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Bladder cancer
Published in Anju Sahdev, Sarah J. Vinnicombe, Husband & Reznek's Imaging in Oncology, 2020
Several different imaging sequences and imaging planes can be used for bladder imaging. Standard sequences include images with T1-weighted (T1W) and T2-weighted (T2W) sequences. For T1W sequences, conventional two-dimensional spin-echo, fast (turbo) spin-echo, or three-dimensional gradient-echo imaging can be used (e.g. three-dimensional magnetization-prepared rapid gradient-echo (MP-RAGE)). The two-dimensional spin-echo sequences have high spatial and contrast resolution with higher signal-to-noise ratio than other sequences, such as gradient-echo MRI and are preferred for anatomical delineation. However, they have relatively long acquisition times whilst fast (turbo) spin-echo sequences allow the whole pelvis to be imaged in under 5 minutes. Gradient-echo images (two- and three-dimensional) have much shorter acquisition times and three-dimensional imaging has the advantage that reconstructions can be obtained in any plane during postprocessing. Using three-dimensional imaging combined with dynamic IV contrast enhancement, Barentsz et al. (57) reported an improved staging accuracy compared with conventional two-dimensional spin-echo sequences.
Biomedical Imaging Magnetic Resonance Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
Following an excitation RF pulse that produces an FID signal, if a gradient is turned on for a fixed amount of time, then a phase dispersion will be produced across the object due to the spatially dependent frequency variation given by Eq. [8] (Fig. 6a). Such phase dispersion causes the signal to decay rapidly, essentially crushing out the signal when the gradient is sufficiently large and/or the duration sufficiently long. After the initial phase dispersion, if the gradient reverses its polarity, then an opposite phase dispersion is introduced (Fig. 6b). When the reversed gradient causes the same amount of phase “dispersion” as the previous gradient, the net phase dispersion becomes zero, resulting in a strong signal which is known as a gradient echo (Figs. 6c and 6d). Although the gradient echo illustrated in Fig. 6 arises from an FID signal, they can also be formed by utilizing a spin echo. Unlike spin echo which removes dephasing caused by magnetic field inhomogeneities, gradient echo contains the effects of magnetic field inhomogeneities, and thus is sensitive to relaxation.
Cardiovascular Imaging for Early Detection of Coronary Artery Disease
Published in Ayman El-Baz, Jasjit S. Suri, Cardiovascular Imaging and Image Analysis, 2018
Giorgos Papanastasiou, George Markousis-Mavrogenis, Sophie I. Mavrogeni
Bypass grafts can be also assessed very well by CMRA, because they are relatively immobile and have larger diameter compared to native coronary arteries. Different imaging protocols have been already used, including spin echo [112–115] (9–12) and gradient echo techniques. The application of contrast agents for better imaging of the blood signal [116, 117] (13, 14) increased the sensitivity to 95%. However, metallic clips in grafts constitute the common limitation of coronary bypass MRA. CMRA can be used at some special centers to detect lesions in bypass grafts [107] (4).
Imaging features of hepatobiliary MRI and the risk of hepatocellular carcinoma development
Published in Scandinavian Journal of Gastroenterology, 2022
Jong-In Chang, Dong Hyun Sinn, Woo Kyoung Jeong, Jeong Ah Hwang, Ho Young Won, Kyunga Kim, Wonseok Kang, Geum-Youn Gwak, Yong-Han Paik, Moon Seok Choi, Joon Hyeok Lee, Kwang Cheol Koh, Seung-Woon Paik
All MR images were acquired using 3.0-T whole-body MRI systems (Achieva TX and Ingenia CX; Philips Healthcare, Best, The Netherlands) with a 32-channel phased-array receiver coil. The MRI examination included dual-echo spoiled 3-D gradient-echo T1-weighted in-phase and opposed phase images, single-shot and multi-shot turbo spin-echo T2-weighted images, and diffusion-weighted imaging with single-shot echo-planar images at b-values of 0, 100 or 800 s/mm2. For gadoxetic acid-enhanced imaging (Primovist, Eovist; Bayer Schering Pharma, Berlin, Germany), unenhanced, arterial phase (20–35 s; with an MR fluoroscopic bolus detection technique), portal venous phase (60 s), delayed phase (3 min) and 20-minute HBP images were obtained using a T1-weighted 3D gradient-echo sequence (THRIVE, Philips Healthcare, Best, The Netherlands). The contrast agent was administered intravenously at a rate of 1–2 mL/s for a total dose of 0.025 mmol/kg body weight, followed by a 20-mL saline flush. DWI with b-values of 0, 100 and 800 s/mm2 were acquired simultaneously. An apparent diffusion coefficient (ADC) map was generated from b values of 0 and 800 s/mm2 (Supplementary Table 1).
What is the potential of paramagnetic rim lesions as diagnostic indicators in multiple sclerosis?
Published in Expert Review of Neurotherapeutics, 2022
Maria Sofia Martire, Lucia Moiola, Maria Assunta Rocca, Massimo Filippi, Martina Absinta
Susceptibility-based MRI is exquisitely sensitive to magnetic properties of the tissue allowing the assessment of the tissue microstructure as well as iron content (i.e. iron-laden microglia of chronic active MS lesions). To date, different susceptibility-based imaging acquisition and post-processing methods have been applied for the detection of PRL. First, 2D T2*-weighted single gradient echo (GRE) or multi-echo gradient echo (ME-GRE) was used on 7 T MRI studies; later on, submillimetric segmented (multi-shot) echo-planar imaging (EPI) sequence [27] providing both magnitude and phase 3D images was applied at 3 T (Figure 1A). Using these sequences, PRL can be seen on magnitude images, however, with much less sensitivity than on phase images. Different post-processing techniques such as filtered unwrapped phase, susceptibility-weighted imaging (SWI), which can combine magnitude and phase contrast, and quantitative susceptibility mapping (QSM), which is a quantitative technique used to measure brain magnetic susceptibility [13,45], are commonly used to visualize PRL in research studies. Of note, QSM algorithms can remove dipole and other susceptibility artifacts more efficiently than other postprocessing techniques. Among these approaches, SWI is often utilized in clinical practice for brain bleeding detection and could foster a prompt use of PRL as a diagnostic biomarker.
Quantitative evaluation of liver function with gadoxetic acid enhanced MRI: Comparison among signal intensity-, T1-relaxometry-, and dynamic-hepatocyte-specific-contrast-enhanced MRI- derived parameters
Published in Scandinavian Journal of Gastroenterology, 2022
Qiang Wang, Savas Kesen, Maria Liljeroth, Henrik Nilsson, Ying Zhao, Ernesto Sparrelid, Torkel B. Brismar
MR examinations were performed on a 1.5 T scanner (Intera; Philips Medical Systems, Best, Netherlands), with a Philips four-channel body coil (sensitivity encoding, SENSE). A T1 weighted three-dimensional spoiled gradient-echo sequence was used for dynamic contrast-enhanced liver MR imaging acquisition (scanning parameters: repetition time, 4.1 ms; echo time, 2.0 ms; flip angle 10°; field of view, 415 mm; acquisition matrix resolution, 192 × 192; reconstruction matrix, 256*256; 40 slices, slice thickness, 10 mm; overlap, 5 mm; SENSE factor R, 2). Each volume was imaged in a single breath-hold (12 s scan time per volume) and the subjects were instructed to hold their breath at the same depth during every acquisition. Gadoxetic acid (Gd-EOB-DTPA, Primovist®, Bayer Healthcare, Berlin, 0.25 mmol · ml−1, 0.1 ml per kg body weight) was injected via the anterior cubital vein at an infusion rate of 2 ml s−1 achieved by a power injector. An additional bolus of 20 ml saline was flushed at the same rate immediately after the contrast agent injection. Images were obtained three times before contrast agent injection and then followed by repetitive sampling with a step-wise increase in sampling intervals up to a total sampling time of 45 min.