Dynamic enhancement of upper abdominal organs in normal volunteers with MRI and effects of contrast dose reduction

Background: To quantify enhancement parameters of the upper abdominal organs over time during magnetic resonance (MR) examinations and to evaluate the effect of a dose reduction of contrast medium on these parameters. Methods: Ten volunteers underwent two separate dynamic enhanced MR examinations with 0.1 and 0.075 mmol/kg of contrast medium, respectively. Breath-hold gradient-echo T1-weighted images were acquired every second for 118 s followed by delayed images. The percentages of enhancement, the time to maximum enhancement, and the area under the time-versus-enhancement curve were calculated for each organ. Results: The mean times to maximum percentage of enhancement were less than 25 s for the pancreas, kidneys, and spleen and 50 s for the liver. The mean values of maximum percentage of enhancement for the standard/reduced doses were 72%/62% (pancreas), 165%/155% (kidneys), 114%/87% (spleen), and 67%/53% (liver). This difference was significant when liver enhancement was considered (p= 0.02). In addition, when the areas under the time-versus-enhancement curves were compared, the difference between the standard dose and reduced dose was significant for all organs tested (p < 0.05). Conclusions: Dynamic scanning of the upper abdomen should start early after contrast injection. Injection parameters should be standardized to capture arterial and venous enhancements in liver examinations. A 25% dose reduction did not significantly affect peak enhancement (except for the liver) but did significantly reduce overall enhancement. Received: 8 September 1998/Revision accepted: 13 January 1999     

CT与MRI应用于极外侧型腰椎间盘突出诊断的对比分析

目的 探析CT和MRI方法诊断极外侧型腰椎间盘突出症（FLLDH）的特点和价值.方法 2008年6月至2012年12月湖北医药学院附属东风医院选取经手术证实确诊为FLLDH的患者30例（混合型、内侧型和外侧型分别为12例、6例和12例）,均行CT及MRI两种检查方法,对比两种诊断方式的诊断率和诊断表现.结果 经过观察,CT和MRI对于FLLDH的总体诊断率对比无统计学意义（P＞0.05）,两种诊断方式显示L4,L5的病变均为66.7%.CT显示为各种形态的软组织密度影,MRI显示的病变特征为髓核信号.两种诊断方式的影像学征象对比均无统计学意义（P＞0.05）.结论 CT和MRI对FLLHD的诊断率均较高,两种方法都具有各自的显著诊断特点,对临床医师手术入路具有指导价值.     

Low-field magnetic resonance imaging in the evaluation of mechanical and biological heart valve function

Magnetic resonance imaging (MRI) has been frequently considered unsafe for patients with ferromagnetic implants: risks to be considered include induction of electric current, heating and dislocation of the prosthesis. Previous in vitro and in vivo studies have indicated the possibility of performing MRI examinations on patients with prosthetic heart valves. The aim of our study was to verify the presence of artifacts at the level of the prosthetic heart valve in vivo using a low-field MR unit (0.2 T) and to define the possibility of a functional analysis of the valve in patients with biomedical or mechanical prostheses. We evaluated 14 patients surgically treated for implantation of nine biological and seven mechanical aortic and mitral valves. A low-field MR unit (0.2 T) was employed using cine-MR technique on long- and short-axis view. The images were acquired on planes parallel and perpendicular to the valvular plane. Semiquantitative analysis with double-blind evaluation for definition of the extent of the artifact was performed. Three classes of artifacts were distinguished from minimal to significant. The examinations showed the presence of minimal artifacts in all biological heart valves and moderate artifacts in mechanical valves giving good qualitative data on blood flow near the valve. Analysis of the flow behind the valve showed signs of normal function in 13 prostheses and pathological findings in the remaining three. In these latter cases, MRI was able to define the presence of a pathologic aortic pressure gradient, mitral insufficiency and malpositioning of the mitral valve causing subvalvular turbulence. Nevertheless, we believe that the application of velocity-encoding cine-MR is more promising than semiquantitative analysis of artifacts.     

胸椎黄韧带肥厚的磁共振表现

目的：回顾性总结了８５例胸椎黄韧带肥厚（ＴＬＦ）的ＭＲＩ特征。材料与方法：５５例患者经术后病理证实，余３０例经ＣＴ扫描证实。椎管的狭窄程度根据Ｔ２ＷＩ上硬膜囊和脊髓的受压改变程度分为０～Ⅲ度。结果：８５例ＴＬＦ中，７１．８％合并韧带骨化。７７例患者的１００个病变位于Ｔ９～１２水平，占病例和病变数的９０．６％和６９．０％。ＴＬＦ典型的ＭＲＩ表现为自椎管后缘向前凸的结节状或条带状突起。在Ｔ２ＷＩ上，７８例呈低信号强度，７例呈中等信号，３６个病灶压迫脊髓可见高信号区。在Ｔ１ＷＩ上，３２个低信号病灶内可见中高信号区，５６个病灶显示不清，检出率为５５．８％。３５例（４１．２％）有外伤史，４３例（５０．６％）伴椎间小关节增生硬化。组织学改变为弹力纤维断裂萎缩、胶原纤维增生、脂肪浸润和钙化。结论：ＴＬＦ是引起胸椎椎管狭窄的常见疾病之一，其形成机制可能与外伤引起的椎间小关节增生有关。矢状位Ｔ２ＷＩ可准确显示ＴＬＦ的大小和范围以及脊髓受压程度。     

Bone marrow blood supply in gadolinium-enhanced magnetic resonance imaging

A retrospective study was performed to determine whether bone blood supply can be assessed on gadolinium-enhanced magnetic resonance imaging. Lumbar spine magnetic resonance imaging (MRI) examinations of 49 patients attending for post-laminectomy examination were reviewed (30 male, 19 female, mean age 46.4 years, age range 23–84 years). Each study included sagittal T1-weighted spin echo sequences before and after gadolinium administration. Regions of interest were drawn within the L3 vertebral body from a parasagittal slice from each sequence. Signal intensity (SI) values were ascertained and the percentage increase in SI was calculated. For each patient, changes in receiver gain for pre and post-gadolinium images were corrected by an image scaling factor. In all cases, a measurable increase in SI was found (mean 15.3%, range 4.4–55.7) due to bone vascularity. The results give no indication of the quantity or timing of blood supply but provide a basis for further work.     

恶性脑膜瘤的CT、MR及病理研究

目的：探讨恶性脑膜瘤CT、MR表现及其病理学特点。方法：分析11例经临床和病理证实的恶性脑膜瘤CT、MR表现及其病理学改变。探讨CT、MRI诊断恶性脑膜瘤的临床价值。结果：11例恶性脑膜瘤中，顶部镰旁4例，额部镰旁3例，颞极1例，大脑凸面3例。边缘光滑者4例，边缘呈不规则分叶状者7例；密度及信号均匀者4例，混杂密度及信号者7例，内部可见囊变、坏死。灶周无水肿2例，轻度水肿2例，中度水肿4例，重度水肿3例；增强后见硬膜尾征4例，形态光整1例，结节状增厚3例；邻近颅骨破坏3例；1例胸腰椎多发转移，骨质破坏。结论：恶性脑膜瘤CT、MRI具有较为特殊的影像学特点。术前正确认识其表现，有助于制订手术方案。     

13C imaging—a new diagnostic platform

The evolution of magnetic resonance imaging (MRI) has been astounding since the early 1980s, and a broad range of applications has emerged. To date, clinical imaging of nuclei other than protons has been precluded for reasons of sensitivity. However, with the recent development of hyperpolarization techniques, the signal from a given number of nuclei can be increased as much as 100,000 times, sufficient to enable imaging of nonproton nuclei. Technically, imaging of hyperpolarized nuclei offers several unique properties, such as complete lack of background signal and possibility for local and permanent destruction of the signal by means of radio frequency (RF) pulses. These properties allow for improved as well as new techniques within several application areas. Diagnostically, the injected compounds can visualize information about flow, perfusion, excretory function, and metabolic status. In this review article, we explain the concept of hyperpolarization and the techniques to hyperpolarize ¹³C. An overview of results obtained within angiography, perfusion, and catheter tracking is given, together with a discussion of the particular advantages and limitations. Finally, possible future directions of hyperpolarized ¹³C MRI are pointed out.     

Assessment of the abdominal aorta and its visceral branches by contrast-enhanced dynamic volumetric hepatic parallel magnetic resonance imaging: feasibility, reliability and accuracy

The purpose of this study was to evaluate a new three-dimensional gradient-echo (GRE) MR sequence performed with a parallel acquisition technique to shorten breath-hold times (parallel GRE MRI) in the detection of arterial variants and stenosis of the abdominal aorta and its visceral branches. A total of 102 patients underwent dynamic parallel GRE MRI, timed to the arterial phase by a test bolus (mean breath-hold time, 17 s). For both quantitative and qualitative analysis, the abdominal aorta and its visceral branches were divided into 13 arterial segments. In a subanalysis of 55/102 patients, the accuracy of parallel GRE MRI compared to MDCT in the detection arterial variants and stenosis was calculated for two independent readers. Mean SNRs and CNRs were 47.2 and 35.6, respectively. Image quality was rated good or excellent in 1,234/1,326 segments (93%). Hepatic and renal arterial variants were identified with an accuracy of 93 and 95%, respectively (reader 1) and 98 and 100%, respectively (reader 2). Both readers detected arterial stenosis with an accuracy of 98%. Interobserver agreement was good to excellent for the detection of hepatic (κ=0.69) and renal (κ=0.92) variants and for the diagnosis of stenosis (κ=0.96). Dynamic three-dimensional parallel GRE MRI is feasible and allows a reliable and accurate diagnosis of arterial variants and stenosis of the abdominal aorta and its visceral branches in a short breath-hold-time. Robert Werder is a medical student at the School of Medicine, Zurich.     

大鼠放射性脑损伤的MRS、PWI研究

目的研究大鼠放射性脑损伤不同时期的MRS、PWI表现,为其早期诊断提供依据。方法将成年大鼠30只随机分为对照组和照射组,照射前均行MRI、MRS及PWI检查。照射组分别于照射后1、3、6、9及12个月行MRI、MRS及PWI检查,计算NAA/Cr和Cho/Cr比值,测量灌注后大鼠双侧侧脑室周围的rCBV值。结果 1各照射组大鼠的NAA/Cr比值与对照组相比逐渐下降,差异均有统计学意义(P0.05);照射后Cho/Cr比值先上升,3个月时达峰值,随后逐渐下降,6个月内各组的Cho/Cr与对照组相比有统计学意义(P0.05);2照射1个月后各组的rCBV值均明显低于对照组,差异有统计学意义(P0.05)。结论 MRS及PWI能在放射性脑损伤发生形态学改变之前检测出脑组织代谢及灌注异常,为放射性脑损伤的早期诊断提供依据。     

纤维肉瘤的MRI诊断与鉴别诊断

目的：探讨纤维肉瘤的影像学表现,提高对该病的诊断水平。方法：回顾性分析本院2011年1月－2013年12月经手术病理证实的14例成人型纤维肉瘤患者的病例资料,其中隆突性皮肤纤维肉瘤5例。14例均行 MRI平扫,其中6例加做增强扫描。结果：5例隆突性皮肤纤维肉瘤均发生在表浅软组织内或隆起于皮肤表面,另外9例纤维肉瘤中6例累及深部肌肉,2例同时累及深部肌肉与表浅软组织,7例病灶与周围深筋膜关系密切。14例纤维肉瘤 MRI 表现为T1 WI等高信号,T2 WI混杂信号,10例病灶内见条状低信号分隔,5例见囊变坏死,1例病灶内可见出血,4例伴周围软组织水肿,4例伴发骨转移。6例增强扫描病灶呈外周强化或＂轮辐状＂强化。结论：MRI能清楚显示病灶的位置、大小、形态及组织结构特点,有助于提高纤维肉瘤的影像学诊断与鉴别诊断水平。