Christian Geppert

Pulmonary Nodules in Patients with Primary Malignancy: Comparison of Hybrid PET/MR and PET/CT Imaging

PURPOSE To assess diagnostic sensitivity of radial T1-weighted gradient-echo (radial volumetric interpolated breath-hold examination [VIBE]) magnetic resonance (MR) imaging, positron emission tomography (PET), and combined simultaneous PET and MR imaging with an integrated PET/MR system in the detection of lung nodules, with combined PET and computed tomography (CT) as a reference. MATERIALS AND METHODS In this institutional review board-approved HIPAA-compliant prospective study, 32 patients with tumors who underwent clinically warranted fluorine 18 ((18)F) fluorodeoxyglucose (FDG) PET/CT followed by PET/MR imaging were included. In all patients, the thorax station was examined with free-breathing radial VIBE MR imaging and simultaneously acquired PET data. Presence and size of nodules and FDG avidity were assessed on PET/CT, radial VIBE, PET, and PET/MR images. Percentage of nodules detected on radial VIBE and PET images was compared with that on PET/MR images by using generalized estimating equations. Maximum standardized uptake value (SUVmax) in pulmonary nodules with a diameter of at least 1 cm was compared between PET/CT and PET/MR imaging with Pearson rank correlation. RESULTS A total of 69 nodules, including 45 FDG-avid nodules, were detected with PET/CT. The sensitivity of PET/MR imaging was 70.3% for all nodules, 95.6% for FDG-avid nodules, and 88.6% for nodules 0.5 cm in diameter or larger. PET/MR imaging had higher sensitivity than PET for all nodules (70.3% vs 61.6%, P = .002) and higher sensitivity than MR imaging for FDG-avid nodules (95.6% vs 80.0%, P = .008). There was a significantly strong correlation between SUVmax of pulmonary nodules obtained with PET/CT and that obtained with PET/MR imaging (r = 0.96, P < .001). CONCLUSION Radial VIBE and PET data acquired simultaneously with PET/MR imaging have high sensitivity in the detection of FDG-avid nodules and nodules 0.5 cm in diameter or larger, with low sensitivity for small non-FDG-avid nodules.

Whole-Body PET/MR Imaging: Quantitative Evaluation of a Novel Model-Based MR Attenuation Correction Method Including Bone

In routine whole-body PET/MR hybrid imaging, attenuation correction (AC) is usually performed by segmentation methods based on a Dixon MR sequence providing up to 4 different tissue classes. Because of the lack of bone information with the Dixon-based MR sequence, bone is currently considered as soft tissue. Thus, the aim of this study was to evaluate a novel model-based AC method that considers bone in whole-body PET/MR imaging. Methods: The new method (“Model”) is based on a regular 4-compartment segmentation from a Dixon sequence (“Dixon”). Bone information is added using a model-based bone segmentation algorithm, which includes a set of prealigned MR image and bone mask pairs for each major body bone individually. Model was quantitatively evaluated on 20 patients who underwent whole-body PET/MR imaging. As a standard of reference, CT-based μ-maps were generated for each patient individually by nonrigid registration to the MR images based on PET/CT data. This step allowed for a quantitative comparison of all μ-maps based on a single PET emission raw dataset of the PET/MR system. Volumes of interest were drawn on normal tissue, soft-tissue lesions, and bone lesions; standardized uptake values were quantitatively compared. Results: In soft-tissue regions with background uptake, the average bias of SUVs in background volumes of interest was 2.4% ± 2.5% and 2.7% ± 2.7% for Dixon and Model, respectively, compared with CT-based AC. For bony tissue, the −25.5% ± 7.9% underestimation observed with Dixon was reduced to −4.9% ± 6.7% with Model. In bone lesions, the average underestimation was −7.4% ± 5.3% and −2.9% ± 5.8% for Dixon and Model, respectively. For soft-tissue lesions, the biases were 5.1% ± 5.1% for Dixon and 5.2% ± 5.2% for Model. Conclusion: The novel MR-based AC method for whole-body PET/MR imaging, combining Dixon-based soft-tissue segmentation and model-based bone estimation, improves PET quantification in whole-body hybrid PET/MR imaging, especially in bony tissue and nearby soft tissue.

Dynamic contrast-enhanced MRI of the prostate with high spatiotemporal resolution using compressed sensing, parallel imaging, and continuous golden-angle radial sampling: Preliminary experience

To demonstrate dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) of the prostate with both high spatial and temporal resolution via a combination of golden‐angle radial k‐space sampling, compressed sensing, and parallel‐imaging reconstruction (GRASP), and to compare image quality and lesion depiction between GRASP and conventional DCE in prostate cancer patients.

Correlation Between Standardized Uptake Value and Apparent Diffusion Coefficient of Neoplastic Lesions Evaluated With Whole-Body Simultaneous Hybrid PET/MRI

OBJECTIVE The purpose of this study was to assess the correlation between standardized uptake value (SUV) and apparent diffusion coefficient (ADC) of neoplastic lesions in the use of a simultaneous PET/MRI hybrid system. SUBJECTS AND METHODS Twenty-four patients with known primary malignancies underwent FDG PET/CT. They then underwent whole-body PET/MRI. Diffusion-weighted imaging was performed with free breathing and a single-shot spin-echo echo-planar imaging sequence with b values of 0, 350, and 750 s/mm(2). Regions of interest were manually drawn along the contours of neoplastic lesions larger than 1 cm, which were clearly identified on PET and diffusion-weighted images. Maximum SUV (SUVmax) on PET/MRI and PET/CT images, mean SUV (SUVmean), minimum ADC (ADCmin), and mean ADC (ADCmean) were recorded on PET/MR images for each FDG-avid neoplastic soft-tissue lesion with a maximum of three lesions per patient. Pearson correlation coefficient was used to asses the following relations: SUVmax versus ADCmin on PET/MR and PET/CT images, SUVmean versus ADCmean, and ratio of SUVmax to mean liver SUV (SUV ratio) versus ADCmin. A subanalysis of patients with progressive disease versus partial treatment response was performed with the ratio of SUVmax to ADCmin for the most metabolically active lesion. RESULTS Sixty-nine neoplastic lesions (52 nonosseous lesions, 17 bone metastatic lesions) were evaluated. The mean SUVmax from PET/MRI was 7.0 ± 6.0; SUVmean, 5.6 ± 4.6; mean ADCmin, 1.10 ± 0.58; and mean ADCmean, 1.48 ± 0.72. A significant inverse Pearson correlation coefficient was found between PET/MRI SUVmax and ADCmin (r = -0.21, p = 0.04), between SUVmean and ADCmean (r = -0.18, p = 0.07), and between SUV ratio and ADCmin (r = -0.27, p = 0.01). A similar inverse Pearson correlation coefficient was found between the PET/CT SUVmax and ADCmin. Twenty of 24 patients had previously undergone PET/CT; five patients had a partial treatment response, and six had progressive disease according to Response Evaluation Criteria in Solid Tumors 1.1. The ratio between SUVmax and ADCmin was higher among patients with progressive disease than those with a partial treatment response. CONCLUSION Simultaneous PET/MRI is a promising technology for the detection of neoplastic disease. There are inverse correlations between SUVmax and ADCmin and between SUV ratio and ADCmin. Correlation coefficients between SUVmax and ADCmin from PET/MRI were similar to values obtained with SUVmax from the same-day PET/CT. Given that both SUV and ADC are related to malignancy and that the correlation between the two biomarkers is relatively weak, SUV and ADC values may offer complementary information to aid in determination of prognosis and treatment response. The combined tumoral biomarker, ratio between SUVmax and ADCmin, may be useful for assessing progressive disease versus partial treatment response.

Toward simultaneous PET/MR breast imaging: Systematic evaluation and integration of a radiofrequency breast coil

PURPOSE With the recent introduction of integrated whole-body hybrid positron emission tomography/magnetic resonance (PET/MR) scanners, simultaneous PET/MR breast imaging appears to be a potentially attractive new clinical application. In this study, the technical groundwork toward performing simultaneous PET/MR breast imaging was developed and systematically evaluated in phantom experiments and breast cancer patient hybrid imaging. METHODS Measurements were performed on a state-of-the-art whole-body simultaneous PET/MR system (Biograph mMR, Siemens AG, Erlangen, Germany). The PET signal attenuating effects of a MR-only four-channel radiofrequency (RF) breast coil that is present in the PET field-of-view (FoV) during a simultaneous PET/MR data acquisition has been investigated and quantified. For this purpose, a dedicated PET/MR visible breast phantom featuring four modular inserts with various structures (no insert, MR insert, PET insert, and PET/MR insert) was developed. In addition to a systematic evaluation of MR-only image quality, the following phantom scans were performed using (18)F radio tracer: (1) PET emission scan with only the homogeneous breast phantom; (2) PET emission scan additionally with the RF breast coil in the PET FoV. Attenuation correction (AC) of PET data was performed with CT-based three-dimensional (3D) hardware attenuation maps (μ-maps) of the RF coil and breast phantom. Finally, a simultaneous PET/MR breast imaging was performed in two breast cancer patients. RESULTS The modular breast phantom allowed for systematic evaluation of various MR, PET, and PET/MR image quality parameters. The RF breast coil provided MR images of good image quality, unaffected by PET imaging. The global attenuation of the RF breast coil on the PET emission data was approximately 11%. This hardware attributed PET signal attenuation was successfully corrected by using an appropriate CT-based 3D μ-map of the RF breast coil. Imaging of two breast cancer patients confirmed the successful integration of the RF breast coil into the concept of simultaneous PET/MR breast imaging. CONCLUSIONS The successful integration of a four-channel RF breast coil with a defined table position together with the CT-based μ-maps provides a technical basis for future clinical PET/MR breast imaging applications.

Comparison of the accuracy of PET/CT and PET/MRI spatial registration of multiple metastatic lesions.

OBJECTIVE The purpose of this study was to compare the accuracy of the spatial registration of conventional PET/CT with that of hybrid PET/MRI of patients with FDG-avid metastatic lesions. SUBJECTS AND METHODS Thirteen patients with known metastatic lesions underwent FDG PET/CT followed by PET/MRI with a hybrid whole-body system. The inclusion criterion for tumor analysis was spherical or oval FDG-avid tumor clearly identified with both CT and MRI. The spatial coordinates (x, y, z) of the visually estimated centers of the lesions were determined for PET/CT (PET and CT independently) and PET/MRI (PET, T1-weighted gradient-echo sequence with radial stack-of-stars trajectory, T2-weighted sequence), and the b0 images of an echo-planar imaging (EPI) diffusion-weighted imaging (DWI) acquisition. All MRI sequences were performed in the axial plane with free breathing. The spatial coordinates of the estimated centers of the lesions were determined for PET and CT and PET and MRI sequences. Distance between the isocenter of the lesion on PET images and on the images obtained with the anatomic modalities was measured, and misregistration (in millimeters) was calculated. The degree of misregistration was compared between PET/CT and PET/MRI with a paired Student t test. RESULTS Nineteen lesions were evaluated. On PET/CT images, the average of the total misregistration in all planes of CT compared with PET was 4.13 ± 4.24 mm. On PET/MR images, lesion misregistration between PET and T1-weighted gradient-echo images had a shift of 2.41 ± 1.38 mm and between PET and b0 DW images was 5.97 ± 2.83 mm. Similar results were calculated for 11 lesions on T2-weighted images. The shift on T2-weighted images compared with PET images was 2.24 ± 1.12 mm. Paired Student t test calculations for PET/CT compared with PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory, b0 DW images, and T2-weighted images showed significant differences (p < 0.05). Similar results were seen in the analysis of six lung lesions. CONCLUSION PET/MRI T1-weighted gradient-echo images with a radial stack-of-stars trajectory and T2-weighted images had more accurate spatial registration than PET/CT images. This may be because that the whole-body PET/MRI system used can perform simultaneous acquisition, whereas the PET/CT system acquires data sequentially. However, the EPI-based b0 DWI datasets were significantly misregistered compared with the PET/CT datasets, especially in the thorax. Radiologists reading PET/MR images should be aware of the potential for misregistration on images obtained with EPI-based DWI sequences because of inherent spatial distortion associated with this type of MRI acquisition.

Resolving arterial phase and temporal enhancement characteristics in DCE MRM at high spatial resolution with TWIST acquisition

To investigate the potential of a view‐sharing 3D fast gradient‐echo sequence using pseudo random trajectories (TWIST) to achieve very short acquisition times with high in‐plane resolution and good volume coverage and its application to dynamic contrast‐enhanced (DCE) breast magnetic resonance imaging (MRI).

Breast MRI at 7 Tesla with a bilateral coil and robust fat suppression.

To develop a bilateral coil and fat suppressed T1‐weighted sequence for 7 Tesla (T) breast MRI.

Contrast-Enhanced Radial 3D Fat-Suppressed T1-Weighted Gradient-Recalled Echo Sequence Versus Conventional Fat-Suppressed Contrast-Enhanced T1-Weighted Studies of the Head and Neck

OBJECTIVE Traditional fat-suppressed T1-weighted spin-echo or turbo spin-echo (TSE) sequences (T1-weighted images) may be degraded by motion and pulsation artifacts in head-and-neck studies. Our purpose is to evaluate the role of a fat-suppressed T1-weighted 3D radial gradient-recalled echo sequence (radial-volumetric interpolated breath-hold examination [VIBE]) in the head and neck as compared with standard contrast-enhanced fat-suppressed T1-weighted images. MATERIALS AND METHODS We retrospectively evaluated 21 patients (age range, 9-67 years) who underwent head-and-neck MRI at 1.5 T. Both contrast-enhanced radial-VIBE and conventional fat-suppressed TSE contrast-enhanced T1-weighted imaging were performed. Two radiologists evaluated multiple parameters of image quality, graded on a 5-point scale. Mixed-model analysis of variance and interobserver variability assessment were performed. RESULTS The following parameters were scored as significantly better for the contrast-enhanced radial-VIBE sequence than for conventional contrast-enhanced T1-weighted imaging: overall image quality (p < 0.0001), degree of fat suppression (p = 0.006), mucosal enhancement (p = 0.004), muscle edge clarity (p = 0.049), vessel clarity (p < 0.0001), respiratory motion artifact (p = 0.002), pulsation artifact (p < 0.0001), and lesion edge sharpness (p = 0.004). Interobserver agreement in qualitative evaluation of the two sequences showed fair-to-good agreement for the following variables: overall image quality (intraclass correlation coefficient [ICC], 0.779), degree of fat suppression (ICC, 0.716), mucosal enhancement (ICC, 0.693), muscle edge clarity (ICC, 0.675), respiratory motion artifact (ICC, 0.516), lesion enhancement (ICC, 0.410), and lesion edge sharpness (ICC, 0.538). Excellent agreement was shown for vessel clarity (ICC, 0.846) and pulsation artifact (ICC, 0.808). CONCLUSION The radial-VIBE sequence is a viable motion-robust improvement on the conventional fat-suppressed T1-weighted sequence.

Diffusion-Weighted MR Imaging of Benign and Malignant Breast Lesions Before and After Contrast Enhancement

PURPOSE Many publications describe the use of diffusion-weighted imaging (DWI) in breast MRI. This article addresses the question of when to apply the DWI sequence in the course of the scan protocol. The effect of T1-shortening contrast media (CM) on the ADC values of breast lesions is investigated. MATERIALS AND METHODS Data were acquired on a 1.5 T scanner. 60 patients with 79 lesions (20 benign, 59 malignant) were included. The DWI sequence (4 mm slice thickness, b-values: 50, 400, 800) was applied before and after CM administration. Before calculating the ADC map, the b50, b400 and b800 series were analyzed concerning lesion displacement. ADC values before and after CM application were compared. RESULTS The mean lesion size was 1.5 ± 0.8 cm. On the basis of the b50 and b400 measurements, the mean ADC value of benign lesions was 1.89 ± 0.30 × 10-3 mm2/s before and 1.85 ± 0.28 ×10-3 mm2/s after CM administration. The consecutive values for two pure mucinous carcinomas were 1.88 × 10-3 mm2/s and 1.81 × 103 mm2/s and for the remaining malignant lesions 1.00 ± 0.18 × 10-3 mm2/s and 0.88 ± 0.21 × 10-3 mm2. On the basis of the b50, b400 and b800 measurements, the mean ADC value of benign lesions was 1.99 ± 0.37 × 10-3 mm2/s before and 1.97 ± 0.30 × 10-3 mm2/s after CM application, whereas the mean ADC value of the malignant lesions was 0.90 ± 0.14 × 10-3 mm2/s before and 0.80 ± 0.14 × 10-3 mm2/s after CM application. While there was no significant change for benign lesions, the ADC value decrease in post-contrast malignant lesions was highly significant. CONCLUSION DWI after CM is possible and even leads to slightly better lesion discrimination between benign and malignant. However, further studies need to be performed to verify this. Citation Format: • Janka R, Hammon M, Geppert C et al. Diffusion-Weighted MR Imaging of Benign and Malignant Breast Lesions Before and After Contrast Enhancement. Fortschr Röntgenstr 2014; 186: 130 - 135.