T1-weighted Spoiled Gradient-echo Images Research Articles

Detection of structural lesions of the sacroiliac joints in patients with spondyloarthritis: A comparison of T1-weighted 3D spoiled gradient echo MRI and MRI-based synthetic CT versus T1-weighted turbo spin echo MRI

ObjectivesTo investigate the detection of erosion, sclerosis and ankylosis using 1 mm 3D T1-weighted spoiled gradient echo (T1w-GRE) MRI and 1 mm MRI-based synthetic CT (sCT), compared with conventional 4 mm T1w-TSE.Materials and methodsProspective, cross-sectional study. Semi-coronal 4 mm T1w-TSE and axial T1w-GRE with 1.6 mm slice thickness and 0.8 mm spacing between overlapping slices were performed. The T1w-GRE images were processed into sCT images using a commercial deep learning algorithm, BoneMRI. Both were reconstructed into 1 mm semi-coronal images. T1w-TSE, T1w-GRE and sCT images were assessed independently by 3 expert and 4 non-expert readers for erosion, sclerosis and ankylosis. Cohen’s kappa for inter-reader agreement, exact McNemar test for lesion frequencies and Wilcoxon signed-rank test for confidence in lesion detection were used.ResultsNineteen patients with axial spondyloarthritis were evaluated. T1w-GRE increased inter-reader agreement for detecting erosion (kappa 0.42 vs 0.21 in non-experts), increased detection of erosion (57 vs 43 of 152 joint quadrants) and sclerosis (26 vs 17 of 152 joint quadrants) among experts, and increased reader confidence for scoring erosion and sclerosis. sCT increased inter-reader agreement for detecting sclerosis (kappa 0.69 vs 0.37 in experts) and ankylosis (0.71 vs 0.52 in non-experts), increased detection of sclerosis (34 vs 17 of 152 joint quadrants) and ankylosis (20 vs 13 of 76 joint halves) among experts, and increased reader confidence for scoring erosion, sclerosis and ankylosis.ConclusionT1w-GRE and sCT increase sensitivity and reader confidence for the detection of erosion, sclerosis and ankylosis, compared with T1w-TSE.Clinical relevance statementThese methods improve the detection of sacroiliac joint structural lesions and might be a useful addition to SIJ MRI protocols both in routine clinical care and as structural outcome measures in clinical trials.

Brain Metastases: Insights from Statistical Modeling of Size Distribution.

Brain metastases are a common finding on brain MRI. However, the factors that dictate their size and distribution are incompletely understood. Our aim was to discover a statistical model that can account for the size distribution of parenchymal metastases in the brain as measured on contrast-enhanced MR imaging. Tumor volumes were calculated on the basis of measured tumor diameters from contrast-enhanced T1-weighted spoiled gradient-echo images in 68 patients with untreated parenchymal metastatic disease. Tumor volumes were then placed in rank-order distributions and compared with 11 different statistical curve types. The resultant R 2 values to assess goodness of fit were calculated. The top 2 distributions were then compared using the likelihood ratio test, with resultant R values demonstrating the relative likelihood of these distributions accounting for the observed data. Thirty-nine of 68 cases best fit a power distribution (mean R 2 = 0.938 ± 0.050), 20 cases best fit an exponential distribution (mean R 2 = 0.957 ± 0.050), and the remaining cases were scattered among the remaining distributions. Likelihood ratio analysis revealed that 66 of 68 cases had a positive mean R value (1.596 ± 1.316), skewing toward a power law distribution. The size distributions of untreated brain metastases favor a power law distribution. This finding suggests that metastases do not exist in isolation, but rather as part of a complex system. Furthermore, these results suggest that there may be a relatively small number of underlying variables that substantially influence the behavior of these systems. The identification of these variables could have a profound effect on our understanding of these lesions and our ability to treat them.

Combined gadoxetic acid and gadobenate dimeglumine enhanced liver MRI: a parameter optimization study.

To demonstrate the feasibility of combined delayed-phase gadoxetic acid (GA) and gadobenate dimeglumine (GD) enhanced liver MRI for improved detection of liver metastases, and to optimize contrast agent dose, timing, and flip angle (FA). Fourteen healthy volunteers underwent liver MRI at 3.0T at two visits during which they received two consecutive injections: 1. GA (Visit1 = 0.025mmol/kg; Visit 2 = 0.05mmol/kg) and 2. GD (both visits = 0.1mmol/kg) 20min after GA administration. Two sub-studies were performed: Experiment-1 Eight subjects underwent multi-phase breath-held 3D-fat-saturated T1-weighted spoiled gradient echo (SGRE) imaging to determine the optimal imaging window for the combined GA + GD protocol to create a homogeneously hyperintense liver and vasculature ("plain-white-liver") with maximum contrast to muscle which served as a surrogate for metastatic lesions in both experiments. Experiment-2 Six subjects underwent breath-held 3D-fat-saturated T1-weighted SGRE imaging at three different FA to determine the optimal FA for best image contrast. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were evaluated. Experiment-1 The combined GA + GD protocol created a homogeneously hyperintense liver and vasculature with maximum CNR liver/muscle at approximately 60-120s after automatic GD-bolus detection. Experiment-2 Flip angles between 25° and 35° at a dose of 0.025mmol/kg GA provided the best combination that minimized liver/vasculature CNR, while maximizing liver/muscle CNR. CNR performance to achieve a "plain-white-liver" was superior with 0.025mmol/kg GA compared to 0.05mmol/kg. Combined GA + GD enhanced T1-weighted MRI is feasible to achieve a homogeneously "plain-white-liver". Future studies need to confirm that this protocol can improve sensitivity of liver lesion detection in patients with metastatic liver disease.

Complementary Roles of Dynamic Contrast-Enhanced MR Imaging and Postcontrast Vessel Wall Imaging in Detecting High-Risk Intracranial Aneurysms.

Individual assessment of the absolute risk of intracranial aneurysm rupture remains challenging. Emerging imaging techniques such as dynamic contrast-enhanced MR imaging and postcontrast vessel wall MR imaging may improve risk estimation by providing new information on aneurysm wall properties. The purpose of this study was to investigate the relationship between aneurysm wall permeability on dynamic contrast-enhanced MR imaging and aneurysm wall enhancement on postcontrast vessel wall MR imaging in unruptured intracranial aneurysms. Patients with unruptured saccular intracranial aneurysms were imaged with vessel wall MR imaging before and after gadolinium contrast administration. Dynamic contrast-enhanced MR imaging was performed coincident with contrast injection using 3D T1-weighted spoiled gradient-echo imaging. The transfer constant (K trans) was measured adjacent to intracranial aneurysm and adjacent to the normal intracranial artery. Twenty-nine subjects were analyzed (mean age, 53.9 ± 13.5 years; 24% men; PHASES score: median, 8; interquartile range, 4.75-10). K trans was higher in intracranial aneurysms compared with the normal intracranial artery (median, 0.0110; interquartile range, 0.0060-0.0390 versus median, 0.0032; interquartile range, 0.0018-0.0048 min-1; P < .001), which correlated with intracranial aneurysm size (Spearman ρ = 0.54, P = .002) and PHASES score (ρ = 0.40, P = .30). Aneurysm wall enhancement, detected in 19 (66%) aneurysms, was associated with intracranial aneurysm size and the PHASES score but not significantly with K trans (P = .30). Aneurysms of 2 of the 9 patients undergoing conservative treatment ruptured during 1-year follow-up. Both ruptured aneurysms had increased K trans, whereas only 1 had aneurysm wall enhancement at baseline. Dynamic contrast-enhanced MR imaging showed increased K trans adjacent to intracranial aneurysms, which was independent of aneurysm wall enhancement on postcontrast vessel wall MR imaging. Increased aneurysm wall permeability on dynamic contrast-enhanced MR imaging provides new information that may be useful in intracranial aneurysm risk assessment.

Contrast-Enhanced Magnetic Resonance Cholangiography: Practical Tips and Clinical Indications for Biliary Disease Management.

Since its introduction, MRCP has been improved over the years due to the introduction of several technical advances and innovations. It consists of a noninvasive method for biliary tree representation, based on heavily T2-weighted images. Conventionally, its protocol includes two-dimensional single-shot fast spin-echo images, acquired with thin sections or with multiple thick slabs. In recent years, three-dimensional T2-weighted fast-recovery fast spin-echo images have been added to the conventional protocol, increasing the possibility of biliary anatomy demonstration and leading to a significant benefit over conventional 2D imaging. A significant innovation has been reached with the introduction of hepatobiliary contrasts, represented by gadoxetic acid and gadobenate dimeglumine: they are excreted into the bile canaliculi, allowing the opacification of the biliary tree. Recently, 3D interpolated T1-weighted spoiled gradient echo images have been proposed for the evaluation of the biliary tree, obtaining images after hepatobiliary contrast agent administration. Thus, the acquisition of these excretory phases improves the diagnostic capability of conventional MRCP—based on T2 acquisitions. In this paper, technical features of contrast-enhanced magnetic resonance cholangiography are briefly discussed; main diagnostic tips of hepatobiliary phase are showed, emphasizing the benefit of enhanced cholangiography in comparison with conventional MRCP.

Mathematical optimization of contrast concentration for T1-weighted spoiled gradient echo imaging.

To develop and validate closed form mathematical expressions that predict the optimal contrast agent concentration for the maximum T1-weighted spoiled gradient echo (SGRE) signal. Gadolinium and iron-based contrast agents can have significant transverse relaxivity that leads to signal dropout with increasing contrast agent concentration. A mathematical expression for the "optimal" contrast agent concentration where recovery of longitudinal magnetization is offset by increasing transverse signal decay was derived. Expressions for the maximum possible SGRE signal were also derived. Three phantoms were constructed, each with varying concentrations of one of the following three agents: gadoteridol, gadobenate dimeglumine, and ferumoxytol. After measuring the longitudinal and transverse relaxivity of the three agents, the SGRE signal was measured in the phantoms over a wide range of flip angles and echo times. Excellent qualitative agreement between the SGRE signal behavior, optimal concentration, and optimal flip angle were observed between experimental measurements and theoretical predictions. This work provides validated mathematical expressions for contrast enhanced T1-weighted SGRE imaging and may provide guidance for contrast dosing and injection protocols, as well as for novel pulse sequence design.

Pelvic magnetic resonance imaging in the ewe: A model for experimental gynecologic research

Our goal was to demonstrate the feasibility of pelvic magnetic resonance imaging (MRI) in the ewe. Two ewes underwent a pelvic 3 Tesla MRI scan, under light anesthesia, with T2-weighted fast spin-echo images and T1-weighted spoiled gradient-echo images. Multiplan T1 weighted images were also obtained after the intravenous injection of a contrast product. One ewe was anestrous and the other one had undergone ovarian stimulation. No incident occurred during the examination. Both the uterus (with two horns) and the ovaries were identified. The intensity of the endometrial, myometrial and ovarian signals was similar to that encountered in women. The uterus and ovaries could be enhanced in both cases. Pelvic vasculature was also studied. In the case of hormonal stimulation, the endometrium was thicker, follicular growth was identified and enhancement seemed greater. MRI in the ewe is feasible and could be helpful in experimental gynecologic research, especially in uterus transplantation.

High signal peripancreatic fat on fat-suppressed spoiled gradient echo imaging in acute pancreatitis: preliminary evaluation of the prognostic significance.

To evaluate peripancreatic signal changes on fat-suppressed T1-weighted spoiled gradient echo images associated with acute pancreatitis and investigate potential utility in regards to relationship to clinical outcome. The abdominal MR images in 31 patients with acute pancreatitis were reviewed, and evaluated for the presence of elevated signal intensity within the peripancreatic fat on fat-suppressed T1-weighted spoiled gradient echo images; the degree of signal changes was graded as mild, moderate, or severe. Ten of 31 patients demonstrated abnormal high signal intensity in the peripancreatic fat on fat-suppressed T1-weighted images. The degree of signal change was mild in three patients, moderate in one, and severe in six patients. All six patients with severe elevated peripancreatic soft tissue signal died within seven to 68 days (mean, 47 days) of their admission. All 21 patients without elevated peripancreatic fat signal survived without any complications. The correlation between the presence and severity of elevated peripancreatic MR signal and patient outcome was significant (P < 0.05). Elevated peripancreatic signal on fat-suppressed T1-weighted images is associated progressively with poor outcome in patients with acute pancreatitis, and may represent a simplified method for prognostic cross-sectional imaging.

Juxtapapillary diverticulum: findings on MRI.

The purpose of our study was to describe the imaging findings of juxtapapillary diverticulum on magnetic resonance imaging (MRI). The MRI and magnetic resonance cholangiopancreatography (MRCP) examinations of 14 patients with juxtapapillary diverticula that were diagnosed on endoscopic retrograde cholangiopancreatography (ERCP) (N = 8) or endoscopy (N = 6) were retrospectively evaluated. T1-weighted spoiled gradient-echo, T2-weighted half Fourier single shot fast spin-echo (HASTE), and T2-weighted True FISP (fast imaging with steady state precession) images and thin-slice MRCP images were obtained on all patients. In five patients, diluted gadolinium DPTA (1/100) was used as an oral contrast. T2-weighted True FISP and HASTE images demonstrated air-fluid levels within all diverticula. Hyperintense oral contrast on T1-weighted spoiled gradient-echo images aided detection of the smaller diverticula. MRCP images obtained in the coronal plane best demonstrated the relationship of the diverticula to the papilla. MRI with the use of HASTE, True FISP, and oral contrast-enhanced T1-weighted sequences was able to depict juxtapapillary diverticula in our series.

Focal hepatic lymphoma: Magnetic resonance demonstration using current techniques including gadolinium enhancement

This study demonstrates the appearance of focal hepatic lymphoma using current magnetic resonance techniques including gadolinium enhancement. Fifteen patients with hepatic lymphoma were imaged at 1.5T. T1-weighted, T2-weighted, immediate, and 5–10-min delayed T1-weighted spoiled gradient echo images were acquired in all patients. Determination was made of lesion size, number, morphology, and signal intensity of lesions on all sequences. Seven patients had solitary lesions and 8 patients had multiple lesions. Focal lesions of hepatic lymphoma ranged in size from 5 mm to 15 cm. They were well defined masses with mild to moderate low signal intensity relative to liver on T1-weighted images. Lymphoma lesions in 6 patients were moderately high in signal intensity on T2-weighted images compared with liver (Type I lesions), and enhancement of lesions was intense on early post-gadolinium images in 5 of these patients. Lymphoma lesions in 6 patients were mildly hypointense to mildly hyperintense on T2-weighted images compared to liver (Type II lesions), and lesions in 5 of these patients enhanced minimally on the early post-gadolinium spoiled gradient echo images. The remaining 3 patients had received chemotherapy before the magnetic resonance examination, and the imaging findings varied reflecting presumed differences in treatment responses. Transient ill defined perilesional enhancement on immediate post-gadolinium spoiled gradient echo images was observed in 9 patients including patients with either type of lesion. Focal lesions of hepatic lymphoma are usually low in signal intensity on T1-weighted images but have variable signal intensity on T2-weighted images. In general, lesions that are mildly hypointense to minimally hyperintense in signal intensity on T2-weighted images enhance minimally, and lesions moderately high in signal intensity on T2-weighted images enhance intensely. Transient increased perilesional enhancement is common.

Laser ablation-induced changes in the prostate: findings at endorectal MR imaging with histologic correlation.

To correlate laser ablation-induced changes in the prostate as depicted at endorectal magnetic resonance (MR) imaging with results at histologic examination. In eight patients with prostate carcinoma, visually guided laser ablation was performed during lymphadenectomy. Radical prostate resection was performed 4-9 days (mean, 6.9 days) after ablation in seven patients and at 70 days in one patient. The study protocol consisted of (a) endorectal T2-weighted fast spin-echo imaging, (b) dynamic T1-weighted spoiled gradient-echo imaging prior to and after injection of contrast material, and (c) gadolinium-enhanced T1-weighted spin-echo imaging. Imaging findings were correlated with macroscopic and histologic findings. Histologic examination revealed periurethral necrosis with a marginal zone that consisted of partially necrotic tissue, dilated vessels, and hemorrhagic areas. Considerable interindividual difference was observed in the extent of morphologic alterations (area, 0-18.0 cm3). Gadolinium-enhanced images were best suited for assessment of laser ablation-induced changes. The correlation between the volume of altered tissue measured on MR images and in macroscopic specimens was excellent (r2 = .96). MR imaging helped monitor changes induced with laser ablation (which differed greatly among individuals). MR monitoring may thus be useful in patients with obstructive benign prostatic hyperplasia after laser ablation.

Small bowel neoplastic disease: demonstration by MRI.

This study demonstrates the appearance of small bowel tumors on MR images. Sixteen patients with tumors involving small bowel were studied by MRI. All tumors were proven with histopathology. Eleven patients had primary tumors of the small bowel, which included the following: four carcinoid tumors, three adenocarcinomas, two lymphomas, one leiomyosarcoma, and one leiomyoma. Five patients had recurrent or metastatic disease to small bowel: two patients had colon cancer, one patient had pancreatic cancer, one patient had uterine leiomyosarcoma, and one patient had chloroma (leukemia). MR examination included breath-hold T1-weighted spoiled gradient echo (all patients), immediate postgadolinium-spoiled gradient echo (10 patients), and 2 to 4 minutes postgadolinium T1-weighted, fat-suppressed images (all patients). Tumor size, local extent, signal intensity, and enhancement features of tumor and adjacent tissue were determined. Tumor ranged in diameter from 1 to 9 cm (mean, 4.0 cm). Tumors had similar signal intensity to normal small bowel on precontrast images. Fourteen malignant tumors showed heterogeneous enhancement greater than adjacent bowel on gadolinium-enhanced images. Tumor local extent was best shown on precontrast-spoiled gradient-echo images and postgadolinium T1-weighted fat-suppressed images. Image quality was most consistent on breath-hold images. The results of this study show that small bowel tumors are demonstrable on MR images. Precontrast breath-hold T1-weighted spoiled gradient-echo images and gadolinium-enhanced fat suppressed images demonstrate tumor extent most reliably.