Soft Tissue Attenuation Research Articles

Magnetic resonance imaging-guided attenuation correction in whole-body PET/MRI using a sorted atlas approach.

Quantitative whole-body PET/MR imaging is challenged by the lack of accurate and robust strategies for attenuation correction. In this work, a new pseudo-CT generation approach, referred to as sorted atlas pseudo-CT (SAP), is proposed for accurate extraction of bones and estimation of lung attenuation properties. This approach improves the Gaussian process regression (GPR) kernel proposed by Hofmann et al. which relies on the information provided by a co-registered atlas (CT and MRI) using a GPR kernel to predict the distribution of attenuation coefficients. Our approach uses two separate GPR kernels for lung and non-lung tissues. For non-lung tissues, the co-registered atlas dataset was sorted on the basis of local normalized cross-correlation similarity to the target MR image to select the most similar image in the atlas for each voxel. For lung tissue, the lung volume was incorporated in the GPR kernel taking advantage of the correlation between lung volume and corresponding attenuation properties to predict the attenuation coefficients of the lung. In the presence of pathological tissues in the lungs, the lesions are segmented on PET images corrected for attenuation using MRI-derived three-class attenuation map followed by assignment of soft-tissue attenuation coefficient. The proposed algorithm was compared to other techniques reported in the literature including Hofmann's approach and the three-class attenuation correction technique implemented on the Philips Ingenuity TF PET/MR where CT-based attenuation correction served as reference. Fourteen patients with head and neck cancer undergoing PET/CT and PET/MR examinations were used for quantitative analysis. SUV measurements were performed on 12 normal uptake regions as well as high uptake malignant regions. Moreover, a number of similarity measures were used to evaluate the accuracy of extracted bones. The Dice similarity metric revealed that the extracted bone improved from 0.58 ± 0.09 to 0.65 ± 0.07 when using the SAP technique compared to Hofmann's approach. This enabled to reduce the SUVmean bias in bony structures for the SAP approach to -1.7 ± 4.8% as compared to -7.3 ± 6.0% and -27.4 ± 10.1% when using Hofmann's approach and the three-class attenuation map, respectively. Likewise, the three-class attenuation map produces a relative absolute error of 21.7 ± 11.8% in the lungs. This was reduced on average to 15.8 ± 8.6% and 8.0 ± 3.8% when using Hofmann's and SAP techniques, respectively. The SAP technique resulted in better overall PET quantification accuracy than both Hofmann's and the three-class approaches owing to the more accurate extraction of bones and better prediction of lung attenuation coefficients. Further improvement of the technique and reduction of the computational time are still required.

Difficult orotracheal intubation in a rabbit resulting from the presence of faecal pellets in the oropharynx

Rabbits have a high rate of anaesthesia-related death compared with other companion animal species. This is influenced by a variety of factors, one of which is difficulty in obtaining a...

Mediastinal Mass Excision-Simple and Safe in Non-specialised Centres

Introduction: The mediastinum is a site for a wide range of various neoplasms, with often rare histologies[1,2], imposing both diagnostic and therapeutic challenges. Particularly large mediastinal masses, or intrathoracic masses with mediastinal compression, offer surgical challenges, due to the complex anatomy of the mediastinum, with obstruction, compression, or invasion of vital surrounding structures. In addition, anesthesiological management during surgery can be complicated by the so-called “Mediastinal Mass Syndrome” (MMS)[3], characterized by acute respiratory and hemodynamic decompensation, due to mechanical compression of mediastinal structures. Therefore, meticulous preoperative assessment, preparation and collaboration between the surgeon and anesthesiologist are essential. Case Presentation: A 26-year old man asymptomatic presented to our hospital with obliteration of the right cardiophrenic sinus by a mass on Chest X-ray (Figure 1). He has no history of fever, weight loss, previous disease, or any neoplasm in his family. A noninvasive investigation CECT of chest demonstrated a tumoral mass which was continuous to the pericardium and caused extrinsic compression to the SVC and right atrium (Figure 2). The diagnosis of this tumor is very difficult through non-invasive investigation. The patient underwent surgical resection en-block via right thoracotomy (Figure 3). Slow and meticulous dissection is must to remove the mass encapsulated without causing it to rupture (Figure 4). Suspicion was a thymoma but surgical and anatomopathologic findings led to the diagnosis of a mature cystic teratoma (Figure 5). Discussion: The typical radiographic appearance of mature teratoma is that of a rounded, sometimes lobulated anterior mediastinal mass with the borders of the mass sharply marginated against the adjacent lung. Calcification has been reported in approximately 20-43% of cases and may be central, curvilinear, or peripheral (Michel et al.) [4]. The radiographic visualization of teeth is pathognomonic of teratoma (Rosai and Levine) [5]. Computed Tomography (CT) is the modality of choice for the diagnostic evaluation of these tumors. Meditational mature teratomas typically manifest on CT as heterogeneous sharply marginated, spherical or lobulated anterior mediastinal masses containing soft tissue, fluid, fat, or calcium attenuation, or any combination of the four. Malignant transformation must be ruled out if contrast enhanced CT scanning reveals a non-homogeneous cystic mass with a fat or oil component and a thick wall with calcification with invasion of the pericardium and great vessels (Dobranowski et al.) [6]. The patient underwent surgical excision. The treatment of mature teratoma consists of complete surgical excision of the mass. The prognosis is very good and 5 year survival rates approach 100%, in contrast to the prognosis of immature teratomas, which may exhibit an aggressive behaviour in adults and may have a poor prognosis (Hueb et al.) [7]. Conclusion: In the perioperative management of surgical treatment of large mediastinal masses or intrathoracic tumors with mediastinal compression, attention to anatomical details of the tumor and it relations with vital mediastinal surrounding structures is essential. Preoperative preparation measures include appropriate preoperative multimodality imaging, with emphasis on the vascular anatomy of the tumor. Multidisciplinary team discussions should assess whether neoadjuvant therapy can be beneficial on a case-by-case basis. With adequate preoperative team planning, a safe anesthesiological and surgical strategy can be realized. The management of these tumors are simple and safe if properly planned and with good anatomical knowledge and technique surgical excision can be done in nonspecialized centers.

A case of expansile ancient schwannoma of the nose and paranasal sinuses

A rare case of a unilateral nasal mass involving the left nasal cavity and the paranasal sinuses in a 54-year old man with progressive left nasal obstruction is presented. A polypoid mass in the left nasal cavity was evident from anterior rhinoscopy. Computed tomography scan revealed soft tissue attenuation in the left nasal cavity and paranasal sinuses with an erosion of the nasal septum and the compression of the lamina papyracea of left orbit with an extension to its extra-conal space, which suggested the expansile nature of the mass. It was excised endoscopically and found to be an ancient schwannoma, known from histopathological and immunohistochemical studies, which was a rare occurrence in nose and paranasal sinuses.

Is Attenuation Correction for Myocardial Perfusion Imaging Underutilized?

Myocardial SPECT remains an important diagnostic technique in patients suspected of significant coronary artery disease. However, the diagnostic accuracy is hampered by several clinical and technical difficulties. Among these, soft tissue attenuation is one of the most frequent causes. Attenuation correction has the power to correct for these artifacts, increasing the diagnostic accuracy of myocardial SPECT. The current review summarizes the available clinical evidence for attenuation correction and raises the question if this technique is not underutilized in current clinical practice.

CT colonography at low tube potential: using iterative reconstruction to decrease noise

To determine the level of iterative reconstruction required to reduce increased image noise associated with low tube potential computed tomography (CT). Fifty patients underwent CT colonography with a supine scan at 120kVp and a prone scan at 100kVp with other scan parameters unchanged. Both scans were reconstructed with filtered back projection (FBP) and increasing levels of adaptive statistical iterative reconstruction (ASiR) at 30%, 60%, and 90%. Mean noise, soft tissue and tagged fluid attenuation, contrast, and contrast-to-noise ratio (CNR) were collected from reconstructions at both 120 and 100kVp and compared using a generalised linear mixed model. Decreasing tube potential from 120 to 100kVp significantly increased image noise by 30-34% and tagged fluid attenuation by 120HU at all ASiR levels (p<0.0001, all measures). Increasing ASiR from 0% (FBP) to 30%, 60%, and 90% resulted in significant decreases in noise and increases in CNR at both tube potentials (p<0.001, all comparisons). Compared to 120kVp FBP, ASiR greater than 30% at 100kVp yielded similar or lower image noise. Iterative reconstruction adequately compensates for increased image noise associated with low tube potential imaging while improving CNR. An ASiR level of approximately 50% at 100kVp yields similar noise to 120kVp without ASiR.

Evaluation of image quality and dose reduction of 80 kVp neck computed tomography in patients with suspected peritonsillar abscess

To evaluate neck computed tomography (CT) with a reduced tube voltage of 80 kVp in patients with suspected peritonsillar abscess (PTA) regarding objective and subjective image quality, and the potential for dose reduction. Forty-seven patients with clinically suspected PTA were retrospectively analysed. Patients were examined using dual-source CT in dual-energy mode. The objective and subjective image quality of 80 kVp images were compared with linearly blended 120 kVp images (M_0.3; 30% of 80 kV, 70% of 140 kV spectrum). Attenuation of abscess rim enhancement, central necrosis, and several other anatomical landmarks were measured. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and rim-to-abscess CNR (raCNR) were calculated. Radiation dose was assessed as size-specific dose estimates (SSDE). Subjective image quality was assessed according to the European guidelines on quality criteria for CT. Interobserver agreement was calculated using the intraclass correlation coefficient (ICC). Attenuation of inflamed soft tissue (141.7 ± 16.3 versus 93.7 ± 9.3 HU, p < 0.001), CNR (9.6 ± 4.8 versus 5.6 ± 3.8, p = 0.001), raCNR (14.3 ± 5.9 versus 12.4 ± 4.4, p = 0.02), and subjective image sharpness (3.6 ± 0.6 versus 2.8 ± 0.7, p < 0.001) were significantly increased in the 80 kVp compared to 120 kVp, whereas subjective and objective image noise were significantly increased with 80 kVp acquisition (p < 0.001). Overall interobserver agreement was almost perfect (ICC, 0.87). Calculated SSDE of 80 kVp acquisition was decreased by 49.7% compared to 120 kVp (10.58 ± 0.76 versus 21.04 ± 1.43 mGy, p < 0.001). Low-tube-voltage 80 kVp neck CT provides increased enhancement of soft-tissue inflammation, CNR, raCNR, and improved abscess delineation in patients with PTA compared to standard 120 kVp acquisition while resulting in a significant reduction of radiation exposure.

An incidental prostatic leiomyoma in a dog

A 12-year-old entire male cocker spaniel presented for re-evaluation of mitral valve disease. Abdominal palpation revealed a large mass caudally. Abdominal ultrasonography identified a large, heterogeneous, mixed echogenicity mass adjacent...

Normal thymus in adults: appearance on CT and associations with age, sex, BMI and smoking.

To investigate CT appearance and size of the thymus in association with participant characteristics. 2540 supposedly healthy participants (mean age 58.9 years, 51 % female) were evaluated for the CT appearance of thymic glands with four-point scores (according to the ratio of fat and soft tissue), size and morphology. These were correlated with participants' age, sex, BMI and smoking history. Of 2540 participants, 1869 (74 %) showed complete fatty replacement of the thymus (Score 0), 463 (18 %) predominantly fatty attenuation (Score 1), 172 (7 %) half fatty and half soft-tissue attenuation (Score 2) and 36 (1 %) solid thymic gland with predominantly soft-tissue attenuation (Score 3). Female participants showed less fatty degeneration of the thymus with higher thymic scores within age 40-69 years (P < 0.001). Participants with lower thymic scores showed higher BMI (P < 0.001) and were more likely to be former smokers (P < 0.001) with higher pack-years (P = 0.04). Visual assessment with four-point thymic scores revealed a sex difference in the fatty degeneration of the thymus with age. Women show significantly higher thymic scores, suggesting less fat content of the thymus, during age 40-69 years. Cigarette smoking and high BMI are associated with advanced fatty replacement of the thymus. 74% of participants (mean age 58.9 years) demonstrated complete fatty thymus. Women show less fatty thymus compared to men at ages 40-69 years. Smoking and high BMI are associated with advanced fatty degeneration in thymus.

Dynamic Computed Tomographic Characteristics of aColorectal Leiomyoma in a Dog

A 12-year-old neutered male Shih Tzu presented with constipation and dyschezia. Abdominal radiographs showed distension of the descending colon and dorsal compression of the colon by a soft tissue mass. The mass was well-marginated with homogeneous soft tissue attenuation and showed no evidence of metastasis on computed tomography (CT). The dynamic CT showed a consistently mild contrast enhancement. The perfusion and capillary permeability were lower than those of the gluteal muscle. The tentative imaging diagnosis was a benign intrapelvic tumor, which rarely shows angiogenesis. The mass was excised, and a leiomyoma was confirmed by histopathologic examination.

Unenhanced third-generation dual-source chest CT using a tin filter for spectral shaping at 100 kVp

ObjectiveTo prospectively investigate image quality and radiation dose of 100kVp spectral shaping chest CT using a dedicated tin filter on a 3rd generation dual-source CT (DSCT) in comparison to standard 100kVp chest CT. MethodsSixty patients referred for a non-contrast chest on a 3rd generation DSCT were prospectively included and examined at 100kVp with a dedicated tin filter. These patients were retrospectively matched with patients that were examined on a 2nd generation DSCT at 100kVp without tin filter. Objective and subjective image quality was assessed in various anatomic regions and radiation dose was compared. ResultsRadiation dose was decreased by 90% using the tin filter (3.0 vs 0.32mSv). Soft tissue attenuation and image noise was not statistically different for both examination techniques (p>0.05), however image noise was found to be significantly higher in the trachea when using the additional tin filter (p=0.002). SNR was found to be statistically similar in pulmonary tissue, significantly lower when measured in air and significantly higher in the aorta for the scans on the 3rd generation DSCT. Subjective image quality with regard to overall quality and image noise and sharpness was not statistically significantly different (p>0.05). Conclusion100kVp spectral shaping chest CT by means of a tube-based tin-filter on a 3rd generation DSCT allows 90% dose reduction when compared to 100kVp chest CT on a 2nd generation DSCT without spectral shaping.

INTRAARTERIAL INJECTION OF IODINATED CONTRAST MEDIUM FOR CONTRAST ENHANCED COMPUTED TOMOGRAPHY OF THE EQUINE HEAD.

Minimizing the volume of contrast administered for contrast-enhanced computed tomography (CT) of the equine head is desirable for reducing costs and risks of adverse reactions, however evidence-based studies on the effects of varying volumes on image quality are currently lacking. The objective of the current study was to determine whether low-volume intraarterial administration of contrast medium would result in an equivalent image quality and tissue attenuation vs. high-volume intravenous bolus administration. A prospective cross-over experimental design was used in a sample of six horses. After anesthetic induction, the right carotid artery was exposed surgically and catheterized. Four CT scans of the cranium were performed for each horse: baseline, immediately following intraarterial contrast injection, five-min postinjection (return to baseline) and a final scan after intravenous contrast administration. Soft tissue attenuation in predetermined regions of interest (ROI); and length, width, and height measurements of the pituitary gland were recorded at each time point. Horses were euthanized and measurements of the pituitary gland were repeated postmortem. No adverse reactions to contrast administration were observed. Intraarterial and intravenous administration of contrast medium resulted in significantly greater soft tissue enhancement of some brain ROI's and the pituitary gland vs. baseline values. Pituitary gland measurements made on postcontrast CT images did not differ from those obtained during postmortem examination. Findings indicated that low-dose intraarterial administration of contrast material in the equine head resulted in comparable soft tissue enhancement vs. high volume intravenous administration.

Spatial and Frequency Compounding in Application to Attenuation Estimation in Tissue

Abstract The soft tissue attenuation is an interesting parameter from medical point of view, because the value of attenuation coefficient is often related to the state of the tissue. Thus, the imaging of the attenuation coefficient distribution within the tissue could be a useful tool for ultrasonic medical diagnosis. The method of attenuation estimation based on tracking of the mean frequency changes in a backscattered signal is presented in this paper. The attenuation estimates are characterized by high variance due to stochastic character of the backscattered ultrasonic signal and some special methods must be added to data processing to improve the resulting images. The following paper presents the application of Spatial Compounding (SC), Frequency Compounding (FC) and the combination of both. The resulting parametric images are compared by means of root-mean-square errors. The results show that combined SC and FC techniques significantly improve the quality and accuracy of parametric images of attenuation distribution.

The Benefits of Prone SPECT Myocardial Perfusion Imaging in Reducing Both Artifact Defects and Patient Radiation Exposure

BackgroundProne imaging has been demonstrated to minimize diaphragmatic and breast tissue attenuation.ObjectivesTo determine the role of prone imaging on the reduction of unnecessary rest perfusion studies and coronary angiographies performed, thus decreasing investigation time and radiation exposure.MethodsWe examined 139 patients, 120 with an inferior wall and 19 with an anterior wall perfusion defect that might represented attenuation artifact. Post-stress images were acquired in both the supine and prone position. Coronary angiography was used as the “gold standard” for evaluating coronary artery patency. The study was terminated and rest imaging was obviated in the presence of complete improvement of the defect in the prone position. Quantitative interpretation was performed. Results were compared with clinical data and coronary angiographic findings.ResultsProne acquisition correctly revealed defect improvement in 89 patients (89/120) with inferior wall and 12 patients (12/19) with anterior wall attenuation artifact. Quantitative analysis demonstrated statistically significant difference in the mean summed stress scores (SSS) of supine and mean SSS of prone studies in patients with disappearing inferior wall defect in the prone position and patent right coronary artery (true negative results). The mean difference between SSS in supine and in prone position was higher with disappearing than with remaining defects.ConclusionTechnetium-99m (Tc-99m) tetrofosmin myocardial perfusion imaging with the patient in the prone position overcomes soft tissue attenuation; moreover it provides an inexpensive, accurate approach to limit the number of unnecessary rest perfusion studies and coronary angiographies performed.

Granulomatosis with Polyangiitis Presenting with Coronary Artery and Pericardial Involvement

Granulomatosis with polyangiitis is a systemic disease resulting in necrotizing vasculitis of small- and medium-sized vessels. Cardiac involvement is rare and when present usually manifests with pericarditis and coronary artery vasculitis. We report here a case of granulomatosis with polyangiitis involving the native coronary arteries, bypass graft, and pericardium with interesting imaging findings on contrast-enhanced CT and MRI. A 57-year-old man with a history of chronic headaches presented to the emergency room with syncope. Contrast-enhanced CT demonstrated extensive soft tissue attenuation around the native coronary arteries and bypass graft. Contrast-enhanced MRI demonstrated enhancing nodular soft tissue surrounding the coronary arteries, bypass graft, and pericardium. Pericardial biopsy revealed a necrotizing granulomatous pericarditis with vasculitis concerning for granulomatosis with polyangiitis. The patient demonstrated MPO-positive and PR-3 negative serologies. After being discharged on rituximab and prednisone, follow-up CT 3 years later showed significant improvement of the soft tissue thickening surrounding the coronary arteries, bypass graft, and pericardium.

Attenuation correction of (111)In planar images by use of dual energy, fundamental study by Monte Carlo simulation.

In this study, we devised and evaluated a method for attenuation correction of the hot spot in (111)In planar images. By use of the difference in transmittance between two energies (171 and 245keV), the depth of the hot spot was calculated. Planar images of point sources in a numerical phantom (water) with depths from 0 to 20cm at 2cm intervals were prepared by Monte Carlo simulation. From the linear attenuation coefficient of the two energies and the 171/245keV count ratio-depth relationship, the depth of the point source was calculated, and an attenuation correction was performed. A simulation was made under conditions taking into account both attenuation and scatter (A(+)S(+)) and attenuation alone (A(+)S(-)). The attenuation correction was evaluated with use of corrected and true counts obtained from homogeneous phantoms mimicking attenuation in soft tissue, bone, and the lungs, and heterogeneous phantoms prepared by combining them. In the A(+)S(+) condition, images were affected markedly by scattered photons in all phantoms at depths of 4-8cm. The errors at depths of 10cm or greater were within±10% in water and within±6% in soft tissue. However, the errors were about -30% in bone and about +70% in lung, indicating that scatter distributions different from those in water increased the errors. In the A(+)S(-) condition, the errors were within±5% in all homogeneous and heterogeneous phantoms, and satisfactory results were obtained. Precise attenuation correction of scatter-corrected planar images was confirmed to be possible with this method.

PET/MR imaging of sarcomas: effect of PET quantification by classification of tissue.

PET quantification in combined PET/MR can be biased, as the standard Dixon-Water-Fat segmentation (DWFS) attenuation correction (AC) method does not account for bone. Here, we assess PET quantification in PET/MR imaging for patients with bone sarcoma (BS) or soft tissue sarcoma (STS). We include eight patients (4 BS, 4 STS, 4 MBq/kg [18F]FDG) imaged with PET/CT and PET/MR. MR-AC was performed based on: (A) DWFS, (B) DWFS with co-registered and segmented CT bone values superimposed (Bone100), and (C) with co-registered full CT-based attenuation image replacing all voxels within the DWFS body contour (FullCT). We report the mean attenuation value in the sarcoma and the relative difference of a ROI (30% of max isocontour in the sarcoma) activity values for (A)-(B) in reference to (C). The mean attenuation value in the sarcomas was 2-8% higher in DWFS (μ = 0.1 cm-1) compared to FullCT (μ = 0.0926-0.098 cm-1) for the voxels not considered bone. The relative difference between PET activity reconstructed using DWFS and FullCT was 5-12% in the STS and insignificant for the BS (max: -2%). Between Bone100 and FullCT we found differences of 10-14% in the STS and 1-9% for the BS. In sarcomas, PET activity based on MR-AC shows a bias correlated to the location of the sarcoma. However, unexpectedly, the largest error is observed in the STS, which is mainly located away from bone. The error is caused by an overestimation of the attenuation value of soft tissue in DWFS causing an overestimation of the reconstructed PET values. Adding bone further increases the PET values. For the BS these errors roughly cancel each other out. In conclusion, both bone and soft tissue attenuation values differ between DWFS and CT attenuation correction, and contribute to PET quantification errors in sarcomas.

Accuracy and reliability of 2D cephalometric analysis in orthodontics

ObjectivesTo evaluate the accuracy of two-dimensional (2D) cephalometric analysis when compared to “gold standard” measurements on skulls. Also to appraise the reliability of 10 linear measurements commonly used in 2D lateral cephalometric analysis. MethodsTwenty dry human skulls and its digital lateral cephalometric images of were taken. The skulls were positioned in an aluminum filter box to mimic soft tissue attenuation. Ten linear measurements were performed both in skulls and radiographs by 2 observers (experienced dentomaxillofacial radiologists). The same procedure was repeated twice, with 1 month interval, to allow calculation of the intra- and inter-observer variability. ResultsStatistically significant differences were found between cephalometric and direct craniometric measurements. In general, measurements were on average lower in skulls with exception of three that were on average significantly higher (Co-Gn, Go-Me, Co-ANS). When a bilateral landmark was included, measurements were significantly higher. Furthermore, no significant differences were observed between measurements by the two observers (p<0.05). ConclusionRadiographic linear measurements systematically overestimated the direct linear measurements performed on the skulls. However, differences found were most often <1mm, which is generally within one standard deviation of “normal” values in conventional cephalometric analysis. It is assumed that such differences are often clinically acceptable, yet further studies are encouraged to evaluate the impact on cephalometry-based therapy planning.

Evaluation and automatic correction of metal-implant-induced artifacts in MR-based attenuation correction in whole-body PET/MR imaging

The aim of this paper is to describe a new automatic method for compensation of metal-implant-induced segmentation errors in MR-based attenuation maps (MRMaps) and to evaluate the quantitative influence of those artifacts on the reconstructed PET activity concentration. The developed method uses a PET-based delineation of the patient contour to compensate metal-implant-caused signal voids in the MR scan that is segmented for PET attenuation correction. PET emission data of 13 patients with metal implants examined in a Philips Ingenuity PET/MR were reconstructed with the vendor-provided method for attenuation correction (MRMaporig, PETorig) and additionally with a method for attenuation correction (MRMapcor, PETcor) developed by our group. MRMaps produced by both methods were visually inspected for segmentation errors. The segmentation errors in MRMaporig were classified into four classes (L1 and L2 artifacts inside the lung and B1 and B2 artifacts inside the remaining body depending on the assigned attenuation coefficients). The average relative SUV differences () between PETorig and PETcor of all regions showing wrong attenuation coefficients in MRMaporig were calculated. Additionally, relative SUVmean differences (εrel) of tracer accumulations in hot focal structures inside or in the vicinity of these regions were evaluated. MRMaporig showed erroneous attenuation coefficients inside the regions affected by metal artifacts and inside the patients' lung in all 13 cases. In MRMapcor, all regions with metal artifacts, except for the sternum, were filled with the soft-tissue attenuation coefficient and the lung was correctly segmented in all patients. MRMapcor only showed small residual segmentation errors in eight patients. (mean ± standard deviation) were: ( − 56 ± 3)% for B1, ( − 43 ± 4)% for B2, (21 ± 18)% for L1, (120 ± 47)% for L2 regions. εrel (mean ± standard deviation) of hot focal structures were: ( − 52 ± 12)% in B1, ( − 45 ± 13)% in B2, (19 ± 19)% in L1, (51 ± 31)% in L2 regions. Consequently, metal-implant-induced artifacts severely disturb MR-based attenuation correction and SUV quantification in PET/MR. The developed algorithm is able to compensate for these artifacts and improves SUV quantification accuracy distinctly.

Epipericardial fat necrosis: an underdiagnosed condition

Epipericardial fat necrosis (EFN) is an uncommon benign and self-limited condition that leads patients to the emergency department (ED) owing to the onset of acute pleuritic chest pain. The aim of this study was to describe the cases of this disease in our institution and to illustrate the associated clinical and radiological findings. We reviewed 3604 chest scans referred by the ED from November 2011 to July 2013. Patients diagnosed with epipericardial necrosis had their medical records and original tomography reports analysed. Chest pain was the primary complaint in 426 patients; 11 of them had definitive EFN findings characterized by a round soft-tissue attenuation lesion with a varying degree of strands. All patients presented with pleuritic chest pain on the same side as the lesion. Pericardial thickening, pleural effusion and mild atelectasis were the associated tomography findings. Cardiac enzyme and D-dimer tests performed during the episode were normal in all cases. 27% of the cases only were correctly diagnosed with EFN at the time of presentation. EFN is a benign inflammatory condition frequently overlooked in the ED by physicians and radiologists but is an important factor in the differential diagnosis of patients with acute chest pain. The article adds clinically and radiologically useful information about the condition and displays the importance of making the correct diagnosis to avoid unnecessary examinations.