Spine needle biopsy simulator using visual and force feedback.

OBJECTIVE: Biopsy with an inserted needle is an important procedure for lesion detection in the spine, but is difficult to perform due to the presence of many critical organs near the spine. This article presents a spine needle biopsy simulator, based on visual and force feedback, which can be used to plan the optimal path of a needle and to practice the procedure without risk. MATERIALS AND METHODS: The simulator is composed of a 3D human model, a visual-feedback component, a force-feedback component, and an evaluation module. The human model is based on 3D CT data. The visual-feedback component provides an oblique section, multiplanar reformatting images, and a volume-rendered image. Of these, the oblique section display is very useful for planning a 3D path for the needle. During simulation, the force-feedback component generates and provides realistic forces acting on the biopsy needle in real time by synchronizing them to visual feedback. After each simulation, the evaluation module provides a performance analysis for the trainee. RESULTS: For an XCT abdomen volume data set of 256 x 256 x 256, the update rate of image rendering due to needle movement is over 25 Hz, with a force-feedback rate of 1 kHz. This performance proved to be good enough for the trainee to learn the relationship between visual and force feedback. CONCLUSIONS: The simulator is useful for the planning of and training in complicated 3D spine needle biopsy procedures. It may be used as an educational tool for beginners, a practice tool to increase expertise, or a test bed for new procedures.

Interslice coding for medical three-dimensional images using an adaptive mode selection technique in wavelet transform domain.

In this article the authors propose a novel interslice coding algorithm especially appropriate for medical 3-dimensional (3D) images. The proposed algorithm is based on a video coding algorithm using motion estimation/compensation and transform coding. In the algorithm, warping is adopted for motion compensation. Then, by using adaptive mode selection, an MC residual image and original image are mixed up in the wavelet transform domain for improvement in coding performance. The mixed image is then compressed by the zerotree coding method. It is proven that the adaptive mode selection technique in the wavelet transform domain is very useful for medical 3D image coding. Simulation results show that the proposed scheme provides good performance, regardless of interslice distance, and is prospective for medical 3D image compression.

An efficient motion vector coding scheme based on minimum bitrate prediction.

Motion vector coding efficiency is becoming an important issue in low bitrate video coding because of its increasing relative bit portion. This work presents a new motion vector coding technique based on minimum bitrate prediction. In the proposed scheme, a predicted motion vector is chosen from the three causal neighboring motion vectors so that it can produce a minimum bitrate in motion vector difference coding. Then the prediction error, or motion vector difference (MVD), and the mode information (MODE) for determining the predicted motion vector at a decoder are coded and transmitted in order. Sending bits for the MVD ahead of bits for the MODE, the scheme can minimize the bit amount for the MODE by taking advantage of the fact that the minimum bitrate predictor is used for motion vector prediction. Adaptively combining this minimum bitrate prediction scheme with the conventional model-based prediction scheme, more efficient motion vector coding can be achieved. The proposed scheme improves the coding efficiency noticeably for various video sequences.

Adaptive learning method in self-organizing map for edge preserving vector quantization.

The Kohonen's self-organizing map algorithm for vector quantization of images is modified to reduce the edge degradation in the coded image. The learning procedure is performed by adaptive learning rates that are determined according to the image block activity. The simulation result of 4x4 vector quantization for 512x512 image coding demonstrates the feasibility of the proposed method.

Improvement on image transform coding by reducing interblock correlation.

We try to improve transform coding efficiency by alleviating the interblock correlation due to the small size of the block. The proposed method needs minor modification from conventional transform coding techniques such as JPEG, and reduces the information loss in the coding procedure for a given bit rate. Simulation results demonstrate that the method drastically diminishes the blocking effects and enhances the subjective visual quality compared with such existing algorithms as JPEG and LOT.

Fast imaging using subencoding data sets from multiple detectors.

A new fast imaging method using a subencoding data acquisition scheme and a multiple coil receiver system is proposed and demonstrated. In this method, a set of aliased images are produced from receiver coils by using the subencoded data without sacrificing the desired resolution, and resolved to an aliasing-free image by using the distance-dependent sensitivity information of each coil. The reduction rate of data acquisition time is proportional to the number of receiver coils. This method can be easily adapted to conventional imaging methods including fast imaging to further reduce the scan time.

Radial scanning technique for volume selective 31P spectroscopy.

An interlaced radial scanning method that is ideally suited for 31P spectroscopy with short T2 components and a wide spectral range is presented. The proposed method, which uses an additional radial gradient and radial scans in the k-space, minimizes T2 decay during the selection time and also optimizes the volume selectivity in a given gradient field strength. Simulation and experimental results with a short selection time of 2 ms demonstrate that the proposed method is suitable for volume selective 31P spectroscopy.

Application of single-shot spiral scanning for volume localization.

A new technique using a spiral scan single-shot RF pulse for localized volume selection has been developed and its experimental results are presented. This technique employs an additional radial-gradient coil in conjunction with the oscillating gradients for the spiral scan to localize the 3D volume. The short selection time in this technique minimizes both signal contamination from unwanted regions and signal attenuation due to T2 decay. We provide both the theoretical background of the technique and the experimental results obtained from a phantom as well as a human volunteer. The proposed method appears simple and accurate in localizing a volume which would be used as either fast imaging or localized spectroscopy.

An algorithm for MR imaging of the short T2 fraction of sodium using the FID signal.

Multiecho magnetic resonance imaging of 23Na in the human body could provide valuable information regarding the distribution of the sodium in the intracellular and extracellular spaces in living tissues. Since it is known that more than half the intracellular sodium has a T2 value of less than 3 ms, the conventional spin-echo imaging technique is not appropriate for the quantitative study of sodium in living tissues. A pulse sequence using the three-dimensional planar-integral projection reconstruction algorithm was developed to provide images from the free induction decay (FID) signal and from the spin-echo. Using this imaging sequence, we are able to produce human head images with the FID signal immediately following the 90 degrees radiofrequency pulse thus preserving the signal from the very short T2 components. This technique with a multiple echo imaging scheme may open the possibility of discriminating between intracellular and extracellular sodium compartments in the human brain based on the T2 relaxation properties.

True three-dimensional cone-beam reconstruction (TTCR) algorithm.

A true three-dimensional cone-beam reconstruction (TTCR) algorithm for direct volume image reconstruction from 2-D cone-beam projections is developed for the complete sphere geometry. The algorithm is derived from the parallel-beam true three-dimensional reconstruction (TTR) algorithm and is based on the modified filtered backprojection technique, which uses a set of 2-D space-invariant filters. The proposed algorithm proved to be superior in spatial resolution to the parallel-beam TTR algorithm and to offer better computational efficiency.

In vivo magnetic resonance imaging of sodium in the human body.

Sodium magnetic resonance imaging of the human body in vivo has been tried and its clinical application is considered. A short T2 imaging algorithm with total volume excitation and a specialized RF coil focused to the region of interest have been adopted to improve the signal-to-noise ratio. Using a 1.5-T human body imaging system, several important organs including heart, liver, gallbladder, kidney, and spine have been examined to demonstrate their sodium concentration in vivo.

A method for in vivo MR imaging of the short T2 component of sodium-23.

A magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium-23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7-3.0 ms and (b) a long component T2e = 16-30 ms. Since our first in vivo imaging of sodium, an echo time of 10-15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE.

Quadrature-multiplexed rf excitation for information doubling in NMR imaging.

A quadrature multiplexed pulse sequence to double the data information in a given acquisition time is proposed for NMR tomography. This technique takes advantage of the Hermitian property of the Fourier transform operation in NMR imaging. The proposed technique uses two rf pulses with 90 degrees phase difference simultaneously applied for the excitation of the spins in two different slices. The method results in truly simultaneous data acquisition coming from two different anatomical slices which can be separated into the real and imaginary parts of the image domain. This technique, therefore, also allows us either to reduce the experiment time by half or double the number of slices in the same examination time, depending on the applied imaging scheme. As a preliminary study, simultaneous dual-slice imaging of a human head using a conventional single-slice imaging scheme was performed.

Chemical-shift artifact correction scheme using echo-time encoding technique.

An investigation has been undertaken to study the effects of chemical shift on NMR image obtained by the projection reconstruction technique. Mathematical simulation studies indicate that chemical shift causes blurring in NMR images regardless of the image reconstruction technique. A systematic study of such artifacts is presented and possible correction schemes are proposed. Exemplary results with and without correction of the chemical-shift artifact and pulse schemes employed for projection reconstruction are presented. The present chemical-shift correction scheme is basically the same as a spectroscopic imaging technique such as the existing 4-D NMR imaging method except that the encoding steps required can be reduced substantially in the case of modest spectroscopic resolution.

In vivo NMR imaging of sodium-23 in the human head.

We report the first clinical nuclear magnetic resonance (NMR) images of cerebral sodium distribution in normal volunteers and in patients with a variety of pathological lesions. We have used a 1.5 T NMR magnet system. When compared with proton distribution, sodium shows a greater variation in its concentration from tissue to tissue and from normal to pathological conditions. Image contrast calculated on the basis of sodium concentration is 7 to 18 times greater than that of proton spin density. Normal images emphasize the extracellular compartments. In the clinical studies, areas of recent or old cerebral infarction and tumors show a pronounced increase of sodium content (300-400%). Actual measurements of image density values indicate that there is probably a further accentuation of the contrast by the increased "NMR visibility" of sodium in infarcted tissue. Sodium imaging may prove to be a more sensitive means for early detection of some brain disorders than other imaging methods.

High-resolution circular ring positron tomograph with dichotomic sampling: Dichotom-I.

The circular ring transaxial positron camera developed earlier was refitted with a new dichotomic sampling scheme and aperture collimators on the detector array to improve the sampling and the overall system resolution. The z-axis slice thickness collimators were also limited to 1 cm, which corresponds to a slice thickness of 0.5 cm FWHM. Two different types of aperture collimators were adopted for high resolution (HR) and very high resolution (VHR) imaging, respectively. In HR mode a resolution of 6.5 mm FWHM was obtained without appreciable degradation of overall sensitivity, which represents a threefold improvement in resolution over the original system. In phantom studies with HR mode a sensitivity of 4500 counts s-1 muCi-1 cm-3 was obtained for a 20 cm diameter uniform phantom filled with water. A VHR mode experiment was also conducted to observe the ultimate resolution capability of the Dichotom-I system, and a resolution of 4.2 mm FWHM was obtained at the expense of sensitivity which was reduced by a factor of four from the HR mode experiment. The experience gained with Dichotom-I suggests a relatively simple and inexpensive modification of the existing NaI(T1) ring positron cameras, most of which suffer from low resolution due to poor sampling and poor intrinsic detector resolution.

An analysis of the interpersonal perceptions of adolescents.

The main purpose of this study is to investigate the concerns, needs, and other characteristics of interpersonal relationships of adolescents as reflected in the stories they write in response to a stimulus provided in the instrument developed by the author. The second objective is to investigate the main sources of influence on the interpersonal perceptions of adolescents. The subjects are 655 adolescents in Virginia; 43% are public high school students attending grades 9 through 12; and 57% are residents of reformatory facilities, ages 15-18. A comparison of these two groups regarding the types and frequency of themes elicited is made. The themes also are analyzed by sex and race. Content analysis indicates that the predominant themes are affiliation (family and friendship), aggression, achievement (sports), and drugs. As to the sources of influence, "personal experience" ranked highest, followed by "from my mind and my imagination," while "TV" and "books" ranked third and fourth with similar percentages.

True Three-Dimensional Reconstruction (TTR) Application of Algorithm toward Full Utilization of Oblique Rays.

The true three-dimensional reconstruction (TTR) algorithm previously proposed by the authors is extended to an algorithm with which full utilization of all the oblique rays is possible. Through this extended TTR (ETTR) algorithm, it is now possible not only to reconstruct an image of a larger object but also possible to obtain images which have substantially better signal-to-noise ratio. The basic TTR algorithm, as well as its extended version, will be discussed together with computer simulation results. In the appendixes, a new two-dimensional Fourier domain weighting function necessary for the implementation of the TTR and ETTR algorithms as well as the generality of the proposed TTR algorithm are discussed.