MR renography: An algorithm for calculation and correction of cortical volume averaging in medullary renographs
Jacobus A. de PriesterJacques A. den BoerEelco L.W. GieleMaarten H. L. ChristiaansAlphons G.H. KesselsArie HasmanJoseph M. A. van Engelshoven
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Abstract:
We evaluated a mathematical algorithm for the generation of medullary signal from raw dynamic magnetic resonance (MR) data. Five healthy volunteers were studied. MR examination consisted of a run of 100 T1-weighted coronal scans (gradient echo; TR/TE 11/3.4 msec, flip angle 60°; slice thickness 6 mm; temporal resolution 2 seconds). Gadolinium-diethylene triamine pentaacetic acid (DTPA; 0.05 mmol/kg) was injected with an injector pump (5 ml/sec). Medullary MR renographs (MRRs) were calculated for regions of interest with strong and moderate cortical volume averaging (CVA). A reference medullary MRR, devoid of CVA, was obtained. Percentual signal differences between calculated and reference medullary MRRs were estimated for each consecutive scan. Run averaged values of these differences were calculated. Mean values, after subtraction of the resting state signal, were +0.2% (SD 9.7%) and +0.7% (SD 9.0%) for areas with strong and moderate CVA, respectively. We conclude that with this algorithm reliable extraction of medullary MRRs is feasible, providing a unique tool for clinical evaluation of medullary disease. J. Magn. Reson. Imaging 2000;12:453–459. © 2000 Wiley-Liss, Inc.Keywords:
Flip angle
Subtraction
鳥類における骨髄腔内組織たる Medullary bone の消長に伴う形態学的変化を追及した. 検索に用いられた材料は, 雌鶏276例および雄鶏34例である. 鶏においては, 産卵事情が複雑であるので, Medul-lary bone の消長像もまた単純なものではない. 用いられた諸材料に関しては, 全身剖検所見および卵巣の解剖学的所見に, できる限りの注意を払った. これは Medullary bone の消長と諸因子との関係を検討する上に, 重要であることを知った. 大腿骨所見に関しては, Medullary bone 第一次新生像に開始され, 完熱像, 退縮像を経て, Medullary bone 第二次新生像に至るまでの諸組織像を分析抽出した. その間, 異常骨, Medullary bone の E 骨化および E 骨塊(著者仮称), その他, 特徴ある組織所見の記載を試みた. 著者は, Medullary bone に関する組織学的研究により, 一抹の不安をも感ずることなく, Medullary bone が鳥類産卵に関連を有する特異組織であることを, 確信することができた.
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Abstract Background Although the relatively high incidence of coronal fractures in the supracondylar–intercondylar fractures is well established, little is currently known about the morphology of those fractures. Herein, we characterized the coronal fractures in AO/OTA type 33-C3 and assessed their differences with Busch–Hoffa fractures (33-B3). Methods We retrospectively collected 61 cases of AO/OTA type 33-B or C fractures with coronal plane fragments and generated three-dimensional fracture maps of those with coronal fractures based on CT imaging and measured angle α (the angle between the coronal fracture and the posterior condyle axis in the axis plane) and angle β (the angle between the coronal fracture and the posterior femoral cortex in the sagittal plane). Results Thirty-three cases (32%) of AO/OTA type 33-C fractures contained coronal fragments. Most of them were type 33-C3 fractures. Angles α and β for type 33-C3 were significantly smaller than for type B3 at the lateral condyle, while the angles at the medial condyle were not significantly different. The fracture maps showed that the coronal fractures and the articular comminution area were more anterior in type 33-C3. Conclusions The incidence of coronal fractures was 32% and 67% in AO/OTA types 33-C and 33-C3, respectively. Our findings suggest that coronal fractures differed between both types, emphasizing the potential need for different treatment approaches.
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Cardiac MRI may benefit from increased polarization at high magnetic field strength of 3 Tesla but is challenged by increased field inhomogeneity. Initial human studies have shown that the radiofrequency (RF) excitation field (B1+) used for signal excitation in the heart is both inhomogeneous and significantly lower than desired, potentially leading to image artifacts and biased quantitative measures. Recently, multi-channel transmit systems have been introduced allowing localized patient specific RF shimming based on acquired calibration B1+ maps. Some prior human studies have shown lower than desired mean flip angles in the hearts of large patients even after RF shimming. Here, 100 cardiac B1+ map pairs before and after RF shimming were acquired in 55 swine. The mean flip angle and the coefficient of variation (CV) of the flip angle in the heart were determined before and after RF shimming. Mean flip angle, CV, and RF shim values (power ratio and phase difference between the two transmit channels) were tested for correlation with cross sectional body area and the Right-Left/Anterior-Posterior ratio. RF shimming significantly increased the mean flip angle in swine heart from 74.4±6.7% (mean ± standard deviation) to 94.7±4.8% of the desired flip angle and significantly reduced CV from 0.11±0.03 to 0.07±0.02 (p<<1e-10 for both). These results compare well with several previous human studies, except that the mean flip angle in the human heart only improved to 89% with RF shimming, possibly because the RF shimming routine does not consider safety constraints in very large patients. Additionally, mean flip angle decreased and CV increased with larger cross sectional body area, however, the RF shimming parameters did not correlate with cross sectional body area. RF shim power ratio correlated weakly with Right-Left/Anterior-Posterior ratio but phase difference did not, further substantiating the need for subject specific cardiac RF shimming.
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Purpose To improve the visualization of fibrous tissues as tendons, ligaments and fibrocartilage structures as menisci by positive contrast using a new 3D Double Echo Steady State (DESS) sequence. Methods The proposed 3D DESS sequence works with separate acquisition of a first echo with an echo time (TE 1 ) of 1.2 ms followed by a more heavily T 2 ‐weighted second echo recorded at time TE 2 . Subtraction of images from both echoes leads to positive signal from fibrous tissues, whereas in other tissues as musculature and fat the subtraction signal nearly vanishes due to almost similar signal strength in both echoes. Systematic measurements in healthy volunteers with different sets of pulse repetition time (TR), TE 1 , readout bandwidth and flip angle were performed to determine optimal sequence parameters. Results The presented 3D sequence with Cartesian readout requires relatively short measuring time, provides reasonable signal‐to‐noise ratio and can be easily implemented in protocols for clinical musculoskeletal MR imaging. Degenerative changes or tears of tendons, ligaments and fibrocartilage are known to cause increased water content and therefore prolongation of transverse relaxation times, which leads to reduced signal intensities in the “subtraction images.” Conclusion Positive contrast of fibrous tissue as demonstrated by the proposed sub‐DESS approach provides improved conspicuity and allows for three‐dimensional reconstruction especially of structures with curved geometry. Magn Reson Med 71:294–301, 2014. © 2013 Wiley Periodicals, Inc.
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目的: MRIを用いて嚥下機能評価を行うには, 超高速のパルス印加により極短時間で撮像可能なシーケンスが必要であり, steady-state free precession sequences (SSFPシーケンス) が適した撮像方法であると考える, SSFPシーケンスではflip angleの条件により種々の嚥下機能に関連する組織のコントラストやノイズ発生様相が変化し, 嚥下の動的観察における画質に影響する.そこで本研究では, SSFPシーケンスを用いた超高速撮像において, flip angleの条件が, 静止状態における嚥下関連組織の信号強度および視覚評価に及ぼす影響を明らかにし, 嚥下機能評価に適用できる至適flip angleの検討を行った.方法: 顎口腔機能に異常を認めない有歯顎者7名 (平均年齢30.1歳) を被験者とし, 1.5Tesla超伝導MRI装置を用いてSSFPシーケンスにより撮像を行った.撮像条件は, 嚥下運動に対応できることが前提であるため, 繰り返し時間 (repetition time, TR) とエコー時間 (echo time, TE) をいずれも極めて短くした超高速撮像が不可欠であるが, 信号強度の測定精度を向上させる目的で, パルス印加を同条件にして頚部の静止状態を撮像した.本研究では, 撮像にあたり嚥下機能領域のコントラストの可変パラメータであるflip angleを10°から100°まで, 10°間隔の10条件と設定し, この各条件で得られた画像における嚥下関連組織 (軟口蓋, 舌筋, 喉頭蓋, 甲状軟骨, オトガイ舌骨筋, 下顎骨, 舌骨) の信号強度変化および視覚評価の検討を行った.結果: 嚥下関連組織の信号強度はflip angleにより有意に変化した.得られた画像においてコントラストを形成する各嚥下関連組織の信号強度の差が最も多く出現したのは, flip angle10°であり, 次いでflip angle20°, 30°の順に多く, flip angle 40°～100°ではほぼ同数で少なかった.嚥下関連組織の信号雑音比 (signa1-to-noise ratio, SNR) を総じて高い値に維持する条件は, flip angle20°, 30°, 40°であった.視覚評価ではflip angle30°および40°が嚥下関連組織の識別および, 画像の明瞭さの点で優れていた.結論: SSFPシーケンスによる超高速MRIを用いた嚥下関連組織の撮像条件は, 信号強度変化と視覚評価から検討した結果, flip angle 30°が至適撮像条件であり, 嚥下機能評価の動的観察における解剖学的形態描出の明瞭化においても有効であることが示唆された.
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This study investigates the significance of flip angle, an imaging parameter, in enhancing Magnetic Resonance image quality under various imaging conditions. It specifically explores the extent to which the Ernst angle, an optimal flip angle, optimizes image quality under different imaging parameters. The investigation begins with a theoretical derivation of the Ernst angle, assuming steady state imaging conditions. Then multiple studies that examine the effect of flip angle on signal-to-noise ratio (SNR), a key indicator of image quality, in different areas of the human body (blood, liver, and brain), are analysed. The study compares the results of these studies and compares their respective optimal flip angles with the Ernst angle. The findings reveal that flip angle plays a crucial role in enhancing SNR and image quality. However, the Ernst angle only optimizes SNR under steady state conditions and when using a spoiled gradient echo (GRE) sequence. Therefore, further investigations are necessary to determine the optimal flip angle under different imaging conditions to optimize SNR and enhance overall image quality.
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Viewing angle
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Femoral medullary pressures and pulmonary embolization of medullary contents during the insertion of cement and a medullary rod in greyhounds were studied. In three animals, insertion of cement into the femoral shaft resulted in medullary pressures of between 290 and 900 torr and the appearance of medullary contents in the lungs within ten to 120 seconds. In five other animals, pulmonary embolization was not detectable when the rise in femoral medullary pressure was prevented by drilling a hole distal to the cemented area.
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Objective:The effects on treatment of coronal fractures with hydrocylapatite have been evaluated.Methods:Flling with hydrocylapatite cataplasm and coronal coverage were performed after disinfections in 68 cases coronal fractures.Results:in 68 cases after treatment of coronal fractures,52 cases succeed,9 cases normal,7 cases failed.Conclusion:it is a ideal method to treat coronal fractures with filling hydroxylapatie.
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Abstract In order to reduce the RF power deposition of fast spin echo sequences operated at high field strength, the flip angles of the refocusing pulse train are varied from pulse to pulse using a modulated angle refocusing train method. The technique employs high flip angle pulses prior to sampling the center of k ‐space in order to preserve T 2 contrast, low flip angles after sampling the center of k ‐space to reduce power and prolong relaxation, and a smooth transition between the high and low flip angle regimes in order to maintain the pseudosteady‐state, maximizing signal and avoiding artifact‐inducing oscillations. An analytical expression is used to predict and correct for the flip angle dependence of the signal, thus eliminating any deleterious effects of flip angle modulation on the point spread function. Analysis of resolution and SNR were performed in simulation and phantom studies. In human imaging studies, it is shown that RF energy deposition per slice in a single‐shot fast spin echo application can be reduced by up to 75%, making the sequence as practical at 3 T as it is has been at 1.5 T. Magn Reson Med 51:1031–1037, 2004. © 2004 Wiley‐Liss, Inc.
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SIGNAL (programming language)
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Modulation (music)
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The bone marrow is commonly present in the medullary cavity of long bones in most mammals at birth. In the present study, the persistence of the osseous tissue was examined in the medullary cavities of piglet bones at and after birth. Immediately after birth, medullary cavities of long bones were almost completely filled with the spongy bone. The persisted spongy bone, i.e., medullary bone was prominent in younger pigs but decreased with advance in age. By 90 days of age, the medullary bone almost disappeared to form the extended medullary cavity. During the disappearing process of the medullary bone, osteoclasts showed significant increase in size and number (p<0.05). In irregular and flat bones, osseous trabeculae of the medullary bone became slender with age. The extramedullary hematopoiesis in the liver and spleen was very active till 30 days of age. This may suggest that the persistence of the medullary bone narrows the medullary cavity to cause poor medullary hematopoiesis and is compensated by extramedullary hematopoiesis. The relationship among the medullary bone, extramedullary hematopoiesis and piglet anemia was discussed.
Extramedullary hematopoiesis
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