| 1. |
- Dustler, Magnus, et al.
(författare)
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A Study of the Feasibility of using slabbing to reduce Tomosynthesis Review Time
- 2013
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Ingår i: Medical Imaging 2013: Image Perception, Observer Performance, And Technology Assessment. - : SPIE. - 0277-786X .- 1996-756X. ; 8673, s. 86731-86731
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Konferensbidrag (refereegranskat)abstract
- This study aimed to investigate whether decreasing the amount of slices in breast tomosynthesis (BT) image volumes reduce reading time. BT slices were combined into so-called slabs, by reconstructing thin slices and merging them into thicker slabs. Sets of slabs where created from 35 clinical BT volumes with malignant or benignant findings and from 50 BT volumes drawn from screening sets (without any prior review). The image sets were reviewed in two separate sessions while the review time was recorded. A total of five experienced radiologists were employed for the image review. Additionally a VGA study was performed to compare slabbed images with the originals in order to ensure that the image quality was not significantly degraded. One set of 27 pathological cases (13 masses and 14 microcalcification clusters) and one of 22 subtle lesions that had been missed on digital mammography but detected on BT were presented to an experienced radiologist and 2 medical physicists who rated the quality of the slabbed versions relative to the originals. The study could find no significant degradation in image quality when using 2 mm slabs instead of 1 mm slices. There was no significant decrease in reading time on clinical cases (P=.133), but on screening images there was a significant decrease of 7.7 +/- 9.6 s from an average level of 32.2 +/- 14.5 s (P<.0001). This suggests that increasing slab thickness can reduce the time radiologists spend studying normal images by 20%.
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| 2. |
- Dustler, Magnus, et al.
(författare)
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Application of the fractal Perlin noise algorithm for the generation of simulated breast tissue
- 2015
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Ingår i: Medical Imaging 2015: Physics of Medical Imaging. - : SPIE. - 1996-756X .- 0277-786X. ; 9412, s. 94123-94123
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Konferensbidrag (refereegranskat)abstract
- Software breast phantoms are increasingly seeing use in preclinical validation of breast image acquisition systems and image analysis methods. Phantom realism has been proven sufficient for numerous specific validation tasks. A challenge is the generation of suitably realistic small-scale breast structures that could further improve the quality of phantom images. Power law noise follows the noise power characteristics of breast tissue, but may not sufficiently represent certain (e.g., non-Gaussian) properties seen in clinical breast images. The purpose of this work was to investigate the utility of fractal Perlin noise in generating more realistic breast tissue through investigation of its power spectrum and visual characteristics. Perlin noise is an algorithm that creates smoothly varying random structures of an arbitrary frequency. Through the use of a technique known as fractal noise or fractional Brownian motion (fBm), octaves of noise with different frequency are combined to generate coherent noise with a broad frequency range. fBm is controlled by two parameters - lacunarity and persistence - related to the frequency and amplitude of successive octaves, respectively. Average noise power spectra were calculated and beta parameters estimated in sample volumes of fractal Perlin noise with different combinations of lacunarity and persistence. Certain combinations of parameters resulted in noise volumes with beta values between 2 and 3, corresponding to reported measurements in real breast tissue. Different combinations of parameters resulted in different visual appearances. In conclusion, Perlin noise offers a flexible tool for generating breast tissue with realistic properties.
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| 3. |
- Förnvik, Daniel, et al.
(författare)
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A human observer study for evaluation and optimization of reconstruction methods in breast tomosynthesis using clinical cases
- 2011
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Ingår i: Medical Imaging 2011: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. ; 7961, s. 79615-79615
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Konferensbidrag (refereegranskat)abstract
- In breast tomosynthesis1 (BT) a number of 2D projection images are acquired from different angles along a limited arc. The imaged breast volume is reconstructed from the projection images, providing 3D information. The purpose of the study was to investigate and optimize different reconstruction methods for BT in terms of image quality using human observers viewing clinical cases. Sixty-six cases with suspected masses and calcifications were collected from 55 patients. Four different reconstructions of each image set were evaluated by four observers (two experienced radiologists, two experienced medical physicists): filtered back projection (FBP), iterative adapted FBP (iFBP) and two ML-convex iterative algorithm (MLCI) reconstructions (8 and 10 iterations) that differed in noise level and contrast of clinical details. Representation of masses and microcalcifications was evaluated. The structures were rated according to the overall appearance in a rank-order study. The differently reconstructed images of the same structure were displayed side by side in random order. The observers were forced to rank the order of the different reconstructed images and their proportions at each rank were scored. The results suggest that even though the FBP contains most noise its reconstructions are considered best overall, followed by iFBP, which contains least noise. In both FBP and iFBP methods the sharp borders and mass speculations were better represented than in iterative reconstructions while out-of-plane artifacts were better suppressed in the latter. However, in clinical practice the differences between the reconstructions may be considered negligible.
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| 4. |
- Förnvik, Daniel, et al.
(författare)
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Pressure distribution in mammography: compression of breasts with malignant tumor masses
- 2013
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Ingår i: Medical Imaging 2013: Physics of Medical Imaging. - : SPIE. - 1996-756X .- 0277-786X. ; 8668, s. 86684-86684
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Konferensbidrag (refereegranskat)abstract
- The pressure distribution over a compressed breast is in general heterogeneous. In this study we investigated the pressure distribution over compressed breasts with tumor masses. Twenty-two women either recalled for work-up of findings suspicious for breast cancer in the screening program or with clinically suspected findings were included in the study. Twenty-one lesions turned out to be malignant and one benign. The distribution of compression pressure was measured using thin FSR (Force Sensing Resistor) pressure sensors attached to the compression plate. The pressure over the breast was ascertained by acquiring an x-ray image of the compressed breast with the pressure sensors present. The pressure data and the mammogram were used to create a composite image with pressure data displayed as a color overlay. The malignant tumor area generally matched an elevated pressure area and this pressure was generally higher than the pressure over surrounding parenchyma. In 11 out of 22 (50%) subjects the maximum pressure over the breast was located over the tumor. Only 4 out of 22 (18%) masses had a lower tumor mean pressure compared to the mean pressure over the breast (including one small < 10 mm tumor and one benign structure). The results suggest that tumors are stiffer, thus, absorbing more pressure compared to the surrounding parenchyma and that this property can be quantified. Refined pressure techniques could possibly be used to demonstrate the relative elasticity distribution in breast tissue, which might provide valuable differential diagnostic information.
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| 5. |
- Petersson, Hannie, et al.
(författare)
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Monte Carlo simulation of breast tomosynthesis: visibility of microcalcifications at different acquisition schemes
- 2015
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Ingår i: Medical Imaging 2015: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. ; 9412, s. 94121-94121
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Konferensbidrag (refereegranskat)abstract
- Microcalcifications are one feature of interest in mammography and breast tomosynthesis (BT). To achieve optimal conditions for detection of microcalcifications in BT imaging, different acquisition geometries should be evaluated. The purpose of this work was to investigate the influence of acquisition schemes with different angular ranges, projection distributions and dose distributions on the visibility of microcalcifications in reconstructed BT volumes. Microcalcifications were inserted randomly in a high resolution software phantom and a simulation procedure was used to model a MAMMOMAT Inspiration BT system. The simulation procedure was based on analytical ray tracing to produce primary images, Monte Carlo to simulate scatter contributions and flatfield image acquisitions to model system characteristics. Image volumes were reconstructed using the novel method super-resolution reconstruction with statistical artifact reduction (SRSAR). For comparison purposes, the volume of the standard acquisition scheme (50 degrees angular range and uniform projection and dose distribution) was also reconstructed using standard filtered backprojection (FBP). To compare the visibility and depth resolution of the microcalcifications, signal difference to noise ratio (SDNR) and artifact spread function width (ASFW) were calculated. The acquisition schemes with very high central dose yielded significantly lower SDNR than the schemes with more uniform dose distributions. The ASFW was found to decrease (meaning an increase in depth resolution) with wider angular range. In conclusion, none of the evaluated acquisition schemes were found to yield higher SDNR or depth resolution for the simulated microcalcifications than the standard acquisition scheme.
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| 6. |
- Timberg, Pontus, et al.
(författare)
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Detection of calcification clusters in digital breast tomosynthesis slices at different dose levels utilizing a SRSAR reconstruction and JAFROC
- 2015
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Ingår i: Medical Imaging 2015: Image Perception, Observer Performance, and Technology Assessment. - : SPIE. - 1996-756X .- 0277-786X. ; 9416, s. 941604-941604
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Konferensbidrag (refereegranskat)abstract
- Purpose: To investigate detection performance for calcification clusters in reconstructed digital breast tomosynthesis (DBT) slices at different dose levels using a Super Resolution and Statistical Artifact Reduction (SRSAR) reconstruction method. Method: Simulated calcifications with irregular profile (0.2 mm diameter) where combined to form clusters that were added to projection images (1-3 clusters per abnormal image) acquired on a DBT system (Mammomat Inspiration, Siemens). The projection images were dose reduced by software to form 35 abnormal cases and 25 normal cases as if acquired at 100%, 75% and 50% dose level (AGD of approximately 1.6 mGy for a 53 mm standard breast, measured according to EUREF v0.15). An FBP algorithm adapted to DBT (called standard FBP) and a SRSAR reconstruction method utilizing iterative reconstruction filtering, and outlier detection using Maximum-Intensity Projections and Average-Intensity Projections) were used to reconstruct single central slices to be used in a free-response task (60 images per observer and dose level). Six observers participated and their task was to detect clusters and assign confidence rating in randomly presented images from the whole image set (balanced by dose level). Each trial was separated by one week to reduce possible memory bias. The outcome was analyzed for statistical differences using Jackknife Alternative Free-response Receiver Operating Characteristics. Results: The results indicate that it is possible to reduce the dose by 50% with SRSAR without jeopardizing cluster detection. Conclusions: The detection performance for clusters can be maintained at a lower dose level by using SRSAR reconstruction.
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| 7. |
- Timberg, Pontus, et al.
(författare)
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Impact of dose on observer performance in breast tomosynthesis using breast specimens
- 2008
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6913, s. 9134-9134
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this study was to investigate the effect of dose on lesion detection† and characterization in breast tomosynthesis (BT), using human breast specimens. Images of 27 lesions in breast specimens were acquired on a BT prototype‡ based on a Mammomat Novation (Siemens) full-field digital mammography (FFDM) system. Two detector modes - binned (2×1 in the scan direction) and full resolution - and four BT exposure levels - approximately 2×, 1.5×, 1×, and 0.5× the total mAs at the same beam quality as used in a single FFDM view with a Mammomat Novation unit under automatic exposure control (AEC) conditions - were examined. The exposure for all BT scans was equally divided among 25 projections. An enhanced filtered back projection reconstruction method was applied with a constant filter setting. A human observer performance study was conducted in which the observers were forced to select the minimum (threshold) exposure level at which each lesion could be both detected and characterized for assessment of recall or not in a screening situation. The median threshold exposure level for all observers and all lesions corresponded to approximately 1×, which is half the exposure of what we currently use for BT. A substantial variation in exposure thresholds was noticed for different lesion types. For low contrast lesions with diffuse borders, an exposure threshold of approximately 2× was required, whereas for spiculated high contrast lesions and lesions with well defined borders, the exposure threshold was lower than 0.5×. The use of binned mode had no statistically significant impact on observer performance compared to full resolution mode. There was no substantial difference between the modes for the detection and characterization of the lesion types.
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| 8. |
- Timberg, Pontus, et al.
(författare)
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Potential for lower absorbed dose in digital mammography: A JAFROC experiment using clinical hybrid images with simulated dose reduction
- 2006
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6146, s. 14614-14614
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To determine how image quality linked to tumor detection is affected by reducing the absorbed dose to 50% and 30% of the clinical levels represented by an average glandular dose (AGO) level of 1.3 mGy for a standard breast according to European guidelines. Materials and methods: 90 normal, unprocessed images were acquired from the screening department using a full-field digital mammography (FFDM) unit Mammomat Novation (Siemens). Into 40 of these, one to three simulated tumors were inserted per image at various positions. These tumors represented irregular-shaped malignant masses. Dose reduction was simulated in all 90 images by adding simulated quantum noise to represent images acquired at 50% and 30% of the original dose, resulting in 270 images, which were subsequently processed for final display. Four radiologists participated in a free-response receiver operating characteristics (FROG) study in which they searched for and marked suspicious positions of the masses as well as rated their degree of suspicion of occurrence on a one to four scale. Using the jackknife FROG (JAFROC) method, a score between 0 and 1 (where 1 represents best performance), referred to as a figure-of-merit (FOM), was calculated for each dose level. Results: The FOM was 0.73, 0.70, and 0.68 for the 100%, 50% and 30% dose levels, respectively. Using Analysis of the Variance (ANOVA) to test for statistically significant differences between any two of the three FOMs revealed that they were not statistically distinguishable (p-value of 0.26). Conclusion: For the masses used in this experiment, there was no significant change in detection by increasing quantum noise, thus indicating a potential for dose reduction.
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| 9. |
- Timberg, Pontus, et al.
(författare)
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Visibility of single spiculations in digital breast tomosynthesis
- 2013
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Ingår i: Medical Imaging 2013: Image Perception, Observer Performance, And Technology Assessment. - : SPIE. - 0277-786X .- 1996-756X. ; 8673, s. 86731-86731
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Konferensbidrag (refereegranskat)abstract
- Purpose: To investigate the visibility of single spiculations in digital breast tomosynthesis (DBT). Method: Simulated spheres (6 mm diameter) with single spiculations were added to projection images acquired on a DBT system (MAMMOMAT Inspiration, Siemens). The spiculations had a cylindrical shape and were randomly, diagonally aligned (at four different positions: +/- pi/4 or +/- 3 pi/4) at a plane parallel to the detector. They were assumed to consist of a fibroglandular tissue composition. The length of the spiculations was 5 mm while the diameter varied (0.12 - 0.28 mm). Reconstructed central slices of the lesion, separated by insertion in fatty or dense breasts (100 images in each), were used in 4-alternative forced choice (4AFC) human observer experiments. Three different reconstructions were used: filtered back projection (FBP) with 1 mm thick slices and a statistical artifact reduction reconstruction (SAR) method generating 1 and 2 mm thick slices. Five readers participated and their task was to locate the spiculation in randomly presented images from the whole image set (4 diameters x 100 images). The percent correct (PC) decision was determined in both fat and dense tissue for all spiculation diameters and reconstructions. Results: At a PC level of 95% the required diameter was about 0.17 - 0.22 mm in dense tissue, and 0.18 - 0.26 mm in fatty tissue (depending upon reconstruction). Conclusions: SAR was found to be a promising alternative to FBP. The visibility of single spiculations was determined. The required diameter depends on both tissue composition and reconstruction.
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