Contrast-enhanced T1-weighted Research Articles

MRI and CT imaging characteristics of myoepithelioma of the parotid gland.

Myoepithelioma is a rare tumor of the salivary gland and only few reports have focused on its imaging characteristics. To characterize the magnetic resonance imaging (MRI) and computed tomography (CT) characteristics of myoepithelioma of the parotid gland. We retrospectively analyzed the MRI and CT findings of nine patients with myoepithelioma in the parotid gland as demonstrated by pathologic analysis. The MRI and CT findings were analyzed regarding the tumor position, size, marginal morphology, and degree and patterns of enhancement. Unilocular and multilocular tumors were found in seven cases (7/9, 77.8%) and two cases (2/9, 22.2%), respectively. Most of the tumors were located in the superficial lobe (6/9, 66.7%) and abutted the capsule of the parotid gland (7/9, 77.8%). Six of the seven unilocular tumors were round. Most of the tumors displayed smooth contours (6/9, 66.7%) and well-defined margins (5/9, 55.6%). Four of five tumors (80%) display the capsule on T2-weighted (T2W) and contrast-enhanced T1-weighted (T1W) imaging. All five examined tumors exhibited homogeneous intermediate signal intensity on T1W imaging and high signal intensity on T2W imaging. On contrast-enhanced T1W imaging, the tumors displayed homogeneous (n = 4) or heterogeneous (n = 1) moderate to marked contrast enhancement. Based on the enhanced CT scans, four tumors exhibited moderate homogeneous (n = 2) or heterogeneous (n = 2) contrast enhancement. Myoepitheliomas are characterized as small, unilocular, round tumors with smooth contours that are located in the superficial lobe and abut the capsule of the parotid gland, display the capsule on T2W and contrast-enhanced T1W imaging, and exhibit homogeneous signal intensities or densities based on MRI and CT.

Carbon fiber intramedullary nails reduce artifact in postoperative advanced imaging.

This study assessed whether radiolucent carbon fiber reinforced-polyetheretherketone (CFR-PEEK) intramedullary nails decreased hardware artifact on magnetic resonance imaging (MRI) and computed tomography (CT) in vitro and in an oncologic patient population. In vitro and clinical evaluations were done. A qualitative assessment of metal artifact was performed using CFR-PEEK and titanium nail MRI phantoms. Eight patients with a femoral or tibial prophylactic CFR-PEEK nail were retrospectively identified. All patients had postoperative surveillance imaging by MRI, CT, and were followed for a median 20months (range, 12-28months). CFR-PEEK images were compared to images from a comparative group of patients with titanium femoral intramedullary nails who had a postoperative MRI or CT. A musculoskeletal-trained radiologist graded visualization of the cortex, corticomedullary junction, and bone-muscle interface, on T1-weighted (T1W), STIR, and contrast-enhanced T1-weighted fat-saturated (T1W FS) sequences of both groups with a five-point scale, performing independent reviews 4months apart. Statistical analysis used the Wilcoxon rank-sum test and a weighted kappa. Substantially less MRI signal loss occurred in the CFR-PEEK phantom than in the titanium phantom simulation, particularly as the angle increased with respect to direction of the static magnetic field. CFR-PEEK nails had less MRI artifact than titanium nails on scored T1W, STIR, and contrast-enhanced T1W FS MRI sequences (p ≤ 0.03). The mean weighted kappa was 0.64, showing excellent intraobserver reliability between readings. CFR-PEEK intramedullary nail fixation is a superior alternative to minimize implant artifact on MRI or CT imaging for patients requiring long bone fixation.

Mesoporous silica-coated luminescent Eu3+doped GdVO4nanoparticles for multimodal imaging and drug delivery

We describe a simple method for synthesizing mesoporous silica-coated luminescent europium-doped gadolinium vanadate (GdVO4:Eu3+@mSiO2) nanoparticles. Their biomedical applications as a potential imaging nanoprobe for both fluorescence imaging and magnetic resonance imaging (MRI) and as a simultaneous anti-cancer drug delivery vehicle are also discussed. Eu3+ doped GdVO4 nanoparticles exhibit strong red photoluminescence and the Gd3+ in GdVO4 can be used as a T1 contrast agent for MRI. T1-weighted MR contrast enhancement as well as sustained intracellular drug delivery can be achieved by the mesoporous silica layer coating onto a single nanoparticle. Enhanced T1 MR contrast was proven by relaxometric studies on water access to the paramagnetic core. GdVO4:Eu3+@mSiO2 nanoparticles as a new type of theragnostic (imaging and treatment) agent can provide new opportunities in a cancer treatment.

Effect of edaravone on radiation-induced brain necrosis in patients with nasopharyngeal carcinoma after radiotherapy: a randomized controlled trial.

Excessive generation of free radicals plays a critical role in the pathogenesis of radiation-induced brain injury. This study was designed to evaluate the protective effect of edaravone, a free radical scavenger, on radiation-induced brain necrosis in patients with nasopharyngeal carcinoma. Eligible patients were randomized 1:1 to the control group and the edaravone group (intravenous 30 mg twice per day for 2 weeks). Both groups received intravenous conventional steroid therapy and were monitored by brain MRI and LENT/SOMA scales prior to the entry of the trial and at 3-months after completing the trial. The primary end point was a 3-month response rate of the proportional changes determined by MRI. The trial is registered at Clinicaltrials.gov Identifier: NCT01865201. Between 2009 and 2012, we enrolled 154 patients. Of whom 137 were eligible for analysis. The volumes of necrosis estimated on T2-weighted image showed that 55.6 % edaravone-treated patients (40 out of 72) showed edema decreases ≥25 %, which was significantly higher than that in the control group (35.4 %, 23 out of 65, p = 0.025). Forty-four patients treated with edaravone (61.1 %) reported improvement in neurologic symptoms and signs evaluated by LENT/SOMA scales, while the rate was 38.5 % in the control group (p = 0.006). MRI of the edaravone group showed a significant decrease in area of T1-weighted contrast enhancement (1.67 ± 4.69 cm2, p = 0.004) and the T2-weighted edema (5.08 ± 10.32 cm2, p = 0.000). Moreover, compared with those in control group, patients with edaravone exhibited significantly better radiological improvement measured by T2-weighted image (p = 0.042). Administration of edaravone, in adjunct to steroid regimen, might provide a better outcome in patients with radiation-induced brain necrosis.

Chain Length Effect of the Multidentate Block Copolymer Strategy to Stabilize Ultrasmall Fe3O4Nanoparticles

A multidentate block copolymer (MDBC) strategy to stabilize ultrasmall superparamagnetic iron oxide nanoparticles (USNPs) as biocompatible T1-positive contrast agents for magnetic resonance imaging (MRI) is explored. The MDBC is designed with a poly(methacrylic acid) (PMAA) block having pendant carboxylates as multidentate anchoring groups and a hydrophilic polymethacrylate block having pendant oligo(ethylene oxide) chains (POEOMA). A series of multifunctional MDBCs with different chain lengths of POEOMA and PMAA blocks were synthesized by atom transfer radical polymerization and subsequent hydrolytic cleavage. The resultant aqueous MDBC/USNP colloids fabricated through a ligand-exchange process were characterized to investigate the effect of chain lengths of POEOMA-b-PMAA copolymers on size, morphology, and colloidal stability as well as relaxometric properties and in vitro MRI performance. The results suggest that the optimal design of chain lengths of both anchoring and hydrophilic blocks is required for enhanced colloidal stability under biologically relevant conditions as well as effective T1-weighted contrast enhancement.

Role of diffusion-weighted MRI in differentiation of hepatic abscesses from non-infected fluid collections

To evaluate the role of diffusion-weighted magnetic resonance imaging (DW-MRI) in the differentiation of hepatic abscesses from non-infected fluid collections. In this retrospective study, 22 hepatic abscesses and 27 non-infected hepatic fluid collections were examined in 27 patients who underwent abdominal MRI including DW-MRI. Two independent observers reviewed T2-weighted+DW-MRI and T2-weighted+contrast-enhanced T1-weighted (CET1W) images in two sessions. Detection rates and confidence levels were calculated and compared using McNemar's and Wilcoxon's signed rank tests, respectively. Apparent diffusion coefficient (ADC) values of abscesses and non-infected fluid collections were compared using the t-test. Receiver operating characteristic (ROC) curves were constructed. There was no statistically significant difference in the accuracy of detecting abscesses using T2-weighted+DW-MRI (both observers: 21/22, 95.5%) versus T2-weighted+CET1W images (observer 1: 21/22, 95.5%; observer 2: 22/22, 100%; p<0.01). Mean ADC values were significantly lower with abscesses versus non-infected fluid collections (0.83±0.24 versus 2.25±0.61×10(-3)mm(2)/s; p<0.001). With ROC analysis there was good discrimination of abscess from non-infected fluid collections at a threshold ADC value of 1.36×10(-3)mm(2)/s. DW-MRI allows qualitative and quantitative differentiation of abscesses from non-infected fluid collections in the liver.

Addition of diffusion-weighted imaging can improve diagnostic confidence in bowel MRI

To evaluate whether the addition of diffusion-weighted imaging (DWI) in bowel abdominal magnetic resonance imaging (MRI) can improve diagnostic confidence. One hundred and eleven consecutive patients with suspected or known inflammatory bowel disease (n = 59), tumour disease (n = 31), unspecific abdominal pain (n = 16), and suspected graft-versus-host disease (n = 5) underwent bowel MRI using a 1.5 T MRI machine. In addition to T2-weighted (T2W) and contrast-enhanced T1-weighted (CE-T1W) data, axial and coronal DWI sequences were collected (b = 50, 500, 1000). Diagnostic confidence for lesion detection with and without DWI was evaluated using a four-point Likert scale [1 = certainly no lesion(s), 2 = probably no lesion(s), 3 = probably lesion(s), 4 = certainly lesion(s)]. In 11 of 111 patients (10%), the diagnostic confidence was improved by DWI. In seven patients, readers changed their diagnosis from "probable" to "certain presence of lesions". In another four patients, lesions were diagnosed based on DWI, which were not delineated on CE-T1W and T2W imaging. DWI of the bowel can provide additional information to the reader and, therefore, improve diagnostic confidence. Hence, additional DWI should be integrated into a standard bowel MRI protocol.

Evolution of the Ablation Region After Magnetic Resonance–Guided High-Intensity Focused Ultrasound Ablation in a Vx2 Tumor Model

Volumetric magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) is a completely noninvasive image-guided thermal ablation technique. Recently, there has been growing interest in the use of MR-HIFU for noninvasive ablation of malignant tumors. Of particular interest for noninvasive ablation of malignant tumors is reliable treatment monitoring and evaluation of response. At this point, there is limited evidence on the evolution of the ablation region after MR-HIFU treatment. The purpose of the present study was to comprehensively characterize the evolution of the ablation region after volumetric MR-HIFU ablation in a Vx2 tumor model using MR imaging, MR temperature data, and histological data. Vx2 tumors in the hind limb muscle of New Zealand White rabbits (n = 30) were ablated using a clinical MR-HIFU system. Twenty-four animals were available for analyses. Magnetic resonance imaging was performed before and immediately after ablation; MR temperature mapping was performed during the ablation. The animals were distributed over 7 groups with different follow-up lengths. Depending on the group, animals were reimaged and then killed on day 0, 1, 3, 7, 14, 21, or 28 after ablation. For all time points, the size of nonperfused areas (NPAs) on contrast-enhanced T1-weighted (CE-T1-w) images was compared with lethal thermal dose areas (ie, the tissue area that received a thermal dose of 240 equivalent minutes or greater [EM] at 43°C) and with the necrotic tissue areas on histology sections. The NPA on CE-T1-w imaging showed an increase in median size from 266 ± 148 to 392 ± 178 mm(2) during the first day and to 343 ± 170 mm(2) on day 3, followed by a gradual decrease to 113 ± 103 mm(2) on day 28. Immediately after ablation, the NPA was 1.6 ± 1.4 times larger than the area that received a thermal dose of 240 EM or greater in all animals. The median size of the necrotic area on histology was 1.7 ± 0.4 times larger than the NPA immediately after ablation. After 7 days, the size of the NPA was in agreement with the necrotic tissue area on histology (ratio, 1.0 ± 0.2). During the first 3 days after MR-HIFU ablation, the ablation region increases in size, after which it gradually decreases in size. The NPA on CE-T1-w imaging underestimates the extent of tissue necrosis on histology in the initial few days, but after 1 week, the NPA is reliable in delineating the necrotic tissue area. The 240-EM thermal dose limit underestimates the necrotic tissue area immediately after MR-HIFU ablation. Reliable treatment evaluation techniques are particularly important for noninvasive, image-guided tumor ablation. Our results indicate that CE-T1-w imaging is reliable for MR-HIFU treatment evaluation after 1 week.

Manganese‐enhanced MRI of rat brain based on slow cerebral delivery of manganese(II) with silica‐encapsulated MnxFe1–xO nanoparticles

In this work, we report a monodisperse bifunctional nanoparticle system, MIO@SiO2 -RITC, as an MRI contrast agent [core, manganese iron oxide (MIO); shell, amorphous silica conjugated with rhodamine B isothiocyanate (RITC)]. It was prepared by thermal decomposition and modified microemulsion methods. The nanoparticles with varying iron to manganese ratios displayed different saturated magnetizations and relaxivities. In vivo MRI of rats injected intravenously with MIO@SiO2-RITC nanoparticles exhibited enhancement of the T1 contrast in brain tissue, in particular a time-delayed enhancement in the hippocampus, pituitary gland, striatum and cerebellum. This is attributable to the gradual degradation of MIO@SiO2-RITC nanoparticles in the liver, resulting in the slow release of manganese(II) [Mn(II)] into the blood pool and, subsequently, accumulation in the brain tissue. Thus, T1-weighted contrast enhancement was clearly detected in the anatomic structure of the brain as time progressed. In addition, T2*-weighted images of the liver showed a gradual darkening effect. Here, we demonstrate the concept of the slow release of Mn(II) for neuroimaging. This new nanoparticle-based manganese contrast agent allows one simple intravenous injection (rather than multiple infusions) of Mn(II) precursor, and results in delineation of the detailed anatomic neuroarchitecture in MRI; hence, this provides the advantage of the long-term study of neural function.

Abstract 452: Novel MRI-based biomarker for early assessment of glioma recurrence

Abstract Gliomas continue to be the most common form of brain malignancy in adult patients. Even with advancements in the clinical management of these patients, assessment of tumor recurrence continues to be based on late or serial changes in tumor volume as measured by CT or MRI [1; 2]. The purpose of this study was to develop and evaluate a new voxel-based method, referred as parametric response mapping (PRM), for early detection of brain tumor progression using standard MR images (FLAIR and contrast-enhanced T1-weighted). PRM results were evaluated relative to standard MRI-based criteria of clinical progression assessment in patients with Grade III/IV gliomas. Fourteen patients with grades III/IV glioma underwent MRI before and during treatment (every 2 months). MRI scans, acquired on a 1.5T or a 3T clinical scanner, consisted of fluid-attenuated inversion recovery imaging (FLAIR) and contrast-enhanced T1-weighted (CE-T1w) images. All images were spatially registered to CE-T1w pre-treatment scans and tumors were manually contoured on the T1w-Gd images. Subsequent to PRM analysis, FLAIR images were normalized to the signal using the white matter (rFLAIR). PRM, applied to the whole brain volume on rFLAIR, was performed by first generating voxel-based difference maps at each longitudinal follow-up scan using the baseline as the subtrahend. Baseline was defined as either the pre-treatment or subsequent rFLAIR image. Individual voxels were classified based on the extent of change observed in the rFLAIR difference maps. Three classifications were used: voxels with a significant increase in rFLAIR values (PRMrFLAIR+), significant decrease (PRMrFLAIR-) or statistically unchanged (PRMrFLAIR0). Disease recurrence was defined by PRM as the sum of red voxels that exceed 20% of the tumor volume as delineated on T1w-Gd. PRMrFLAIR detected tumor recurrence on average 18±3 weeks earlier than the MacDonald criteria. It was also observed that PRMrFLAIR+ found outside the tumor CE-T1w regions revealed the spatial location at which the tumor would progress on subsequent scans based on current standard progression criteria. These results show that the PRM approach provides for the early detection and spatial depiction of brain tumor progression prior to detection by currently available conventional MRI-based criteria. While further validation of PRM for detection of tumor recurrence is currently underway, the ability to detect tumor progression significantly earlier than currently possible is anticipated to have a major impact on patient care. [1] Macdonald, D. R., et al. (1990). J Clin Oncol 8(7): 1277-1280. [2] Wen, P. Y., et al. (2010). J Clin Oncol 28(11): 1963-1972. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 452. doi:1538-7445.AM2012-452

Detection of Prostate Cancer With Magnetic Resonance Imaging

The aim of this study was to optimize and predict the most efficient magnetic resonance imaging (MRI) sequences; T1-weighted (T1W), T2-weighted (T2W), dynamic contrast-enhanced (DCE) T1W, diffusion-weighted imaging (DWI) apparent diffusion coefficient (ADC) mapping sequences and proton MR spectroscopy (H-MRS) for the detection of prostate cancer. After institutional review board approval and informed consent taken from all the patients, 40 patients with prostate cancer were included in this research. Two readers independently evaluated the results of T1W, T2W, DCE T1W, and DWI-ADC mapping sequences and proton H-MRS for the depiction of prostate cancer. Reference standard was the transrectal ultrasonography-guided biopsy and the surgical histopathological results. Statistical analysis was assessed by the Fisher exact t test, Wilcoxon signed rank test, variance analysis test with kappa (κ) values and receiver operating characteristics (ROC) curve for ADC values, choline (Cho)/citrate (Cit) and Cho+creatine (Cre)/Cit ratios for each observer. Based on both readers' results, sensitivity declined to 31% and specificity to 75% for the T1W sequence, sensitivity declined to 43% and specificity to 67% for the DCE T1W sequence, sensitivity declined to 46% and specificity to 68% for the T2W sequence, sensitivity declined to 29% and specificity to 82% for the DWI-ADC mapping; and specificity was 49% for the Cho/Cit and Cho+Cre/Cit ratios, sensitivity was 69% for the Cho/Cit ratio, and sensitivity was 70% for the Cho+Cre/Cit ratio for H-MRS. The T2W sequence and H-MRS presented significant statistical differences for the depiction of prostatic cancer (P < 0.05), the most efficient sequence to detect prostatic cancer was H-MRS: Cho+Cre/Cit and Cho/Cit ratios. Instead of using either sequences alone owing to low sensitivity and specificity rates, combined use of MRI techniques could easily improve the detection and staging of prostate cancer.

Primary malignant mixed müllerian tumor of the fimbriated end of the Fallopian tube causing hematosalpinx and hematometra

Primary malignant mixed müllerian tumor of the fimbriated end of the Fallopian tube causing hematosalpinx and hematometra

Hyperacute injury marker (HARM) in primary hemorrhage

The objective of the study was to characterize a previously unreported form of CNS barrier disruption in intracerebral hemorrhage (ICH): hyperacute injury marker (HARM). In this retrospective cohort analysis of patients presenting with primary ICH, precontrast and postcontrast MRI scans obtained within 5 days of symptom onset were analyzed. The presence of CNS barrier disruption was defined by (1) perihematomal or intrahematomal enhancement visualized on postcontrast T1-weighted MRI or (2) HARM: sulcal or ventricular hyperintensity visualized on postcontrast fluid-attenuated inversion recovery sequences (graded on a 5-point scale). Forty-six patients were included in the analysis. Mean age was 65 years, median NIH Stroke Scale score was 7, and mean ICH volume was 12.2 mL (range 0.3-46.9 mL). HARM was visualized in 85% of patients, and this was moderate to severe in 50%. In all cases, the sulcal enhancement was noncontiguous with the hematoma. Of those patients with postcontrast T1-weighted imaging, perihematomal or intrahematomal contrast enhancement was visualized in 75% of patients. This study demonstrates that HARM occurs in intracerebral hemorrhage and that it likely represents a second type of CNS barrier disruption distinct from parenchymal postcontrast T1-weighted enhancement. Similar to T1 enhancement, this phenomenon may serve as a clinically useful biomarker to test therapies aimed at stabilizing acute ICH and CNS barrier disruption. Future studies are needed to further define the time course and prognostic implications of this finding.

Application of diffusion tensor imaging of magnetic resonance imaging in the diagnosis of cerebral gliomas

Objective To investigate the clinical significance of diffusion tensor imaging of magnetic resonance imaging in the diagnosis of cerebral gliomas. Methods Diffusion tensor images were obtained in 23 patients with cerebral gliomas,meanwhile the routing T1-weighted(T1W) ,T2-weighted(T2W) ,contrast-enhanced T1W imaging, FLAIR imaging and diffusion tensor of the brain were acquired. Anatomic relationship between intracranial tumors and surrounding fibers was analyzed on fractional anisotropic(FA) map,color-coded directional map,three-dimensional white matter tractography. Results White matter fiber anatomy maps of the brain by means of FA maps of DTI at high resolution were successfully completed in all patients. The white matter tracts appeared as strongly hyperintense signal,while the grey matter presented an isointense area in contrast to the strongly hypointense signal of the CSF. Glioma boundaries were less sharper than on contrast-enhanced T1W images,but delineation could still be easily seen as hypointense lesion on FA map. The principal fiber tracts were well observed in all cases, including the tracts nearby the lesions. Apparently significant differences of MD were found in solid tumor,surrounding edema,compared with normal white matter regions(P ＜0.05). But there was no significant difference among solid tumor and surrounding edema region(P＞0. 05). There were significant differences of FA between solid tumor,surrounding edema and normal white matter region (P ＜0. 05). Conclusion The FA map of DTI offered the optimal visualization of white matter tracts. The combination of the DTI and other conventional MRI could accurately determine the tumor and surrounding proximity to the white matter fiber tracts in the diagnosis of cerebral glioma. Key words: Glioma; Diffusion magnetic resonance imaging

Neuroimagen de los tumores cerebrales

Advances in neuroimaging have modified diagnosis, treatment and clinical management of brain tumors. However, neuropathological study remains necessary in order to get the best clinical management. Surgery and radiotherapy planning are imaging-dependent procedures, and MRI is the standard imaging modality for determining precisely tumor location and its anatomical relationship with surrounding brain structures. In high-grade tumors it has been accepted that tumoral areas with contrast uptake in CT, or T1-weighted MRI contrast enhancement corresponds to solid tumor. However, relationship between MRI and invasive tumor areas remains less defined. Therefore, it is generally accepted that conventional MRI is not sufficient to delineate the real extension of brain tumors. In recent years, PET using 18FDG and amino acid radiotracers ( 11C-Methionine, 18FDOPA, 18FET) and SPECT with 201-Thallium, as well as advanced MRI sequences (Perfusion, Diffusion-weighted, Diffusion tensor imaging and tractography), and functional MRI, have added important complementary information in the characterization, therapy planning and recurrence differential diagnosis of brain tumors. In this continuing education review of neuroimaging in brain tumors, technical aspects and clinical applications of different imaging modalities are approached in a multidisciplinary way.

Pulse sequence and timing of contrast‐enhanced MRI for assessing blood–brain barrier disruption after transcranial focused ultrasound in the presence of hemorrhage

To optimize the timing of contrast-enhanced magnetic resonance imaging (MRI) that best indicates blood-brain barrier (BBB) disruption induced by focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) and to verify that the contrast-enhanced spin-echo MRI sequence can indicate the degree and location of BBB disruption in the presence of hemorrhage better than a gradient-echo sequence. Sonication was applied to 12 rat brains with four different doses of UCA to cause variable degrees of hemorrhage. Two imaging sequences were performed to acquire T1-weighted (T1W) images at two time-points after the administration of a T1-shortening contrast agent. The contrast enhancement at the sonicated regions was quantified and correlated against Evans blue (EB) staining. The spin-echo T1W images at 10 minutes post-contrast enhancement showed the best correlation with EB staining in both quantity of EB extravasation (r = 0.812; P < 0.01) and spatial distribution (r = 0.528, P < 0.01). This capability was more robust than the gradient-echo sequence. Our results suggest that contrast-enhanced T1W spin-echo sequence acquired in the early phase post-contrast enhancement should be considered to monitor the degree and location of BBB disruption under the possibility of hemorrhage induced by FUS.

Evaluation of the necessity of contrast for the follow up MR imaging of schwannomas

The purpose of our study was to determine whether gadolinium is necessary in follow-up MRIs for evaluating vestibular schwannomas. A retrospective analysis of 49 magnetic resonance imaging (MRI) examinations of 20 vestibular schwannoma patients was performed. Patients received between 1 and 4 follow-up scans, and the mean follow-up period was 15.3 months. Two radiologists independently reviewed the initial and follow-up MRI examinations. Tumor measurements obtained using the constructive interference in steady state (CISS) and contrast-enhanced T1-weighted (T1W) sequences were compared. Both radiologists used both of the sequences to analyze any differences in the tumor sizes measured in consecutive MRI scans. The linear anteroposterior and transverse tumor diameter measurements obtained by the two observers using both sequences were strongly correlated (r = 0.962-0.987, P < 0.001). The observers agreed to a very high degree when detecting changes in the tumor size using the CISS sequence (κ = 0.902, P = 0.0001), whereas the agreement with the contrast-enhanced T1W sequence was good but not as good (κ = 0.706, P = 0.001). CISS, as a contrast-free sequence, may be an option in regular follow-up MRIs of vestibular schwannomas.

Rat model of reperfused partial liver infarction: Characterization with multiparametric magnetic resonance imaging, microangiography, and histomorphology

Rat model of reperfused partial liver infarction (RPLI) has been increasingly used in studying new diagnostics and therapeutics. To characterize the RPLI model using magnetic resonance imaging (MRI), microangiography, and histopathology. RPLI was induced in eight rats by occluding hepatic inflow to the right liver lobe for 3 hours. MRI was performed at a 1.5 T clinical scanner 6 hours after reperfusion to obtain T2-weighted (T2WI), T1-weighted (T1WI), contrast-enhanced (CE) T1WI, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps, T1-weighted dynamic contrast-enhanced (T1-DC) perfusion-weighted imaging (PWI), and T2*-weighted dynamic susceptibility contrast-enhanced (T2*-DSC) PWI images. Rats were sacrificed for microangiography and histomorphology. In vivo morphological and functional MRI parameters, including maximum initial slope (MIS), K value, relative blood flow (rBF), relative blood volume (rBV), time to peak (TTP), and mean transit time (MTT), were matched with postmortem findings. The infarcted lobe was conspicuous from normal liver with lower and higher signal intensity on T1WI (P=0.018) and T2WI (P=0.001), respectively. Contrast between infarcted and normal liver reversed on CE-T1WI after gadolinium injection. The infarction averaged 37.5% of total liver volume. DWI and ADC maps were able to detect subtle perfusion-related differences (P<0.05). With T1-DC-PWI, increased extravasation and vascular permeability were reflected by significantly greater MIS (P=0.034) and K value (P=0.014) in infarction. T2*-DSC-PWI showed lower rBF and rBV with shorter TTP and MTT in infarcted liver (P<0.05). In vivo MRI findings corresponded well with postmortem outcomes. RPLI in rats could be characterized by multiparametric MRI and postmortem assessments, with insight into the no-reflow phenomenon, which implies its further application for preclinical assessments of new pharmaceutics.

MR Molecular Imaging of Thrombus: Development and Application of a Gd-based Novel Contrast Agent Targeting to P-selectin

Molecular imaging of thrombus formation at initial stage requires a robust thrombus-specific contrast agent with high sensitivity. In this study, we report a novel P-selectin-targeted paramagnetic molecular imaging agent and the agent's potential to sensitively detect occult microthrombi on the intimal surface of endothelium. Platelet clots and blood clots targeted in vitro with paramagnetic nanoparticles presented a highly detectable, homogeneous T1-weighted contrast enhancement that was improved with increasing gadolinium level. In vivo contrast enhancement under part of circulation conditions was assessed in dogs. The micro-thrombi around the femoral vein of dog demonstrated higher signal intensities than the control clots and the adjacent muscle. Histology was performed on regions likely to contain thrombus as indicated by MRI. These results suggest that molecular imaging of P-selectin-targeted paramagnetic nanoparticles can provide sensitive detection and localization of P-selectin and may allow for early, direct identification of microthrombi, leading to early diagnosis.

Apparent diffusion coefficient maps of pediatric mass lesions with free-breathing diffusion-weighted magnetic resonance: feasibility study

To assess the technical feasibility of apparent diffusion coefficient (ADC) mapping based on free-breathing diffusion-weighted magnetic resonance (DW-MR) outside the CNS in children. Twelve children with mass lesions of varied histopathology were scanned with short-tau inversion recovery (STIR), contrast-enhanced T1-weighted (CE-T1W), and diffusion-weighted (b=0, 500 and 1000 s/mm2) sequences. ADC maps were calculated. Lesion-to-background signal intensity ratios were measured and compared between STIR/CE-T1W/ADC overall (Friedman test) and between viable embryonal tumors and other lesions (Kruskal-Wallis test). ADC maps clearly depicted all lesions. Lesion-to-background signal intensity ratios of STIR (median 3.7), CE-T1W (median 1.4), and ADC (median 1.6) showed no overall difference (chi-square=3.846; P=0.146), and there was no difference between viable embryonal tumors and other lesions within STIR/CE-T1W/ADC (chi-square 1.118/0.669/<0.001; P=0.290/0.414/1.000, respectively). ADC mapping is feasible in free-breathing imaging of pediatric mass lesions outside the CNS using standard clinical equipment.