Matthias P. Lichy

Simultaneous PET-MRI: a new approach for functional and morphological imaging

Noninvasive imaging at the molecular level is an emerging field in biomedical research. This paper introduces a new technology synergizing two leading imaging methodologies: positron emission tomography (PET) and magnetic resonance imaging (MRI). Although the value of PET lies in its high-sensitivity tracking of biomarkers in vivo, it lacks resolving morphology. MRI has lower sensitivity, but produces high soft-tissue contrast and provides spectroscopic information and functional MRI (fMRI). We have developed a three-dimensional animal PET scanner that is built into a 7-T MRI. Our evaluations show that both modalities preserve their functionality, even when operated isochronously. With this combined imaging system, we simultaneously acquired functional and morphological PET-MRI data from living mice. PET-MRI provides a powerful tool for studying biology and pathology in preclinical research and has great potential for clinical applications. Combining fMRI and spectroscopy with PET paves the way for a new perspective in molecular imaging.

Volumetric computed tomography (VCT): a new technology for noninvasive, high-resolution monitoring of tumor angiogenesis.

Volumetric computed tomography (VCT) is a technology in which area detectors are used for imaging large volumes of a subject with isotropic imaging resolution. We are experimenting with a prototype VCT scanner that uses flat-panel X-ray detectors and is designed for high-resolution three-dimensional (3D) imaging. Using this technique, we have demonstrated microangiography of xeno-transplanted skin squamous cell carcinomas in nude mice. VCT shows the vessel architecture of tumors and animals with greater detail and plasticity than has previously been achieved, and is superior to contrast-enhanced magnetic resonance (MR) angiography. VCT and MR images correlate well for larger tumor vessels, which are tracked from their origin on 3D reconstructions of VCT images. When compared with histology, small tumor vessels with a diameter as small as 50 μm were clearly visualized. Furthermore, imaging small vessel networks inside the tumor tissue improved discrimination of vital and necrotic regions. Thus, VCT substantially improves imaging of vascularization in tumors and offers a promising tool for preclinical studies of tumor angiogenesis and antiangiogenic therapies.

Magnetic resonance imaging of the body trunk using a single-slab, 3-dimensional, T2-weighted turbo-spin-echo sequence with high sampling efficiency (SPACE) for high spatial resolution imaging: Initial clinical experiences

Purpose:The authors conducted a clinical evaluation of single-slab, 3-dimensional, T2-weighted turbo-spin-echo (TSE) with high sampling efficiency (SPACE) for high isotropic body imaging with large field-of-view (FoV). Materials and Methods:Fifty patients were examined in clinical routine with SPACE (regions of interest: pelvis n = 30, lower spine n = 12, upper spine n = 6, extremities n = 4) at 1.5 T. For achieving a high sampling efficiency, parallel imaging, high turbofactor, and magnetization restore pulses were used. In contrast to a conventional TSE imaging technique with constant flip angle refocusing, the refocusing pulse train of the SPACE sequence consists of variable flip angle radiofrequency pulses along the echo train. Results:Signal-to-noise ratio and contrast-to-noise ratio of SPACE images were of sufficient diagnostic value. The possibility of image reconstruction in multiple planes was of clinical relevance in all cases and simplified data analysis. Conclusion:The achievement of 3-dimensional, T2-weighted TSE magnetic resonance imaging with isotropic and high spatial resolution and interactive 3-dimensional visualization essentially improve the diagnostic potential of magnetic resonance imaging.

Tumor detection by Diffusion Weighted MRI and ADC-Mapping - Initial Clinical Experiences in Comparison to PET-CT

Objective:To evaluate the clinical potential of diffusion-weighted-imaging (DWI) with apparent diffusion coefficient (ADC)-mapping for tumor detection. Materials and Methods:A single-shot echo-planar-imaging DWI sequence with fat suppression and ability for navigator-based respiratory triggering was implemented. Nineteen patients (11 melanoma, 4 prostate cancer, 1 non-Hodgkin lymphoma, and 3 lung cancer) were examined by positron emission tomography (PET) with an integrated computed tomography scanner (PET-CT) and DWI. Images at b = 0, 400, and 1000 s/mm2 were acquired and ADC maps were generated. PET examinations were used as a reference for tumor detection. Four hundred twenty-four regions of interest were used for DWI and 73 for PET data evaluation. Results:DWI and ADC maps were of diagnostic quality. Metastases with increased tracer uptake were clearly visualized at b = 1000 s/mm2 with the exception of mediastinal lymph node metastases in cases of lung cancer. ADC mapping did not improve detection rates. Conclusions:DWI is a feasible clinical technique, improving the assessment of metastatic spread in routine magnetic resonance imaging examinations.

Assessment of irradiated brain metastases by means of arterial spin-labeling and dynamic susceptibility-weighted contrast-enhanced perfusion MRI: Initial results

Rationale and Objectives:To assess if preradiation and early follow-up measurements of relative regional cerebral blood flow (rrCBF) can predict treatment outcome in patients with cerebral metastases and to evaluate rrCBF changes in tumor and normal tissue after stereotactic radiosurgery using arterial spin-labeling (ASL) and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI. Methods:In 25 patients with a total of 28 brain metastases, DSC MRI and ASL perfusion MRI using the Q2TIPS sequence were performed with a 1.5-T unit. Measurements were performed prior to and at 6 weeks, 12 weeks, and 24 weeks after stereotactic radiosurgery. Follow-up examinations were completely available in 25 patients for Q2TIPS and 17 patients with 18 metastases for DSC MRI. The rrCBF of the metastases and the normal brain tissue was determined by a region-of-interest analysis. rrCBF values were correlated with the treatment outcome that was classified according to tumor volume changes at 6 months. Results:The alteration of the rrCBF at the 6-week follow-up was highly predictive for treatment outcome. A decrease of the rrCBF value predicted tumor response correctly in all metastases for Q2TIPS and in 13 of 16 metastases for DSC MRI. The pretherapeutic rrCBF was not able to predict treatment outcome. The rrCBF values in normal brain tissue affected by radiation doses less than 0.5 Gy remained unchanged after therapy. Conclusion:These preliminary results suggest that ASL and DSC MRI techniques determining rrCBF changes in brain metastases after stereotactic radiosurgery allow the prediction of treatment outcome.

Whole-body diffusion-weighted MRI with apparent diffusion coefficient mapping for early response monitoring in multiple myeloma: preliminary results.

OBJECTIVE The purpose of our study was to prospectively assess the feasibility of whole-body diffusion-weighted imaging (DWI) for short-term evaluation of response to treatment in multiple myeloma patients using a single-shot echo-planar imaging DWI sequence with a Stejskal-Tanner diffusion encoding scheme and spectral fat suppression. SUBJECTS AND METHODS Twelve consecutive patients (nine men and three women; mean age, 61.4 years; age range, 54-79 years) underwent whole-body DWI (b = 50, 400, and 800 s/mm(2)) both at baseline and 3 weeks (mean, 23 days) after onset of therapy. Bone marrow and extramedullary manifestations were evaluated by quantitative image analysis using measurements of the mean apparent diffusion coefficient (ADC). These parameters were correlated with myeloma response according to standard criteria and were evaluated parallel to MRI and continuously for more than 6 months afterward. RESULTS Fifty-three myeloma lesions, 50 medullary (28 axial and 22 appendicular skeleton) and three extramedullary, were analyzed. Eleven patients were classified as responders and one as a nonresponder. DWI results accurately (100%) correlated with disease course according to standard clinical and laboratory criteria. All involved lesions showed restricted diffusion at baseline. ADC quantification yielded an increase of 63.9% (range, 8.7-211.3%) in responders and a decrease of 7.8% in the sole nonresponding patient during therapy. In parallel, M-gradient measurement showed a mean decrease of 45.1% (range, 19.6-88.8%) in responders and an increase of 21.8% in the nonresponder. Amplitude of response measured by the course of ADC values proved higher in the appendicular skeleton (99.8%) compared with the axial skeleton (54.3%) (p = 0.037). CONCLUSION Whole-body DWI with ADC analysis represents a feasible diagnostic tool for assessment of short-term treatment response in myeloma patients.

Comparison of arterial spin-labeling techniques and dynamic susceptibility-weighted contrast-enhanced MRI in perfusion imaging of normal brain tissue

Objectives:To evaluate relative cerebral blood flow (rCBF) in normal brain tissue using arterial spin-labeling (ASL) methods and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) magnetic resonance imaging (MRI). Methods:Sixty-two patients with brain metastases were examined on a 1.5 T-system up to 6 times during routine follow-up after stereotactic radiosurgery. Perfusion values in normal gray and white matter were measured using the ASL techniques ITS-FAIR in 38 patients, Q2TIPS in 62 patients, and the first-pass DSC echo-planar (EPI) MRI after bolus administration of gadopentetate dimeglumine in 42 patients. Precision of the ASL sequences was tested in follow-up examinations in 10 healthy volunteers. Results:Perfusion values in normal brain tissue obtained by all sequences correlated well by calculating Pearson’s correlation coefficients (P < 0.0001) and remained unchanged after stereotactic radiosurgery as shown by analysis of variance (P > 0.05). Conclusion:Both ASL and DSC EPI MRI yield highly comparable perfusion values in normal brain tissue.

High-resolution three-dimensional MR angiography of rodent tumors: morphologic characterization of intratumoral vasculature.

To evaluate high‐resolution three‐dimensional MR angiography (MRA) for the visualization and morphologic characterization of intratumoral vasculature.

Tumorsize dependent detection rate of endorectal MRI of prostate cancer - A histopathologic correlation with whole-mount sections in 70 patients with prostate cancer

PURPOSE To evaluate the value of T2w endorectal MRI (eMRI) for correct detection of tumor foci within the prostate regarding tumor size. MATERIALS AND METHODS 70 patients with histologically proven prostate cancer were examined with T2w eMRI before radical prostatectomy at a 1.5T scanner. For evaluation of eMRI, two radiologists evaluated each tumor focus within the gland. After radical prostatectomy, the prostates were prepared as whole-mount sections, according to transversal T2w eMRI. For each slice, tumor surroundings were marked and compared with eMRI. Based on whole-mount section, 315 slices were evaluated and 533 tumor lesions were documented. RESULTS Based on the T2w eMRI, 213 tumor lesions were described. In 137/213, histology could prove these lesions. EMRI was able to visualize 0/56 lesions with a maximum size of <0.3 cm (detection rate 0%), between 0.3 and 0.5 cm 4/116 (3%), between 1 and 0.5 cm 22/169 (13%), between 2 and 1cm 61/136 (45%) and for >2 cm 50/56 (89%). False positive eMRI findings were: <0.3 cm n=0, 0.5-0.3 cm n=12, 0.5-1cm n=34, 1-2 cm n=28 and >2 cm n=2. CONCLUSION T2w eMRI cannot exclude prostate cancer with lesions smaller 10mm and 0.4 cm(3) respectively. The detection rate for lesions more than 20mm (1.6 cm(3)) is to be considered as high.

Time‐resolved contrast‐enhanced three‐dimensional pulmonary MR‐angiography: 1.0 M gadobutrol vs. 0.5 M gadopentetate dimeglumine

To compare contrast characteristics and image quality of 1.0 M gadobutrol with 0.5 M Gd‐DTPA for time‐resolved three‐dimensional pulmonary magnetic resonance angiography (MRA).