Analytical propagation of errors in dynamic SPECT: estimators, degrading factors, bias and noise.
(33/5118)
Dynamic SPECT is a relatively new technique that may potentially benefit many imaging applications. Though similar to dynamic PET, the accuracy and precision of dynamic SPECT parameter estimates are degraded by factors that differ from those encountered in PET. In this work we formulate a methodology for analytically studying the propagation of errors from dynamic projection data to kinetic parameter estimates. This methodology is used to study the relationships between reconstruction estimators, image degrading factors, bias and statistical noise for the application of dynamic cardiac imaging with 99mTc-teboroxime. Dynamic data were simulated for a torso phantom, and the effects of attenuation, detector response and scatter were successively included to produce several data sets. The data were reconstructed to obtain both weighted and unweighted least squares solutions, and the kinetic rate parameters for a two-compartment model were estimated. The expected values and standard deviations describing the statistical distribution of parameters that would be estimated from noisy data were calculated analytically. The results of this analysis present several interesting implications for dynamic SPECT. Statistically weighted estimators performed only marginally better than unweighted ones, implying that more computationally efficient unweighted estimators may be appropriate. This also suggests that it may be beneficial to focus future research efforts upon regularization methods with beneficial bias-variance trade-offs. Other aspects of the study describe the fundamental limits of the bias variance trade-off regarding physical degrading factors and their compensation. The results characterize the effects of attenuation, detector response and scatter, and they are intended to guide future research into dynamic SPECT reconstruction and compensation methods. (+info)
Contrast-enhanced power Doppler sonography for the differentiation of cystic renal lesions: preliminary study.
(34/5118)
The objective of this study was to investigate the potential usefulness of contrast-enhanced power Doppler ultrasonography in the differentiation of benign and malignant cystic renal lesions. Our study group was limited to patients who had complex cystic renal lesions of uncertain malignancy at screening ultrasonography. During the previous 6 months, 485 patients have been referred to ultrasonography for evaluation of renal cystic lesions, but only 13 patients participated in this study. Focusing on tumor vascularity in the intracystic septa or solid component, we analyzed power Doppler sonographic images before and after intravenous injection of contrast agent and compared them with contrast-enhanced CT scans or MR images and pathologic results. The visualization of vascularity was best on contrast-enhanced power Doppler sonography (n = 7). The use of contrast agent with power Doppler sonography showed improved diagnostic accuracy (77%) that was superior to non-contrast-enhanced power Doppler sonography or contrast-enhanced CT. In conclusion, contrast-enhanced power Doppler sonography provides better visualization of tumor vascularity in complicated cystic renal lesions than other imaging modalities, leading to more exact differential diagnosis. We therefore expect that this imaging modality might be very useful in differential diagnosis of problematic cystic renal lesions, benign or malignant. (+info)
Extended field-of-view two-dimensional ultrasonography of the breast: improvement in lesion documentation.
(35/5118)
The purpose of this study was to evaluate the use of extended field-of-view two-dimensional ultrasonographic imaging for improvement in overall breast lesion documentation. Sonographic images of 59 patients with breast lesions or silicone implants were evaluated by three radiologists retrospectively to compare traditional static linear array images alone with images obtained with the addition of an extended field of view to determine if documentation of lesions was improved. The addition of extended field-of-view imaging improved lesion conspicuity by 21% over traditional images. It provided overall improvement in lesion documentation by including a reference point (nipple) or by more completely imaging large masses in 79% and implants in 69%. The larger field of view of this technique is promising as an adjunct to traditional sonography for breast lesion documentation. (+info)
Estimation of the systolic pulmonary arterial pressure using contrast-enhanced continuous-wave Doppler in patients with trivial tricuspid regurgitation.
(36/5118)
Noninvasive estimation of pulmonary arterial pressure is important for hemodynamic monitoring of patients with heart disease. In patients with tricuspid regurgitation (TR), the peak velocity of TR on continuous-wave (CW) Doppler can be used to estimate the systolic pulmonary arterial pressure (PAPs) using the simplified Bernoulli equation. We evaluated a new technique of contrast-enhanced CW Doppler for calculating PAPs in patients with trivial TR. Forty-one patients without visible TR detected by color Doppler, pulsed Doppler or CW Doppler were evaluated. Age ranged from 19 to 73 (55 +/- 12) years old. Tricuspid flow signals were recorded on CW Doppler after intravenous administration of indocyanin green (ICG) or Albunex. PAPs was calculated as; PAPs = 4 x VTR2 + 10 mmHg, where VTR is the peak velocity of TR. PAPs calculated using contrast-enhanced CW Doppler was compared with PAPs measured by the following cardiac catheterization. 1) TR signals were recorded using the contrast-enhanced CW Doppler technique in 39 of 41 patients (95%) after intravenous administration of contrast agents. 2) The error of estimate of PAPs using the contrast-enhanced CW Doppler technique was -2.4 +/- 7.5 mmHg, and the percent error was -10.7 +/- 32.4% in all patients. In 20 of 39 patients (51%), the error of estimate was within +/- 5 mmHg. 3) PAPs was overestimated by 12.2 +/- 6.1 mmHg in patients with good contrast enhancement of TR signals. The contrast-enhanced CW Doppler technique is useful for estimating PAPs noninvasively in patients with trivial TR. It is better to assume the right atrial pressure as 3-5 mmHg, not 10 mmHg, in patients with good enhancement of trivial TR. Physiological TR may be enhanced by contrast agents in these patients. (+info)
Normal myelination of the pediatric brain imaged with fluid-attenuated inversion-recovery (FLAIR) MR imaging.
(37/5118)
BACKGROUND AND PURPOSE: As in adult imaging, FLAIR can be applied to pediatric brain imaging, and this requires an appreciation of the normal pediatric brain appearance by FLAIR imaging. The purpose of this study was to describe the MR appearance of the brain in normal infants and young children as demonstrated by fluid-attenuated inversion-recovery (FLAIR) MR imaging. METHODS: We retrospectively examined MR brain studies, interpreted as normal by pediatric radiologists, from 29 patients (aged 1 to 42 months) to catalog the appearance of myelination in multiple brain areas. RESULTS: On T2-weighted images, white matter progressed from hyperintense to hypointense relative to adjacent gray matter over the first 2 years of life. An analogous, although slightly delayed sequence was observed on FLAIR images with the exception of the deep cerebral hemispheric white matter, which followed a triphasic sequence of development. On FLAIR images, the deep cerebral white matter was heterogeneously hypointense relative to gray matter in the young infant, became hyperintense early in the first few months of life, and then reverted to hypointense during the second year of life. CONCLUSION: The normal appearance and development of brain white matter must be taken into account when interpreting FLAIR images of infants and young children. (+info)
HTLV-I-associated myelopathy: acute progression and atypical MR findings.
(38/5118)
We describe serial MR imaging findings in a patient with HTLV-I-associated myelopathy. The patient had acute progression of neurologic symptoms and exhibited swelling of the entire length of the spinal cord with increased T2 signal and contrast enhancement on MR imaging. The spinal cord became atrophic a few years later. (+info)
Diffusion-weighted MR imaging in a rat model of syringomyelia after excitotoxic spinal cord injury.
(39/5118)
BACKGROUND AND PURPOSE: Recent experimental data have shown that an increase of excitatory amino acids and the initiation of inflammatory responses within the injured spinal cord may play a role in post-traumatic syringomyelia. The purpose of this study was to determine whether diffusion-weighted MR imaging with apparent diffusion coefficient (ADC) maps could provide earlier evidence of spinal cord cavitation in a rat model of syringomyelia than available with conventional MR imaging. METHODS: The spinal cord gray matter of four rats was injected with the alpha-amino-3 hydroxy-5 methyl-4 isoxazole propionic acid/metabotropic receptor agonist quisqualic acid. Animals were sacrificed at 1, 4, or 8 weeks after injection, and the spinal cords were fixed in formalin for 1 week and imaged with T1-, T2-, and diffusion-weighted sequences. One control specimen was also imaged. ADC maps were constructed from the diffusion-weighted data. Histopathologic analyses of sections stained with cresyl violet were compared with the MR images. RESULTS: By 1 week after injection, ADC maps at the level of injection showed areas within the gray matter of increased intensity and increased ADC values as compared with the control specimen. These bright areas corresponded to cysts or cavities within the cord parenchyma on the histopathologic sections. The ADC values within affected gray matter areas progressively increased at 4 and 8 weeks, also corresponding to cyst formation. Conventional T1- and T2-weighted images showed corresponding lesions with cystic characteristics at 4 and 8 weeks, but not at 1 week. CONCLUSION: In an animal model of syringomyelia, diffusion-weighted imaging with ADC maps detected cystic lesions within spinal cord gray matter before they were seen on conventional T1- and T2-weighted images. (+info)
BACKGROUND AND PURPOSE: Dynamic gadolinium-enhanced MR imaging has been used successfully to identify post-treatment recurrence or postoperative changes in rectal and cervical carcinoma. Our purpose was to evaluate the usefulness of dynamic gadolinium-enhanced MR imaging for distinguishing recurrent inverted papilloma (IP) from postoperative changes. METHODS: Fifteen patients with 20 pathologically proved lesions (recurrent IP, 12; fibrosis or granulation tissue, eight) were enrolled in the study. Three observers, blinded to pathologic results, independently evaluated conventional MR images, including T1-weighted (unenhanced and postcontrast), proton-density-weighted, and T2-weighted spin-echo images. Results then were determined by consensus. Dynamic images were obtained using fast spin-echo sequences at 5, 30, 60, 90, 120, 150, 180, and 300 seconds after the injection of gadolinium-diethylene-triamine penta-acetic acid. Time-signal intensity curves of suspected lesions were analyzed by a pharmacokinetic model. The calculated amplitude and tissue distribution time were used to characterize tissue, and their values were displayed as a color-coded overlay. RESULTS: T2-weighted images yielded a sensitivity of 67%, a specificity of 75%, and an accuracy of 70% in the diagnosis of recurrent IP. Contrast-enhanced T1-weighted images yielded a sensitivity of 75%, a specificity of 50%, and an accuracy of 65%. Pharmacokinetic analysis showed that recurrent IP had faster (distribution time, 41 versus 88 seconds) and higher (amplitude, 2.4 versus 1.2 arbitrary units) enhancement than did fibrosis or granulation tissue. A cut-off of 65 seconds for distribution time and 1.6 units for amplitude yielded a sensitivity of 100% and a specificity of 100% for diagnosing recurrent IP. CONCLUSION: Dynamic MR imaging can differentiate accurately recurrent IP from postoperative changes and seems to be a valuable diagnostic tool. (+info)