Martin Poulus

University of Amsterdam, Amsterdam, North Holland, Netherlands

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Publications (8)18.28 Total impact

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    ABSTRACT: To evaluate the diagnostic performance of radiographers compared to radiologists in the detection of colorectal lesions in MR colonography. 159 patients at increased risk of colorectal cancer were included. Four different experienced observers, one MR radiologist, one radiologist in training and two radiographers evaluated all MR colonography examinations. The protocol included T1-weighted and T2-weighted sequences in prone and supine position. Colonoscopy was used as reference standard. Mean sensitivity rates with 95% confidence intervals (CIs) were determined on a per-patient and per-polyp basis, segmented by size (>or= 6mm and >or= 10mm). Specificity was calculated on a per-patient basis. The McNemar and chi-square (chi(2)) test was used to determine significant differences. At colonoscopy 74 patients (47%) had normal findings; 23 patients had 40 polyps with a size > or = 6mm. In 10 patients at least 1 polyp >or= 10mm was found (20 polyps in total). Similar sensitivities for patients with lesions >or= 10mm were found for radiologists and radiographers (65% (95%CI: 44-86%) vs. 50% (95%CI: 28-72%)) (p=n.s.). For lesions >or=10mm combined per-patient specificity for radiologists and radiographers was 96% (95%CI: 94-98%) and 73% (95%CI: 68-79%) (p<0.0001). Combined per-patient sensitivity for lesions >or=6mm differed significantly between both groups of observers (57% (95%CI: 42-71%) vs. 33% (95%CI: 19-46%)) (p=0.03). Radiographers have comparable sensitivity but lower specificity relative to radiologists in the detection of colorectal lesions >or= 10mm at MR colonography. Adequate training in evaluating MR colonography is necessary, especially for readers with no prior experience with colonography.
    European journal of radiology 11/2009; 75(2):e12-7. · 2.65 Impact Factor
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    ABSTRACT: Our purpose was to assess the effect of reader experience, fatigue, and scan findings on interpretation time for CT colonography. Nine radiologists (experienced in CT colonography); nine radiologists and ten technicians (both groups trained using 50 validated examinations) read 40 cases (50% abnormal) under controlled conditions. Individual interpretation times for each case were recorded, and differences between groups determined. Multi-level linear regression was used to investigate effect of scan category (normal or abnormal) and observer fatigue on interpretation times. Experienced radiologists (mean time 10.9 min, SD 5.2) reported significantly faster than less experienced radiologists and technicians; odds ratios of reporting times 1.4 (CI 1.1, 1.8) and 1.6 (1.3, 2.0), respectively (P<or=0.001). Experienced and less-experienced radiologists took longer to report abnormal cases; ratio 1.2 (CI 1.1,1.4, P<0.001) and 1.2 (1.0, 1.3, P=0.03), respectively. All groups took 70% as long to report the final five cases as they did with an initial five; ratio 0.7 (CI 0.6 to 0.8), P<0.001. For technicians only, accuracy increased with longer reporting times (P=0.04). Experienced radiologists report faster than do less-experienced observers and proportionally spend less time interpreting normal cases. Technicians who report more slowly are more accurate. All groups reported faster as the study period progressed.
    European Radiology 09/2006; 16(8):1745-9. · 4.34 Impact Factor
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    ABSTRACT: The extent measurement error on CT colonography influences polyp categorisation according to established management guidelines is studied using twenty-eight observers of varying experience to classify polyps seen at CT colonography as either 'medium' (maximal diameter 6-9 mm) or 'large' (maximal diameter 10 mm or larger). Comparison was then made with the reference diameter obtained in each patient via colonoscopy. The Bland-Altman method was used to assess agreement between observer measurements and colonoscopy, and differences in measurement and categorisation was assessed using Kruskal-Wallis and Chi-squared test statistics respectively. Observer measurements on average underestimated the diameter of polyps when compared to the reference value, by approximately 2-3 mm, irrespective of observer experience. Ninety-five percent limits of agreement were relatively wide for all observer groups, and had sufficient span to encompass different size categories for polyps. There were 167 polyp observations and 135 (81%) were correctly categorised. Of the 32 observations that were miscategorised, 5 (16%) were overestimations and 27 (84%) were underestimations (i.e. large polyps misclassified as medium). Caution should be exercised for polyps whose colonographic diameter is below but close to the 1-cm boundary threshold in order to avoid potential miscategorisation of advanced adenomas.
    European Radiology 09/2006; 16(8):1737-44. · 4.34 Impact Factor
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    ABSTRACT: A rare, complete ancient Roman burial site was discovered near the Dutch village of Bocholtz. In addition to many preserved grave offerings, there were countless fragments of deteriorated glass objects still buried in the ground. This glass was in very poor condition, however, and there was no possibility of excavating it directly. Instead, archeologists working at the site decided to dig up blocks of soil containing the glass fragments. High-resolution spiral computed tomography (CT) with multiplanar reformation, shaded-surface-display rendering, and volume rendering was used to obtain detailed information about the position, number, and form of the deteriorated glass fragments. CT-guided removal of the soil made it possible to restore some of the objects excavated from the blocks. In five of the 14 excavated objects, a correct Isings classification could be made based on the CT findings. In addition, CT was very important for the reconstruction of the layout of the burial chamber, the compilation of a list of grave contents, and the positioning of these contents within the chamber.
    Radiographics 01/2006; 26(6):1837-44. · 2.73 Impact Factor
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    ABSTRACT: PURPOSE To determine sensitivity and specificity of MR colonography (MRC) using limited bowel prep in a surveillance population. METHOD AND MATERIALS 180 consecutive surveillance patients at increased risk for colorectal cancer ((family-) history of colorectal cancer or polyps), all scheduled for surveillance colonoscopy were included. Two days prior to scanning patients started a low-fiber diet, ingested 10 ml of gadolinium three times a day for fecal tagging together with Lactulose. Prior to scanning water/gadolinium mixture was used for distension of the large bowel and opacification of the lumen. The MR protocol included prone and supine T1 and T2-weighted breath hold sequences. Prior to colonoscopy standard bowel preparation was used. One experienced MR radiologist (observer 1) and one research fellow (observer 2) evaluated the MRC two-dimensionally for polyps and cancer. Lesions detected at MRC were defined true positive if they corresponded exactly with lesions found at colonoscopy (reference standard). A lesion at MRC was defined false positive if it did not match with CS. RESULTS Of the 180 patients, 39% was female, and the mean age was 58 (SD 12) years. In none of the patients a carcinoma was present. Patient sensitivity: Observer 1 and 2 correctly identified respectively 5 (56%) and 6 (67%) of 9 patients with polyps ≥10mm and 5 (25%) and 12 (60%) of 20 patients with polyps ≥6mm. Retrospectively in 7 (78%) of 9 patients a polyp ≥10mm was visible at MR. Patient specificity: Observer 1 and 2 correctly identified respectively 166 (97%) and 169 (99%) of 171 patients without polyps ≥10mm and 123 (77%) and 147 (92%) of 160 patients without polyps ≥6mm. Polyp sensitivity: Observer 1 and 2 correctly identified respectively 11 (58%) and 9 (47%) of 19 polyps ≥10mm and 13 (35%) and 18 (49%) of 37 polyps ≥6mm. Retrospectively 14 (73%) of 19 polyps ≥10mm were visible at MR. CONCLUSION Specificity of MRC using limited bowel prep was good, sensitivities varied ranging from 56% to 67% for patients with polyps ≥10mm. These results are in line with larger studies on CT colonography in low prevalence populations using a 2D display method for evaluation.
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 11/2005
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    ABSTRACT: LEARNING OBJECTIVES 1. To describe the technique and potential value of high resolution spiral CT with multiplanar reformatting, surface- and volume rendering in the study of ancient glass still in situ in the ground. ABSTRACT Introduction: A Roman tomb revealed many well-kept grave deposits and countless fragments of glass still in situ in the ground. This glass could not be excavated. Blocks of soil containing these fragments were dug up. Purpose: To study multi-slice CT with reformatting and rendering in determining position and shape of glass fragments in blocks of soil. Material and methods: Six blocks were studied. An archeologist experienced in Roman glass analyzed the images in collaboration with a technician experienced in radiology of archeological objects. Results: 23 glass objects were identified e.g. 9 bottles type Ising 50 and type Isings 51. In all cases position, typification and numbers of the objects could be obtained. CT-guided removal of soil aided restoration of some of the objects. The typification based on the CT was in concordance with the findings at restoration. Conclusion: HRCT can accurately visualize ancient glass still in situ in soil.
    Radiological Society of North America 2005 Scientific Assembly and Annual Meeting; 11/2005
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    ABSTRACT: Ancient Egyptians used mummification techniques to prevent their deceased from decay. This study evaluates the potential of computed tomography (CT) in determining these techniques in a non-destructive way. Twenty-five mummies were studied by using high-resolution spiral CT, 1mm slice thickness for the head and 3mm slice thickness for the rest of the body. Images were reconstructed with 3D, multiplanar reformatting and volume rendering. In all cases the used mummification techniques could be reconstructed. The way the brain was removed, the presence of chemicals, like resin and natron, could be detected and the way the intestines were handled could be made visible. The use of CT is indispensable as a non-destructive method in the reconstruction of mummification techniques.
    Computerized Medical Imaging and Graphics 07/2002; 26(4):211-6. · 1.50 Impact Factor
  • Radiographics 01/2002; 22(1):63-6. · 2.73 Impact Factor