Maria Lyra

Filtering in SPECT image reconstruction

Single photon emission computed tomography (SPECT) imaging is widely implemented in nuclear medicine as its clinical role in the diagnosis and management of several diseases is, many times, very helpful (e.g., myocardium perfusion imaging). The quality of SPECT images are degraded by several factors such as noise because of the limited number of counts, attenuation, or scatter of photons. Image filtering is necessary to compensate these effects and, therefore, to improve image quality. The goal of filtering in tomographic images is to suppress statistical noise and simultaneously to preserve spatial resolution and contrast. The aim of this work is to describe the most widely used filters in SPECT applications and how these affect the image quality. The choice of the filter type, the cut-off frequency and the order is a major problem in clinical routine. In many clinical cases, information for specific parameters is not provided, and findings cannot be extrapolated to other similar SPECT imaging applications. A literature review for the determination of the mostly used filters in cardiac, brain, bone, liver, kidneys, and thyroid applications is also presented. As resulting from the overview, no filter is perfect, and the selection of the proper filters, most of the times, is done empirically. The standardization of image-processing results may limit the filter types for each SPECT examination to certain few filters and some of their parameters. Standardization, also, helps in reducing image processing time, as the filters and their parameters must be standardised before being put to clinical use. Commercial reconstruction software selections lead to comparable results interdepartmentally. The manufacturers normally supply default filters/parameters, but these may not be relevant in various clinical situations. After proper standardisation, it is possible to use many suitable filters or one optimal filter.

Cancer consequences of the Chernobyl accident in Europe outside the former USSR : A review

The accident which occurred during the night of April 25–26, 1986 in reactor 4 of the Chernobyl nuclear power plant in the Ukraine released considerable amounts of radioactive substances into the environment. Outside the former USSR, the highest levels of contamination were recorded in Bulgaria, Austria, Greece and Romania, followed by other countries of Central, Southeast and Northern Europe. Studies of the health consequences of the accident have been carried out in these countries, as well as in other countries in Europe. This report presents the results of a critical review of cancer studies of the exposed population in Europe, carried out on the occasion of the 10th anniversary of the Chernobyl accident. Overall, there is no evidence to date of a major public health impact of the Chernobyl accident in the field of cancer in countries of Europe outside the former USSR.

Rhenium-188 Production in Hospitals, by W-188/Re-188 Generator, for Easy Use in Radionuclide Therapy

Rhenium-188 (Re-188) is a high energy β-emitting radioisotope obtained from the tungsten-188/rhenium-188 (W-188/Re-188) generator, which has shown utility for a variety of therapeutic applications in nuclear medicine, oncology, and interventional radiology/cardiology. Re-188 decay is accompanied by a 155 keV predominant energy γ-emission, which could be detected by γ-cameras, for imaging, biodistribution, or absorbed radiation dose studies. Its attractive physical properties and its potential low cost associated with a long-lived parent make it an interesting option for clinical use. The setup and daily use of W-188/Re-188 generator in hospital nuclear medicine departments are discussed in detail. The clinical efficacy, for several therapeutic applications, of a variety of Re-188-labeled agents is demonstrated. The high energy of the β-emission of Re-188 is particularly well suited for effective penetration in solid tumours. Its total radiation dose delivered to tissues is comparable to other radionuclides used in therapy. Furthermore, radiation safety and shielding requirements are an important subject of matter. In the case of bone metastases treatment, therapeutic ratios are presented in order to describe the efficacy of Re-188 usage.

Quantification of myocardial perfusion in 3D SPECT images- stress/rest volume differences

Our attempt consists of modelling the heart left ventricle at stress and rest situation, using the myocardial scintigraphic data and focuses on how to demonstrate differences in obtained 3D stress/rest images. 70 cardiac patients had completed myocardium tests by Tc-99m tetrofosmin and a GE-Starcam - 4000 SPECT gamma - camera. SPECT (Single Photon Emission Computed Tomography) slices were created and used. The myocardial perfusion was estimated by comparing those slices and the suspicion of an ischemia was indicated.

Digital mammography texture analysis by computer assisted image processing

We investigate the use of mammograms texture features in a clinical evaluation in mammography in order to assist in the classification of an image based on the breast tissue index. Breast tissue indices give the possibility to analyze images and determine the similarity of the images and evaluate the classification of the obtained image The measures of similarity of images used for the texture analysis are based upon textural characteristics and the distribution of density in the breast. The features used include the gray-level histogram, and texture features based upon the gray-level co-occurrence matrix, moment-based features obtained by Matlab program application. The performance of the method was measured in terms of precision of retrieval measurements. The results indicate improvement that is related to breast density classification in mammograms. Image processing assisted by computer give the characterization of masses and micro-calcification texture. The methodology proposed in the present work is generic, and can be applied also to other imaging modalities and clinical applications, as for example, Ultrasound breast evaluation and Scintimammography.

Radiation protection of staff in 111In radionuclide therapy—is the lead apron shielding effective?

(111)In (Eγ = 171-245 keV, t1/2 = 2.83 d) is used for targeted therapies of endocrine tumours. An average activity of 6.3 GBq is injected into the liver by catheterisation of the hepatic artery. This procedure is time-consuming (4-5 min) and as a result, both the physicians and the technical staff involved are subjected to radiation exposure. In this research, the efficiency of the use of lead apron has been studied as far as the radiation protection of the working staff is concerned. A solution of (111)In in a cylindrical scattering phantom was used as a source. Close to the scattering phantom, an anthropomorphic male Alderson RANDO phantom was positioned. Thermoluminescent dosemeters were located in triplets on the front surface, in the exit and in various depths in the 26th slice of the RANDO phantom. The experiment was repeated by covering the RANDO phantom by a lead apron 0.25 mm Pb equivalent. The unshielded dose rates and the shielded photon dose rates were measured. Calculations of dose rates by Monte Carlo N-particle transport code were compared with this studys measurements. A significant reduction of 65 % on surface dose was observed when using lead apron. A decrease of 30 % in the mean absorbed dose among the different depths of the 26th slice of the RANDO phantom has also been noticed. An accurate correlation of the experimental results with Monte Carlo simulation has been achieved.

Patient-specific dosimetry in radionuclide therapy

This study presents an attempt to compare individualised palliative treatment absorbed doses, by planar images data and Monte Carlo simulation, in two in vivo treatment cases, one of bone metastases and the other of liver lesions. Medical Internal Radiation Dose schema was employed to estimate the absorbed doses. Radiopharmaceutical volume distributions and absorbed doses in the lesions as well as in critical organs were also calculated by Monte Carlo simulation. Individualised planar data calculations remain the method of choice in internal dosimetry in nuclear medicine, but with the disadvantage of attenuation and scatter corrections lack and organ overlay. The overall error is about 7 % for planar data calculations compared with that using Monte Carlo simulation. Patient-specific three-dimensional dosimetric calculations using single-photon emission computed tomography with a parallel computed tomography study is proposed as an accurate internal dosimetry with the additional use of dose-volume histograms, which express dose distributions in cases with obvious inhomogeneity.

Filters in 2D and 3D Cardiac SPECT Image Processing

Nuclear cardiac imaging is a noninvasive, sensitive method providing information on cardiac structure and physiology. Single photon emission tomography (SPECT) evaluates myocardial perfusion, viability, and function and is widely used in clinical routine. The quality of the tomographic image is a key for accurate diagnosis. Image filtering, a mathematical processing, compensates for loss of detail in an image while reducing image noise, and it can improve the image resolution and limit the degradation of the image. SPECT images are then reconstructed, either by filter back projection (FBP) analytical technique or iteratively, by algebraic methods. The aim of this study is to review filters in cardiac 2D, 3D, and 4D SPECT applications and how these affect the image quality mirroring the diagnostic accuracy of SPECT images. Several filters, including the Hanning, Butterworth, and Parzen filters, were evaluated in combination with the two reconstruction methods as well as with a specified MatLab program. Results showed that for both 3D and 4D cardiac SPECT the Butterworth filter, for different critical frequencies and orders, produced the best results. Between the two reconstruction methods, the iterative one might be more appropriate for cardiac SPECT, since it improves lesion detectability due to the significant improvement of image contrast.

Volume quantification of 123I-DaTSCAN imaging by MatLab for the differentiation and grading of parkinsonism and essential tremor

123I-DaTSCAN imaging studies have shown the ability to detect loss of striatal dopamine transporters. Aim of this work is to evaluate whether mathematical approach of striatum imaging data by Matlab program processing can differentiate between parkinsonian syndromes, of various stages, and essential tremor, and thus increase diagnostic accuracy. The extraction of parameters by digitized processing of 123I-DaTSCAN (123I-ioflupane) images to differentiate between parkinsonism and essential tremor and evaluation of SPECT imaging of the dopamine transporters (DAT) in vivo, will produce a display of pattern recognition. Eccentricity, major & minor axis length, orientation, area, equivalent diameter and integral intensity of both left & right ganglia were determined. A specific ratio of both ganglia parameters gives a classification indication and contributes in diagnosis decision.

Texture characterization in ultasonograms of the thyroid gland

This study tries a quantitative characterization of the thyroid tissue as far as homogeneity and echogenicity are concerned, to quantitatively evaluate thyroid texture. Digital image processing techniques offer the opportunity for texture description. Although there is no formal definition of texture, this particular method of description can quantify properties such as smoothness, coarseness and regularity. First-order and co-occurrence features are quantified and multi factor analysis is used to evaluate the optimal subset of parameters for thyroid texture.