Scatter and attenuation correction changes interpretation of gated myocardial perfusion imaging

Attenuation correction may improve the diagnostic accuracy of myocardial perfusion imaging (MPI). However, few studies have dealt with the clinical consequences for reporting. We compared routine reports based on scatter-corrected MPI (MPI-routine) with consensus readings of scatter-corrected (MPI-scatter) and scatter plus attenuation-corrected studies (MPI-attenuation) to investigate the impact of attenuation correction on reporting. One hundred consecutive stable angina patients (including 55 men) were investigated in a ^99mTc-sestamibi 2-day gated protocol with scatter and attenuation correction. With MPI-routine, 53 patients had normal perfusion and 47 abnormal perfusion, compared to 62 and 38 with MPI-attenuation, and 54 and 46, respectively, with MPI-scatter. Agreement between MPI-routine and MPI-attenuation with respect to overall diagnosis (normal/abnormal perfusion) was 89% (kappa=0.78) compared to 95% (kappa=0.90) between MPI-routine and MPI-scatter. With MPI-attenuation, the overall routine diagnosis changed in 11 patients, of which ten cases were judged normal after scatter plus attenuation correction. The majority of the normalised studies were among patients with apparently single-vessel RCA disease as judged from MPI. Agreement rates with regard to normal, reversible or irreversible defects between MPI-attenuation and MPI-routine for the LAD, LCX and RCA territories were 88%, 97% and 85%, respectively, without significant sex differences. In conclusion, attenuation correction caused a change in diagnosis in approximately 10% of the patients, corresponding to one-fifth of the abnormal studies. In all but one case, the shift was from abnormal to normal, mostly because of a different interpretation in the RCA territory.This work was presented in part (as a poster) at the 6th International Conference of Nuclear Cardiology, Florence, Italy, April 29, 2003     

A ROC study of AMBER and conventional chest imaging in the detection of simulated interstitial lung disease

Purpose: The aim of this study was to compare the detection of simulated interstitial lung disease with Advanced Multiple Beam Equalization Radiography (AMBER) and conventional wide latitude screen-film radiography.Materials and methods: Interstitial disease of varying severity was simulated with overlays on an anthropomorphic chest phantom. A total of 60 images per modality was used in a Receiver Operating Characteristic (ROC) study.Results: AMBER performed significantly better than conventional radiography for all readers (P < 0.02). The difference was even more significant for the radiologist readers (P = 0.001). In each case the difference in ROC areas was between 5% and 9%.Conclusion: AMBER is superior to conventional wide latitude screen-film imaging in detecting the subtle patterns used to simulate interstitial lung disease.     

Scatter correction for clinical cone beam CT breast imaging based on breast phantom studies

In flat-panel detector-based cone beam CT breast imaging (CBCTBI) systems, scattering is an important factor that degrades image quality. It is not practical to measure the scattering profiles of a breast for all view angles in a patient study, but it is possible to develop a method to estimate the scattering profiles based on information acquired from breast phantom studies. A new scattering correction method is proposed for clinical CBCTBI in this study. The scattering profiles of three anthropomorphic uncompressed breast phantoms of different sizes were thoroughly investigated, and the results indicated that though phantom size differed, the scattering profiles were mainly determined by local breast diameters, which are the approximate diameters of coronal slices that are perpendicular to the nipple-to-chestwall direction. Thus for scattering correction purposes it is possible to establish a relationship between location breast diameters and local scattering profiles, namely the fitted smooth curves of scatter-to-primary ratios (SPR) and normalized scattered radiations (NSR). In clinical CBCTBI studies, after the local breast diameters are sampled and measured on projection images, the scattering image for every projection image can be generated based on the established relationship, and the projection images can be corrected using either the SPR based method or the NSR based method. Phantom studies and clinical studies showed that both the SPR and NSR methods are able to correct cupping artifacts and reduce reconstruction error. The SPR method does not increase tissue contrast or noise while the NSR method increases both.     

Small object contrast in AMBER and conventional chest radiography

The ability of a commercially available scanning equalization system for chest radiography to render small object contrast in the lung-, mediastinum-, and subdiaphragm-equivalent regions of an acrylic chest phantom was quantitatively evaluated. Images from nine chest phantoms that represented a wide range of patient sizes and dynamic ranges of x-ray transmittance were analyzed. Subject contrast was measured with a photostimulable phosphor detector, and images were acquired in both equalized and nonequalized (conventional) imaging modes. Available subject contrast in the lung-equivalent region was 8%-15% lower in the equalized images compared with the nonequalized images in all phantoms (patient types); contrast in the mediastinum-, retro-cardiac-, and subdiaphragm-equivalent regions was 11%-63% higher in the equalized images, with the degree of improvement increasing as patient size and dynamic range increased. Images of each phantom were also acquired with the screen-film systems currently in use at the authors' institution, permitting an assessment of the relative performance (in terms of radiographic contrast) of these imagers with and without use of equalization.     

数字X射线摄影中散射线滤除模板成像质量与辐射剂量学评价

目的比较散射线滤除模板及常规滤线栅对数字X射线影像进行散射线校正所成影像质量与辐射剂量差异。方法 以对比度-细节体模(CDRAD 2.0)及ROC统计学体模(ALVIM TRS)为成像对象,分别使用散射线滤除模板技术和常规滤线栅技术,获取经散射线校正的体模数字X射线影像,比较两种散射线滤除方法所得的体模影像图像质量因子(IQF)和信号检出概率,分析两种方法图像质量及体模表面入射剂量差别。结果 在不同体模表面照射剂量条件下,应用散射线滤除模板技术和常规滤线栅技术,消除散射线后的数字影像其图像质量因子(IQF)和信号检出概率(P_det)差异均有统计学意义(P<0.05)。结论 数字X射线摄影时,应用散射线滤除模板技术(SFTT)可以有效滤除散射线。与滤线栅相比,相同照射条件下SFTT能够明显改善图像质量;在获得相同图像质量前提下,应用SFTT,体模表面入射剂量比使用滤线栅降低30%;SFTT为数字X射线摄影中有效滤除散射线、提高X射线图像质量、降低患者剂量的可选择方法。     

Scatter modelling and compensation in emission tomography

In nuclear medicine, clinical assessment and diagnosis are generally based on qualitative assessment of the distribution pattern of radiotracers used. In addition, emission tomography (SPECT and PET) imaging methods offer the possibility of quantitative assessment of tracer concentration in vivo to quantify relevant parameters in clinical and research settings, provided accurate correction for the physical degrading factors (e.g. attenuation, scatter, partial volume effects) hampering their quantitative accuracy are applied. This review addresses the problem of Compton scattering as the dominant photon interaction phenomenon in emission tomography and discusses its impact on both the quality of reconstructed clinical images and the accuracy of quantitative analysis. After a general introduction, there is a section in which scatter modelling in uniform and non-uniform media is described in detail. This is followed by an overview of scatter compensation techniques and evaluation strategies used for the assessment of these correction methods. In the process, emphasis is placed on the clinical impact of image degradation due to Compton scattering. This, in turn, stresses the need for implementation of more accurate algorithms in software supplied by scanner manufacturers, although the choice of a general-purpose algorithm or algorithms may be difficult.     

Scatter correction based on an artificial neural network for99mTc and123I dual-isotope SPECT in myocardial and brain imaging

The aim of this study was to elucidate the clinical usefulness of scatter correction with an artificial neural network (ANN) in 99mTc and 123I dual-isotope SPECT. METHODS: Two algorithms for ANN scatter correction were tested: ANN-10 and ANN-3 employing 10 and 3 energy windows for data acquisition, respectively. Three patients underwent myocardial or brain SPECT with one of the following combinations of radiopharmaceuticals administered: 99mTc-tetrofosmin and 123I-metaiodobenzylguanidine (MIBG), 99mTc-methoxyisobutylisonitrile (MIBI) and 123I-beta-methyl-paraiodophenyl-pentadecanoic acid (BMIPP), or 99mTc-ethyl-cistainate dimmer (ECD) and 123I-iomazenil. The patients were also referred for single-isotope imaging incorporating conventional triple-energy window (TEW) scatter correction. Crosstalk- and scatter-corrected 99mTc- and 123I-SPECT images in dual-isotope acquisition with ANN were compared with those in single-isotope acquisition. RESULTS: The ANN method well separated 123I and 99mTc primary photons. Although ANN-10 yielded images of poor quality, ANN-3 offered comparable image quality with the single-isotope scan without significant increase of acquisition time. CONCLUSION: The proposed method is clinically useful because it provides various combinations of information without anatomical misregistration with one acquisition.     

Scatter fraction: measurement and correction

The concept of scatter in Positron Emission Tomography is reviewed regarding origin and influence on data. Different ways to measure and correct for scatter are discussed.     

Scatter radiation from abdominal CT examinations

Several water phantoms were scanned under a number of conditions and radiation exposure due to scatter was measured at the center of one end. The decrease of the scatter radiation exposure is nearly exponential with distance from the slice plane. The half-value distance is a function of the slice cross-sectional area. An empirical equation is presented to relate exposure to the pertinent variables.     

Scatter fraction: measurement and correction

The concept of scatter in Positron Emission Tomography is reviewed regarding origin and influence on data. Different ways to measure and correct for scatter are discussed.This article was presented at the 1st EEC workshop on accuracy determination in PET, January 19–20th. 1989 Pisa, Italy (COMACBME Concerted Project Characterization and Standardization of PET Instrumentation)     

Scatter radiation exposure during knee arthrography

Knee arthrography, as performed at the authors' institution, was simulated and scattered radiation exposure to a radiologist's gonads, thyroid, and eye lens was measured with a sensitive ionization chamber. Results show that radiologists who regularly conduct knee arthrography examinations can incur doses to the gonads that are less than 6% of the U.S. limits, and to the thyroid and eye that are approximately 10% of the U.S. limits. Since the scatter radiation from overhead imaging of stress views constituted most (greater than or equal to 60%) of the dose to the lens of the eye and the thyroid, spot imaging was evaluated as a substitute for overhead imaging in the assessment of the anterior cruciate ligament. This substitution resulted in no loss of clinical information and has now completely replaced overhead imaging of stress views at this institution.     

Scatter dose calculation for anti-scatter linear grids in mammography

Monte Carlo simulations were used to optimize the geometry of a mammography anti-scatter linear grid to achieve minimum scatter-to-primary ratio (SPR) for different X-ray tube voltages. A single optimum design of the grid with 0.9 mm septa height, 12 μm septa thickness and 100 μm interspace thickness was found for breast phantom thicknesses between 30 and 80 mm. The optimal grid has 0.153–0.330 scatter-to-primary ratio, a Bucky factor (BF) less than 2.5 and a contrast improvement factor (CIF) of 1.3.     

Scatter distribution in transmission measurements with positron emission tomography

The distribution of scattered radiation was measured for transmission scans in positron emission tomography by adding the scattered radiation distributions in different projections from line source experiments. It is shown that in a 20 cm diameter water-filled phantom the scattered radiation effects contribute approximately one-third of the events centrally in the field of view. This may lead to systematic errors of the order of 15-25% in reconstructed images. A scheme for correction for scattered radiation effects in the transmission scans is described and tested in phantom experiments.     

Scatter compensation in digital chest radiography using Fourier deconvolution

The authors present a numerical deconvolution technique to compensate for image degrading effects caused by scattered photons in radiographic chest images. Fourier transform techniques are used to deconvolve a shift invariant model of the two dimensional point spread response functions of the scattered radiation. This approach uses a digitized radiograph acquired with a standard chest imaging protocol, so no specialized imaging equipment is required. While the shift variant shape of the scatter model is optimized for the lung field, effective compensation is provided when this model shape is applied to other chest regions. Preliminary evaluation suggests that this technique can provide improved image contrast over the entire chest region.     

AMBER: a scanning multiple-beam equalization system for chest radiography

Conventional chest radiography is limited by the small useful exposure range of radiographic film. The wide variation in absorption thickness of different parts of the chest results in areas of under- and over-exposure. An advanced multiple-beam equalization system, AMBER, controls local exposure delivered to the film. The system has a row of 20 modulators in front of the x-ray tube, each able to change the height of the local slit beam during scanning. Changes are made in response to measurements from a linear detector array in front of the film cassette. This array consists of 20 individually functioning detectors coupled through electronic feedback loops to the 20 modulators. A scan is obtained in 0.8 second with a local exposure time of approximately 50 msec. AMBER results in radiographs with significantly improved exposure of the mediastinum without overexposure of the lungs.     

Scatter correction in scintigraphy: the state of the art

In scintigraphy, the detection of scattered photons degrades both visual image analysis and quantitative accuracy. Many methods have been proposed and are still under investigation to cope with scattered photons. The main features of the problem of scattering in radionuclide imaging are presented first, to provide a sound foundation for a critical review of the existing scatter correction techniques. These are described using a classification relating to their aims and principles. Their theoretical potentials are analysed, as well as the difficulties of their practical implementation. Finally, the problems of their evaluation and comparison are discussed. Correspondence to: I. Buvat