns included: rim enhancing (n = 9), homogeneous (n = 7), nodule-in-nodule (n = 5), or heterogeneous (n = 3). A late peritumoral rim was observed in four (17%) of the hepatocellular carcinomas. Most metastases (17 of 18; 94%) demonstrated peripheral rim enhancement. The progressive centripetal enhancement of hemangiomas (n = 6) was clearly depicted. Focal nodular hyperplasia (n = 4) showed early homogeneous enhancement and one lesion demonstrated a central scar. CONCLUSION: The THRIVE-CENTRA-keyhole technique can be used to acquire single breath-hold, multiarterial images depicting improved enhancement characteristics of focal hepatic lesions. This technique will allow accurate timing of arterial scanning with 3D acquisition and high temporal resolution.     

Determination of arterial input function using fuzzy clustering for quantification of cerebral blood flow with dynamic susceptibility contrast-enhanced MR imaging

An accurate determination of the arterial input function (AIF) is necessary for quantification of cerebral blood flow (CBF) using dynamic susceptibility contrast-enhanced magnetic resonance imaging. In this study, we developed a method for obtaining the AIF automatically using fuzzy c-means (FCM) clustering. The validity of this approach was investigated with computer simulations. We found that this method can automatically extract the AIF, even under very noisy conditions, e.g., when the signal-to-noise ratio is 2. The simulation results also indicated that when using a manual drawing of a region of interest (ROI) (manual ROI method), the contamination of surrounding pixels (background) into ROI caused considerable overestimation of CBF. We applied this method to six subjects and compared it with the manual ROI method. The CBF values, calculated using the AIF obtained using the manual ROI method [CBF(manual)], were significantly higher than those obtained with FCM clustering [CBF(fuzzy)]. This may have been due to the contamination of non-arterial pixels into the manually drawn ROI, as suggested by simulation results. The ratio of CBF(manual) to CBF(fuzzy) ranged from 0.99-1.83 [1.31 +/- 0.26 (mean +/- SD)]. In conclusion, our FCM clustering method appears promising for determination of AIF because it allows automatic, rapid and accurate extraction of arterial pixels. J. Magn. Reson. Imaging 2001;13:797-806.     

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.     

Comparison of gadoxetic acid-enhanced dynamic imaging and diffusion-weighted imaging for the preoperative evaluation of colorectal liver metastases

Purpose:

To retrospectively compare the diagnostic accuracy for the detection of colorectal liver metastases between gadoxetic acid‐enhanced MRI (EOB‐MRI) and diffusion‐weighted imaging (DWI) on 3.0 Tesla (T) system, and then to determine whether a combination of the two techniques may improve the diagnostic performance.

Materials and Methods:

Forty‐seven patients underwent MR imaging at 3.0T, including DWI (DWI set) and dynamic and hepatobiliary phase EOB‐MRI (EOB set) for the preoperative evaluation of colorectal liver metastases. All suspicious metastases were confirmed by hepatic surgery. Two blinded readers independently reviewed three different image sets, which consisted of DWI set, EOB set, and combined set. The accuracy was assessed by the area (Az) under the alternative‐free response receiver operating characteristic curve, and the sensitivity and positive predictive value (PPV) were calculated.

Results:

We found a total of 78 confirmed colorectal liver metastases in 42 of 47 patients. Each reader noted higher diagnostic accuracy of combined set of EOB‐MRI and DWI than DWI set and EOB set, without statistical significance. Regardless of the size of colorectal liver metastasis, each reader detected significantly more metastases on combined set than on DWI set, and PPV was significantly higher with DWI set than with EOB set or with combined set for one reader.

Conclusion:

EOB‐MRI was more useful for the detection of colorectal liver metastases, while DWI was more useful for their characterization. The combination of EOB‐MRI and DWI showed significantly higher accuracy and sensitivity for the preoperative detection of small colorectal liver metastases than DWI. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Blind estimation of the arterial input function in dynamic contrast‐enhanced MRI using purity maximization

Uncertainty in arterial input function (AIF) estimation is one of the major errors in the quantification of dynamic contrast‐enhanced MRI. A blind source separation algorithm was proposed to determine the AIF by selecting the voxel time course with maximum purity, which represents a minimal contamination from partial volume effects. Simulations were performed to assess the partial volume effect on the purity of AIF, the estimation accuracy of the AIF, and the influence of purity on the derived kinetic parameters. In vivo data were acquired from six patients with hypopharyngeal cancer and eight rats with brain tumor. Results showed that in simulation the AIF with the highest purity is closest to the true AIF. In patients, the manually selection had reduced purity, which could lead to underestimations of K^trans and V_e and an overestimation of V_p when compared with those obtained by the proposed blind source separation algorithm. The derived kinetic parameters in the tumor were more susceptible to the changes in purity when compared with those in the muscle. The animal experiment demonstrated good reproducibility in blind source separation‐AIF derived parameters. In conclusion, the blind source separation method is feasible and reproducible to identify the voxel with the tracer concentration time course closest to the true AIF. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Multifocal inflammatory pseudotumor of the liver: dynamic gadolinium-enhanced, ferumoxides-enhanced, and mangafodipir trisodium-enhanced MR imaging findings

The MRI characteristics of a multifocal inflammatory pseudotumor of the liver are described. Emphasis is placed on the appearances following intravenous administration of both non-specific and liver-specific MR contrast agents. On post-gadolinium gradient-echo (GE) images an early, intense, and peripheral enhancement was followed by a homogeneous, complete, and persistent enhancement. Lesions showed no uptake following administration of ferumoxides particles nor mangafodipir trisodium, respectively. During follow-up, a peripheral hyperintense rim appeared on precontrast T1-weighted images, a feature not previously described.     

Quantitative evaluation of nonrepetitive phase-encoding orders for first-pass, 3D contrast-enhanced MR angiography.

In this work, a detailed quantitative comparison was made of many alternative phase-encoding strategies for first-pass 3D MR angiography where each phase encode is only sampled once during the transient passage of contrast agent. A series of standard sequential and centric phase-encoding orders including elliptical centric were tested, as well as a new order called elliptical sequential. The characteristics of the different phase-encoding orders were tested using a computer simulation followed by experimental verification using a variable flip angle scheme. The characteristics to be considered included: arterial intensity, arterial-to-venous contrast, degree of artifact, and the blurring of the point-spread function. By making use of a wide range of start times and a rapidly varying contrast curve, the quantitative results clearly indicate the widely varying merits of each phase-encoding order. In general, when an optimal start time is used techniques that sample the low k-space views most compactly will produce the best results; however, the same methods are more problematic when the bolus arrival time deviates substantially from that expected.     

Two different types of ring‐like enhancement on dynamic MR imaging in breast cancer: Correlation with the histopathologic findings

Purpose

To describe two different types of “ring‐like enhancement” seen on dynamic magnetic resonance imaging (MRI) of breast cancer, and compare their histopathological features.

Materials and Methods

A total of 326 breast carcinomas in 311 patients were evaluated regarding the existence and appearance of “ring‐like enhancement” in comparison to other MR imaging and histopathological findings.

Results

Early peripheral enhancement (EPE) was observed in 81 of 326 lesions (24.8%) and delayed rim enhancement (DRE) in 110 (33.7%). Spiculated mass, invasive ductal carcinoma with abundant stroma, central fibrosis/necrosis, and a higher degree of fat invasion correlated with EPE (P < 0.001). DRE correlated with lobulated or round mass with a smooth border, invasive ductal carcinoma with scanty stroma, higher degrees of inflammatory change and surrounding compressed tissue, and less fat invasion (P <0.001). EPE correlated with the ratio of the peripheral to central blood vessel density (P = 0.0036) and DRE with the ratio of the peritumoral to peripheral lymph vessel density (P = 0.0298).

Conclusion

The appearance of two different types of ring‐like enhancement on dynamic MRI in breast cancers was affected by the morphologic features, various histological factors reflecting the growth pattern of the mass, and angiogenesis and lymphangiogenesis. J. Magn. Reson. Imaging 2008;28:1435–1443. © 2008 Wiley‐Liss, Inc.