Nina F. Schwenzer

Non-invasive assessment and quantification of liver steatosis by ultrasound, computed tomography and magnetic resonance

Hepatic steatosis is the most prevalent liver disorder in the developed world. It is closely associated with features of metabolic syndrome, especially insulin resistance and obesity. The two most common conditions associated with fatty liver are alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD). Liver biopsy is considered the gold standard for the assessment of liver fat, but there is a need for less invasive diagnostic techniques. New imaging modalities are emerging, which could provide more detailed information about hepatic tissue or even replace biopsy. In the present review, available imaging modalities (ultrasound, computed tomography, magnetic resonance imaging and proton magnetic resonance spectroscopy) are presented which are employed to detect or even quantify the fat content of the liver. The advantages and disadvantages of the above-mentioned imaging modalities are discussed. Although none of these techniques is able to differentiate between microvesicular and macrovesicular steatosis and to reveal all features visible using histology, the proposed diagnostic modalities offer a wide range of additional information such as anatomical and morphological information non-invasively. In particular, magnetic resonance imaging and proton magnetic resonance spectroscopy are able to quantify the hepatic fat content hence avoiding exposure to radiation. Except for proton magnetic resonance spectroscopy, all modalities offer additional information about regional fat distribution within the liver. MR elastography, which can estimate the amount of fibrosis, also appears promising in the differentiation between simple steatosis and steatohepatitis.

Pulmonary Lesion Assessment: Comparison of Whole-Body Hybrid MR/PET and PET/CT Imaging—Pilot Study

PURPOSE To compare the performance of magnetic resonance (MR)/positron emission tomography (PET) imaging in the staging of lung cancer with that of PET/computed tomography (CT) as the reference standard and to compare the quantification accuracy of a new whole-body MR/PET system with corresponding PET/CT data sets. MATERIALS AND METHODS Institutional review board approval and informed consent were obtained. Ten patients in whom bronchial carcinoma was proven or clinically suspected underwent clinically indicated fluorine 18 fluorodeoxyglucose (FDG) PET/CT and, immediately thereafter, whole-body MR/PET imaging with a new hybrid whole-body system (3.0-T MR imager with integrated PET system). Attenuation correction of MR/PET images was segmentation based with fat-water separation. Tumor-to-liver ratios were calculated and compared between PET/CT and MR/PET imaging. Tumor staging on the basis of the PET/CT and MR/PET studies was performed by two readers. Spearman rank correlation was used for comparison of data. RESULTS MR/PET imaging provided diagnostic image quality in all patients, with good tumor delineation. Most lesions (nine of 10) showed pronounced FDG uptake. One lesion was morphologically suspicious for malignancy at CT and MR imaging but showed no FDG uptake. MR/PET imaging had higher mean tumor-to-liver ratios than did PET/CT (4.4 ± 2.0 [standard deviation] for PET/CT vs 8.0 ± 3.9 for MR/PET imaging). Significant correlation regarding the tumor-to-liver ratio was found between both imaging units (ρ = 0.93; P < .001). Identical TNM scores based on MR/PET and PET/CT data were found in seven of 10 patients. Differences in T and/or N staging occurred mainly owing to modality-inherent differences in lesion size measurement. CONCLUSION MR/PET imaging of the lung is feasible and provides diagnostic image quality in the assessment of pulmonary masses. Similar lesion characterization and tumor stage were found in comparing PET/CT and MR/PET images in most patients.

Simultaneous Whole-Body PET/MR Imaging in Comparison to PET/CT in Pediatric Oncology: Initial Results

PURPOSE To compare positron emission tomography (PET)/magnetic resonance (MR) imaging and PET/computed tomography (CT) for lesion detection and interpretation, quantification of fluorine 18 ((18)F) fluorodeoxyglucose (FDG) uptake, and accuracy of MR-based PET attenuation correction in pediatric patients with solid tumors. Materials and Methods This prospective study had local ethics committee and German Federal Institute for Drugs and Medical Devices approval. Written informed consent was obtained from all patients and legal guardians. Twenty whole-body (18)F-FDG PET/CT and (18)F-FDG PET/MR examinations were performed in 18 pediatric patients (median age, 14 years; range, 11-17 years). (18)F-FDG PET/CT and (18)F-FDG PET/MR data were acquired sequentially on the same day for all patients. PET standardized uptake values (SUVs) were quantified with volume of interest measurements in lesions and healthy tissues. MR-based PET attenuation correction was compared with CT-derived attenuation maps (µ-maps). Lesion detection was assessed with separate reading of PET/CT and PET/MR data. Estimates of radiation dose were derived from the applied doses of (18)F-FDG and CT protocol parameters. Descriptive statistical analyses were performed to report correlation coefficients and relative deviations for comparison of SUVs, rates of lesion detection, and percentage reductions in radiation dose. RESULTS PET SUVs showed strong correlations between PET of PET/CT (PETCT) and PET of PET/MR (PETMR) (r > 0.85 for most tissues). Apart from drawbacks of MR-based PET attenuation correction in osseous structures and lungs, similar SUVs were found on PET images corrected with CT-based µ-maps (13.1% deviation of SUVs for bone marrow and <5% deviation for other tissues). Lesion detection rate with PET/MR imaging was equivalent to that with PET/CT (61 areas of focal uptake on PETMR images vs 62 areas on PETCT images). Advantages of PET/MR were observed especially in soft-tissue regions. Furthermore, PET/MR offered significant dose reduction (73%) compared with PET/CT. CONCLUSION Pediatric oncologic PET/MR is technically feasible, showing satisfactory performance for PET quantification with SUVs similar to those of PET/CT. Compared with PET/CT, PET/MR demonstrates equivalent lesion detection rates while offering markedly reduced radiation exposure. Thus, PET/MR is a promising modality for the clinical work-up of pediatric malignancies. Online supplemental material is available for this article.

Feasibility of simultaneous PET/MR imaging in the head and upper neck area.

ObjectiveThe aim of this pilot study was to test and demonstrate the feasibility of simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) of the head and upper neck area using a new hybrid PET/MRI system.MethodsEight patients with malignant head and neck tumours were included in the pilot study. Directly after routine PET/CT imaging with a whole-body system using the glucose derivative 2-[18F]fluoro-2deoxy-D-glucose (FDG) as a radiotracer additional measurements were performed with a prototype PET/MRI system for simultaneous PET and MR imaging. Physiological radiotracer uptake within regular anatomical structures as well as tumour uptake were evaluated visually and semiquantitatively (metabolic ratios) in relation to cerebellar uptake on the PET/MRI and PET/CT systems.ResultsThe MR datasets showed excellent image quality without any recognisable artefacts caused by the inserted PET system. PET images obtained with the PET/MRI system exhibited better detailed resolution and greater image contrast in comparison to those from the PET/CT system. An excellent agreement between metabolic ratios obtained with both PET systems was found: R = 0.99 for structures with physiological tracer uptake, R = 0.96 for tumours.ConclusionSimultaneous PET/MRI of the head and upper neck area is feasible with the new hybrid PET/MRI prototype.

Respiratory Motion Correction in Oncologic PET Using T1-Weighted MR Imaging on a Simultaneous Whole-Body PET/MR System

Hybrid PET/MR combines the exceptional molecular sensitivity of PET with the high resolution and versatility of MR imaging. Simultaneous data acquisition additionally promises the use of MR to enhance the quality of PET images, for example, by respiratory motion correction. This advantage is especially relevant in thoracic and abdominal areas to improve the visibility of small lesions with low radiotracer uptake and to enhance uptake quantification. In this work, the applicability and performance of an MR-based method of respiratory motion correction for PET tumor imaging was evaluated in phantom and patient studies. Methods: PET list-mode data from a motion phantom with 22Na point sources and 5 patients with tumor manifestations in the thorax and upper abdomen were acquired on a simultaneous hybrid PET/MR system. During the first 3 min of a 5-min PET scan, the respiration-induced tissue deformation in the PET field of view was recorded using a sagittal 2-dimensional multislice gradient echo MR sequence. MR navigator data to measure the location of the diaphragm were acquired throughout the PET scan. Respiration-gated PET data were coregistered using the MR-derived motion fields to obtain a single motion-corrected PET dataset. The effect of motion correction on tumor visibility, delineation, and radiotracer uptake quantification was analyzed with respect to uncorrected and gated images. Results: Image quality in terms of lesion delineation and uptake quantification was significantly improved compared with uncorrected images for both phantom and patient data. In patients, in head–feet line profiles of 14 manifestations, the slope became steeper by 66.7% (P = 0.001) and full width at half maximum was reduced by 20.6% (P = 0.001). The mean increase in maximum standardized uptake value, lesion-to-background ratio (contrast), and signal-to-noise ratio was 28.1% (P = 0.001), 24.7% (P = 0.001), and 27.3% (P = 0.003), respectively. Lesion volume was reduced by an average of 26.5% (P = 0.002). As opposed to the gated images, no increase in background noise was observed. However, motion correction performed worse than gating in terms of contrast (−11.3%, P = 0.002), maximum standardized uptake value (−10.7%, P = 0.003), and slope steepness (−19.3%, P = 0.001). Conclusion: The proposed method for MR-based respiratory motion correction of PET data proved feasible and effective. The short examination time and convenience (no additional equipment required) of the method allow for easy integration into clinical routine imaging. Performance compared with gating procedures can be further improved using list-mode–based motion correction.

Pancreatic fat is negatively associated with insulin secretion in individuals with impaired fasting glucose and/or impaired glucose tolerance: a nuclear magnetic resonance study.

The pathogenesis of type 2 diabetes is characterized by insulin resistance and β‐cell dysfunction. Pancreatic fat load may add to the development of β‐cell dysfunction. The aim was to thoroughly quantify the fat content of pancreas sections (caput, corpus, and cauda) and to compare the impact of pancreatic, intrahepatic, and visceral fat on insulin secretion in humans.

Follow-up Whole-Body Assessment of Adipose Tissue Compartments during a Lifestyle Intervention in a Large Cohort at Increased Risk for Type 2 Diabetes

PURPOSE To assess adipose body compartments with magnetic resonance (MR) imaging and MR spectroscopy during a lifestyle intervention program that included optimized nutrition and controlled physical activity in subjects at increased risk for type 2 diabetes to determine factors that may help predict an increase in insulin sensitivity following the intervention. MATERIALS AND METHODS This prospective study was approved by the local review board. All participants gave written informed consent. MR imaging and MR spectroscopy were performed in 243 subjects (99 men and 144 women) before and 9 months after enrollment in a lifestyle intervention program. The results of whole-body MR imaging were used to calculate tissue profiles, differentiating between adipose tissue--especially visceral adipose tissue--and lean tissue. The concentration of hepatic lipids and intramyocellular lipids in the anterior tibial and soleus muscles was determined with MR spectroscopy, and insulin sensitivity was estimated by using an oral glucose tolerance test. The Student t test was used to assess differences between groups, and multivariate regression models were used to assess the value of adipose tissue compartments in the prediction of insulin sensitivity. RESULTS Compared with women, men had almost twice the amount of visceral adipose tissue and a smaller amount of total adipose tissue (25.9% for men and 36.9% for women) at baseline. In addition, their insulin sensitivity was significantly lower than that of women. The most pronounced changes in adipose tissue were detected for visceral adipose tissue (from 4.9 L to 4.1 L [ie, -15.1%] in men and from 2.3 L to 1.9 L [ie, -15.8%] in women) and hepatic lipids (from 8.6% to 5.4% [ie, -36.8%] in men and from 5.1% to 4.3% [ie, -16.5%] in women). The mean insulin sensitivity improved significantly (from 11.3 arbitrary units [au] to 14.6 au [ie, +29.9%] in men and from 13.6 au to 14.6 au [ie, +7.5%] in women), with 70 of the 99 men (71%) and 84 of 144 women (58%) showing an increase in insulin sensitivity. In men, low concentrations of visceral adipose tissue, hepatic lipids, and abdominal subcutaneous fat at baseline were predictive of successful intervention in terms of changes in insulin sensitivity; in women, only low hepatic lipid levels were significantly predictive of successful intervention. CONCLUSION Visceral adipose tissue and hepatic lipids, as assessed with MR imaging and MR spectroscopy, can be significantly reduced during lifestyle intervention. Their baseline values emerged as predictive factors for an improvement of insulin sensitivity.

Quantification of pancreatic lipomatosis and liver steatosis by MRI: comparison of in/opposed-phase and spectral-spatial excitation techniques.

Objectives:The goal of the present study was the assessment of pancreatic and hepatic fat content applying 2 established magnetic resonance (MR) imaging techniques: in-phase/opposed-phase gradient-echo MR imaging and fat-selective spectral-spatial gradient-echo imaging. Results of both approaches were compared, and influences of T1- and T2*-related corrections were assessed. The possibility of a correlation between pancreatic lipomatosis and liver steatosis was investigated. Materials and Methods:Seventeen volunteers at risk for type 2 diabetes (6 male, 11 female; age, 26–70 years; body mass index, 19.4–41.3 kg/m2; mean, 31.7 kg/m2) were examined. Liver and pancreas fat content were quantified with 2 different gradient-echo techniques: one uses a spectral-spatial excitation technique with 6 binomial radio frequency pulses, which combines chemical shift selectivity with simultaneous slice-selective excitation. The other technique based on double-echo chemical shift gradient-echo MR provides in- and opposed-phase images simultaneously. Influences of T1 and individual T2* effects on results using in-phase/opposed-phase imaging were estimated and corrected for, based on additional T2* measurements. Results:The fat content calculated from images recorded with the fat-selective spectral-spatial gradient-echo sequence correlated well with the fat fraction determined with in-phase/opposed-phase imaging and following correction for T1/T2* effects: pancreas r = 0.93 (P < 0.0001) and liver r = 0.96 (P < 0.0001). In-phase/opposed-phase imaging revealed a pancreatic fat content between 1.6% and 22.2% (mean, 8.8% ± 5.7%) and a hepatic fat fraction between 0.6% and 33.3% (mean, 7.9% ± 9.1%). The fat-selective spectral-spatial gradient-echo sequence revealed a pancreatic lipid content between 3.4% and 16.1% (mean, 9.8% ± 4.0%) and a hepatic fat content between 0% and 28.5% (mean, 8.8% ± 8.3%). With neither technique was a substantial correlation between pancreatic and hepatic fat content found. Conclusion:The presented results suggest that both methods are reliable tools for pancreatic and hepatic fat quantification. However, for reliable assessment of quantitative fat by the in-phase/opposed-phase technique, an additional measurement of T2* seems crucial.

Diffusion-Weighted MRI of Advanced Hepatocellular Carcinoma During Sorafenib Treatment: Initial Results

OBJECTIVE The objective of our study was to evaluate signal changes of advanced hepatocellular carcinoma in diffusion-weighted MRI in the early-response monitoring of oral therapy with the multikinase inhibitor sorafenib. CONCLUSION Hepatocellular carcinoma lesions exhibit characteristic but unusual apparent diffusion coefficient (ADC) changes during sorafenib therapy, consisting of early decrease in ADC after therapy onset followed by a reincrease. The ADC changes seem to reflect the underlying pathophysiologic mechanisms in tumor necrosis (most probably hemorrhagic) induced by this novel targeted agent early after therapy onset and may indicate tumor reactivation in the later follow-up period.

Quantitative 3D soft tissue analysis of symmetry prior to and after unilateral cleft lip repair compared with non-cleft persons (performed in Cambodia)

OBJECT The aim of this study was to evaluate the clinical application of three-dimensional (3D) imaging and morphological analysis with subsequent individual therapy planning and postoperative 3D symmetry control in comparison with data from non-cleft persons. DESIGN This was a prospective study using a 3D surface-imaging and evaluation system in cleft patients and non-cleft persons. The pre- and postoperative 3D facial profiles were recorded from the patients using a 3D laser scanner. The preoperative 3D image was analyzed qualitatively and quantitatively for an individual therapy planning. On the basis of ratios and scores, based on empirical regions of interest, the technique of cleft repair was designed individually. The postoperative result was evaluated regarding symmetry. The surgically created soft tissue shift was defined quantitatively and visualized with vectors. The postoperative symmetry was compared with 3D data from a group of non-cleft persons of the same ethnical group. PATIENTS Eleven patients (mean age 13.8 years, median 13, minimum 2, maximum 41 years) with either a unilateral isolated cleft lip, a cleft lip and alveolus or a complete unilateral cleft lip, alveolus and palate and 25 non-cleft persons (8 children between 4 and 12 years, 17 adults (9 men, 8 women) between 18 and 50 years). All these persons investigated were Asians of Khmer origin. RESULTS The analysis permitted quantitative 3D evaluation. The 3D anthropometric data of the non-cleft Khmer persons were collected and named the gold standard of symmetry in this ethnical group. All postoperative 3D images reached symmetrical values within the range of the normal cohort. Soft tissue shifts from pre- to postoperative sites could be visualized. CONCLUSION A new method for registration was described enabling follow-up registration in patients when growing older. This 3D soft tissue analysis can be a useful tool in quantitative analysis and objective follow-up control in cleft patients. It offers deeper insight into the complex morphology to be treated and could contribute to individualisation of surgical procedures.