Spoiled Gradient-echo Magnetic Resonance Imaging Research Articles

Clinical Breast MRI-based Radiomics for Distinguishing Benign and Malignant Lesions: An Analysis of Sequences and Enhanced Phases.

Previous studies have used different imaging sequences and different enhanced phases for breast lesion calsification in radiomics. The optimal sequence and contrast enhanced phase is unclear. To identify the optimal magnetic resonance imaging (MRI) radiomics model for lesion clarification, and to simulate its incremental value for multiparametric MRI (mpMRI)-guided biopsy. Retrospective. 329 female patients (138 malignant, 191 benign), divided into a training set (first site, n = 192) and an independent test set (second site, n = 137). 3.0-T, fast spoiled gradient-echo and fast spin-echo T1-weighted imaging (T1WI), fast spin-echo T2-weighted imaging (T2WI), echo-planar diffusion-weighted imaging (DWI), and fast spoiled gradient-echo contrast-enhanced MRI (CE-MRI). Two breast radiologists with 3 and 10 years' experience developed radiomics model on CE-MRI, CE-MRI + DWI, CE-MRI + DWI + T2WI, CE-MRI + DWI + T2WI + T1WI at each individual phase (P) and for multiple combinations of phases. The optimal radiomics model (Rad-score) was identified as having the highest area under the receiver operating characteristic curve (AUC) in the test set. Specificity was compared between a traditional mpMRI model and an integrated model (mpMRI + Rad-score) at sensitivity >98%. Wilcoxon paired-samples signed rank test, Delong test, McNemar test. Significance level was 0.05 and Bonferroni method was used for multiple comparisons (P = 0.007, 0.05/7). For radiomics models, CE-MRI/P3 + DWI + T2WI achieved the highest performance in the test set (AUC = 0.888, 95% confidence interval: 0.833-0.944). The integrated model had significantly higher specificity (55.3%) than the mpMRI model (31.6%) in the test set with a sensitivity of 98.4%. The CE-MRI/P3 + DWI + T2WI model is the optimized choice for breast lesion classification in radiomics, and has potential to reduce benign biopsies (100%-specificity) from 68.4% to 44.7% while retaining sensitivity >98%. 3 TECHNICAL EFFICACY: Stage 2.

Caudolenticular gray bridges of the brain: A magnetic resonance imaging study.

The caudolenticular (or transcapsular) gray bridges (CLGBs) connect the caudate nucleus (CN) and putamen across the internal capsule. The CLGBs function as the main efferent terminus from premotor and supplementary motor area cortex to the basal ganglia (BG). We conjectured if inherent variations in numbers and sizes of CLGBs could contribute to abnormal cortical-subcortical connectivity in Parkinson's disease (PD), a neurodegenerative disorder featuring a hindrance of BG processing. However, there are no literature accounts of normative anatomy and morphometry of CLGBs. We therefore retrospectively analyzed axial and coronal 3T fast spoiled gradient-echo magnetic resonance images (MRIs) of 34 healthy individuals for bilateral CLGBs symmetry, their numbers, dimensions of thickest and longest bridge, and axial surface areas of CN head and putamen. We calculated Evans' index (EI) to account for any brain atrophy. We statistically tested associations between sex or age and measured dependent variables, and linear correlations between all measured variables (significance at p < 0.05). Study subjects were F:M=23:11 with mean age 49.9 years. All EI's were normal (<0.3). All but three CLGBs were bilaterally symmetrical with a mean 7.4 CLGBs per side. Mean CLGBs thickness and lengths were 1.0 and 4.6 mm, respectively; CN head and putamen areas were 205and 382.0 mm2 , respectively. Females had thicker CLGBs (p=0.02) but we found no significant interactions between sex or age and measured dependent variables, and no correlations between CN head or putamen areas and CLGBs dimensions. These normative MRI dimensions of the CLGBs will help guide future studies on the possible role of CLGBs morphometry in PD predisposition.

A Deep Learning-Based Computer Aided Detection (CAD) System for Difficult-to-Detect Brain Metastases

We sought to develop a computer-aided detection (CAD) system that optimally augments human performance, excelling especially at identifying small inconspicuous brain metastases (BMs), by training a convolutional neural network on a unique magnetic resonance imaging (MRI) data set containing subtle BMs that were not detected prospectively during routine clinical care. Patients receiving stereotactic radiosurgery (SRS) for BMs at our institution from 2016 to 2018 without prior brain-directed therapy or small cell histology were eligible. For patients who underwent 2 consecutive courses of SRS, treatment planning MRIs from their initial course were reviewed for radiographic evidence of an emerging metastasis at the same location as metastases treated in their second SRS course. If present, these previously unidentified lesions were contoured and categorized as retrospectively identified metastases (RIMs). RIMs were further subcategorized according to whether they did (+DC) or did not (-DC) meet diagnostic imaging-based criteria to definitively classify them as metastases based upon their appearance in the initial MRI alone. Prospectively identified metastases (PIMs) from these patients, and from patients who only underwent a single course of SRS, were also included. An open-source convolutional neural network architecture was adapted and trained to detect both RIMs and PIMs on thin-slice, contrast-enhanced, spoiled gradient echo MRIs. Patients were randomized into 5 groups: 4 for training/cross-validation and 1 for testing. One hundred thirty-five patients with 563 metastases, including 72 RIMS, met criteria. For the test group, CAD sensitivity was 94% for PIMs, 80% for +DC RIMs, and 79% for PIMs and +DC RIMs with diameter <3 mm, with a median of 2 false positives per patient and a Dice coefficient of 0.79. Our CAD model, trained on a novel data set and using a single common MR sequence, demonstrated high sensitivity and specificity overall, outperforming published CAD results for small metastases and RIMs - the lesion types most in need of human performance augmentation.

MetNet: Computer-aided segmentation of brain metastases in post-contrast T1-weighted magnetic resonance imaging

PurposeBrain metastases are manually contoured during stereotactic radiosurgery (SRS) treatment planning, which is time-consuming, potentially challenging, and laborious. The purpose of this study was to develop and investigate a 2-stage deep learning (DL) approach (MetNet) for brain metastasis segmentation in pre-treatment magnetic resonance imaging (MRI). Materials and methodsWe retrospectively analyzed postcontrast 3D T1-weighted spoiled gradient echo MRIs from 934 patients who underwent SRS between August 2009 and August 2018. Neuroradiologists manually identified brain metastases in the MRIs. The treating radiation oncologist or physicist contoured the brain metastases. We constructed a 2-stage DL ensemble consisting of detection and segmentation models to segment the brain metastases on the MRIs. We evaluated the performance of MetNet by computing sensitivity, positive predictive value (PPV), and Dice similarity coefficient (DSC) with respect to metastasis size, as well as free-response receiver operating characteristics. ResultsThe 934 patients (mean [±standard deviation] age 59 ± 13 years, 474 women) were randomly split into 80% training and 20% testing groups (748:186). For patients with metastases 1–52 mm (n = 766), 648 (85%) were detected and segmented with a mean segmentation DSC of 81% ± 15%. Patient-averaged sensitivity was 88% ± 19%, PPV was 58% ± 25%, and DSC was 85% ± 13% with 3 ± 3 false positives (FPs) per patient. When considering only metastases ≥6 mm, patient-averaged sensitivity was 99% ± 5%, PPV was 67% ± 28%, and DSC was 87% ± 13% with 1 ± 2 FPs per patient. ConclusionMetNet can segment brain metastases across a broad range of metastasis sizes with high sensitivity, low FPs, and high segmentation accuracy in postcontrast T1-weighted MRI, potentially aiding treatment planning for SRS.

Ferumoxytol Is Not Retained in Kidney Allografts in Patients Undergoing Acute Rejection.

To evaluate whether ultrasmall superparamagnetic iron oxide nanoparticle (USPIO)-enhanced magnetic resonance imaging (MRI) can detect allograft rejection in pediatric kidney transplant patients. The USPIO ferumoxytol has a long blood half-life and is phagocytosed by macrophages. In an IRB-approved single-center prospective clinical trial, 26 pediatric patients and adolescents (age 10-26years) with acute allograft rejection (n=5), non-rejecting allografts (n=13), and normal native kidneys (n=8) underwent multi-echo T2* fast spoiled gradient-echo (FSPGR) MRI after intravenous injection (p.i.) of 5mg Fe/kg ferumoxytol. T2* relaxation times at 4h p.i. (perfusion phase) and more than 20h p.i. (macrophage phase) were compared with biopsy results. The presence of rejection was assessed using the Banff criteria, and the prevalence of macrophages on CD163 immunostains was determined based on a semi-quantitative scoring system. MRI and histology data were compared among patient groups using t tests, analysis of variance, and regression analyses with a significance threshold of p<0.05. At 4h p.i., mean T2* values were 6.6±1.5ms for native kidneys and 3.9ms for one allograft undergoing acute immune rejection. Surprisingly, at 20-24h p.i., one rejecting allograft showed significantly prolonged T2* relaxation times (37.0ms) compared to native kidneys (6.3±1.7ms) and non-rejecting allografts (7.6±0.1ms). Likewise, three additional rejecting allografts showed significantly prolonged T2* relaxation times compared to non-rejecting allografts at later post-contrast time points, 25-97h p.i. (p=0.008). Histological analysis revealed edema and compressed microvessels in biopsies of rejecting allografts. Allografts with and without rejection showed insignificant differences in macrophage content on histopathology (p=0.44). After ferumoxytol administration, renal allografts undergoing acute rejection show prolonged T2* values compared to non-rejecting allografts. Since histology revealed no significant differences in macrophage content, the increasing T2* value is likely due to the combined effect of reduced perfusion and increased edema in rejecting allografts.

Effect of r1 and r2 relaxivity of gadolinium‐based contrast agents on the T1‐weighted MR signal at increasing magnetic field strengths

Most contrast agents for magnetic resonance imaging (MRI) are gadolinium-based T₁ shortening agents. At increasing magnetic field strengths their r1 relaxivity tends to decrease while the r₂ relaxivity increases. In parallel, at high fields the tissue T1 times increase and may mitigate the loss in contrast enhancement in T₁-weighted images owing to improved background suppression. In the present work we explored the MR signal for T₁-weighted spoiled gradient echo MRI sequences by simulations at three magnetic field strengths: 3, 7 and 9.4 T. The maximal available contrast enhancement (maxCE) was evaluated in absolute terms with the purpose of assessing how much of the full, underlying magnetization can be exploited, for a wide range of compound properties (r₁, 2-45 mM⁻¹ s⁻¹ ; r₂ /r₁, 1.2-30). Despite the theoretically predicted loss in r1 relaxivity at high fields, the same maxCE can be obtained as at low fields if the r₂ /r₁ ratio remains unchanged, albeit at the cost of a longer sequence repetition time and 1.5-2 times higher administered doses. For a fixed maximum tissue concentration, there is an optimum field-dependent value for the r1 relaxivity that yields the greatest maxCE. If the upper bound for the gadolinium concentration is 2 mM, the greatest maxCE is found for compounds with a r₂/r₁ ratio of 1.2 and an r₁ relaxivity of 20.5 mM⁻¹ s⁻¹ at 3 T, 18 mM⁻¹ s⁻¹ at 7 T and 16.5 mM⁻¹ s⁻¹ at 9.4 T. For compounds that do not change their r1 relaxivity or r₂ /r₁ ratios, the necessary dose can be reduced by 10-15% owing to the improved background suppression at higher fields.

Magnetic resonance imaging-guided focused ultrasound surgery for symptomatic uterine fibroids: estimation of treatment efficacy using thermal dose calculations

ObjectiveTo study the correlation between the predicted thermal dose volume (TDV) and the actual ablation volumes in MR-guided focused ultrasound surgery (MRgFUS) for symptomatic uterine fibroids, and to follow up the outcome for 12 months post-treatment. Study designPhase-difference fast spoiled gradient-echo MR images were used to analyze thermal change during the energy deliveries of MRgFUS in 60 consecutive patients treated for symptomatic uterine fibroids. The TDV obtained through analysis of these MR images was compared with the non-perfused volume (NPV) measured on post-treatment contrast enhanced T1-weighted images. Final values of TDV ratio and NPV ratio were obtained by dividing these values by original fibroid volume. Patients were followed for 12 months post-treatment to assess symptomatic relief using the symptom severity score (SSS). ResultsTreatments in which we managed to reach a TDV ratio larger than 27% of the treated fibroid yielded a ratio of NPV to TDV of 1.1±0.5, indicating accurate control of the non-invasive procedure. Patient symptoms, as measured by the SSS, continuously decreased from a mean baseline score of 50±22 to 19±12 (P<0.0001) 12 months post-treatment. ConclusionsAt large treatment volumes (exceeding 27% TDV ratio), thermal dose estimates correspond very closely to non-perfused volumes measured immediately post treatment. These large treatment volumes result in continuous clinical improvement throughout the first 12 months after MRgFUS.

Repeated Delayed Onset Cerebellar Radiation Injuries After Linear Accelerator-Based Stereotactic Radiosurgery for Vestibular Schwannoma

A 63-year-old woman presented with right hearing disturbance and vertigo. Magnetic resonance (MR) imaging revealed the presence of right vestibular schwannoma (VS). Stereotactic radiosurgery (SRS) was performed with a tumor marginal dose of 14 Gy using two isocenters. She was followed up clinically and neuroradiologically using three-dimensional spoiled gradient-echo MR imaging. She experienced temporal neurological deterioration due to peritumoral edema in her right cerebellar peduncle and pons for a few months beginning 1.5 years after SRS, when she experienced transient right facial dysesthesia and hearing deterioration. Ten years after SRS, the patient presented with sudden onset of vertigo, gait disturbance, diplopia, dysarthria, and nausea. MR imaging demonstrated a new lesion in the right cerebellar peduncle, which was diagnosed as radiation-induced stroke. The patient was followed up conservatively and her symptoms disappeared within a few months. Multiple delayed onset radiation injuries are possible sequelae of SRS for VS.

Fiducial Registration With Spoiled Gradient-Echo Magnetic Resonance Imaging Enhances the Accuracy of Subthalamic Nucleus Targeting

A variety of imaging strategies may be used to derive reliable stereotactic coordinates when performing deep brain stimulation lead implants. No single technique has yet proved optimal. To compare the relative accuracy of stereotactic coordinates for the subthalamic nucleus (STN) derived either from fast spin echo/inversion recovery (FSE/IR) magnetic resonance imaging MRI alone (group 1) or FSE/IR in conjunction with T1-weighted spoiled gradient-echo MRI (group 2). A retrospective analysis of 145 consecutive STN deep brain stimulation lead placements (group 1, n = 72; group 2, n = 73) was performed in 81 Parkinson disease patients by 1 surgical team. From the operative reports, we recorded the number of microelectrode recording trajectories required to localize the desired STN target and the span of STN traversed along the implantation trajectory. In addition, we calculated the 3-dimensional vector difference between the initial MRI-derived coordinates and the final physiologically refined coordinates. The proportion of implants completed with just 1 microelectrode recording trajectory was greater (81% vs 58%; P < .001) and the 3-dimensional vector difference between the anatomically selected target and the microelectrode recording-refined target was smaller (0.6 ± 1.2 vs 0.9 ± 1.3; P = .04) in group 2 than in group 1. At the same time, the mean expanse of STN recorded along the implantation trajectory was 8% greater in group 2 (4.8 ± 0.6 vs 5.2 ± 0.6 mm; P < .001). A combination of stereotactic FSE/IR and spoiled gradient-echo MRI yields more accurate coordinates for the STN than FSE/IR MRI alone.

Exact algebraization of the signal equation of spoiled gradient echo MRI

The Ernst equation for Fourier transform nuclear magnetic resonance (MR) describes the spoiled steady-state signal created by periodic partial excitation. In MR imaging (MRI), it is commonly applied to spoiled gradient-echo acquisition in the steady state, created by a small flip angle α at a repetition time TR much shorter than the longitudinal relaxation time T1. We describe two parameter transformations of α and TR/T1, which render the Ernst equation as a low-order rational function. Computer algebra can be readily applied for analytically solving protocol optimization, as shown for the dual flip angle experiment. These transformations are based on the half-angle tangent substitution and its hyperbolic analogue. They are monotonic and approach identity for small α and small TR/T1 with a third-order error. Thus, the exact algebraization can be readily applied to fast gradient echo MRI to yield a rational approximation in α and TR/T1. This reveals a fundamental relationship between the square of the flip angle and TR/T1 which characterizes the Ernst angle, constant degree of T1-weighting and the influence of the local radio-frequency field.

Multimodal Localization of Electrodes in Deep Brain Stimulation: Comparison of Stereotactic CT and MRI with Teleradiography

Objective: In cross-sectional imaging, like CT or MRI, electrodes for deep brain stimulation are visualized by an artifact, which can differ from the real physical size of the electrode and even have an asymmetric appearance on MRI. The accuracy of such artifact-based estimation of the real position of the electrode using CT or MRI is investigated here. Stereotactic teleradiography was used as the gold standard. Methods: Twenty-three patients with implanted electrodes in the subthalamic nucleus (DBS type 3389; Medtronic, Minneapolis, Minn., USA) were included in a retrospective study on multimodal estimation of electrode position by 2 raters. Short spoiled gradient echo MRI (n = 10) and multi-row CT (n = 13) data were compared with teleradiography. Results: Mean radial differences between CT and X-ray for both raters were 0.6 ± 0.2 and 0.7 ± 0.3 mm, with maximum values of 1.0 and 1.2 mm, respectively. Both raters showed quite similar assessments in their ratings. Mean radial differences between MRI and X-ray were 1.2 ± 0.4 and 1.1 ± 0.4 mm, with maximum values of 1.7 and 2.2 mm. Concordance of the assessment was lower compared to CT. Conclusion: Spoiled gradient echo MR imaging cannot be recommended for visual localization of the quadripolar macroelectrode type 3389 from Medtronic. In contrast, CT imaging in absolute terms and with quite similar assessments by both raters is intra- and postoperatively a satisfactory alternative to teleradiography.

Osteochondral Lesions of the Talus

Background: Conventional magnetic resonance imaging (MRI) has been demonstrated to be a valuable tool in diagnosing osteochondral lesions of the talus. No previous study, to our knowledge, has evaluated the diagnostic ability of fat-suppressed fast spoiled gradient-echo (FSPGR) MRI in osteochondral lesions of the talus. We sought to compare three-dimensional fat-suppressed FSPGR MRI with conventional MRI in diagnosing osteochondral lesions of the talus. Methods: Thirty-two consecutive patients with clinically suspected cartilage lesions undergoing three-dimensional fat-suppressed FSPGR MRI and conventional MRI were assessed. Sensitivity, specificity, and accuracy of diagnosis were determined using arthroscopic findings as the standard of reference for the different imaging techniques. The location of the lesion on the talar dome was recorded on a nine-zone anatomical grid on MRIs. Results: Arthroscopy revealed 21 patients with hyaline cartilage defects and 11 with normal ankle joints. The sensitivity, specificity, and accuracy of the two methods for detecting articular cartilage defect were 62%, 100%, and 75%, respectively, for conventional MRI and 91%, 100%, and 94% for three-dimensional fat-suppressed FSPGR MRI. Sensitivity and accuracy were significantly higher for FSPGR imaging than for conventional MRI (P &lt; .05), but there was no difference in specificity between these two methods. According to the nine-zone anatomical grid, the area most frequently involved was the middle of the medial talar dome (16 lesions, 76%). Conclusions: T1-weighted three-dimensional fat-suppressed FSPGR MRI is more sensitive than is conventional MRI in detecting defects of articular cartilage covering osteochondral lesions of the talus. (J Am Podiatr Med Assoc 100(3): 189–194, 2010)

18F-FDG-PET and MRI in patients with malignancies of the liver and pancreas

Summary Purpose: To evaluate the accuracy of retrospective rigid image registration and fusion between F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) of the upper abdomen. Patients, material, methods: Image fusion of PET and MRI was performed in 30 patients with suspected malignancy of the liver or pancreas. Using a commercially available image fusion tool capable of rigid manual point-based registration, PET-Images were retrospectively registered and fused by matching eight homologous points in the 3D spoiled gradient echo (GRE) MRI sequences acquired in portal venous phase and in the CT-component of PET/CT. Two separate observers (R1, R2) assessed accuracy of image registration by determining the distances in the x-, y- and z-axis as well as the absolute distance between anatomical landmarks which differed from the landmarks chosen for registration. Quality of fusion was graded using a three point grading scale (1 poorly fused; 2 satisfactory fused; 3 correctly fused) and compared to hybrid PET/CT fusion. Results: Mean time of registration per patient was less than 2 minutes. Objective registration assessment showed errors between 2.4–6.3 mm in x-axis: mean 3.6 mm (R1); 4.6 mm (R2), 2.3–9.3 mm in y-axis (mean 5.1 mm; 5.5 mm) and 3.3–12.0 mm in z-axis (mean 5.9 mm; 5.9 mm.) The mean error in absolute distance between points was 6.0–16.8 mm (mean 9.9 mm; 10.6 mm). In visual assessment, most fusions were graded to be satisfactory or correctly fused: R1, R2: grade 3, 11/30 (36.7%), 22/30 (73.3%); grade 2, 13/30 (43.3%), 8/30 (26.7%); grade 1, 6/30 (20%), 0/30 (0%). Fusions were mostly comparable to hybrid PET/ CT fusions. All of the fusions were defined as diagnostically relevant by both observers. Conclusion: Retrospective rigid image fusion of FDGPET and MRI of the upper abdomen using the CT-component of PET/CT for registration is feasible without adaptation in image acquisition protocols and shows sub-centimeter registration errors in most cases.

Prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects—a 3.0 T magnetic resonance imaging study

To determine the prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects. To compare the diagnostic performance of cartilage-dedicated magnetic resonance imaging (MRI) sequences at 3.0 T. Ten marathon runners underwent 3.0 T MRI 2-3 days before and after competition. Twelve physically active asymptomatic subjects not performing long-distance running were examined as controls. Pathologic condition was assessed with the whole-organ magnetic resonance imaging score (WORMS). Cartilage abnormalities and bone marrow edema pattern (BMEP) were quantified. Visualization of cartilage pathology was assessed with intermediate-weighted fast spin-echo (IM-w FSE), fast imaging employing steady-state acquisition (FIESTA) and T1-weighted three-dimensional (3D) high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) MRI sequences. Eight of ten marathon runners and 7/12 controls showed knee abnormality. Slightly more and larger cartilage abnormalities, and BMEP, in marathon runners yielded higher but not significantly different WORMS (P > 0.05) than in controls. Running a single marathon did not alter MR findings substantially. Cartilage abnormalities were best visualized with IM-w FSE images (P < 0.05). A high prevalence of knee abnormalities was found in marathon runners and also in active subjects participating in other recreational sports. IM-w FSE sequences delineated more cartilage MR imaging abnormalities than did FIESTA and SPGR sequences.

Effect of Raloxifene on Mammographic Density and Breast Magnetic Resonance Imaging in Premenopausal Women at Increased Risk for Breast Cancer

Mammographic density is a risk factor for breast cancer. Mammographic density and breast magnetic resonance imaging (MRI) volume (MRIV) assess the amount of fibroglandular tissue in the breast. Mammographic density and MRIV can be modulated with hormonal interventions, suggesting that these imaging modalities may be useful as surrogate endpoint biomarkers for breast cancer chemoprevention trials. We evaluated the effect of raloxifene on mammographic density and MRIV in premenopausal women at increased risk for breast cancer. Mammograms and MRI were obtained at baseline and after 1 and 2 years of 60 mg raloxifene by mouth daily for 27 premenopausal women. Mammographic percent dense area was calculated using a semiquantitative thresholding technique. T(1)-weighted spoiled gradient-echo MRI with fat suppression was used to determine breast MRIV using a semiautomatic method. Mean change in mammographic density and median change in MRIV were assessed by the Wilcoxon signed-rank test. No significant change in mammographic density was seen after treatment with raloxifene. Mean change after 1 year was 1% [95% confidence interval (95% CI), -3 to +5] and after 2 years was 1% (95% CI, -2 to +5). MRIV decreased on raloxifene. Median relative change in MRIV after 1 year was -17% (95% CI, -28 to -9; P = 0.0017) and after 2 years was -16% (95% CI, -31 to -4; P = 0.0004). In high-risk premenopausal women, mammographic density did not change on raloxifene, whereas MRIV significantly declined. Our findings suggest that MRIV is a promising surrogate biomarker in premenopausal women at increased risk for breast cancer and should be investigated further in breast cancer prevention trials.

Accuracy and reliability of MRI vs. laboratory measurements in an ex vivo porcine model of arthritic cartilage loss

To quantify the accuracy of magnetic resonance imaging (MRI) measurement of change in cartilage volume due to thin linear excisions, simulating arthritic cartilage losses, by comparison with laboratory volume measurements in an ex vivo porcine model. We scanned 15 porcine patellae by T1-weighted spoiled gradient echo (SPGR) MRI at baseline and after excision of up to three thin layers of articular cartilage. Excised fragment volume was determined from density and weight. Postexcision scans were "fused" to the baseline scan by three-dimensional (3D) registration. This allowed automated recalculation of the remaining cartilage volume within a baseline region of interest (ROI) following each excision. We compared MRI estimates of change in cartilage volume to direct laboratory measurement of fragment volume. Our 38 excised fragments averaged 0.16 mL, or approximately 7% of cartilage volume. MRI and laboratory estimates of total cartilage volume loss differed by 1.6% +/- 13.2% (mean, coefficient of variation [CV]). Accuracy was +/-0.1 mL for 95% of scans. MRI estimates of small changes in porcine patellar cartilage volume were unbiased, reliable, and accurate to 0.1 mL. Despite a proportionately high error in the very thin fragments tested, achievement of similar accuracy in vivo would be adequate to detect approximately two years of osteoarthritic cartilage loss.

Angiographically occult spinal dural arteriovenous fistula located using selective computed tomography angiography

Spinal dural arteriovenous fistula (DAVF) is the most common type of spinal arteriovenous malformation and may cause progressive myelopathy but is usually treatable in the early stages by direct surgery or intravascular embolization. Selective spinal angiography has been the gold standard for diagnosis, but angiographically occult DAVF is not uncommon. A 67-year-old man presented with a 2-year history of progressive paraparesis. Magnetic resonance (MR) imaging demonstrated segmental atrophy of the spinal cord and dilated coronary veins on the dorsal surface of the spinal cord. A DAVF was suspected, but repeated selective angiography failed to demonstrate the fistula. Findings from spoiled gradient echo MR imaging suggested that the draining vein flowed into the dilated venous plexus at the T-9 level. Selective computed tomography (CT) angiography of the right T-9 intercostal artery confirmed the location of the fistula. The authors successfully occluded the draining vein through surgery, and they observed that the fistula was low flow. The patient exhibited improvement in his symptoms, and postoperative MR imaging confirmed closure of the fistula. Selective CT angiography is useful in locating the draining vein of angiographically occult DAVF and therefore minimizing the extent of the surgical procedure.

Supratentorial Low-Grade Glioma Resectability: Statistical Predictive Analysis Based on Anatomic MR Features and Tumor Characteristics

To retrospectively assess the main variables that affect the complete magnetic resonance (MR) imaging-guided resection of supratentorial low-grade gliomas. Institutional review board approval was obtained for this retrospective HIPAA-compliant study, with the requirement for informed consent waived. Data from 101 patients (61 men, 40 women; mean age, 39 years; age range, 18-72 years) who had nonenhancing supratentorial mass lesions that were histopathologically diagnosed as low-grade (World Health Organization grade II) gliomas and consecutively underwent surgery with intraoperative MR imaging guidance were analyzed. There were 21 low-grade astrocytomas, 64 oligodendrogliomas, and 16 mixed oligoastrocytomas. Initial and residual tumor volumes were measured on intraoperative T2-weighted MR images and three-dimensional spoiled gradient-echo MR images. The anatomic relationships between the tumor and eloquent cortical and/or subcortical regions and the influence of these relationships on the extent of resection were analyzed on the basis of preoperative MR imaging findings. Summary measures, univariate Fisher exact test and t test, and multivariate logistic regression analyses were performed. Tumor volume ranged from 2.7-231.0 mL. Univariate analyses revealed the following tumor characteristics to be significant predictive variables of incomplete tumor resection: diffuse tumor margin on T2-weighted MR images, oligodendroglioma or oligoastrocytoma histopathologic type, and large tumor volume (P < .05 for all). Tumor involvement of the following structures was associated with incomplete resection: corpus callosum, corticospinal tract, insular lobe, middle cerebral artery, motor cortex, optic radiation, visual cortex, and basal ganglia (P < .05 for all). Multivariate analyses revealed that incomplete tumor resection was due to tumor involvement of the corticospinal tract (P < .01), large tumor volume (P < .01), and oligodendroglioma histopathologic type (P = .02). The main variables associated with incomplete tumor resection in 101 patients were identified by using statistical predictive analyses.

Comparison of the diagnostic performance of FDG-PET and VBM-MRI in very mild Alzheimer’s disease

The aim of this study was to compare the diagnostic performance of( 18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and voxel-based morphometry (VBM) on magnetic resonance imaging (MRI) in the same group of patients with very mild Alzheimer's disease (AD). Thirty patients with very mild AD (age 67.0+/-5.8 years; MMSE score 25.5+/-1.2, range 24-28), 32 patients with mild AD (age 67.0+/-4.5 years, MMSE score 22.1+/-0.8, range 21-23) and 60 age- and sex-matched normal volunteers underwent both FDG-PET and three-dimensional spoiled gradient echo MRI. Statistical parametric mapping was used to conduct voxel by voxel analysis and Z score mapping. First, the region of interest (ROI) maps of significant reductions in glucose metabolism and grey matter density in the mild AD patients were defined. Secondly, analysis of receiver operating characteristic (ROC) curves for Z scores in the ROI maps discriminating very mild AD patients and normal controls was performed. In mild AD patients, FDG-PET indicated significant reductions in glucose metabolism in the bilateral posterior cingulate gyri and the right parietotemporal area, while VBM analysis showed a significant decrease in grey matter volume density in the bilateral amygdala/hippocampus complex, compared with the normal control group. ROC analysis showed that in very mild AD patients the accuracy of FDG-PET diagnosis was 89% and that of VBM-MRI diagnosis was 83%. The accuracy of the combination of FDG-PET and VBM-MRI diagnosis was 94%. In very mild AD, both FDG-PET and VBM-MRI had high accuracy for diagnosis, but FDG-PET showed slightly higher accuracy than VBM-MRI. Combination of the two techniques will yield a higher diagnostic accuracy in very mild AD by making full use of functional and morphological images.

Magnetic Targeting of Magnetoliposomes to Solid Tumors with MR Imaging Monitoring in Mice: Feasibility

To establish the feasibility of magnetoliposome tumor targeting with an extracorporeal magnet. Animal experiments were performed in compliance with Institut National de la Santé Et de la Recherche Médicale animal protection guidelines and were approved by local government authorities. Magnetophoresis was used to measure the velocity of magnetoliposomes constituted of polyethylene glycol-lipids and anionic maghemite nanocrystals in a calibrated magnetic field in vitro. For in vivo studies, 38 male Swiss nude mice bearing a PC3 human prostate carcinoma tumor in each flank received an intravenous injection of magnetoliposomes (n = 27), saline (n = 9), or nonencapsulated superparamagnetic particles (n = 2) after a small magnet with a magnetic field of 0.3 T and a field gradient of 11 T/m was fixed to the skin above one tumor. The animals were examined at magnetic resonance (MR) imaging with eight different sequences, iron doses (13 mice), and magnet-application durations (12 mice). Their excised tumors were then stained with Perls Prussian blue and hematoxylin-eosin and were examined histologically. With use of the paired Student t test, signal intensity, tumor surface enhancement, and number of stained cells were compared between the control and magnet-exposed tumors to determine significant differences (P </= .01). The mean magnetoliposome velocity ranged from 10 to 40 mum/sec when the magnetic field equaled 0.13 T and the field gradient equaled 25 T/m. At T1-weighted three-dimensional spoiled gradient-echo MR imaging in vivo, the tumor exposed to the magnet showed strong negative enhancement, -52%, compared with the -7% enhancement of the other tumor. Maximal enhancement occurred after 3 hours of magnet application. After 24 hours of magnet application, intracapillary iron particle accumulation was observed in the targeted tumors only. Magnetic targeting of sterically stabilized magnetoliposomes after they are intravenously injected is feasible in vivo.