Three-dimensional alignment of functional and morphological tomograms

A method has been developed to create corresponding brain slices from morphological [CT, magnetic resonance (MR)] and functional [positron emission tomography (PET), single photon emission computed tomography] tomographic studies in individual patients. It does not require special headholders or definition of specific landmarks and is fully retrospective. Three-dimensional image registration in corresponding orientation is achieved by linear interpolation of original slices and a variety of interactively controlled video display options. These include simultaneous display of multiple slices and brain cuts in all three dimensions for comparison of positioning. Brain contours in one imaging modality may be enhanced by appropriate filtering and superimposed onto reference images of another modality. Matching accuracy depends on image resolution; misalignment of 4 mm was detected unambiguously in sample studies (fluoro-2-deoxy-D-glucose PET matched with MR). The technique is equally well applicable to normals and to patients with structural brain lesions. Additional options for shaded surface display enhance the power to identify neuroanatomical structures in functional image analysis. As demonstrated in the example of MR-guided PET, this modeling procedure can be successfully used for identification of brain structures on functional images, even in patients with pathologically altered brain morphology.     

Marching cube algorithm: review and trilinear interpolation adaptation for image-based dosimetric models.

Current internal organ dose assessment methodologies utilize three-dimensional (3D) medical images of the body to model organ shapes and tissue interfaces. These models are coupled to computer programs that measure radionuclide energy deposition or chord-length distributions directly within these images. Previous studies have shown that the rectangular shape of image voxels generates voxel effects that alter the outcome of these calculations. To minimize voxel effects, the present study proposes to use the Marching Cube (MC) algorithm to generate isosurfaces delineating tissue interfaces from the gray-level images. First, a review of the different techniques surrounding the MC algorithm is presented. Next, an adaptation of the algorithm is proposed in which a trilinear interpolation of the gray levels is used to generate a hyperboloid surface within the MCs. This new technique is shown to solve the classic ambiguity problem of the MC algorithm and also to reduce the data size inherent to the triangulated surface. It also provides a simple algorithm to accurately measure distances within the image. The technique is then tested with a mathematical model of trabecular bone. The trilinear interpolation method is shown to remove voxel effects and to produce reliable chord-length distributions across image regions. The technique is thus recommended for use with digital medical images needed for internal radiation transport simulations. The current study is performed for a single isosurface that separates two media within the same image, but it is proposed that the technique can be extended to multiple isosurfaces that delineate several organs or organ regions within 3D tomographic voxels of human anatomy.     

Modern gray-scale sonography of the breast

Recently, the diagnosis of breast diseases by ultrasound has changed radically. It is no longer a complementary modality to mammography but a separate method to investigate breast disease. Innovative high-resolution ultrasound allows more specific diagnosis of breast tumors. Tissue-harmonic imaging not only uses the transmitted, fundamental frequency to obtain an image but also the harmonic frequency. The harmonic signal is processed by the ultrasound system with the result of better delineation of tissue structures and spatial compounding assembles an image from multiple images taken from different angles of echo waves. The effect is the reduction of artifacts with optimized contrast. Finally the advanced speckle reduction technique is used to smooth and homogenize the image. Additionally continuous advancement of new high-resolution linear transducers is responsible for the essential improvement of image quality. In conclusion, it is recommended to integrate all of the described modalities in order to obtain diagnostically conclusive image quality. This article demonstrates the new techniques and applications exemplified using images.     

Moderne B-Bild-Sonographie der Mamma

Recently, the diagnosis of breast diseases by ultrasound has changed radically. It is no longer a complementary modality to mammography but a separate method to investigate breast disease. Innovative high-resolution ultrasound allows more specific diagnosis of breast tumors. Tissue-harmonic imaging not only uses the transmitted, fundamental frequency to obtain an image but also the harmonic frequency. The harmonic signal is processed by the ultrasound system with the result of better delineation of tissue structures and spatial compounding assembles an image from multiple images taken from different angles of echo waves. The effect is the reduction of artifacts with optimized contrast. Finally the advanced speckle reduction technique is used to smooth and homogenize the image. Additionally continuous advancement of new high-resolution linear transducers is responsible for the essential improvement of image quality. In conclusion, it is recommended to integrate all of the described modalities in order to obtain diagnostically conclusive image quality. This article demonstrates the new techniques and applications exemplified using images.     

评价喉部螺旋CT三维成像的临床应用价值

目的：研究喉部螺旋ＣＴ三维成像的临床应用价值。方法：１５例行喉部螺旋ＣＴ扫描。将容积扫描数据传送至ＧＥＳｕｎＳｐａｒｃ２０工作站,使用表面覆盖重建方法（ｓｈａｄｅｄｓｕｒｆａｃｅｄｉｓｐｌａｙ,ＳＳＤ）和内表面重建模式进行后处理,得到喉ＳＳＤ影像（ＳＳＤ－ｉｍ－ａｇｅ）和ＣＴ仿真喉镜（ＣＴｖｉｒｔｕａｌＬａｒｙｎｇｏｓｃｏｐｙＣＴＶＬ）。由两位放射科医生和一位耳鼻喉科医生分别对喉部螺旋ＣＴ轴位影像,喉ＳＳＤ影像,ＣＴ仿真喉镜（ＣＴＶＬ）的影像质量,提供诊断信息进行分析。结果：对喉部肿瘤的诊断,喉部螺旋ＣＴ轴位影像比三维成像提供更多的信息,但是,喉部三维成像直观地显示肿瘤侵犯上下范围,受到耳鼻喉科医生的高度评价。对于喉部炎症的诊断,ＣＴ仿真喉镜比ＣＴ轴位影像提供更多的信息。结论：将螺旋ＣＴ轴位影像,喉ＳＳＤ影像,ＣＴ仿真喉镜三种影像结合起来,可以提高诊断准确性,并且为临床提供更直观的影像,指导制定手术方案。     

Craniosynostosis: image quality, confidence, and correctness in diagnosis

The authors used the diagnosis of craniosynostosis to compare subjective evaluation of image quality with objective diagnostic utility. They studied in detail the responses of one observer, who read plain radiographs, computed tomographic (CT) scans, and three-dimensional reconstructions of CT scans (obtained with three different methods) for 82 patients with this diagnosis. The observer rated image quality and certainty in diagnosis made from each image. Subjective and objective performances were found to be strongly linked. High-quality images served as the basis for more accurate diagnoses than low-quality images. The increase in diagnostic performance results primarily from increased specificity, a fact that suggests that specificity and the concomitant diagnosis of normalcy are the focus of attention when image quality is evaluated.     

Digital tomosynthesis: technique for electronic reconstructive tomography

A technique is described for obtaining tomographic images through retrospective reconstruction of digital data. The apparatus used for this technique, called digital tomosynthesis consists of a linear tomographic x-ray machine that has been modified by the addition of a fluoroscope and TV system, a video disk recorder, an analog-to-digital converter, and a small computer for data processing and manipulation. Video frames are collected and stored during a single tomographic sweep. The stored data are then digitized and retrospectively processed in the computer for reconstruction of any desired tomographic plane within the body. The major advantages of DTS include short patient study time, low radiation dose compared with conventional tomography, the ability to enhance the digitized image through manipulation of window and level display, and the applicability of this technique to dynamic studies such as angiotomography. Phantom studies show good diagnostic quality of the resulting images, and preliminary vascular studies in dogs indicate the clinical potential of this technique for use in digital subtraction angiotomography.     

Comparison of information-preserving and information-losing data- compression algorithms for CT images

Data compression increases the number of images that can be stored on magnetic disks or tape and reduces the time required for transmission of images between stations. Two algorithms for data compression are compared in application to computed tomographic (CT) images. The first, an information-preserving algorithm combining differential and Huffman encoding, allows reconstruction of the original image. A second algorithm alters the image in a clinically acceptable manner. This second algorithm combines two processes: the suppression of data outside of the head or body and the combination of differential and Huffman encoding. Because the final image is not an exact copy, the second algorithm is information losing. Application of the information-preserving algorithm can double or triple the number of CT images that can be stored on hard disk or magnetic tape. This algorithm may also double or triple the speed with which images may be transmitted. The information-losing algorithm can increase storage or transmission speed by a factor of five. The computation time on this system is excessive, but dedicated hardware is available to allow efficient implementation.     

基于CT图像的跨模态转换研究进展

医学图像在临床诊断和治疗上起着至关重要的作用。放射治疗过程中采用计算机体层成像（CT）进行靶区定位和勾画。为了从多个角度获取病变体信息,需利用医学图像多模态的优势。然而,获取多种模态的医学图像是比较耗费资源的,同时无法保证患者状态的一致性。医学图像跨模态转换,可以利用一种模态图像预测另一种模态图像。本文详细综述了基于CT图像的超声图像、磁共振（magnetic resonance,MR）图像、正电子发射计算机断层显像（positron emission tomography,PET）跨模态模型研究,分类阐述了各模型的特点和存在的挑战,指出尚待开展的研究领域。     

Avascular necrosis of the femoral head: morphologic assessment by MR imaging, with CT correlation

To better understand the morphologic appearance of avascular necrosis (AVN) of the femoral head on magnetic resonance (MR) images (1.5 T) and computed tomographic (CT) scans, the records of 21 lesions were reviewed retrospectively. All MR imaging studies included T1-weighted images (T1WI) (repetition times [TR] of 400-1,000 msec, and echo times [TE] of 20-25 msec), and 15 included T2-weighted images (T2WI) (TR = 2,000-2,500 msec; TE = 60-80 msec). MR signal features of the lesions were compared with features on the corresponding CT scans. Abnormalities in the superoanterior aspect of the femoral head were noted on both image types in all 21 lesions but were more obvious on MR images in two. A characteristic margin of peripheral sclerosis seen on CT scans in 95% (20 of 21) of lesions corresponded to a line of low intensity on MR images. Fractures complicating AVN were seen in eight lesions at CT scanning. On T1WI, fractures were not clearly delineated. On T2WI, fractures were of high intensity but were depicted less clearly than on CT scans. Central signal intensity of the lesions on T1WI correlated with the presence or absence of fracture: 88% (seven of eight) of the lesions with fractures appeared less intense than fat, compared with only 8% (one of 13) of lesions without fractures (P less than .005). While MR imaging is a sensitive method for early diagnosis of AVN, CT scanning can more accurately identify fractures and is thus important for staging.     

MR imaging of blood vessels using three-dimensional reconstruction: methodology

Multisection, dual-echo magnetic resonance (MR) transaxial images of blood vessels contain both anatomic and qualitative information about flow. Even so, the images are produced as a series of two-dimensional tomographic sections from which full visualization of connected structures is difficult. A computer algorithm was developed that automatically detects flowing blood based on pixel intensity and calculated T2 and provides reconstructed views of vessels while analyzing and displaying flow characteristics. Images of abdominal vessels, aortic aneurysms, and the heart were encoded by flow and color to demonstrate depth. In addition, these data were reconstructed to derive a more accurate assessment of patency. With this technique, transaxial images can be used to analyze flow patterns, determine patent areas, and visualize all levels of vessels in a single image.     

Neuroanatomical localization for clinical SPECT perfusion brain imaging: a practical proportional grid method.

For the purpose of facilitating anatomical localization in interpretation of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomographic (SPECT) scans, a stereotaxic proportional grid system was applied in the form of an interactive computer program. This method takes advantage of a rotating gamma camera system which permits planar scout imaging for the determination of anatomical reference lines, and standardization of tomographic slices for brain size. Using measurements made on a lateral planar HMPAO image, proportional grids were constructed onto standardized transaxial images. This method was implemented for 33 clinical HMPAO SPECT studies. It required less than 15 min of an operator's time. This simple and practical neuroanatomical localization technique can be instrumental as an aid to the interpretation of routine clinical HMPAO SPECT images.     

Tomographic DSA using temporal filtration: initial neurovascular application

A preliminary study showed that encouraging laboratory results reported previously using tomographic digital subtraction angiography (DSA) can be transferred to clinical application for neurovascular imaging. Tomography may show cervical carotid disease more clearly than standard DSA images, and it eliminates the interference caused by overlapping vessels. Production of multiple tomographic image planes from a single set of projection data, tomosynthesis, must be incorporated into this imaging system before tomographic DSA becomes clinically useful. This is a practical reality with the present equipment; clinical evaluation of this new capability is underway.     

Hybrid imaging in planar scintigraphy: new implementations and historical precedents

Fusion of tomographic radionuclide studies with anatomical examinations has become standard practice in positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging. Nonetheless, fusion of planar scintigraphic images with an anatomical modality remains distinctly uncommon, although methods to do so have appeared sporadically in the literature during the past 2 decades. In this article we review several techniques that have been used to combine planar scintigraphic images with radiographs and visual (photographic) images. Rigid or affine transformations have been performed to co-register the planar images with each other using custom, commercial, or public domain software. Display of the hybrid images has been achieved primarily with nonselective color-fusion methods. Promising efforts are underway to develop a technique of fusing planar lymphoscintigraphic images with CT topograms (scout images) obtained on the SPECT-CT camera in a manner that compensates for position-dependent variation in magnification that affects the CT scout. An advantage of this approach is that both of the component images are acquired on the same gantry, without need for repositioning of the patient. It is instructive to note that techniques of fusing rectilinear scans with radiographic and visual images were first developed more than 50 years ago. The revisiting of these methods after many decades reflects a fundamental need for spatial orientation in nuclear medicine that fusion imaging can also bring to planar scintigraphic studies.     

Simulation of liver lesions for pediatric CT

PURPOSE: To develop and validate a technique based on characteristics of real lesions for simulating realistic small liver lesions on pediatric computed tomographic (CT) images. MATERIALS AND METHODS: The institutional review board provided exempt status for this study, determined that it was not subject to HIPAA compliance, and did not require informed consent. Patient identification information was removed from clinical images from contrast material-enhanced multi-detector row CT examinations performed in 10 children. Patients were infants or children up to 18 years old. Information about sex was not available. Children had one or more liver lesions of 2-6 mm in maximum transverse diameter. Images with more than one lesion were rendered multiple times, and each time, all but one of the lesions were digitally removed in sequence. This process provided images (n = 19) with a single real lesion. For consistency, the same image backgrounds (images with all real lesions removed) were used to create an identical number of images (n = 19), each with a single simulated lesion. Subsequently, three radiologists independently assessed images of real and simulated lesions that were presented in random order with a score on a continuous scale of 0 (definitely simulated) to 100 (definitely real). Mixed-model analysis of variance was used to test the null hypothesis that the difference in population mean scores between the two lesion types was zero. RESULTS: The observer study did not reveal a significant difference in the ability of any radiologist to discriminate between real and simulated lesions (P > .31). The differences in mean scores for discrimination between real and simulated lesions for the three observers were -6, 9, and -7, respectively. The estimated overall difference was -1. CONCLUSION: Mathematic simulation of liver lesions is a feasible technique for creating realistic lesions for image quality or dose reduction studies in pediatric CT.     

Use of MR angiography for stereotactic planning.

With the introduction of MR angiography (MRA) into clinical routine MR protocols, it has become possible now to image flowing as well as stationary tissue with excellent contrast using a single modality. This has opened up new perspectives for planning stereotactic approaches, which are characterized by high risks for damaging intracerebral vessels or vital brain structures. In this article we present an MRA based planning method for the treatment of arteriovenous malformations by stereotactic radiosurgery. It includes flow compensated gradient echo pulse sequences for the acquisition of angiographic MR datasets, a stereotactic MR marker system, an algorithm for the correction of geometric distortion of MR image data, and a three-dimensional workstation system for the creation and evaluation of treatment plans. The latter is based on the concept of simultaneously displaying both MR slice and angiographic projection images. This allows the evaluation of intracerebral vasculature together with brain anatomy. The MRA guided planning approach was tested and compared to a conventional X-ray angiographic technique in a clinical study. Our satisfactory results suggest that MRA is a technique that can be used advantageously for stereotactic planning.     

Three-dimensional reconstruction and fusion for multi-modality spinal images.

Medical diagnosis can benefit from the complementary information in different modality images. Multi-modal image registration and fusion is an essential task in numerous three-dimensional (3D) medical image-processing applications. Registered images are not only providing more correlative information to aid in diagnosis, but also assisting with the planning and monitoring of both surgery and radiotherapy. This research is directed at registering different images captured from Computed Tomography (CT) and Magnetic Resonance (MR) imaging devices, respectively, to acquire more thorough information for disease diagnosis. Because MR bone model segmentation is difficult, this research used a 3D model obtained from CT images. This model accomplishes image registration by optimizing the gradient information accumulated around the bony boundary areas with respect to the 3D model. This system involves pre-processing, 2D segmentation, 3D registration, fusion and sub-system rendering. This method provides desired image operation, robustness verification, and multi-modality spinal image registration accuracy. The proposed system is useful in observing the foramen and nerve root. Because the registration can be performed without external markers, a better choice for clinical usage is provided for lumbar spine diagnosis.     

SPECT liver imaging using an iterative attenuation correction algorithm and an external flood source

The results obtained from the inclusion of a new intrinsic attenuation correction algorithm into a protocol for SPECT liver imaging are presented in this study. A total of six patients were evaluated with this protocol. The new algorithm uses a transmission tomographic acquisition that is obtained before a standard emission tomograph, and requires the use of an external flood source. The transmission tomograph results in an attenuation image, or map, of the patient. The attenuation map then serves as input into the final intrinsic correction algorithm, that also uses data from a standard emission acquisition. The results of the six patients studied show that the algorithm can correct for attenuation effects without degrading image quality. In all the cases studied, the attenuation corrected images made the cases easier to interpret than did the images obtained without attenuation correction.     

Dual-modality imaging: combining anatomy and function

The extensive development of image fusion techniques over the past 20 y has shown that the fusion of images from complementary modalities offers a more complete and accurate assessment of disease than do images from a single modality. Although software techniques have been successful in fusing images of the brain from different modalities, they have achieved rather limited success for other parts of the body. The recent introduction of technology that can acquire both anatomic and functional images in a single scan has addressed many of the limitations of software fusion. The combination of CT and PET was introduced commercially in 2001, followed by CT and SPECT in 2004. Clinical adoption of PET/CT has been surprisingly rapid, and despite continuing debate, the new technology has advanced the use of clinical molecular imaging, particularly for oncology.     

Simultaneous MRI acquisition of blood volume, blood flow, and blood oxygenation information during brain activation.

Simultaneous acquisition of complementary functional hemodynamic indices reflecting different aspects of brain activity would be a valuable tool for functional brain-imaging studies offering enhanced detection power and improved data interpretation. As such, a new MRI technique is presented that is able to achieve concurrent acquisition of three hemodynamic images based primarily on the changes of cerebral blood volume, blood flow, and blood oxygenation, respectively, associated with brain activation. Specifically, an inversion recovery pulse sequence has been designed to measure VASO (vascular space occupancy), ASL (arterial spin labeling) perfusion, and BOLD (blood-oxygenation-level-dependent) signals in a single scan. The MR signal characteristics in this sequence were analyzed, and image parameters were optimized for the simultaneous acquisition of these functional images. The feasibility and efficacy of the new technique were assessed by brain activation experiments with visual stimulation paradigms. Experiments on healthy volunteers showed that this technique provided efficient image acquisition, and thus higher contrast-to-noise ratio per unit time, compared with conventional techniques collecting these functional images separately. In addition, it was demonstrated that the proposed technique was able to be utilized in event-related functional MRI experiments, with potential advantages of obtaining accurate transient information of the activation-induced hemodynamic responses.