Marcel Gratz

Correlation of Standardized Uptake Value and Apparent Diffusion Coefficient in Integrated Whole-Body PET/MRI of Primary and Recurrent Cervical Cancer

Background To evaluate a potential correlation of the maximum standard uptake value (SUVmax) and the minimum apparent diffusion coefficient (ADCmin) in primary and recurrent cervical cancer based on integrated PET/MRI examinations. Methods 19 consecutive patients (mean age 51.6 years; range 30–72 years) with histopathologically confirmed primary cervical cancer (n = 9) or suspected tumor recurrence (n = 10) were prospectively enrolled for an integrated PET/MRI examination. Two radiologists performed a consensus reading in random order, using a dedicated post-processing software. Polygonal regions of interest (ROI) covering the entire tumor lesions were drawn into PET/MR images to assess SUVmax and into ADC parameter maps to determine ADCmin values. Pearson’s correlation coefficients were calculated to assess a potential correlation between the mean values of ADCmin and SUVmax. Results In 15 out of 19 patients cervical cancer lesions (n = 12) or lymph node metastases (n = 42) were detected. Mean SUVmax (12.5±6.5) and ADCmin (644.5±179.7×10−5 mm2/s) values for all assessed tumor lesions showed a significant but weak inverse correlation (R = −0.342, p<0.05). When subdivided in primary and recurrent tumors, primary tumors and associated primary lymph node metastases revealed a significant and strong inverse correlation between SUVmax and ADCmin (R = −0.692, p<0.001), whereas recurrent cancer lesions did not show a significant correlation. Conclusions These initial results of this emerging hybrid imaging technique demonstrate the high diagnostic potential of simultaneous PET/MR imaging for the assessment of functional biomarkers, revealing a significant and strong correlation of tumor metabolism and higher cellularity in cervical cancer lesions.

Simultaneous positron emission tomography/magnetic resonance imaging for whole-body staging in patients with recurrent gynecological malignancies of the pelvis: a comparison to whole-body magnetic resonance imaging alone.

ObjectivesThe objective of this study was to assess the diagnostic value of integrated positron emission tomography/magnetic resonance imaging (PET/MRI) for whole-body staging of patients with recurrent gynecological pelvic malignancies, in comparison to whole-body MRI alone. Materials and MethodsThe study was approved by the local institutional ethics committee. Written informed consent was obtained before each examination. Thirty-four consecutive patients with a suspected recurrence of cervical (n = 18) or ovarian (n = 16) cancer were prospectively enrolled for an integrated PET/MRI examination, which comprised a diagnostic, contrast-enhanced whole-body MRI protocol including dedicated sagittal dynamic imaging of the pelvis. Two radiologists separately evaluated the data sets regarding lesion count, lesion detection, lesion characterization, and diagnostic confidence. Mean and median values were calculated for each rating. Statistical analyses were performed both per-patient and per-lesion bases using a Wilcoxon signed-rank test to indicate potential significant differences among PET/MRI and MRI (alone) data sets. ResultsMalignant lesions were present in 25 of the 34 patients. Positron emission tomography/magnetic resonance imaging offered correct and superior identification of all 25 patients with cancer recurrence, compared with MRI alone (23/25). A total of 118 lesions (malignant, 89; benign, 29) were detected. Positron emission tomography/magnetic resonance imaging correctly identified 88 (98.9%) of 89 malignant lesions, whereas MRI alone allowed for correct identification of 79 (88.8%) of the 89 malignant lesions. In addition, PET/MRI provided significantly higher lesion contrast and diagnostic confidence in the detection of malignant lesions (P < 0.001) compared with MRI alone. ConclusionsThese first results demonstrate the high diagnostic potential of integrated PET/MRI for the assessment of recurrence of female pelvic malignancies compared with MRI alone.

High and ultra-high b-value diffusion-weighted imaging in prostate cancer: a quantitative analysis

Background Diffusion-weighted imaging (DWI) is routinely used in magnetic resonance imaging (MRI) of prostate cancer. However, the routine use of b values higher than 1000 s/mm2 is not clear up to present. Moreover, the complex diffusion behavior of malignant and benign prostate tissues hampers precise predictions of contrast in DWI images and apparent diffusion coefficient (ADC) maps. Purpose To quantitatively analyze DWI with different b values in prostate cancer and to identify b values best suitable for cancer detection. Material and Methods Forty-one patients with histologically proven prostate cancer were examined with high resolution T2-weighted imaging and DWI at 3 Tesla. Five different b values (0, 800, 1000, 1500, 2000 s/mm2) were applied. ADC values of tumors and reference areas were measured on ADC maps derived from different pairs of b values. Furthermore, signal intensities of DW images of tumors and reference areas were measured. For analysis, contrast ratios of ADC values and signal intensities of DW images were calculated and compared. Results No significant differences were found between contrast ratios measured on ADC maps of all analyzed b value pairs (P = 0.43). Contrast ratios calculated from signal intensities of DW images were highest at b values of 1500 and 2000 s/mm2 and differed significantly from contrast ratios at b values of 800 and 1000 s/mm2 (P < 0.01). Conclusion Whereas contrast in ADC maps does not significantly change with different b values, contrast ratios of DW images are significantly higher at b-values of 1500 and 2000 s/mm2 in comparison to b values of 800 and 1000 s/mm2. Therefore, diagnostic performance of DWI in prostate cancer might be increased by application of b values higher than 1000 s/mm2.

Fast and accurate multi-channel B1+ mapping based on the TIAMO technique for 7T UHF body MRI: Fast and Accurate B1 + Mapping With TIAMO

Current methods for mitigation of transmit field B1+ inhomogeneities at ultrahigh field (UHF) MRI by multi‐channel radiofrequency (RF) shimming rely on accurate B1+ mapping. This can be time consuming when many RF channels have to be mapped for in vivo body MRI, where the B1 maps should ideally be acquired within a single breath‐hold. Therefore, a new B1+ mapping technique (B1TIAMO) is proposed.

Compressed sensing cine imaging with high spatial or high temporal resolution for analysis of left ventricular function.

To assess two compressed sensing cine magnetic resonance imaging (MRI) sequences with high spatial or high temporal resolution in comparison to a reference steady‐state free precession cine (SSFP) sequence for reliable quantification of left ventricular (LV) volumes.

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

Object In this work an 8-channel array integrated into the gap between the gradient coil and bore liner of a 7-Tesla whole-body magnet is presented that would allow a workflow closer to that of systems at lower magnetic fields that have a built-in body coil; this integrated coil is compared to a local 8-channel array built from identical elements placed directly on the patient. Materials and Methods SAR efficiency and the homogeneity of the right-rotating B1 field component (B_1^+) are investigated numerically and compared to the local array. Power efficiency measurements are performed in the MRI System. First in vivo gradient echo images are acquired with the integrated array. Results While the remote array shows a slightly better performance in terms of B_1^+ homogeneity, the power efficiency and the SAR efficiency are inferior to those of the local array: the transmit voltage has to be increased by a factor of 3.15 to achieve equal flip angles in a central axial slice. The g-factor calculations show a better parallel imaging g-factor for the local array. The field of view of the integrated array is larger than that of the local array. First in vivo images with the integrated array look subjectively promising. Conclusion Although some RF performance parameters of the integrated array are inferior to a tight-fitting local array, these disadvantages might be compensated by the use of amplifiers with higher power and the use of local receive arrays. In addition, the distant placement provides the potential to include more elements in the array design.

A dual-tuned 13C/1H head coil for PET/MR hybrid neuroimaging: Development, attenuation correction, and first evaluation

PURPOSE This study aims to develop, implement, and evaluate a dual-tuned 13 C/1 H head coil for integrated positron emission tomography/magnetic resonance (PET/MR) neuroimaging. The radiofrequency (RF) head coil is designed for optimized MR imaging performance and PET transparency and attenuation correction (AC) is applied for accurate PET quantification. MATERIAL AND METHODS A dual-tuned 13 C/1 H RF head coil featuring a 16-rung birdcage was designed to be used for integrated PET/MR hybrid imaging. While the open birdcage design can be considered inherently PET transparent, all further electronic RF components were placed as far as possible outside of the field-of-view (FOV) of the PET detectors. The RF coil features a rigid geometry and thin-walled casing. Attenuation correction of the RF head coil is performed by generating and applying a dedicated 3D CT-based template attenuation map (μmap). Attenuation correction was systematically evaluated in phantom experiments using a large-volume cylindrical emission phantom filled with 18-F-Fluordesoxyglucose (FDG) radiotracer. The PET/MR imaging performance and PET attenuation correction were then evaluated in a patient study including six patients. RESULTS The dual-tuned RF head coil causes a mean relative attenuation difference of 8.8% across the volume of the cylindrical phantom, while the local relative differences range between 1% and 25%. Applying attenuation correction, the relative difference between the two measurements with and without RF coil is reduced to mean value of 0.5%, with local differences of ±3.6%. The quantitative results of the phantom measurements were corroborated by patient PET/MR measurements. Patient scans using the RF head coil show a decrease of PET signal of 5.17% ± 0.81% when compared to the setup without RF head coil in place, which served as a reference scan. When applying attenuation correction of the RF coil in the patient measurements, the mean difference to a measurement without RF coil was reduced to -0.87% ± 0.65%. CONCLUSION A dual-tuned 13 C/1 H RF head coil was designed and evaluated regarding its potential use in integrated PET/MR hybrid imaging. Attenuation correction was successfully applied. In conclusion, the RF head coil was successfully integrated into PET/MR hybrid imaging and can now be used for 13 C/1 H multinuclear hybrid neuroimaging in future studies.

Parallel transmit capability of various RF transmit elements and arrays at 7T MRI: pTx Capabilities of 7T Arrays

In this work, 22 configurations for remote radiofrequency (RF) coil arrays consisting of different transmit element designs for 7 Tesla (T) ultrahigh‐field MRI are compared by numerical simulations.