Improved perfusion quantification in FAIR imaging by offset correction.

Perfusion quantification using pulsed arterial spin labeling has been shown to be sensitive to the RF pulse slice profiles. Therefore, in Flow-sensitive Alternating-Inversion Recovery (FAIR) imaging the slice selective (ss) inversion slab is usually three to four times thicker than the imaging slice. However, this reduces perfusion sensitivity due to the increased transit delay of the incoming blood with unperturbed spins. In the present article, the dependence of the magnetization on the RF pulse slice profiles is inspected both theoretically and experimentally. A perfusion quantification model is presented that allows the use of thinner ss inversion slabs by taking into account the offset of RF slice profiles between ss and nonselective inversion slabs. This model was tested in both phantom and human studies. Magn Reson Med 46:193-197, 2001.     

Influence of different movement systems on image quality: comparison of the sliding gantry CT system and the sliding table CT system

The combination of angiography and CT angiography (CTA) is increasingly being used for the diagnosis and treatment of hepatic cancer. Recently, a CT system with sliding gantry was developed to optimize patient safety and to shorten transfer time between the angiography and CTA tables. As the CT gantry itself undergoes considerable movement in sliding over the patient table, it was considered necessary to evaluate this system regarding the precision of movement and any possible effect on image quality. Therefore, in this preliminary study, we compared image quality between the sliding gantry CT (SGCT) system and the sliding table CT (STCT) system. Comparative analysis revealed that there was no significant difference in image noise, low contrast resolution, modulation transfer function (MTF) , or precision in gantry or table movement. It was also noted that although the effective slice thickness for the SGCT system was 1-4% thinner than the STCT system it had no influence on image quality. It was thus concluded that the sliding movement of the gantry does not influence the quality of images obtained with this CT system.     

Study of improvement in X-ray computed tomography images with a radiation treatment planning system: image noise and slice thickness

In radiotherapy, dose distribution and calculation of dose monitor units (DMU) are generally performed by a radiation treatment planning system using CT images. Therefore, differences in calculation can arise as a result of the quality of the CT image data. The quality of CT images involves contrast resolution, resolution, noise, slice thickness, and other factors. Among these factors, we examined noise and slice thicknesses. Results demonstrated that, even if noise increased, CT value did not change, and, therefore, did not influence DMU. Examination of slice thickness showed that, when the radiation field was rectangular, it was not influenced by slice thickness. However, when a multi-leaf collimator (MLC) was used, if slice thickness was thicker than the size of the MLC, a difference arose in the position of the MLC, and, therefore, some difference arose in dose. Therefore, slice thickness should be thinner than the size of the MLC.     

Multidetector CT of the kidney

The technological development of multidetector CT offers new possibilities for better imaging of organic structures that can be used in diagnosis of the kidney. The thinner slices allow a better spatial resolution, and slice fusion allows improved contrast resolution. The isotropic voxel has been realized in the latest 64-channel scanners. The image quality of arbitrarily reconstructed planes has arrived at the image quality of the scan plane. Faster scanning allows studies in different contrast phases, which is helpful for better discrimination of benign or malignant lesions especially in the highly vascularized kidney. Different phases of contrast uptake can be differentiated (arterial, cortico-medullary, nephrographic, and excretory phase). Multidetector CT brings along the risk of increased dose due to thinner slice collimation and overranging phenomena. Indications for CT investigation of the kidney include urolithiasis, tumor diagnosis and staging, renal trauma, and vascular disease. Even in children, special indications for CT of the kidney remain in polytrauma and tumor staging. Multidetector CT of the kidney has become a very valuable tool in urology, but a careful protocol strategy is mandatory.     

Evaluation of the retrospective ECG-gated helical scan using half-second multi-slice CT: motion phantom study for volumetry

ECG synchronized technique on multi-slice CT provide the thinner (less 2 mm slice thickness) and faster (0.5sec/rotation) scan than that of the single detector CT and can acquire the coverage of the entire heart volume within one breath-hold. However, temporal resolution of multi-slice CT is insufficient on practical range of heart rate. The purpose of this study was to evaluate the accuracy of volumetry on cardiac function measurement in retrospective ECG-gated helical scan. We discussed the influence of the degradation of image quality and limitation of the heart rate in cardiac function measurement (volumetry) using motion phantom.     

Fundamentals of multichannel CT

Multichannel computed tomography (MCCT) has created a technical revolution in CT scanning. Following the introduction of single-channel helical scanning in 1989, 4-channel systems were introduced in 1998 and 16-channel systems in 2002. The core of this new technique is the X-ray detector array design, which allows for multiple simultaneous registration of slice information during gantry rotation. This design allows for faster scanning and acquisition of thinner slice widths. The high-speed scanning also minimizes motion artifacts. The ability to scan with very thin slice thickness creates a scanned volume with isotropic voxels. This allows for two- and three-dimensional reconstructions with similar resolution as the source images. MCCT also allows for higher X-ray tube currents, which create better penetration of metallic orthopedic fixation devices. Musculoskeletal imaging benefits from MCCT because large anatomic areas may be covered with thin slices. When needed, high tube currents can be applied for scanning areas of interest in the presence of metal. Thin slice acquisition allows isotropic viewing, which we use routinely.     

Association between size of the lateral ventricle and asymmetry of the fornix in patients with temporal lobe epilepsy.

PURPOSEOur goal was to determine whether the size of the lateral ventricle influences asymmetry of the fornix in patients with mesial temporal sclerosis.METHODSThe cross-sectional area of the lateral ventricle was measured along with the thickness of the fornix in 18 patients with pathologically proved mesial temporal sclerosis. Two additional patients with ventricular asymmetry and seizures but without mesial sclerosis were also studied.RESULTSTen of 18 patients with mesial temporal sclerosis had equally sized ventricular areas or less than a 25% difference between the two sides. In seven of these 10, the left and right fornices were equal; in the other three patients, the fornix was thinner on the side of mesial sclerosis. Among the eight patients with ventricular area differences greater than 25%, the larger ventricle was on the side of mesial sclerosis in five cases. In all of these, the ipsilateral fornix was thinner. In three of eight cases, the contralateral ventricle was larger; in two, the left and right fornix were equal; and in one, the fornix contralateral to the side of mesial sclerosis was smaller. The greatest difference in fornix thickness was noted in patients with ventricular asymmetry greater than 40%, regardless of side or presence of mesial temporal sclerosis.CONCLUSIONThe size of the lateral ventricle may influence the apparent thickness of the fornix.     

A thin-section collimator for the EMI scanner.

The thinnest pair of slices provided by the EMI scanner is 8 mm, producing an overlap of 6 mm. Resolution is reduced by averaging the density of structures throughout the thickness of the slice. The authors described special collimators which provide thinner slices with no overlap and thereby improve the quality of orbital scans.     

64层螺旋CT 的自动管电流调制技术（ATCM）的控制参数和辐射剂量的胸部模体实验研究

目的：通过胸部模体扫描探讨影响自动管电流技术的控制参数及影响因素对管电流mA调制效果和辐射剂量以及图像噪声的影响。方法使用GE lightspeed VCT 对模拟胸部模体进行扫描,实验组使用不同的噪声指数（noise index ,NI）,调制方法,扫描层厚,定位像,管电压等组合扫描,并记录CTDIvol值以及测量图像的中心,右侧和体前空气的感兴趣区的标准差（standard deviation ,SD）值。对照组使用固定管电流200mA扫描,比较各种组合的辐射剂量和成像噪声。结果对照组的 CTDIvol 为10．07mGy ,实验组 A ,B ,C ,D ,E 的 CTDIvol 分别为18．58mGy ,24．56mGy ,14.98mGy ,12.46mGy ,11．49mGy均大于对照组。使用smartmA进行角度调制的C组比A组的CTDIvol降低约15％;而使用侧位定位像扫描的实验组D的辐射剂量也与使用正位像的实验组C辐射剂量不同;使用相同的NI值扫描,层厚越薄,调制的管电流越大,辐射剂量越大。图像中心区域的噪声（6．12±0．85）H U的变化要比体侧和体前的噪声（6．73±1．78）HU ,（7．29±1．23）HU的变化小,各层的一致性要好于体侧和体前的噪声。但由于有最大mA调制800mA的限制,在实验组B的肩部几乎都是最大mA扫描,而最后的CTDIvol为31．76mGy。使用联合调制后,各层的平均mA明显减少,而图像噪声的没有统计学改变;NI值升高,辐射剂量减少;管电压改变,辐射剂量改变,但图像噪声不变。结论ATCM技术可以通过实时调整管电流获得各层图像一致的噪声水平。联合调制比Z轴调制更有效的控制辐射剂量而不会带来图像质量的损失。定位像的选择,NI值的设定,扫描层厚的选择,最大mA的设定会影响辐射剂量。     

CT血管成像技术在下肢动脉疾病中的应用价值

下肢动脉疾病是动脉系统疾病中的常见病，目前彩色多普勒超声、磁共振血管成像、CT血管成像等无创性血管成像技术为诊断及制定外科治疗方案提供重要依据，尤其是随着多层螺旋CT的问世，以其亚秒级的扫描速度、薄的层厚及多种后处理重建方式使CTA成像技术在显示下肢动脉病变方面有独特优势。本文主要阐述有关螺旋CTA成像技术在诊断下肢动脉疾病的应用及三种无创性检查方法的比较。     

The influence of heart rate, slice thickness, and calcification density on calcium scores using 64-slice multidetector computed tomography: a systematic phantom study

OBJECTIVE: The purpose of this study was to investigate the influence of heart rate, slice thickness, and calcification density on absolute value and variability of calcium score using 64-slice multidetector computed tomography (MDCT). METHODS AND MATERIALS: Three artificial arteries containing each 3 lesions with varying density were scanned using a moving cardiac phantom at rest and at 50 to 110 beats per minute (bpm) at 10-bpm intervals on a 64-slice MDCT. Images were reconstructed at slice thicknesses (increment) of 0.6 (0.4), 0.75 (0.5), 1.5 (1.5), and 3.0 (3.0) mm. The amount of calcium was expressed as an Agatston score, volume score, and equivalent mass. RESULTS: Absolute coronary artery calcium (CAC) scores decreased [average -37% for low density calcification (LDC)] or increased [average +32% for high density calcification (HDC)] at heart rates over 60 bpm depending on slice thickness and scoring method. Thinner slice thicknesses yielded higher CAC scores. Variability of the CAC scores increased with increasing heart rates especially for low density calcifications (8% at rest vs. 50% at 110 bpm). Variability also increased for thicker slices (average 6% for 0.6 mm vs. 18% for 3.0 mm). Variability was lower for HDC compared with LDC (approximately 5% for HDC vs. 27% for LDC at 70 bpm, averaged over all methods and slice thicknesses). CONCLUSION: CAC-scoring is strongly influenced by cardiac motion, calcification density, and slice thickness. CAC scores increase for high density calcifications and decrease for low density calcifications at increasing heart rates. Heart rate should be reduced on 64-slice MDCT to obtain a lower degree of variability of CAC-scoring, preferably below 70 bpm. A thinner slice thickness further enhances the reproducibility.     

Osteochondritis dissecans of the temporomandibular joint

A case is reported of a 43-year-old female patient presenting bilateral osteochondritis dissecans (OCD) of the temporomandibular joint (TMJ), in different stages for each side, associated with avascular necrosis (AVN) of the right condyle. Additionally observed was anterior disk displacement without reduction for both sides. We have proposed an adaptation of the previous classification of OCD for cases affecting the TMJ. We have also stressed the fundamental role of panoramic radiography on the diagnosis of stage 3 and stage 4 OCD of the TMJ. In relation to MRI, we have recommended sagittal (slice thickness of 2 mm) and coronal (slice thickness of 1 mm) fast spin-echo proton density-weighted sequences to better identify bone lesions (stage 1 and 2) and also localize osteochondral loose bodies; and coronal (slice thickness of 1 mm) fat-suppressed fast spin-echo T2 weighted sequence to better evaluate OCD (stable or unstable) and the features of the occasionally associated AVN (acute or chronic).     

Does the trabecular bone structure depicted by high-resolution MRI of the calcaneus reflect the true bone structure?

RATIONALE AND OBJECTIVES: The purpose of this study was to compare trabecular bone structure parameters assessed with high-resolution magnetic resonance imaging (HR-MRI) with those determined in specimen sections. METHODS: High-resolution MR images were obtained for 30 calcaneus specimens with a three-dimensional, T1-weighted spin-echo sequence (spatial in-plane resolution 0.195 mm, slice thicknesses of 0.3 and 0.9 mm). Thirty-eight sections were obtained from the specimens, and contact radiography was performed. In the corresponding sections, structural parameters analogous to bone histomorphometry were determined. RESULTS: Significant correlations between MRI-derived structural parameters and those derived from macro pathological sections were found: r values of up to 0.75 were obtained (P < 0.01). The highest correlations were found for apparent bone volume/total volume and trabecular thickness. Image thresholding techniques showed a significant impact on these correlations (P < 0.01). The thinner MR sections were less susceptible to the different thresholding algorithms. CONCLUSIONS: Trabecular bone structure depicted by HR-MR images is significantly correlated with that shown in macro sections (P < 0.01); however, a number of limitations have to be considered, including the substantial impact of thresholding techniques and slice thickness.     

常规剂量下影响CT检出肺结节的因素

目的：复习文献，并进一步讨论常规剂量下影响CT检出肺结节的因素。方法：选择肺转移瘤20例，分别在不同层厚、重建问隔以及螺距情况下扫描，统计在每一扫描条件下检出的肺结节的大小、数量、部位，讨论扫描条件、结节大小、结节部位与肺结节检出率之问的关系。结果：扫描层厚薄、重建问隔小、螺距值小、检出的肺结节数越多，更多的是提高了微结节的检出；与肺血管影、肺门影、心旁纵隔影、横膈影重叠的肺结节容易漏检。结论：常规剂量扫描条件下，扫描层厚、重建间隔、螺距、结节大小、结节位置均可影响结节的检出。     

Physics properties of non-helical scan using 320-row multi detector computed tomography

Recently, clinical applications utilizing 320-row multi detector computed tomography (320MDCT) have increased, and the physical image properties of 320MDCT have been more concerned. We evaluated the spatial resolution in scan plane and z-direction, image noise and low-contrast sensitivity of non-helical mode (320NH), 640 slices mode by a double slice reconstruction technology (640DS), and 64-row helical mode (64HE) by using a 320MDCT. The spatial resolution in z-direction was evaluated by the section sensitivity profile (SSP) measurement with the micro coin phantom and the contrast transfer ratio (CTR) with the 0.5-mm comb phantom. The in-plane spatial resolution of 320NH was uniform over all the slice positions. The spatial resolution in z-direction decreased from the cathode side toward the anode side. The image noise of the anode side was higher than that of the cathode side. The contrast to noise ratio as index of the low contrast sensitivity was uniform over all the slice position. The CTR of 320NH fluctuated in the z-position, and the fluctuation was improved by 640DS except for the center of rotation.     

MR imaging of olfactory bulbs and tracts

Olfactory bulbs are easily detected on coronal T1-weighted MR images. They are situated almost symmetrically opposite either side of the lower end of the olfactory sulci, and, on sagittal images, they are observed as thin soft-tissue bands immediately beneath the frontal lobe base. On axial images they are shown as oval, paramedian structures of intermediate intensity. Visualization of the olfactory tract, however, is not always possible. Our study reveals that, on axial images, detection of the olfactory bulb depends on technical factors; we recommend a 256 x 256 matrix, a 3-mm-thick slice, and less than a 0.6-mm gap. Despite the lack of complete visualization of olfactory bulbs and tracts, MR may be effective in demonstrating diseases of these entities.     

Magnetic resonance imaging of articular cartilage and evaluation of cartilage disease

Clinical magnetic resonance imaging of articular cartilage is possible by using techniques that offer high contrast between articular cartilage and adjacent structures in reasonable examination times. The fat-suppressed, three-dimensional, spoiled gradient-echo sequence has been reported to be accurate and reliable, and the addition of this sequence to a routine examination does not significantly compromise patient throughput. Fast spin-echo imaging also shows promise in the clinical evaluation of articular cartilage, because the newer, stronger-gradient systems allow thinner slice acquisition with two-dimensional sequences. Together, these sequences allow the evaluation of intrachondral lesions and surface defects. Furthermore, quantitative measurements of cartilage volume for follow-up studies are possible with the use of the fat-suppressed, three-dimensional, spoiled gradient-echo sequence.     

多层螺旋CT成像技术对输尿管微小结石的临床应用价值

目的 探讨多层螺旋CT（MSCT）在输尿管重建中显示输尿管结石的临床应用价值。资料与方法 实验组：27个取自患者的泌尿系结石,分别经设置不同扫描参数的单层螺旋CT（SSCT）和MSCT扫描。比较在设置不同扫描参数下SSCT和MSCT的结石检出率,检验不同扫描层厚与检出结石数的关系。临床组：35例腹部平片（KUB）阴性但临床高度怀疑输尿管结石患者均行B超和MSCT扫描及输尿管重建。输尿管重建方法有：曲面重建、最大密度投影和表面遮盖成像。结果 实验组MSCT 5mm和10mm层厚扫描,然后分别以0．62．5mm和1．25mm层厚重建所得的图像,其质量及其显示出的结石数与MSCT相应同等薄层扫描（0．625mm和1．25mm层厚扫描）所得的结果完全一致。临床组35例40个输尿管结石,B超发现23例25个,检出率为62．5％;MSCT薄层重建结合输尿管重建后结石检出率为100％。并能清楚显示结石位置、大小及输尿管梗阻扩张的程度及范围。结论 MSCT常规平扫结合薄层重建特别是CT尿路造影（CTU）可提高结石检出率及评价输尿管有元梗阻及其程度。必要时增强扫描可评价患侧肾功能。     

Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging

The experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase-sensitive picture of the profile of a slice are discussed. A distinction is made between the “excitation profile” (distribution of the transverse magnetization immediately after the RF pulse) and the “slice profile” (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.     

Future cost-effective MRI will be at high field

The most cost effective MR imaging system is the one that provides the highest quality images (allowing the earliest possible diagnosis), the largest number of applications (allowing bundling of services and one-stop shopping for consumers), and the highest throughput (should it become necessary to scan a large number of patients in a capitated world). When all other parameters are normalized (eg, the skill and training of the radiologist and technologist as well as the RF, computer, and gradient subsystems), high field provides faster, higher resolution, thinner slice, and higher contrast MR images than low field. For these reasons, high field MRI will remain more cost effective than its lower field counterparts in the future.