Free autologous buccal mucosal graft transplantation to treat ocular complications after toxic epidermal necrolysis: case report.

BACKGROUND: Toxic epidermal necrolysis (TEN) can lead to ocular surface scarring associated with pain, dry eye symptoms, and decreased visual acuity that often are difficult to treat. HISTORY AND SIGNS: A 34-year-old woman was referred to our department two-years after TEN induced by lamotrigin (lamictal(R)). She was complaining of severe visual acuity loss, pain, and dry eye symptoms. Visual acuity was reduced to light perception in the right eye (RE) and to 0.2 in left eye (LE). Basal Schirmer test was 2 mm in RE and 3 mm in LE. With or without therapeutic contact lenses, the patient was experiencing severe discomfort requiring tear supplementation up to 50 - 80 times/day in both eyes. THERAPY AND OUTCOME: A free autologous mucosal graft (3.5 x 2.0 cm) was transplanted from the lower lip into the upper RE fornix. Six months after surgery, with therapeutic contact lenses, the need for tear supplementation was markedly reduced to 3 - 4 times/day in RE while it remained unchanged in LE. In RE, slit-lamp examination revealed decreases in the corneal stromal edema and in the diameter of neo-vessels associated with an improvement of visual acuity (counting fingers at 30 cm). Basal Schirmer test values were unchanged. It has to be mentioned that the improvement observed after surgery was markedly dependent on wearing a therapeutic contact lens. CONCLUSIONS: Free autologous buccal graft transplantation (with its presumably accessory salivary glands) in association with the use of a therapeutic contact lens can be an efficient approach to treat ocular complication following drug-induced TEN (Lyell's syndrome).

Improved image quality and computation reduction in 4-D reconstruction of cardiac-gated SPECT images.

Spatiotemporal reconstruction of cardiac-gated SPECT images permits us to obtain valuable information related to cardiac function. However, the task of reconstructing this four-dimensional (4-D) data set is computation intensive. Typically, these studies are reconstructed frame-by-frame: a nonoptimal approach because temporal correlations in the signal are not accounted for. In this work, we show that the compression and signal decorrelation properties of the Karhunen-Loève (KL) transform may be used to greatly simplify the spatiotemporal reconstruction problem. The gated projections are first KL transformed in the temporal direction. This results in a sequence of KL-transformed projection images for which the signal components are uncorrelated along the time axis. As a result, the 4-D reconstruction task is simplified to a series of three-dimensional (3-D) reconstructions in the KL domain. The reconstructed KL components are subsequently inverse KL transformed to obtain the entire spatiotemporal reconstruction set. Our simulation and clinical results indicate that KL processing provides image sequences that are less noisy than are conventional frame-by-frame reconstructions. Additionally, by discarding high-order KL components that are dominated by noise, we can achieve savings in computation time because fewer reconstructions are needed in comparison to conventional frame-by-frame reconstructions.

Noise characterization of block-iterative reconstruction algorithms: I. Theory.

Researchers have shown increasing interest in block-iterative image reconstruction algorithms due to the computational and modeling advantages they provide. Although their convergence properties have been well documented, little is known about how they behave in the presence of noise. In this work, we fully characterize the ensemble statistical properties of the rescaled block-iterative expectation-maximization (RBI-EM) reconstruction algorithm and the rescaled block-iterative simultaneous multiplicative algebraic reconstruction technique (RBI-SMART). Also included in the analysis are the special cases of RBI-EM, maximum-likelihood EM (ML-EM) and ordered-subset EM (OS-EM), and the special case of RBI-SMART, SMART. A theoretical formulation strategy similar to that previously outlined for ML-EM is followed for the RBI methods. The theoretical formulations in this paper rely on one approximation, namely, that the noise in the reconstructed image is small compared to the mean image. In a second paper, the approximation will be justified through Monte Carlo simulations covering a range of noise levels, iteration points, and subset orderings. The ensemble statistical parameters could then be used to evaluate objective measures of image quality.

Channelized hotelling and human observer correlation for lesion detection in hepatic SPECT imaging.

UNLABELLED: Mathematic "model" observers that predict human performance are of interest in medical imaging as substitutes in psychophysical studies. We have examined the correlations between human observers and several forms of the channelized Hotelling observer (CHO) for a tumor detection task with simulated SPECT liver images that were used to study the effects of scatter and scatter correction on detection. METHODS: A receiver operating characteristic (ROC) study was devised to investigate the relative value of a scatter-subtraction strategy in SPECT imaging. The study used simulated images of the biodistribution of 99mTc-labeled FO23C5 anticarcinoembryonic antigen antibodies within the liver. Projection data for 3 separate tumor locations and 5 strategies for handling scatter were obtained using Monte Carlo software applied to an anthropomorphic phantom. The strategies were (a) perfect scatter rejection, (b) no scatter correction, (c) no scatter correction under an assumption of an elevated amount of scatter, (d) an energy-spectrum-based scatter compensation of the normal-scatter case (b), and (e) similar scatter compensation for the elevated-scatter case (c). Image reconstruction approximated current clinical procedures at the University of Massachusetts Medical School. Human performance for each combination of location and strategy was based on averaging the areas under the ROC curve for 7 individuals. A set of 15 signal-to-noise ratios (SNRs) was derived from these averages for comparison with SNRs for CHO models featuring constant-Q and difference-of-gaussian (DOG) filters. RESULTS: The Spearman rank correlation coefficient was 0.92 (P = 0.000001) when comparing task performances for the average human and a constant-Q CHO using 4 square-profile channels. For the DOG version of the CHO, comparison with the average human found a coefficient of 0.84 (P = 0.00005). CONCLUSION: The significant positive correlations found between the rankings of the average human observer and the CHOs for our detection task indicate that a channelized model observer could eventually serve as a replacement for human observers. The specific CHO models we have used are best suited to screen for significant differences between strategies before a human psychophysical study.

Effects of scatter substraction on detection and quantitation in hepatic SPECT.

UNLABELLED: The purpose of this investigation was to examine the effects of subtractive scatter compensation methods on lesion detection and quantitation. METHODS: Receiver operating characteristic (ROC) methodology was used to measure human observer detection accuracy for tumors in the liver using synthetic images. Furthermore, ROC results were compared with mathematical models for detection and activity quantitation to examine (a) the potential for predicting human performance and (b) the relationship between the detection and quantitation tasks. Images with both low and high amounts of scatter were compared with the ideal case of images of primary photons only (i.e., perfect scatter rejection) and with images corrected by subtracting a scatter image estimated by the dual photopeak window method. RESULTS: With low contrast tumors in a low count background, the results showed that scatter subtraction improved quantitation but did not produce statistically significant increases in detection accuracy. However, primary images did produce some statistically significant improvements in detection accuracy when compared with uncorrected images, particularly for high levels of scatter. CONCLUSION: Although scatter subtraction methods may provide improved activity quantitation, they may not significantly improve detection for liver SPECT. The results imply that significant improvement in detection accuracy for the conditions tested may depend on the development of gamma cameras with better scatter rejection.

Attenuation compensation for cardiac single-photon emission computed tomographic imaging: Part 2. Attenuation compensation algorithms.

Attenuation is believed to be one of the major causes of false-positive cardiac single-photon emission computed tomographic perfusion images. This article provides an introduction to the approaches used to correct for nonuniform attenuation once a patient-specific attenuation map is available. Comparison is made of specific attenuation-correction algorithms from each of three major categories of compensation methods that are or will be available commercially. Examples of the use of the algorithms on simulated projections of a mathematic phantom modeling the anatomy of the upper torso are used to illustrate the ability of the methods to compensate for attenuation. The advantages and disadvantages of each approach are summarized, as well as areas that need further investigation.

An analytical approach for compensation of non-uniform attenuation in cardiac SPECT imaging.

Photon attenuation can reduce the diagnostic accuracy of cardiac SPECT imaging. Bellini et al have previously derived a mathematically exact method to compensate for attenuation in a uniform attenuator. Since the human thorax contains structures with differing attenuation properties, non-uniform attenuation compensation is required in cardiac SPECT. Given an estimate of the patient attenuation map, we show that the Bellini attenuation compensation method can be used in cardiac SPECT to provide a quantitatively accurate reconstruction of a central region in the image which includes the heart and surrounding soft tissue. Simulations using a mathematical cardiac-torso phantom were conducted to evaluate the Bellini method and to compare its performance to the ML-EM iterative algorithm, and to 180 degrees and 360 degrees filtered backprojection (FBP) with no attenuation compensation. 'Bulls-eye' polar maps and circumferential profiles showed that both the Bellini method and the ML-EM algorithm provided quantitatively accurate reconstructions of the myocardium, with a substantial reduction in attenuation-induced artifacts that were observed in the FBP images. The computational load required to implement the Bellini method is approximately equivalent to that required for one iteration of the ML-EM algorithm, thus it is suitable for routine clinical use.

The effect of intrinsic attenuation correction methods on the stationarity of the 3-D modulation transfer function of SPECT.

The application of stationary restoration techniques to SPECT images assumes that the modulation transfer function (MTF) of the imaging system is shift invariant. It was hypothesized that using intrinsic attenuation correction (i.e., methods which explicitly invert the exponential radon transform) would yield a three-dimensional (3-D) MTF which varies less with position within the transverse slices than the combined conjugate view two-dimensional (2-D) MTF varies with depth. Thus the assumption of shift invariance would become less of an approximation for 3-D post- than for 2-D pre-reconstruction restoration filtering. SPECT acquisitions were obtained from point sources located at various positions in three differently shaped, water-filled phantoms. The data were reconstructed with intrinsic attenuation correction, and 3-D MTFs were calculated. Four different intrinsic attenuation correction methods were compared: (1) exponentially weighted backprojection, (2) a modified exponentially weighted backprojection as described by Tanaka et al. [Phys. Med. Biol. 29, 1489-1500 (1984)], (3) a Fourier domain technique as described by Bellini et al. [IEEE Trans. ASSP 27, 213-218 (1979)], and (4) the circular harmonic transform (CHT) method as described by Hawkins et al. [IEEE Trans. Med. Imag. 7, 135-148 (1988)]. The dependence of the 3-D MTF obtained with these methods, on point source location within an attenuator, and on shape of the attenuator, was studied. These 3-D MTFs were compared to: (1) those MTFs obtained with no attenuation correction, and (2) the depth dependence of the arithmetic mean combined conjugate view 2-D MTFs.(ABSTRACT TRUNCATED AT 250 WORDS)

Histiocitoma fibroso benigno da orbita.(Relato de um caso). / Benign fibrous histiocytoma of the orbit. Report of a case

Os autores relatam um caso de histiocitoma fibroso benigno na orbita, mostrando os aspectos clinicos e os achados histopatologicos da lesao. Com base na literatura chamam a atencao para a raridade do tumor e tecem comentarios sobre o diagnostico diferencial e o tratamenteo