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PubMedDate not supplied

Compression CT urography: a comparison with IVU in the opacification of the collecting system and ureters.

OBJECTIVE: The purpose of this study was to evaluate opacification of the collecting system and ureters using compression computed tomography (CT) urography compared with conventional intravenous urography (IVU). MATERIALS AND METHODS: Fifty consecutive patients underwent compression CT urography as part of a dedicated renal CT. A compression belt was applied prior to nephrographic phase imaging. Excretory phase scans were acquired through the kidneys 3 minutes post injection with the compression belt in place. The compression belt was then released, and scans were obtained through the ureters. Three independent readers then scored opacification of the collecting system and ureters on a scale of 0-2 (0 = no opacification, 1 = partial opacification, 2 = full opacification and distension). Fifty consecutive nonmatched IVUs were scored by segment by the same readers. Comparison of the two modalities was made using the Mann-Whitney U test. Interobserver agreement was assessed by the Kappa coefficient. RESULTS: CT demonstrated significantly better opacification (p < or = 0.02) of the upper and lower pole pelvicalyceal systems and midureters bilaterally. There was no difference in opacification of the proximal and distal ureters by CT compared with IVU. The Kappa coefficient was 0.53. CONCLUSIONS: Compression CT urography yields equal or better opacification of the collecting system and ureters when compared with IVU, and shows promise for the routine evaluation of the renal excretory system.

Adult↗

PubMed2002

Noninvasive reduction of open-book pelvic fractures by circumferential compression.

OBJECTIVES: To determine the efficacy and optimal application parameters of circumferential compression to reduce external rotation-type pelvic fractures. DESIGN: Biomechanical investigation on human cadaveric specimens. SETTING: Biomechanics laboratory. INTERVENTION: Partially stable and unstable external rotation injuries of the pelvic ring (OTA classification 61-B1 and 61-C1) were created in seven human cadaveric specimens. A prototype pelvic strap was applied subsequently at three distinct transverse levels around the pelvis. Circumferential pelvic compression was induced by gradual tensioning of the strap to attempt complete reduction of the symphysis diastasis. MAIN OUTCOME MEASUREMENTS: Pelvic reduction was evaluated with respect to strap tension and the strap application site. The effect of circumferential compression on intraperitoneal pressure and skin-strap interface pressure was measured. RESULTS: A successive increase in circumferential compression consistently induced a gradual decrease in symphysis diastasis. An optimal strap application site was determined, at which circumferential compression most effectively yielded pelvic reduction. The minimum strap tension required to achieve complete reduction of symphysis diastasis was determined to be 177 +/- 44 Newtons and 180 +/- 50 Newtons in the partially stable and unstable pelvis, respectively. CONCLUSIONS: Application of circumferential compression to the pelvic soft tissue envelope with a pelvic strap was an efficient means to achieve controlled reduction of external rotation-type pelvic fractures. This study derived application parameters with direct clinical implication for noninvasive emergent management of traumatic pelvic ring disruptions.

Aged↗

PubMedDate not supplied

Effects of three groin compression methods on patient discomfort, distress, and vascular complications following a percutaneous coronary intervention procedure.

BACKGROUND: Incidence of vascular complications (VCs) after sheath removal following a percutaneous coronary intervention procedure (PCIP) vary widely by the compression method used to achieve femoral artery hemostasis. OBJECTIVE: To determine if one groin compression method causes the least discomfort and distress for patients and results in fewer VCs. METHODS: Patients (n = 306, mean age = 62.3 years, 77% male, 96.4% Caucasian) undergoing PCIPs at a tertiary care center in the urban Midwest participated in this three-group experimental design study. They were randomly assigned to Femostop, C-clamp, or manual compression and rated level of groin discomfort and distress on a 0-10 Numeric Rating Scale (NRS) prior to, during, and after arterial compression was released. The groin area was assessed for any VCs (oozing, ecchymosis, hematoma) prior to sheath removal, after compression released, and 12 and 24 hr after sheath removal. RESULTS: No significant differences were found by compression method for discomfort, distress, or VCs. Regardless of method, not having a VC prior to femoral sheath removal contributes to less oozing (z = -3.1, p = .0019), hematoma (z = -9.4, p < .0001), and ecchymosis(z = -10.1, p < .0001). C-clamp contributes to less oozing when hemostasis time is < 30 min (z = -2.2, p = .03), and Femostop is superior when time to hemostasis is >30 min (z = -2.3, p = .02). Not receiving eptifibatide (Integrilin) contributes to less ecchymosis (z = -2.9, p = .004). CONCLUSIONS: Nurses need to be vigilant when caring for patients who have a VC prior to femoral sheath removal and have received antiplatelet medications. Further research is needed to identify patient characteristics that may contribute to VCs.

Adult↗

PubMedDate not supplied

The scanning electron microscopy of compressed vertebral bodies.

Scanning electron microscopy was used in this study to determine the effects of compression at different rates on the structure of trabecular bone in primate vertebral bodies. Rhesus monkey vertebral bodies were subjected to compressive loads at two different strain rates (8.89 x 10(-1) m/sec and 8.89 x 10(-5) m/sec). Each vertebral body was compressed to 50% of its original height. S-shaped bending of trabeculae was present in bodies compressed at the lower strain rate, while fractures were more predominant at the higher strain rate. The percentage of recovered height following compression was greater at the lower strain rate. Recovery of compressed vertebral bodies probably occurs through an unfolding of bent trabeculae. The more severe the damage to the vertebral trabeculae, the less recovery occurs.

Animals↗

PubMed2004

The effect of compressive axial preload on the flexibility of the thoracolumbar spine.

STUDY DESIGN: An in vitro flexibility study of the human thoracolumbar spine under compressive preload. OBJECTIVE: To attain kinematics descriptive of the thoracolumbar spine in vitro by applying a pure bending moment under a range of physiologic compressive preloads. SUMMARY OF BACKGROUND DATA: Many studies on the mechanical behavior of the spine under pure moment have been conducted; however, little is known regarding variations in the range of motion of the thoracolumbar spine attributable to simulated body weight and other physiologic load conditions. METHODS: Five fresh human cadaveric thoracolumbar spine specimens (T9-L3) were used. Five compressive axial preloads ranging from 75 to 975 N were applied to each specimen along the spinal curvature through four adjustable brackets attached to each vertebral body. Flexibility measurements were taken by applying a maximum of 5 Nm pure bending moment to the specimen in flexion and extension. The flexibilities in flexion and extension for each loading case were compared. RESULTS: The thoracolumbar spine supported compressive preloads as much as 975 N without damage or instability in the sagittal plane when the preload was applied along the natural curvature of the spine through estimated centers of rotation. The flexibility in bending (flexion/extension) of the ligamentous thoracolumbar spine decreased with increasing compressive preload. CONCLUSION: A higher bending stiffness was reached after the compressive load exceeded 500 N. Such knowledge could be used to establish better testing guidelines for implant evaluation and more realistic loading conditions.

Aged↗

PubMed2002

Treatment of lower lumbar radiculopathy caused by osteoporotic compression fracture: the role of vertebroplasty.

The authors used vertebroplasty for the treatment of severe lower lumbar radicular pain caused by osteoporotic compression fracture. Patients presented with severe radiating leg pain rather than lower back pain from recent osteoporotic compression fracture of lower lumbar vertebra. Radiologic findings showed osteoporotic compression fracture combined with preexisting stenosis of the intervertebral foramen resulting in root compression. After injection of polymethylmethacrylate into the compressed vertebral body through the pedicle of the symptomatic side, all seven patients experienced dramatic pain relief that lasted throughout the mean follow-up duration of 9.1 months. They conclude that vertebroplasty may be an effective way of relieving radicular pain caused by osteoporotic compression fracture combined with foraminal stenosis.

Aged↗

PubMed2004

Use of the talon hip compression screw in intertrochanteric fractures of the hip.

A retrospective analysis of a compression hip screw with four reversibly deployable talons was done. Fifty-four patients had sufficient radiographs to be included in this analysis. One-year mortality was 17% and increased to 41% by 2 years. No lag screws cut out, and postoperative slide was reduced compared with that in many published series. Three patients had revision of a failed alternate-type hip pin with the Talon hip compression screw. Previous studies showed the talons provide the definitive difference in allowing enhanced compression at the time of surgery, preventing cut-out by enhanced rotational stability, and allowing immediate postoperative weightbearing without excessive limb shortening. The failure mode of the Talon compression hip screw seems to be side-plate loosening rather than varus deformity and lag screw cut-out. The Talon compression hip screw especially is effective with weak, osteoporotic bone and in unstable, three-part and four-part fractures. A previous study showed that Talon deployment notably improved interfragment compression and torsional strength, and that engagement or penetration into or through the cortical bone at the base of the femoral head-neck junction in the inferior lag screw position was the critical technical step to maximize the talon lag screw purchase.

Adolescent↗

PubMed2003

Amorphous silicon, flat-panel, x-ray detector versus storage phosphor-based computed radiography: contrast-detail phantom study at different tube voltages and detector entrance doses.

RATIONALE AND OBJECTIVES: Evaluation of the contrast-detail performance of an active-matrix flat-panel x-ray detector in comparison with a storage phosphor system with special regard to the potential of dose reduction. METHODS: A digital x-ray detector based on cesium iodide (CsI) and amorphous silicon (a-Si) technology was compared with a fifth-generation storage phosphor system. A lucite plate with 36 drilled holes of varying diameters and depths was used as contrast-detail phantom. At 45 kVp, 70 kVp, and 113 kVp, images at 8 different detector entrance doses ranging between 0.3 microGy and 40 microGy were obtained. On soft-copy displays, 3 masked observers evaluated the detectability of each aperture in each image according to a 5-point scale. The mean sum scores of corresponding images were compared. RESULTS: For all tube voltages and detector entrance doses, the images obtained with the CsI/a-Si detector resulted in better observer contrast-detail performance as compared with the images of the storage phosphor system. The CsI/a-Si system allowed a calculated dose reduction of 39% at 45 kVp, 68% at 70 kVp, and 81% at 113 kVp as compared with the storage phosphor system, without loss of contrast-detail detectability. CONCLUSIONS: Under the conditions of the chosen experimental design, the CsI/a-Si system provided a superior contrast-detail performance as compared with the storage phosphor system. The potential of dose reduction increased with rising tube voltage.

Cesium↗

PubMed2000

Effect of slow compression on the linear stability of an accelerated shear layer

An analysis is given of the effect of a slow uniform anisotropic compression or expansion on the linear stability of a normally accelerated planar interface between two fluids with different densities and tangential velocities, i.e., a combined Kelvin-Helmholtz and Rayleigh-Taylor instability, but generalized to an arbitrary time-dependent acceleration history. The compression is presumed to be sufficiently slow that the density remains uniform within each fluid and hence depends only on time. The perturbation is taken to be sinusoidal with amplitude h(t). The time evolution of h is determined by requiring pressure continuity across the interface in the usual way. The resulting linearized stability equation is a second-order linear ordinary differential equation for h(t). Compared to the corresponding well-known result for incompressible fluids, it is found that normal compression has the effect of reducing the perturbation growth rate &hdot; by an obvious geometrical correction, while transverse compression does not directly affect the net growth rate but rather has the dynamical effect of increasing its time derivative. When attention is focused on the masses transported across the initial interface rather than h, the purely geometrical effects of compression no longer appear explicitly, while the dynamical effects remain. It is thereby shown that both normal and transverse compression dynamically enhance the mixing of material masses, in spite of the corresponding purely geometrical reduction in &hdot;.

Journal Article↗

PubMed2005

Quasi-isentropic compression by ablative laser loading: response of materials to dynamic loading on nanosecond time scales.

The TRIDENT laser was used to induce quasi-isentropic compression waves to approximately 15 GPa in samples of Si, by ablative loading using a laser pulse whose intensity increased smoothly over 2.5 ns. The intensity history of the pulse and the velocity history at the opposite surface of the sample were recorded. Experiments were performed using samples of two different thicknesses simultaneously, in which the evolution of the compression wave was clearly visible. Isentropic stress states deduced were consistent with the previously investigated response of Si to uniaxial loading. The ablative loading was simulated using radiation hydrodynamics, with different equations of state in the plasma and condensed regions and including elasticity in the solid Si. These calculations reproduced the measured velocity histories quite well, demonstrating that quasi-isentropic compression was induced with no preheat from the laser drive. Normal continuum behavior was demonstrated to hold below nanosecond time scales for isentropic compression waves, with no evidence for nonequilibrium effects in the crystal lattice. Details of the velocity history over about 10 GPa were reproduced less well, suggesting a deficiency in the model used for compressed Si, which may be consistent with recent theoretical predictions of uniaxial compression at high strain rates.

Journal Article↗

PubMed2003

Self-compression of laser pulses in plasma.

We study self-compression of weakly relativistically intense laser pulses in subcritical plasmas using one- (1D) and three-dimensional (3D) direct particle-in-cell (PIC) simulations. The self-compression works in the density window from 1/4 critical to slightly below critical density, where the Raman instability is prohibited. An analytical model is developed to describe the self-compression. The model admits pulsing Gaussian solutions and a long-lived running soliton solution. The 1D PIC results agree well with the analytical model, and compressions by an order of magnitude are observed. In the 3D geometry, the longitudinal self-compression competes with the transverse self-focusing/filamentation. To damp the filamentation we use a periodic plasma-vacuum structure. The 3D PIC simulations suggest that a 30 fs long laser pulse is efficiently compressed to 5 fs.

Journal Article↗

PubMed1991

Compression of the ambulatory ECG by average beat subtraction and residual differencing.

We implemented a method for compression of the abulatory ECG that includes average beat subtraction and first differencing of residual data. Our previous investigations indicated that this method is superior to other compression methods with respect to data rate as a function mean-squared-error distortion. Based on previous results we selected a sample rate of 100 samples per second and a quantization step size of 35 microV. These selections allow storage of 24 h of two-channel ECG data in 4 Mbytes of memory with a minimum rms distortion. For this sample rate and quantization level, we show that estimation of beat location and quantizer location can significantly affect compression performance. Improved compression resulted when beats were located with a temporal resolution of 5 ms and coarse quantization was performed in the compression loop. For the 24-h MIT/BIH arrhythmia database our compression algorithm coded a single-channel of ECG data with an average data rate of 174 bits per second.

Algorithms↗

PubMed1997

Wavelet and wavelet packet compression of electrocardiograms.

Wavelets and wavelet packets have recently emerged as powerful tools for signal compression. Wavelet and wavelet packet-based compression algorithms based on embedded zerotree wavelet (EZW) coding are developed for electrocardiogram (ECG) signals, and eight different wavelets are evaluated for their ability to compress Holter ECG data. Pilot data from a blind evaluation of compressed ECG's by cardiologists suggest that the clinically useful information present in original ECG signals is preserved by 8:1 compression, and in most cases 16:1 compressed ECG's are clinically useful.

Algorithms↗

PubMed1999

Mean-shape vector quantizer for ECG signal compression.

A direct waveform mean-shape vector quantization (MSVQ) is proposed here as an alternative for electrocardiographic (ECG) signal compression. In this method, the mean values for short ECG signal segments are quantized as scalars and compression of the single-lead ECG by average beat substraction and residual differencing their waveshapes coded through a vector quantizer. An entropy encoder is applied to both, mean and vector codes, to further increase compression without degrading the quality of the reconstructed signals. In this paper, the fundamentals of MSVQ are discussed, along with various parameters specifications such as duration of signal segments, the wordlength of the mean-value quantization and the size of the vector codebook. The method is assessed through percent-residual-difference measures on reconstructed signals, whereas its computational complexity is analyzed considering its real-time implementation. As a result, MSVQ has been found to be an efficient compression method, leading to high compression ratios (CR's) while maintaining a low level of waveform distortion and, consequently, preserving the main clinically interesting features of the ECG signals. CR's in excess of 39 have been achieved, yielding low data rates of about 140 bps. This compression factor makes this technique especially attractive in the area of ambulatory monitoring.

Electrocardiography↗

PubMed1997

Compression guidelines for diagnostic telepathology.

As the healthcare community has begun to rely increasingly upon digital technologies for acquisition, storage, and transmission of pictorial data, image compression has become an indispensable tool. We have investigated the feasibility of lossy compression in a well-defined task domain, the clinical assessment of digitized images of chromatic microscopic pathology specimens. The effect of compression was measured under two distinct perceptual criteria, just noticeable difference (j.n.d.) and largest tolerable distortion (l.t.d.), differing in the involvement required from subjects, who were experts in pathology. For standard JPEG compressed images it was found that when the experiment is performed under the l.t.d. criterion, a significantly larger compression ratio is reported as satisfactory. It is concluded that lossy compression holds promise for diagnostic telepathology.

Algorithms↗

PubMed2001

ECG data compression using truncated singular value decomposition.

The method of truncated singular value decomposition (SVD) is proposed for electrocardiogram (ECG) data compression. The signal decomposition capability of SVD is exploited to extract the significant feature components of the ECG by decomposing the ECG into a set of basic patterns with associated scaling factors. The signal informations are mostly concentrated within a certain number of singular values with related singular vectors due to the strong interbeat correlation among ECG cycles. Therefore, only the relevant parts of the singular triplets need to be retained as the compressed data for retrieving the original signals. The insignificant overhead can be truncated to eliminate the redundancy of ECG data compression. The Massachusetts Institute of Technology-Beth Israel Hospital arrhythmia database was applied to evaluate the compression performance and recoverability in the retrieved ECG signals. The approximate achievement was presented with an average data rate of 143.2 b/s with a relatively low reconstructed error. These results showed that truncated SVD method can provide an efficient coding with high-compression ratios. The computational efficiency of the SVD method in comparing with other techniques demonstrated the method as an effective technique for ECG data storage or signals transmission. Index Terms-Data compression, electrocardiogram, feature extraction, quasi-periodic signal, singular value decomposition.

Algorithms↗

PubMed2002

Medical image compression by sampling DCT coefficients.

Advanced medical imaging requires storage of large quantities of digitized clinical data. Due to the constrained bandwidth and storage capacity, however, a medical image must be compressed before transmission and storage. Among the existing compression schemes, transform coding is one of the most effective strategies. Image data in spatial domain will be transformed into spectral domain after the transformation to attain more compression gains. Based on the quantization strategy, coefficients of low amplitude in the transformed domain are discarded and significant coefficients are preserved to increase the compression ratio without inducing salient distortion. In this paper, we use an adaptive sampling algorithm by calculating the difference area between correct points and predicted points to decide the significant coefficients. Recording or transmitting the significant coefficients instead of the whole coefficients achieves the goal of compression. On the decoder side, a linear equation is employed to reconstruct the coefficients between two sequent significant coefficients. Simulations are carried out to different medical images, which include sonogram, angiogram, computed tomography, and X-ray images. Consequent images demonstrate the performance at compression ratios of 20-45 without perceptible alterations. In addition, two doctors are invited to verify that the decoded quality is acceptable for practical diagnosis. Therefore, our proposed method is found to preserve information fidelity while reducing the amount of data.

Algorithms↗

PubMed2002

Four-dimensional wavelet compression of arbitrarily sized echocardiographic data.

Wavelet-based methods have become most popular for the compression of two-dimensional medical images and sequences. The standard implementations consider data sizes that are powers of two. There is also a large body of literature treating issues such as the choice of the "optimal" wavelets and the performance comparison of competing algorithms. With the advent of telemedicine, there is a strong incentive to extend these techniques to higher dimensional data such as dynamic three-dimensional (3-D) echocardiography [four-dimensional (4-D) datasets]. One of the practical difficulties is that the size of this data is often not a multiple of a power of two, which can lead to increased computational complexity and impaired compression power. Our contribution in this paper is to present a genuine 4-D extension of the well-known zerotree algorithm for arbitrarily sized data. The key component of our method is a one-dimensional wavelet algorithm that can handle arbitrarily sized input signals. The method uses a pair of symmetric/antisymmetric wavelets (10/6) together with some appropriate midpoint symmetry boundary conditions that reduce border artifacts. The zerotree structure is also adapted so that it can accommodate noneven data splitting. We have applied our method to the compression of real 3-D dynamic sequences from clinical cardiac ultrasound examinations. Our new algorithm compares very favorably with other more ad hoc adaptations (image extension and tiling) of the standard powers-of-two methods, in terms of both compression performance and computational cost. It is vastly superior to slice-by-slice wavelet encoding. This was seen not only in numerical image quality parameters but also in expert ratings, where significant improvement using the new approach could be documented. Our validation experiments show that one can safely compress 4-D data sets at ratios of 128:1 without compromising the diagnostic value of the images. We also display some more extreme compression results at ratios of 2000:1 where some key diagnostically relevant key features are preserved.

Algorithms↗