Application of diffusion kurtosis imaging in differential diagnosis of focal liver lesions.

Purpose: Diffusion kurtosis imaging (DKI) is an MRI method related to diffusion imaging (DWI) that is distinguished by a non-Gaussian calculation of water particles movements in tissues. The aim of the study was to assess DKI advantage over DWI in differentiating benign and malignant liver lesions. Material and methods: Analysis included prospectively acquired group of 83 patients referred consecutively for 3T-MRI liver tumor examination, with 95 liver lesions (31 benign, 59 malignant). MRI assessments were performed with standard protocol and DKI sequence with seven b-values (0-2,000 s/mm2). Quantitative data were acquired by placing ROIs in liver tumors on all b-value images, ROI data extracted, and calculation of DWI and DKI parameters. ADC was calculated for all b-values (ADC0-2000) and for three values of b = 0, 500, and 750 (s/mm2) (ADC0-500-750). DKI and ADC parameters for benign and malignant lesions were compared, and ROC curves were plotted. Results: Significant differences were obtained for all DKI and ADC parameters. ROC analysis showed AUC of DK, K, ADC0-2000, and ADC0-500-750 was 0.74, 0.77, 0.77, and 0.75, respectively. The highest sensitivity (of 0.91) was obtained for ADC0-2000. The highest specificity (0.65) and accuracy (0.80) was obtained for K. Conclusion: DKI technique yields statistically comparable results with DWI technique.

The impact of studying on the hippocampal volume in medical students and its correlation with the results of the Final Medical Examination: a single-centre, prospective observational cohort study.

Purpose: The hippocampus forms part of the limbic system and is involved in the learning process; it is responsible for transferring information from short-term to long-term memory. The aim of our study was to assess the effect of intensive studying on hippocampal volume and whether this correlates with exam results. Material and methods: The analysis included volunteer final-year medical students who underwent 2 volumetric 3D T1 magnetic resonance imaging scans with an interval of 20 weeks: 19 weeks before and one week after the Final Medi-cal Examination. FreeSurfer software was used to compare the volumes of the whole hippocampus and its subfields between the 2 measurements. We assessed correlations between changes in hippocampal volume and the time students spent studying, between changes in hippocampal volume and the results of the exam, and between time spent studying and exam results. Results: Forty participants (25 women and 15 men; mean age 25 years) were included in the analysis. The right hippocampus presubiculum area increased significantly over the study period (p = 0.029), whereas the volume of the left hippocampus remained unchanged. An increase in the volume of the right hippocampus correlated with longer study time (r = 0.371 in percentage and r = 0.397 in mm3) and better LEK exam results (r = 0.441 in percentage and r = 0.456 in mm3). Conclusions: Our research confirms the role of the hippocampus, particularly the subicular complex, in the process of learning and remembering, and suggest that the plastic abilities of the hippocampus depend on the intensity of learning and translate into better skills.

New Software for DQE Calculation in Digital Mammography Compliant with IEC 62220-1-2.

Significant improvements in mammography systems have been achieved with the introduction of active matrix flat-panel digital detectors. The advent of this technology also makes it possible to implement computational methods for quantitative image analysis. This study describes new software created to perform detective quantum efficiency (DQE) calculations fully compliant with the IEC 62220-1-2 standard. Python-based software was developed that contains modules to calculate inverse conversion function, modulation transfer function (MTF), noise power spectrum (NPS), and DQE itself. A graphical user interface (GUI) and further add-ons make this software more user-friendly. Results are immediately displayed diagrammatically, and complete output data are exported to a .csv file. The code is available freely, as a compiled, executable file (.exe). The program was successfully tested using DICOM images obtained from mammography units from different manufacturers. This study also includes validation of the new software, based on comparisons of results obtained for the same set of data with two other, freely available programs.

Perfusion-Diffusion Ratio: A New IVIM Approach in Differentiating Solid Benign and Malignant Primary Lesions of the Liver.

INTRODUCTION: In order to improve the efficacy of intravoxel incoherent motion (IVIM) parameters in characterising specific tissues, a new concept is introduced: the perfusion-diffusion ratio (PDR), which expresses the relationship between the signal S(b) decline rate as a result of IVIM and the rate of signal S(b) decline due to diffusion. The aim of this study was to investigate this novel approach in the differentiation of solid primary liver lesions. Material and Methods. Eighty-three patients referred for liver MRI between August 2017 and January 2020 with a suspected liver tumour were prospectively examined with the standard liver MRI protocol extended by DWI-IVIM sequence. Patients with no liver lesions, haemangiomas, or metastases were excluded. The final study population consisted of 34 patients with primary solid liver masses, 9 with FNH, 4 with regenerative nodules, 10 with HCC, and 11 with CCC. The PDR coefficient was introduced, defined as the ratio of the rate of signal S(b) decrease due to the IVIM effect to the rate of signal S(b) decrease due to the diffusion process, for b = 0. RESULTS: No significant differences were found between benign and malignant lesions in the case of IVIM parameters (f, D, or D ∗) and ADC. Significant differences were observed only for PDR, with lower values for malignant lesions (p = 0.03). The ROC analysis yielded an AUC value for PDR equal to 0.74, with a cut-off value of 5.06, sensitivity of 81%, specificity of 77%, and accuracy of 79%. CONCLUSION: PDR proved to be more effective than IVIM parameters and ADC in the differentiation of solid benign and malignant primary liver lesions.

Dependence of photon registration efficiency on LaBr3(Ce) detector orientation for in situ radionuclide monitoring.

Knowledge of a radiation detector's numerical characteristics allows its energy efficiency to be calibrated theoretically for any measurement geometry. Here, energy efficiency calibration is discussed for oriented LaBr3(Ce) detectors used for in situ radiation monitoring. Vertical and horizontal detector orientations relative to the ground surface are compared using efficiency calibrations based on the detector's numerical characteristics and are equally effective. Quantitative assessment of the different measurement geometries was performed using a new analytical approach: integrated absolute full energy peak efficiency.

Intravoxel incoherent motion MRI in evaluating inflammatory activity in ulcerative colitis: a pilot study.

BACKGROUND: A non-invasive tool for the assessment of ulcerative colitis (UC) activity is needed for treatment control. PURPOSE: To determine the efficacy of intravoxel incoherent motion (IVIM) in assessing inflammatory activity in UC. MATERIAL AND METHODS: In this prospective study, 20 adult patients underwent 3.0-T magnetic resonance imaging (MRI) IVIM diffusion-weighted imaging (DWI) with 10 b-values (0-900 s/mm2) 0-6 days after biopsies entailing colonoscopy. The inflammatory activity of large bowel segments was graded on endoscopy with Mayo score and on pathology with a six­grade classification system. IVIM­derived parameters (f, D, and D*) calculated from regions of interest placed within the bowel wall were correlated with both scores (56 and 34 bowel segments, respectively). Radiologists were blinded to endoscopy and pathology results. A T-test and Wilcoxon rank sum test was used in comparisons and receiver operating characteristic curve analysis was performed. RESULTS: Statistically significant differences were found between histopathologically inactive or mild activity and moderate to severe activity in f (respectively: mean = 0.19 and mean = 0.28, P = 0.024; area under the curve [AUC] = 0.723, sensitivity 0.82, specificity 0.59, accuracy 0.67 for a 0.185 cut-off value) and D (mean = 1.34 × 10-3mm2/s and mean = 1.07 × 10-3mm2/s, P = 0.0083; AUC = 0.735, sensitivity 0.91, specificity 0.54, accuracy 0.66 for cut-off value 1.24 × 10-3mm2/s). No significant difference in D* was noted. No significant correlation between Mayo endoscopic subscore, and f, D, nor D* was found. CONCLUSION: IVIM perfusion fraction correlates with UC activity and might represent emerging tool in assessment of inflammatory activity.

Intravoxel incoherent motion magnetic resonance imaging: basic principles and clinical applications.

The purpose of this article was to show basic principles, acquisition, advantages, disadvantages, and clinical applications of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI). IVIM MRI as a method was introduced in the late 1980s, but recently it started attracting more interest thanks to its applications in many fields, particularly in oncology and neuroradiology. This imaging technique has been developed with the objective of obtaining not only a functional analysis of different organs but also different types of lesions. Among many accessible tools in diagnostic imaging, IVIM MRI aroused the interest of many researchers in terms of studying its applicability in the evaluation of abdominal organs and diseases. The major conclusion of this article is that IVIM MRI seems to be a very auspicious method to investigate the human body, and that nowadays the most promising clinical application for IVIM perfusion MRI is oncology. However, due to lack of standardisation of image acquisition and analysis, further studies are needed to validate this method in clinical practice.

Optimal b-values for diffusion kurtosis imaging of the liver and pancreas in MR examinations.

PURPOSE: The objective was to optimise the number of b-values for diffusion kurtosis imaging (DKI) of the liver and pancreas in MR examinations to ensure reliable results with the shortest possible acquisition time. METHODS: Twenty healthy volunteers underwent DKI at 3.0 T Siemens Magnetom Skyra using 7 b-values (b = 0, 200, 500, 750, 1000, 1500, 2000 s/mm2). The regions of interest (ROIs) were placed in the liver (right lobe, left lobe) and pancreas (head, tail). DKI parameters (Dapp, Kapp) for ROIs were calculated for 7 b-values utilising the nonlinear least-squares (NLLS) Marquardt-Levenberg algorithm. All calculations were repeated for ten subsets of data, with the number of b-values reduced to 4. DKI parameters calculated for subsets were compared with parameters calculated for all 7 b-values. RESULTS: The correlation coefficient between DKI parameters calculated for 7 b-values and subsets ranged from 0.65 to 1.00. The coefficient of variation (CoV) of DKI parameters calculated for a group of volunteers varied from 8% to 42% and was not affected by the reduction of the b-values number. Only one subset of data (b = 0, 500, 1500 and 2000 s/mm2) simultaneously met two criteria: no statistical difference (p < 0.05) from results obtained for 7 b-values and very good correlation with them. CONCLUSIONS: DKI acquisition with 4 b-values (b = 0, 500, 1500 and 2000 s/mm2), compared to DKI acquisition utilising 7 b-values, allowed for the reduction of acquisition time by 36%, without affecting the calculated DKI parameters.

Reproducibility of intravoxel incoherent motion of liver on a 3.0T scanner: free-breathing and respiratory-triggered sequences acquired with different numbers of excitations.

PURPOSE: To optimise the intravoxel incoherent motion (IVIM) imaging of the liver on a 3.0T scanner by assessing parameter reproducibility on free-breathing (FB) and respiratory-triggered (RT) sequences acquired with different numbers of signal averages (NSA). MATERIAL AND METHODS: In this prospective study 20 subjects (M/F: 10/10; age: 25-62 years, mean: 39 years) underwent IVIM magnetic resonance imaging (MRI) on a 3.0T scanner using an 18-channel phase-arrayed coil and four different echo-planar sequences, each with 10 b values: 0, 10, 30, 50, 75, 100, 150, 200, 500, and 900 s/mm2. Images were acquired with FB and RT with NSA = 1-4 (FBNSA1-4, RTNSA1-4) and with NSA = 3-6 (FBNSA3-6, RTNSA3-6). Subsequently, for the assessment of reproducibility of IVIM-derived parameters (f, D, D*), each subject was scanned again with an identical protocol during the same session. IVIM parameters were calculated. The distribution of IVIM-parameters for each DWI sequence were given as the median value with first and third quartile. Inter-scan reproducibility for each IVIM parameter was evaluated using coefficient of variance and Bland-Altman difference. Differences between FB sequence and RT sequence were tested using non-parametric Wilcoxon signed-rank test. RESULTS: Mean coefficient of variance (%) for f, D, and D* ranged from 60 to 64, from 58 to 84, and from 82 to 99 for FBNSA1-4 sequence; from 50 to 69, from 41 to 97, and from 80 to 82 for RTNSA1-4 sequence; from 22 to 27, 15, and from 70 to 80 for FBNSA3-6 sequence; and from 21 to 32, from 12 to, and from 50 to 80 for RTNSA3-6 sequence, respectively. CONCLUSIONS: Increasing the number of signal averages for IVIM acquisitions allows us to improve the reproducibility of IVIM-derived parameters. The sequence acquired during free-breathing with NSA = 3-6 was optimal in terms of reproducibility and acquisition time.

Evaluation of Imaging Parameters of Ultrasound Scanners: Baseline for Future Testing.

BACKGROUND: Regular quality control is required in Poland only for those methods of medical imaging which involve the use of ionizing radiation but not for ultrasonography. It is known that the quality of ultrasound images may be affected by the wearing down or malfunctioning of equipment. MATERIAL/METHODS: An evaluation of image quality was carried out for 22 ultrasound scanners equipped with 46 transducers. The CIRS Phantom model 040GSE was used. A set of tests was established which could be carried out with the phantom, including: depth of penetration, dead zone, distance measurement accuracy, resolution, uniformity, and visibility of structures. RESULTS: While the dead zone was 0 mm for 89% of transducers, it was 3 mm for the oldest transducer. The distances measured agreed with the actual distances by 1 mm or less in most cases, with the largest difference of 2.6 mm. The resolution in the axial direction for linear transducers did not exceed 1 mm, but it reached even 5 mm for some of the convex and sector transducers, especially at higher depths and in the lateral direction. For 29% of transducers, some distortions of anechoic structures were observed. Artifacts were detected for several transducers. CONCLUSIONS: The results will serve as a baseline for future testing. Several cases of suboptimal image quality were identified along with differences in performance between similar transducers. The results could be used to decide on the applicability of a given scanner or transducer for a particular kind of examination.

Evaluation of Doses and Image Quality in Mammography with Screen-Film, CR, and DR Detectors - Application of the ACR Phantom.

BACKGROUND: Different methods of image quality evaluation are routinely used for analogue and digital mammography systems in Poland. In the present study, image quality for several screen-film (SF), computed radiography (CR), and fully digital (DR) mammography systems was compared directly with the use of the ACR mammography accreditation phantom. MATERIAL/METHODS: Image quality and mean glandular doses were measured and compared for 47 mammography systems in the Mazovia Voivodeship in Poland, including 26 SF systems, 12 CR systems, and 9 DR systems. The mean glandular dose for the breast simulated by 4.5 cm of PMMA was calculated with methods described in the "European guidelines for quality assurance in breast cancer screening and diagnosis". Visibility of the structures in the image (fibers, microcalcifications, and masses) was evaluated with the mammographic accreditation ACR phantom. RESULTS: Image quality for DR systems was significantly higher than for SF and CR systems. Several SF systems failed to pass the image quality tests because of artifacts. The doses were within acceptable limits for all of the systems, but the doses for the CR systems were significantly higher than for the SF and DR systems. CONCLUSIONS: The best image quality, at a reasonably low dose, was observed for the DR systems. The CR systems are capable of obtaining the same image quality as the SF systems, but only at a significantly higher dose. The ACR phantom can be routinely used to evaluate image quality for all types of mammographic systems.

Mean glandular doses in mammography: a comparison of values displayed by a mammography unit with in-house values, both using the method proposed by Dance.

The purpose of this work is to compare the mean glandular dose (MGD) displayed by the mammography system and the MGD calculated according to the method proposed by Dance for women. This study also attempts to analyse whether the relationship between the calculated and the displayed values is constant and what factors influence this relationship. Material for this study included data from 1200 exposures (i.e. six series; each series consisting of 200 exposures) performed with one full-field digital mammography unit. Based on collected parameters of exposures, values of the MGD for individual mammography examinations were calculated according to the methods proposed by Dance. Obtained values of the MGD were compared with the values displayed by the mammography system. The MGD displayed by the mammography system and the MGD calculated according to the method proposed by Dance for women are significantly different. This result emphasises the importance of verifying MGD values for patient radiation protection, particularly after machine servicing.

Measurement of image rotation angle in CT for radiotherapy treatment planning.

The geometric accuracy of CT images is essential when they are used for planning radiation therapy. In this study, a method of quantitative testing of image rotation in CT is presented, based on the automated analysis of an image of a phantom half-filled with water. A plug-in was written for ImageJ software for automated detection of a water surface in an image and measurement of its angle relative to a horizontal line. A water phantom can be used for the evaluation of image rotation for axial mode. In helical mode the movement of the table would cause movement of the water. The difference between image rotation for axial and helical scans can be evaluated by measuring and comparing the angles of the tabletop surface for both modes. Preliminary results of measurements for three CT scanners show that image rotation does not exceed 0.5°, and is less than 0.1° for the dedicated CT simulator. It was observed that, for one CT scanner image, the rotation angle depended on tube rotation time.

The medical physics specialization system in Poland.

This paper presents the situation of the profession of medical physicists in Poland. The official recognition of the profession of medical physicist in Polish legislation was in 2002. In recent years, more and more Universities which have Physics Faculties introduce a medical physics specialty. At present, there are about 15 Universities which offer such programmes. These Universities are able to graduate about 150 medical physicists per year. In 2002, the Ministry of Health introduced a programme of postgraduate specialization in medical physics along the same rules employed in the specialization of physicians in various branches of medicine. Five institutions, mostly large oncology centres, were selected as teaching institutions, based on their experience, the quality of the medical physics professionals, staffing levels, equipment availability, lecture halls, etc. The first cycle of the specialization programme started in 2006, and the first candidates completed their training at the end of 2008, and passed their official state exams in May 2009. As of January 2016, there are 196 specialized medical physicists in Poland. Another about 120 medical physicists are undergoing specialization. The system of training of medical physics professionals in Poland is well established. The principles of postgraduate training and specialization are well defined and the curriculum of the training is very demanding. The programme of specialization was revised in 2011 and is in accordance with EC and EFOMP recommendations.

Measurement-based model of a wide-bore CT scanner for Monte Carlo dosimetric calculations with GMCTdospp software.

The aim of this work was to create a model of a wide-bore Siemens Somatom Sensation Open CT scanner for use with GMCTdospp, which is an EGSnrc-based software tool dedicated for Monte Carlo calculations of dose in CT examinations. The method was based on matching spectrum and filtration to half value layer and dose profile, and thus was similar to the method of Turner et al. (Med. Phys. 36, pp. 2154-2164). Input data on unfiltered beam spectra were taken from two sources: the TASMIP model and IPEM Report 78. Two sources of HVL data were also used, namely measurements and documentation. Dose profile along the fan-beam was measured with Gafchromic RTQA-1010 (QA+) film. Two-component model of filtration was assumed: bow-tie filter made of aluminum with 0.5 mm thickness on central axis, and flat filter made of one of four materials: aluminum, graphite, lead, or titanium. Good agreement between calculations and measurements was obtained for models based on the measured values of HVL. Doses calculated with GMCTdospp differed from the doses measured with pencil ion chamber placed in PMMA phantom by less than 5%, and root mean square difference for four tube potentials and three positions in the phantom did not exceed 2.5%. The differences for models based on HVL values from documentation exceeded 10%. Models based on TASMIP spectra and IPEM78 spectra performed equally well.

Individual doses for women undergoing screening mammography examinations in Poland in 2007.

Exposure doses to women undergoing screening mammography examinations should be kept as low as reasonably achievable, but they should ensure high enough image quality for adequate diagnosis. The aim of this study was to estimate the radiation risk according to the 'European guidelines for quality assurance in breast cancer screening and diagnosis', fourth edition (European Commission 2006). Materials for this study were obtained from data from 250 screening mammography facilities in Poland. For every mammography facility, a standard average glandular dose for routine exposure was calculated. Furthermore, average glandular doses for individual mammography examinations obtained according to the methods proposed by Dance et al (2000 Phys. Med. Biol. 45 3225-40) were calculated. The average glandular doses determined for 250 mammography facilities ranged from 0.12 to 14.56 mGy (the mean values ranged from 0.62 to 4.53 mGy). Only for 39 mammography facilities were all exposures found to be below the acceptable level for an average glandular dose, and for only 18 mammography facilities did no exposures exceed the achievable levels for an average glandular dose. Average glandular doses to women undergoing mammography screening attained unnecessary high values, and they were found to depend on the technical parameters of the mammography equipment and maintenance of mammography units by personnel in various mammography facilities.

Computed tomography as a source of electron density information for radiation treatment planning.

PURPOSE: To evaluate the performance of computed tomography (CT) systems of various designs as a source of electron density (rho(el)) data for treatment planning of radiation therapy. MATERIAL AND METHODS: Dependence of CT numbers on relative electron density of tissue-equivalent materials (HU-rho(el) relationship) was measured for several general-purpose CT systems (single-slice, multislice, wide-bore multislice), for radiotherapy simulators with a single-slice CT and kV CBCT (cone-beam CT) options, as well as for linear accelerators with kV and MV CBCT systems. Electron density phantoms of four sizes were used. Measurement data were compared with the standard HU-rhoel relationships predefined in two commercial treatment-planning systems (TPS). RESULTS: The HU-rho(el) relationships obtained with all of the general-purpose CT scanners operating at voltages close to 120 kV were very similar to each other and close to those predefined in TPS. Some dependency of HU values on tube voltage was observed for bone- equivalent materials. For a given tube voltage, differences in results obtained for different phantoms were larger than those obtained for different CT scanners. For radiotherapy simulators and for kV CBCT systems, the information on rhoel was much less precise because of poor uniformity of images. For MV CBCT, the results were significantly different than for kV systems due to the differing energy spectrum of the beam. CONCLUSION: The HU-rho(el) relationships predefined in TPS can be used for general-purpose CT systems operating at voltages close to 120 kV. For nontypical imaging systems (e.g., CBCT), the relationship can be significantly different and, therefore, it should always be measured and carefully analyzed before using CT data for treatment planning.