George K. Matsopoulos

Automatic retinal image registration scheme using global optimization techniques

Retinal image registration is commonly required in order to combine the complementary information in different retinal modalities. In this paper, a new automatic scheme to register retinal images is presented and is currently tested in a clinical environment. The scheme considers the suitability and efficiency of different image transformation models and function optimization techniques, following an initial preprocessing stage. Three different transformation models-affine, bilinear and projective-as well as three optimization techniques-downhill simplex method, simulated annealing and genetic algorithms-are investigated and compared in terms of accuracy and efficiency. The registration of 26 pairs of fluoroscein angiography and indocyanine green chorioangiography images with the corresponding red-free retinal images, showed the superiority of combining genetic algorithms with the affine and bilinear transformation models. A comparative study of the proposed automatic registration scheme against the manual method, commonly used in clinical practice, is finally presented showing the advantage of the proposed automatic scheme in terms of accuracy and consistency.

Multimodal registration of retinal images using self organizing maps

In this paper, an automatic method for registering multimodal retinal images is presented. The method consists of three steps: the vessel centerline detection and extraction of bifurcation points only in the reference image, the automatic correspondence of bifurcation points in the two images using a novel implementation of the self organizing maps and the extraction of the parameters of the affine transform using the previously obtained correspondences. The proposed registration algorithm was tested on 24 multimodal retinal pairs and the obtained results show an advantageous performance in terms of accuracy with respect to the manual registration.

Amifostine as radioprotective agent for the rectal mucosa during irradiation of pelvic tumors: A phase II randomized study using various toxicity scales and rectosigmoidoscopy

Aim: To evaluate the cytoprotective effect of amifostine against radiation-induced acute toxicity to the rectal mucosa. Patients and Methods: 36 patients irradiated for prostate or gynecologic cancer were randomized to receive amifostine (n = 18, group A) or not (n = 18, group B). The radiation-induced acute rectal toxicity was evaluated by using three different toxicity scales: WHO scale, EORTC/RTOG toxicity criteria, and a modified toxicity scale based on the LENT-SOMA grading scale and the endoscopic terminology of the World Organization for Digestive Endoscopy. The objective measurements were coming from flexible rectosigmoidoscopy performed at baseline and 1–2 days after completion of the radiotherapy schedule. Anterior-posterior fields were used in the gynecologic patients while 3-D conformal 4-field technique was applied in the prostate cancer patients. The area under the curve (AUC) for dose-volume histograms (DVHs) of the rectum was also assessed during a 3-D treatment planning schedule, and no significant differences were assessed between the two groups, indicating a homogeneous dose-volume effect. Results: Amifostine was well tolerated. No grade 2 or higher WHO and EORTC/RTOG acute toxicity was noted in group A, while acute rectal toxicity (≥ grade 1) was observed in 16/18 patients of group B versus 2/18 of group A (p < 0.001). The onset as well as the duration of acute rectal toxicity were significantly improved in group A (p = 0.002). Rectosigmoidoscopy revealed more severe rectal mucositis in noncytoprotected patients (group B), and modified LENT-SOMA overall mucositis grading score was significantly lower in group A (p = 0.003). Conclusion: Amifostine seems to have a significant cytoprotective efficacy in acute radiation-induced rectal mucositis in terms of symptomatic and objective endpoints.Ziel: Auswertung der zytoprotektiven Wirkung von Amifostin hinsichtlich der strahlungsinduzierten akuten Toxizität auf die Rektumschleimhaut. Patienten und Methodik: 36 aufgrund eines Prostata- oder gynäkologischen Karzinoms bestrahlte Patienten nahmen an einer randomisierten Studie teil. Die eine Hälfte (n = 18, Gruppe A) erhielt Amifostin, die andere Hälfte (n = 18, Gruppe B) nicht. Die strahlungsinduzierte akute Toxizität auf die Rektumschleimhaut wurde mit Hilfe von drei verschiedenen Toxizitätsskalen ausgewertet: der WHO-Skala, den Toxizitätskriterien der EORTC/RTOG und einer modifizierten Toxizitätsskala, die sowohl auf der LENTSOMA-Skala als auch auf der endoskopischen Terminologie der Weltorganisation für intestinale Endoskopie beruht. Zu Beginn und 1-2 Tage nach Beendigung der Strahlentherapie wurden mit Hilfe der flexiblen Rektosigmoidoskopie objektive Messungen vorgenommen. Für die gynäkologischen Patienten wurden ventrodorsale Felder benutzt, wohingegen bei den Patienten mit Prostatakarzinom eine 3-D konformale 4-Felder-Technik appliziert wurde. Während des 3-D-Therapieplans wurde auch die Fläche unter der Kurve (AUC) für die Auswertung in rektalen Dosis-Volumen-Histogrammen (DVH) bestimmt. Zwischen den beiden Gruppen war jedoch kein signifikanter Unterschied festzustellen, was auf eine homogene Dosis-Volumen-Wirkung hindeutet. Ergebnisse: Amifostin war gut verträglich. In Gruppe A wurde der Toxizitätsgrad 2 nach WHO und EORTC/RTOG weder erreicht noch überschritten. In Gruppe A wurde in 16 von 18 Fällen eine akute rektale Toxizität ≥ Grad 1 festgestellt, in Gruppe B dagegen nur in zwei von 18 Fällen (p < 0.001). Bei Gruppe A war hinsichtlich der Zeit bis zum Auftreten der Proktitis sowie deren Dauer eine deutliche Überlegenheit zu verzeichnen (p = 0.002). In der Kontrollgruppe (Gruppe B) deckte die Rektosigmoidoskopie eine wesentlich schwerere Rektumschleimhautentzündung auf, während dir Toxizität entsprechend der modifizierten LENT-SOMA-Skala in der Amifostingruppe bedeutend niedriger war (p = 0.003). Schlussfolgerung: Amifostin scheint in Anbetracht der beobachteten Symptome, gemessen an objektiven Endpunkten, bei akuter strahlungsinduzierter Proktitis eine zytoprotektive Wirkung zu haben

Contrast enhancement of images using Partitioned Iterated Function Systems

A new algorithm for the contrast enhancement of images, based on the theory of Partitioned Iterated Function System (PIFS), is presented. A PIFS consists of contractive transformations, such that the original image is the fixed point of the union of these transformations. Each transformation involves the contractive affine spatial transform of a square block, as well as the linear transform of the gray levels of its pixels. The transformation of the gray levels is determined by two parameters which adjust the brightness and the contrast of the transformed block. The PIFS is used in order to create a lowpass version of the original image. The contrast-enhanced image is obtained by adding the difference of the original image with its lowpass version, to the original image itself. The proposed algorithm uses a predefined constant value for the contrast parameter, whereas, the parameters of the affine spatial transform, as well as the parameter adjusting the brightness, are calculated using k-dimensional trees. The lowpass version of the original image is obtained applying the PIFS on the original image repeatedly while using a value for the contrast parameter that is lower than the predefined one. Quantitative and qualitative results stress the superior performance of the proposed contrast enhancement algorithm against four other widely used contrast enhancement methods; namely, linear and nonlinear unsharp masking, Contrast Limited Adaptive Histogram Equalization and Local Range Modification.

Radiotherapy in conjunction with intravenous infusion of 180 mg of disodium pamidronate in management of osteolytic metastases from breast cancer: Clinical evaluation, biochemical markers, quality of life, and monitoring of recalcification using assessments of gray-level histogram in plain radiographs

PURPOSE To evaluate the clinical improvement and radiographically monitor the effect of local radiotherapy in conjunction with disodium pamidronate (DP) on metastatic osteolytic disease. METHODS AND MATERIALS Thirty-three patients with osteolytic metastasis from advanced breast cancer received radiotherapy with a 6-MV linear accelerator up to a dose of 30 Gy (3 Gy/fraction, 5 d/wk) combined with 24 monthly sessions of a 180-mg DP infusion. Conventional X-rays were obtained during the first six sessions of DP treatment, retaining the same settings for each exposure. The analysis of the image attributes was based on measuring the first-order statistics of the mean value and energy of gray-level histograms in the osteolytic region. RESULTS The 6-month measurements compared with baseline showed statistically significant differences (p < 0.01, Wilcoxon test) in energy of gray-level histogram (-10.8%), mean value of gray-level histogram (+9.5%), pain score (-5.8 points), Eastern Cooperative Oncology Group status (-2.4 points), urine hydroxyproline/creatinine ratio (-41.7%), urine calcium/creatinine ratio (-58.8%), and bone alkaline phosphatase (-42.4%). Quality of life as determined by the European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire (version 3) also improved. During follow-up, 88% of patients had complete and 12% partial responses (International Union Against Cancer radiologic criteria). On multivariate analysis, greater changes in the mean value of the gray-level histogram and negative nodal status were predictors for a reduction in the number of skeletal complications after therapy. Flu-like syndrome occurred in 13 patients (39%) and was well managed with mild antipyretics. CONCLUSION Image-processing in plain radiographs offers an objective way to assess recalcification. The image-processing indexes, along with the measurements of performance status, quality of life, and biochemical markers, improved significantly. Local radiotherapy combined with long-term high-dose DP up to 180 mg is tolerable and has a high therapeutic response.

A comparative study of surface‐ and volume‐based techniques for the automatic registration between CT and SPECT brain images

Image registration of multimodality images is an essential task in numerous applications in three-dimensional medical image processing. Medical diagnosis can benefit from the complementary information in different modality images. Surface-based registration techniques, while still widely used, were succeeded by volume-based registration algorithms that appear to be theoretically advantageous in terms of reliability and accuracy. Several applications of such algorithms for the registration of CT-MRI, CT-PET, MRI-PET, and SPECT-MRI images have emerged in the literature, using local optimization techniques for the matching of images. Our purpose in this work is the development of automatic techniques for the registration of real CT and SPECT images, based on either surface- or volume-based algorithms. Optimization is achieved using genetic algorithms that are known for their robustness. The two techniques are compared against a well-established method, the Iterative Closest Point-ICP. The correlation coefficient was employed as an independent measure of spatial match, to produce unbiased results. The repeated measures ANOVA indicates the significant impact of the choice of registration method on the magnitude of the correlation (F = 4.968, p = 0.0396). The volume-based method achieves an average correlation coefficient value of 0.454 with a standard deviation of 0.0395, as opposed to an average of 0.380 with a standard deviation of 0.0603 achieved by the surface-based method and an average of 0.396 with a standard deviation equal to 0.0353 achieved by ICP. The volume-based technique performs significantly better compared to both ICP (p<0.05, Neuman Keuls test) and the surface-based technique (p<0.05, Neuman-Keuls test). Surface-based registration and ICP do not differ significantly in performance.

Amifostine as Radioprotective Agent for the Rectal Mucosa during Irradiation of Pelvic Tumors

Aim: To evaluate the cytoprotective effect of amifostine against radiation-induced acute toxicity to the rectal mucosa. Patients and Methods: 36 patients irradiated for prostate or gynecologic cancer were randomized to receive amifostine (n = 18, group A) or not (n = 18, group B). The radiation-induced acute rectal toxicity was evaluated by using three different toxicity scales: WHO scale, EORTC/RTOG toxicity criteria, and a modified toxicity scale based on the LENT-SOMA grading scale and the endoscopic terminology of the World Organization for Digestive Endoscopy. The objective measurements were coming from flexible rectosigmoidoscopy performed at baseline and 1–2 days after completion of the radiotherapy schedule. Anterior-posterior fields were used in the gynecologic patients while 3-D conformal 4-field technique was applied in the prostate cancer patients. The area under the curve (AUC) for dose-volume histograms (DVHs) of the rectum was also assessed during a 3-D treatment planning schedule, and no significant differences were assessed between the two groups, indicating a homogeneous dose-volume effect. Results: Amifostine was well tolerated. No grade 2 or higher WHO and EORTC/RTOG acute toxicity was noted in group A, while acute rectal toxicity (≥ grade 1) was observed in 16/18 patients of group B versus 2/18 of group A (p < 0.001). The onset as well as the duration of acute rectal toxicity were significantly improved in group A (p = 0.002). Rectosigmoidoscopy revealed more severe rectal mucositis in noncytoprotected patients (group B), and modified LENT-SOMA overall mucositis grading score was significantly lower in group A (p = 0.003). Conclusion: Amifostine seems to have a significant cytoprotective efficacy in acute radiation-induced rectal mucositis in terms of symptomatic and objective endpoints.Ziel: Auswertung der zytoprotektiven Wirkung von Amifostin hinsichtlich der strahlungsinduzierten akuten Toxizität auf die Rektumschleimhaut. Patienten und Methodik: 36 aufgrund eines Prostata- oder gynäkologischen Karzinoms bestrahlte Patienten nahmen an einer randomisierten Studie teil. Die eine Hälfte (n = 18, Gruppe A) erhielt Amifostin, die andere Hälfte (n = 18, Gruppe B) nicht. Die strahlungsinduzierte akute Toxizität auf die Rektumschleimhaut wurde mit Hilfe von drei verschiedenen Toxizitätsskalen ausgewertet: der WHO-Skala, den Toxizitätskriterien der EORTC/RTOG und einer modifizierten Toxizitätsskala, die sowohl auf der LENTSOMA-Skala als auch auf der endoskopischen Terminologie der Weltorganisation für intestinale Endoskopie beruht. Zu Beginn und 1-2 Tage nach Beendigung der Strahlentherapie wurden mit Hilfe der flexiblen Rektosigmoidoskopie objektive Messungen vorgenommen. Für die gynäkologischen Patienten wurden ventrodorsale Felder benutzt, wohingegen bei den Patienten mit Prostatakarzinom eine 3-D konformale 4-Felder-Technik appliziert wurde. Während des 3-D-Therapieplans wurde auch die Fläche unter der Kurve (AUC) für die Auswertung in rektalen Dosis-Volumen-Histogrammen (DVH) bestimmt. Zwischen den beiden Gruppen war jedoch kein signifikanter Unterschied festzustellen, was auf eine homogene Dosis-Volumen-Wirkung hindeutet. Ergebnisse: Amifostin war gut verträglich. In Gruppe A wurde der Toxizitätsgrad 2 nach WHO und EORTC/RTOG weder erreicht noch überschritten. In Gruppe A wurde in 16 von 18 Fällen eine akute rektale Toxizität ≥ Grad 1 festgestellt, in Gruppe B dagegen nur in zwei von 18 Fällen (p < 0.001). Bei Gruppe A war hinsichtlich der Zeit bis zum Auftreten der Proktitis sowie deren Dauer eine deutliche Überlegenheit zu verzeichnen (p = 0.002). In der Kontrollgruppe (Gruppe B) deckte die Rektosigmoidoskopie eine wesentlich schwerere Rektumschleimhautentzündung auf, während dir Toxizität entsprechend der modifizierten LENT-SOMA-Skala in der Amifostingruppe bedeutend niedriger war (p = 0.003). Schlussfolgerung: Amifostin scheint in Anbetracht der beobachteten Symptome, gemessen an objektiven Endpunkten, bei akuter strahlungsinduzierter Proktitis eine zytoprotektive Wirkung zu haben

A Phase II Randomized Study of Topical Intrarectal Administration of Amifostine for the Prevention of Acute Radiation-Induced Rectal Toxicity

Purpose:To investigate the cytoprotective effect of intrarectal amifostine administration on acute radiation-induced rectal toxicity.Patients and Methods:67 patients with T1b–2 N0 M0 prostate cancer were randomized to receive amifostine intrarectally (group A, n = 33) or not (group B, n = 34) before irradiation. Therapy was delivered using a four-field technique with three-dimensional conformal planning. In group A, 1,500 mg amifostine was administered intrarectally as an aqueous solution in a 40-ml enema. Two different toxicity scales were used: EORTC/RTOG rectal and urologic toxicity criteria along with a Subjective-RectoSigmoid (S-RS) scale based on the endoscopic terminology of the World Organization for Digestive Endoscopy. Objective measurements with rectosigmoidoscopy were performed at baseline and 1–2 days after the completion of radiotherapy. The area under curve for the time course of mucositis (RTOG criteria) during irradiation represented the mucositis index (MI).Results:Intrarectal amifostine was feasible and well tolerated without any systemic or local side effects. According to the RTOG toxicity scale, five out of 33 patients showed grade 1 mucositis in group A versus 15 out of 34 patients with grade 1/2 in group B (p = 0.026). Mean rectal MI was 0.3 ± 0.1 in group A versus 2.2 ± 0.4 in group B (p < 0.001), while S-RS score was 3.9 ± 0.5 in group A versus 6.3 ± 0.7 in group B (p < 0.001). The incidence of urinary toxicity was the same in both groups.Conclusion:Intrarectal administration of amifostine seems to have a cytoprotective efficacy in acute radiation-induced rectal mucositis. Further randomized studies are needed for definitive therapeutic decisions.Ziel:Untersuchung des zytoprotektiven Effekts von intrarektal verabreichtem Amifostin zur Verhinderung akuter rektaler Strahlentoxizität.Patienten und Methodik:67 Patienten mit einem Prostatakarzinom im Stadium T1b–2 N0 M0 wurden randomisiert zwei Gruppen zugeteilt: Gruppe A (n = 33) mit und Gruppe B (n = 34) ohne intrarektale Verabreichung von Amifostin vor der Bestrahlung. Zur Behandlung wurde eine Vier-Felder-Technik mit dreidimensionaler konformaler Bestrahlungsplanung eingesetzt. Die Patienten in Gruppe A erhielten 1 500 mg Amifostin intrarektal als wässrige Lösung in einem 40-ml-Klysma. Zwei verschiedene Toxizitätsskalen wurden verwendet, die rektalen und urologischen Toxizitätskriterien der EORTC/RTOG und die auf der endoskopischen Terminologie der WODE (World Organization for Digestive Endoscopy) basierende S-RS-Skala („Subjective-RectoSigmoid scale“). Mittels Rektosigmoidoskopie wurden objektive Messungen vor und 1–2 Tage nach der Beendigung der Strahlentherapie durchgeführt. Der Bereich unter der Kurve (AUC) für den zeitlichen Verlauf einer Mukositis (RTOG-Kriterien) während der Bestrahlung stellte den Mukositis-Index (MI) dar.Ergebnisse:Die intrarektale Verabreichung von Amifostin erwies sich als einfach und gut verträglich und führte zu keinen systemischen oder lokalen Nebenwirkungen. Gemäß der RTOG-Toxizitätsskala zeigten fünf von 33 Patienten der Gruppe A eine Mukositis Grad 1 und 15 von 34 Patienten der Gruppe B eine Mukositis Grad 1/2 (p = 0,026). Der mittlere rektale MI betrug in Gruppe A 0,3 ± 0,1 gegenüber 2,2 ± 0,4 in Gruppe B (p < 0,001), während der S-RS-Score in Gruppe A bei 3,9 ± 0,5 gegenüber 6,3 ± 0,7 in Gruppe B lag (p < 0,001). Toxische Wirkungen an den Harnwegen traten in beiden Gruppen gleich häufig auf.Schlussfolgerung:Die intrarektale Verabreichung von Amifostin scheint bei akuter strahleninduzierter Entzündung der Rektumschleimhaut zytoprotektiv zu wirken. Weitere randomisierte Studien sind erforderlich, um definitive Therapieentscheidungen treffen zu können.

Application of Morphological Pyramids

A hierarchical image fusion scheme is presented which preserves the details of the input images regardless of their scale. The technique is demonstrated by fusing phantom images derived from magnetic resonance (MR) and computed tomography (CT) scanners. Results are given to show that fused images preserve a more detailed representation of the scene and provide information that cannot be obtained by viewing the input images separately.

Thoracic non-rigid registration combining self-organizing maps and radial basis functions

An automatic three-dimensional non-rigid registration scheme is proposed in this paper and applied to thoracic computed tomography (CT) data of patients with stage III non-small cell lung cancer (NSCLC). According to the registration scheme, initially anatomical set of points such as the vertebral spine, the ribs, and shoulder blades are automatically segmented slice by slice from the two CT scans of the same patient in order to serve as interpolant points. Based on these extracted features, a rigid-body transformation is then applied to provide a pre-registration of the data. To establish correspondence between the feature points, the novel application of the self-organizing maps (SOMs) is adopted. In particular, the automatic correspondence of the interpolant points is based on the initialization of the Kohonen neural network model capable to identify 500 corresponding pairs of points approximately in the two CT sets. Then, radial basis functions (RBFs) using the shifted log function is subsequently employed for elastic warping of the image volume, using the correspondence between the interpolant points, as obtained in the previous phase. Quantitative and qualitative results are also presented to validate the performance of the proposed elastic registration scheme resulting in an alignment error of 6 mm, on average, over 15 CT paired datasets. Finally, changes of the tumor volume in respect to each reference dataset are estimated for all patients, which indicate inspiration and/or movement of the patient during acquisition of the data. Thus, the practical implementation of this scheme could provide estimations of lung tumor volumes during radiotherapy treatment planning.