Faculty Bibliography

Non-Cartesian magnetic resonance imaging (MRI) sequences have shown great promise for abdominal examination during free breathing, but break down in the presence of bulk patient motion (i.e. voluntary or involuntary patient movement resulting in translation, rotation or elastic deformations of the body). This work describes a data-consistency-driven image stabilization technique that detects and excludes bulk movements during data acquisition. Bulk motion is identified from changes in the signal intensity distribution across different elements of a multi-channel receive coil array. A short free induction decay signal is acquired after excitation and used as a measure to determine alterations in the load distribution. The technique has been implemented on a clinical MR scanner and evaluated in the abdomen. Six volunteers were scanned and two radiologists scored the reconstructions. To show the applicability to other body areas, additional neck and knee images were acquired. Data corrupted by bulk motion were successfully detected and excluded from image reconstruction. An overall increase in image sharpness and reduction of streaking and shine-through artifacts were seen in the volunteer study, as well as in the neck and knee scans. The proposed technique enables automatic real-time detection and exclusion of bulk motion during MR examinations without user interaction. It may help to improve the reliability of pediatric MRI examinations without the use of sedation.

PURPOSE: Conventional fat/water separation techniques require that patients hold breath during abdominal acquisitions, which often fails and limits the achievable spatial resolution and anatomic coverage. This work presents a novel approach for free-breathing volumetric fat/water separation. METHODS: Multiecho data are acquired using a motion-robust radial stack-of-stars three-dimensional GRE sequence with bipolar readout. To obtain fat/water maps, a model-based reconstruction is used that accounts for the off-resonant blurring of fat and integrates both compressed sensing and parallel imaging. The approach additionally enables generation of respiration-resolved fat/water maps by detecting motion from k-space data and reconstructing different respiration states. Furthermore, an extension is described for dynamic contrast-enhanced fat-water-separated measurements. RESULTS: Uniform and robust fat/water separation is demonstrated in several clinical applications, including free-breathing noncontrast abdominal examination of adults and a pediatric subject with both motion-averaged and motion-resolved reconstructions, as well as in a noncontrast breast exam. Furthermore, dynamic contrast-enhanced fat/water imaging with high temporal resolution is demonstrated in the abdomen and breast. CONCLUSION: The described framework provides a viable approach for motion-robust fat/water separation and promises particular value for clinical applications that are currently limited by the breath-holding capacity or cooperation of patients. Magn Reson Med, 2016. (c) 2016 International Society for Magnetic Resonance in Medicine.

BACKGROUND: Interest in MR-only treatment planning for radiation therapy is growing rapidly with the emergence of integrated MRI/linear accelerator technology. The purpose of this study was to evaluate the feasibility of using synthetic CT images generated from conventional Dixon-based MRI scans for radiation treatment planning of lung cancer. METHODS: Eleven patients who underwent whole-body PET/MR imaging following a PET/CT exam were randomly selected from an ongoing prospective IRB-approved study. Attenuation maps derived from the Dixon MR Images and atlas-based method was used to create CT data (synCT). Treatment planning for radiation treatment of lung cancer was optimized on the synCT and subsequently copied to the registered CT (planCT) for dose calculation. Planning target volumes (PTVs) with three sizes and four different locations in the lung were planned for irradiation. The dose-volume metrics comparison and 3D gamma analysis were performed to assess agreement between the synCT and CT calculated dose distributions. RESULTS: Mean differences between PTV doses on synCT and CT across all the plans were -0.1% +/- 0.4%, 0.1% +/- 0.5%, and 0.4% +/- 0.5% for D95, D98 and D100, respectively. Difference in dose between the two datasets for organs at risk (OARs) had average differences of -0.14 +/- 0.07 Gy, 0.0% +/- 0.1%, and -0.1% +/- 0.2% for maximum spinal cord, lung V20, and heart V40 respectively. In patient groups based on tumor size and location, no significant differences were observed in the PTV and OARs dose-volume metrics (p > 0.05), except for the maximum spinal-cord dose when the target volumes were located at the lung apex (p = 0.001). Gamma analysis revealed a pass rate of 99.3% +/- 1.1% for 2%/2 mm (dose difference/distance to agreement) acceptance criteria in every plan. CONCLUSIONS: The synCT generated from Dixon-based MRI allows for dose calculation of comparable accuracy to the standard CT for lung cancer treatment planning. The dosimetric agreement between synCT and CT calculated doses warrants further development of a MR-only workflow for radiotherapy of lung cancer.

Purpose: The purpose of this study is to assess the dosimetric equivalence of MR-generated synthetic CT and conventional CT for treatment planning in radiotherapy of rectal cancer. Methods: This study was conducted on eleven patients who underwent whole-body PET/MR and PET/CT examination in a prospective IRB-approved study. MR data were obtained on a 3T Siemens PET/MR hybrid scanner using a 2-point Dixon sequence. Synthetic CT (synCT) was generated from Dixon MR using a model-based method and then registered to CT using a deformable registration. Rectal tumors were artificially contoured in the synCT by a physician to define a planning tumor volume (PTV) for treatment planning comparison. Standard treatment planning directives were used to create a four-field box (4F), an oblique four-field box (O4F) and a volumetric modulated arc therapy (VMAT) plans on synCT for each PTV. The plans were recalculated on registered planCT with the same MUs as on synCT. Dose-volume metrics and gamma analysis were evaluated between synCT and CT plans. Results: Differences in PTV Dmin, D95% and Dmax between synCT and CT plans across all patients were 0.02 +/- 0.82% for 4F, -0.16 +/- 0.78% for O4F and -0.31 +/- 0.97% for VMAT plans. In any of the treatment techniques, no significant differences were observed in organs at risk (OAR) dose metrics including small bowel (V45 Gy), bladder (V40 Gy) and femoral head (V30 Gy). Gamma Analysis with 2%/2 mm dose difference/distance to agreement showed percentage pass rates of 98.7 +/- 3.1, 98.0 +/- 3.6, and 98.8 +/- 2.7 for 4F, O4F and VMAT, respectively between SynCT and CT plan. Conclusion: Planning on synCT agreed well with the dose recalculated on planning CT for conventional treatment techniques in rectal cancer radiotherapy. These results suggest the potential of MR-only radiotherapy using MR generated synCT

Magnetic resonance (MR)/PET scanners provide an imaging platform that enables simultaneous acquisition of MR and PET data in perfect spatial and temporal registration. This feature allows improving image quality for the MR and PET images obtained during the course of an examination. In this work the authors demonstrate the use of prospective MR-based motion tracking information for removing motion blur in MR/PET images of small pulmonary nodules. The theoretical basis for the algorithms is presented alongside clinical examples of its use.

OBJECTIVE: To determine whether patient-specific 3D printed renal tumor models change pre-operative planning decisions made by urological surgeons in preparation for complex renal mass surgical procedures. MATERIALS AND METHODS: From our ongoing IRB approved study on renal neoplasms, ten renal mass cases were retrospectively selected based on Nephrometry Score greater than 5 (range 6-10). A 3D post-contrast fat-suppressed gradient-echo T1-weighted sequence was used to generate 3D printed models. The cases were evaluated by three experienced urologic oncology surgeons in a randomized fashion using (1) imaging data on PACS alone and (2) 3D printed model in addition to the imaging data. A questionnaire regarding surgical approach and planning was administered. The presumed pre-operative approaches with and without the model were compared. Any change between the presumed approaches and the actual surgical intervention was recorded. RESULTS: There was a change in planned approach with the 3D printed model for all ten cases with the largest impact seen regarding decisions on transperitoneal or retroperitoneal approach and clamping, with changes seen in 30%-50% of cases. Mean parenchymal volume loss for the operated kidney was 21.4%. Volume losses >20% were associated with increased ischemia times and surgeons tended to report a different approach with the use of the 3D model compared to that with imaging alone in these cases. The 3D printed models helped increase confidence regarding the chosen operative procedure in all cases. CONCLUSIONS: Pre-operative physical 3D models created from MRI data may influence surgical planning for complex kidney cancer.

The introduction of compressed sensing for increasing imaging speed in magnetic resonance imaging (MRI) has raised significant interest among researchers and clinicians, and has initiated a large body of research across multiple clinical applications over the last decade. Compressed sensing aims to reconstruct unaliased images from fewer measurements than are traditionally required in MRI by exploiting image compressibility or sparsity. Moreover, appropriate combinations of compressed sensing with previously introduced fast imaging approaches, such as parallel imaging, have demonstrated further improved performance. The advent of compressed sensing marks the prelude to a new era of rapid MRI, where the focus of data acquisition has changed from sampling based on the nominal number of voxels and/or frames to sampling based on the desired information content. This article presents a brief overview of the application of compressed sensing techniques in body MRI, where imaging speed is crucial due to the presence of respiratory motion along with stringent constraints on spatial and temporal resolution. The first section provides an overview of the basic compressed sensing methodology, including the notion of sparsity, incoherence, and nonlinear reconstruction. The second section reviews state-of-the-art compressed sensing techniques that have been demonstrated for various clinical body MRI applications. In the final section, the article discusses current challenges and future opportunities. LEVEL OF EVIDENCE: 5 J. Magn. Reson. Imaging 2016.

PURPOSE: To define important elements of a structured radiology report of a CT or MRI performed to evaluate an indeterminate renal mass. METHODS: IRB approval was waived for this multi-site prospective quality improvement study. A 35-question survey investigating elements of a CT or MRI report describing a renal mass was created through an iterative process by the Society of Abdominal Radiology Disease-Focused Panel on renal cell carcinoma. Surveys were distributed to consenting abdominal radiologists and urologists at nine academic institutions. Consensus within and between specialties was defined as >/=70% agreement. Respondent rates were compared with Chi Square test. RESULTS: The response rate was 68% (117/171; 55% [39/71] urologists, 78% [78/100] radiologists). Inter-specialty consensus was that the following were essential: mass size with comparison to prior imaging, mass type (cystic vs. solid), presence of fat, presence of enhancement, and radiologic stage. Urologists were more likely to prefer the Nephrometry score (75% [27/36] vs. 22% [17/76], p < 0.0001), quantitative reporting of enhancement on CT (85% [32/38] vs. 46% [36/77], p < 0.0001), and mass position with respect to the renal polar lines (67% [24/36] vs. 36% [27/76], p = 0.002). There was inter-specialty consensus that the Bosniak classification for cystic masses was preferred. Most urologists (60% [21/35]) preferred management recommendations be omitted for solid masses or Bosniak III-IV cystic masses. CONCLUSIONS: Important elements to include in a CT or MRI report of an indeterminate renal mass are critical diagnostic features, the Bosniak classification if relevant, and the most likely specific diagnosis when feasible; including management recommendations is controversial.

Incidental detection of renal mass results in management dilemma. Historically all enhancing renal tumours without imaging evidence of bulk fat were considered surgical. However, it is clear that many of these small renal masses are either benign such as angiomyolipoma (AML) or oncocytoma, or are neoplasms with indolent behavior [1]. Surgical resection of these benign or indolent tumours, especially in patients with decreased renal function or other co-morbidities, results in increased cost without improvement in survival or mortality [2]. Use of advance imaging, such as diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI), to non-invasively investigate renal tumour histopathology and aggressiveness can impact treatment decision and lower treatment cost. Number of key observations highlighting the role of MR including advance imaging techniques in evaluation of renal masses is as listed below: 1. Differentiating benign renal masses from malignant tumours.-Certain MRI features such as homogenous T2 signal, uniform enhancement, restricted diffusion with low ADC, and without evidence for necrosis and calcification can differentiate lipid poor AML from clear cell and papillary subtype of kidney cancers [3, 4].-It is nearly impossible to discriminate benign oncocytoma from chromophobe and clear cell subtypes of kidney cancers on conventional imaging [5]. However, DWI and PWI have shown some promise in small studies. 2. Tumour aggressiveness of solid RCC-Kidney cancers with different histologic subtypes differ in aggressiveness. Conventional MR imaging has shown some promise in differentiating papillary subtype of RCC from other subtypes based on hypovascularity, homogenous low T2 signal, T1 hyperintensity, and low ADC values. Advance DWI and PWI may further improve accuracy of MRI in discriminating papillary subtype from other types of kidney cancers.-Clear cell subtype of kidney cancers is hypervascular with heterogeneous T2 and diffusion signal [6]. 3. Tumour aggressiveness/outcome of cystic RCC-Cystic RCC with less than 25% solid enhancing component tend to be less aggressive than solid RCC [7]