Search

Background T2 mapping is of great interest in abdominal imaging but current methods are limited by low resolution, slice coverage, motion sensitivity, or lengthy acquisitions. Purpose Develop a radial turbo spin-echo technique with refocusing variable flip angles (RADTSE-VFA) for high spatiotemporal T2 mapping and efficient slice coverage within a breath-hold and compare to the constant flip angle counterpart (RADTSE-CFA). Study type Prospective technical efficacy. Subjects Testing performed on agarose phantoms and 12 patients. Focal liver lesion classification tested on malignant (N = 24) and benign (N = 11) lesions. Field strength/sequence 1.5 T/RADTSE-VFA, RADTSE-CFA. Assessment A constrained objective function was used to optimize the refocusing flip angles. Phantom and/or in vivo data were used to assess relative contrast, T2 estimation, specific absorption rate (SAR), and focal liver lesion classification. STATISTICAL TESTS: t-Tests or Mann-Whitney Rank Sum tests were used. Results Phantom data did not show significant differences in mean relative contrast (P = 0.10) and T2 accuracy (P = 0.99) between RADTSE-VFA and RADTSE-CFA. Adding noise caused T2 overestimation predominantly for RADTSE-CFA and low T2 values. In vivo results did not show significant differences in mean spleen-to-liver (P = 0.62) and kidney-to-liver (P = 0.49) relative contrast between RADTSE-VFA and RADTSE-CFA. Mean T2 values were not significantly different between the two techniques for spleen (T2VFA = 109.2 ± 12.3 msec; T2CFA = 110.7 ± 11.1 msec; P = 0.78) and kidney-medulla (T2VFA = 113.0 ± 8.7 msec; T2CFA = 114.0 ± 8.6 msec; P = 0.79). Liver T2 was significantly higher for RADTSE-CFA (T2VFA = 52.6 ± 6.6 msec; T2CFA = 60.4 ± 8.0 msec) consistent with T2 overestimation in the phantom study. Focal liver lesion classification had comparable T2 distributions for RADTSE-VFA and RADTSE-CFA for malignancies (P = 1.0) and benign lesions (P = 0.39). RADTSE-VFA had significantly lower SAR than RADTSE-CFA increasing slice coverage by 1.5. Data conclusion RADTSE-VFA provided noise-robust T2 estimation compared to the constant flip angle counterpart while generating T2-weighted images with comparable contrast. The VFA scheme minimized SAR improving slice efficiency for breath-hold imaging. Level of evidence 2 TECHNICAL EFFICACY STAGE: 1.

Background T1 mapping is often used in some clinical protocols. Existing techniques are limited in slice coverage, and/or spatial-temporal resolution, or require long acquisitions. Here we present a multi-slice inversion-recovery (IR) radial steady-state free precession (radSSFP) pulse sequence combined with a principal component (PC) based reconstruction that overcomes these limitations. Purpose To develop a fast technique for multi-slice high-resolution T1 mapping. Study type Technical efficacy study done prospectively. Phantom/subjects IR-radSSFP was tested in phantoms, five healthy volunteers, and four patients with abdominal lesions. Field strength/sequence IR-radSSFP was implemented at 3T. Assessment Computer simulations were performed to optimize the flip angle for T1 estimation; testing was done in phantoms using as reference an IR spin-echo pulse sequence. T1 mapping with IR-radSSFP was also assessed in vivo (brain and abdomen) and T1 values were compared with literature. T1 maps were also compared with a radial IR-FLASH technique. Statistical tests A two-tailed t-test was used to compare T1 values in phantoms. A repeatability study was carried out in vivo using Bland-Altman analysis. Results Simulations and phantom experiments showed that a flip angle of 20˚ was optimal for T1 mapping. When comparing single to multi-slice experiments in phantoms there were no significant differences between the means T1 values (P = 0.0475). In vivo results show that T1 maps with spatial resolution as high as 0.69 mm × 0.69 mm × 2.00 mm (brain) and 0.83 mm × 0.83 mm × 3.00 mm (abdomen) can be generated for 84 brain slices in 3 min and 10 abdominal slices in a breath-hold; T1 values were comparable to those reported in literature. The coefficients of variation from the repeatability study were 1.7% for brain and 2.5-2.7% in the abdomen. Data conclusion A multi-slice IR-radSSFP technique combined with a PC-based reconstruction was demonstrated for higher resolution T1 mapping. This technique is fast, motion-insensitive and yields repeatable T1 values comparable to those in literature. Level of evidence 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:239-252.

Technology and Research Initiative Fund (TRIF) - Improving Health and Arizona Biomedical Research Commission (ABRC) [ADHS14-082996]

Cardiac implanted electronic devices (CIEDs) have historically been regarded as a contraindication for performing magnetic resonance imaging (MRI), limiting the availability of this exam for large numbers of patients who may have otherwise benefited from the unique diagnostic capabilities of MRI. Interactions between CIEDs and the magnetic field associated with MRI systems have been documented, and include potential effects on CIED function, lead heating, and force/torque on the generator. Several device manufacturers have developed "MR-Conditional" CIEDs with specific hardware and software design changes to optimize the device for the MR environment. However, a substantial body of evidence has been accumulating that suggests that MRI may be safely performed in patients with either conditional or nonconditional CIEDs. Institutional policies and procedures, including preexam screening and assessment by skilled electrophysiology personnel and intraexam monitoring, allow MRI to be safely performed in CIED patients, as evidenced by at least two, large multicenter prospective studies and multiple smaller, single-institution studies. Cross-departmental collaboration and a robust safety infrastructure at sites that perform MRI should allow for the safe imaging of CIED patients who have a clinical indication for the study, regardless of the conditionality status of the device. LEVEL OF EVIDENCE 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018;47:595-603.

Purpose To develop a novel multiresolution MRI methodology for accurate estimation of glomerular filtration rate (GFR) in vivo. Materials and methods A three-dimensional golden-angle radial stack-of-stars (SoS) trajectory was used for data acquisition on a 3 Tesla MRI scanner. Multiresolution reconstruction and analysis was performed using arterial input function reconstructed at 1-s. temporal resolution and renal dynamic data reconstructed using compressed sensing (CS) with 4-s temporal resolution. The method was first validated using simulations and the clinical utility of the technique was evaluated by comparing the GFR estimates from the proposed method to the estimated GFR (eGFR) obtained from serum creatinine for 10 subjects. Results The 4-s temporal resolution CS images minimized streaking artifacts and noise while the 1-s temporal resolution AIF minimized errors in GFR estimates. A paired t-test showed that there was no statistically significant difference between MRI based total GFR values and serum creatinine based eGFR estimates (P = 0.92). Conclusion We have demonstrated the feasibility of multiresolution MRI using a golden angle radial stack-of-stars scheme to accurately estimate GFR as well as produce diagnostic quality dynamic images in vivo. Level of evidence 1 Technical Efficacy: Stage 3 J. MAGN. RESON. IMAGING 2017;46:303-311.

Purpose Lung function is typically characterized by spirometer measurements, which do not offer spatially specific information. Imaging during exhalation provides spatial information but is challenging due to large movement over a short time. The purpose of this work is to provide a solution to lung imaging during forced expiration using accelerated magnetic resonance imaging. The method uses radial golden angle stack-of-stars gradient echo acquisition and compressed sensing reconstruction. Methods A technique for dynamic three-dimensional imaging of the lungs from highly undersampled data is developed and tested on six subjects. This method takes advantage of image sparsity, both spatially and temporally, including the use of reference frames called bookends. Sparsity, with respect to total variation, and residual from the bookends, enables reconstruction from an extremely limited amount of data. Results Dynamic three-dimensional images can be captured at sub-150 ms temporal resolution, using only three (or less) acquired radial lines per slice per timepoint. The images have a spatial resolution of mm. Lung volume calculations based on image segmentation are compared to those from simultaneously acquired spirometer measurements. Conclusion Dynamic lung imaging during forced expiration is made possible by compressed sensing accelerated dynamic three-dimensional radial magnetic resonance imaging. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

Purpose: To evaluate intrinsic hepatic enhancement patterns on multiphase, gadolinium-enhanced, fat-suppressed, 3D T1-weighted, gradient echo magnetic resonance imaging (MRI) as a quantitative correlate for severity of pathological changes in chronic liver disease (CLD). Materials and Methods: This study was HIPAA-compliant and Institutional Review Board-approved. In all, 75 patients were studied by contrast-enhanced multiphase abdominal MRI. CLD patients had liver histology correlation derived from right lobe liver biopsies. Contrast-enhanced arterial- and delayed-phase 3D gradient recalled echo (GRE) liver MRI were scored using feature categorization templates to quantify enhancement patterns by three independent readers. Liver histopathology was staged/graded for fibrosis/inflammation using the Scheuer system. Statistical testing for MRI histology correlates used a Pearson's product moment correlation and a Wilcoxon–Mann–Whitney two-sample rank-sum test. Reader agreement was analyzed by a modified Fleiss' kappa test. Results: MRI histology correlation was high for delayed-phase MRI versus fibrosis stage (95% confidence interval [CI] 0.941 < r < 0.976, P = 5 × 10−7), but lower for all other comparisons (delayed-phase vs. inflammation and arterial-phase vs. inflammation or fibrosis all showed a CI no greater than 0.64). Paired testing between delayed-phase MRI score and histology fibrosis staging incremental levels was significant (from P < 10−2 to P < 10−5). Conclusion: A standard gadolinium-enhanced liver MRI may provide a correlate measure of hepatic fibrosis over a spectrum of severity. J. Magn. Reson. Imaging 2012;36:422–429. © 2012 Wiley Periodicals, Inc.

Purpose: To measure contrast agent enhancement kinetics in the liver and to further evaluate and develop an optimized gadolinium enhanced MRI using a single injection real-time bolus-tracking method for reproducible imaging of the transient arterial-phase. Materials and Methods: A total of 18 subjects with hypervascular liver lesions were imaged with four dimensional (4D) perfusion scans to measure time-to-peak (TTP) delays of arterial (aorta-celiac axis), liver parenchyma, liver lesion, portal, and hepatic veins. Time delays were calculated from the TTP-aorta signal, and then related to the gradient echo (GRE) k-space acquisition design, to determine optimized timing for real-time bolus-track triggering methodology. As another measure of significance, 200 clinical patients were imaged with 3D-GRE using either a fixed time-interval or by individualized arterial bolus real-time triggering. Bolus TTP-aorta was calculated and arterial-phase acquisitions were compared for accuracy and reproducibility using specific vascular enhancement indicators. Results: The mean bolus transit-time to peak-lesion contrast was 8.1 ± 2.7 seconds following arterial detection, compared to 32.1 ± 5.4 seconds from contrast injection, representing a 62.1% reduction in the time-variability among subjects (N = 18). The real-time bolus-triggered technique more consistently captured the targeted arterial phase (94%), compared to the fixed timing technique (73%), representing an expected improvement of timing accuracy in 28% of patients (P = 0.0001389). Conclusion: Our results show detailed timing window analysis required for optimized arterial real-time bolus-triggering acquisition of transient arterial phase features of liver lesions, with optimized arterial triggering expected to improve reproducibility in a significant number of patients. J. Magn. Reson. Imaging 2011;33:110–118. © 2010 Wiley-Liss, Inc.

Purpose: Realization of combined positron emission tomography (PET)—magnetic resonance (MR) scanners has the potential to significantly change healthcare and revolutionize clinical practice as it allows, simultaneously, visualization of molecular imaging and anatomical imaging. PET-MR, acquired in one imaging study, will likely become the advanced imaging modality of choice for neurological studies, certain forms of cancer, stroke, and the emerging study of stem cell therapy. A challenge toward the implementation and operation of combined PET-MR scanners is that attenuation corrections maps are not directly available due to space and cost constraints. This article presents a method to obtain accurate patient-specific PET attenuation coefficients maps in head imaging by warping an atlas computed tomography(CT) data set to the patient-specific MR data set using a deformable registration model. Methods: A multimodality optical flow deformable model has been developed that establishes a voxel-to-voxel correspondence between the CT atlas and patient MR images. Once the mapping is established, the atlas is warped with the deformation field obtained by the registration to create a simulated CTimage study that matches the patient anatomy, which could be used for attenuation correction. Results: To evaluate the accuracy of the deformable-based attenuation correction, 17 clinical braintumor cases were studied using acquired MR-CT images. A simulated CT was compared to the patient’s true CT to assess geometrical accuracy of the deformation module as well as voxel-to-voxel comparison of Hounsfield units (HUs). In all cases, mapping from the atlas CT to the individual MR was achieved with geometrical accuracy as judged using quantitative inspection tools. The mean distance between simulated and true CT external contour and bony anatomy was 1.26 and 2.15 mm, respectively. In terms of HU unit comparison, the mean voxel-to-voxel difference was less than 2 HU for all cases. Conclusions: Attenuation correction for hybrid PET-MR scanners was easily achieved by individualizing an atlas CT to the MR data set using a deformable model without requiring user interaction. The method provided clinical accuracy while eliminating the need for an additional CT scan for PET attenuation correction.

Purpose: To describe a new category of liver cyst we propose calling “giant bile duct hamartoma (giant-BDH)” and to provide a more complete record of the magnetic resonance imaging (MRI) features of BDHs with potential for clinical impact. Materials and Methods: This study was Institutional Review Board (IRB)-approved and Health Insurance Portability and Accountability Act (HIPPA)-compliant. Fifteen patients were identified with surgical liver pathology in keeping with complicated BDH and MRI findings of giant cysts. Results: In all, 14/15 patients presented with pain that resolved in 14/14 with surgery. Imaging features common to pretreatment cysts included sharply defined, lobulated margins with thin, smooth rim-enhancement. Treated symptomatic cysts measured 9.8 cm on average and 21.6 cm maximum. The 14/15 patients had coexistent

Purpose To investigate the accuracy and reproducibility of hepatic lipid measurements using 1H magnetic resonance spectroscopy (MRS) with T2 relaxation correction, compared to measurements without correction. Materials and Methods Experiments were conducted in phantoms of varying lipid and iron-induced susceptibility to simulate fatty liver with variable T2. Single-voxel 1H MRS was conducted with multiple TE values, and percent lipid content (lipid%) was determined at each TE to assess accuracy and TE dependency. Concurrently, T2 and equilibrium values of water and lipid were determined separately, and T2 effects on the lipid% were corrected. A similar procedure was conducted in 12 human subjects to determine susceptibility effects on water and lipid MRS signals and lipid%. Multiple measurements were used to test reproducibility. Results The use of T2-correction was found to be more accurate than uncorrected lipid% in phantom samples ( 20% when TE > 24 msec) and with increasing susceptibility effect. In humans, while measurement repeatability was high for both corrected and uncorrected MRS, uncorrected lipid% was sensitive to acquisition TE, with 83.6% of all measurements significantly different than T2-corrected measures (P < 0.05). Conclusion Separate T2-correction of water and lipid 1H MRS signals provides more accurate and consistent measurements of lipid%, in comparison to uncorrected estimations. J. Magn. Reson. Imaging 2009;29:629–635. © 2009 Wiley-Liss, Inc.

Purpose To retrospectively evaluate the efficacy of spectral presaturation attenuated inversion-recovery (SPAIR) fat-suppressed (FS) partial Fourier single shot (SSH) T2-weighted (T2W) and gadolinium-enhanced (Gd) FS 3D-gradient echo (3DGRE) T1-weighted (T1W) delayed phase MRI to differentiate active bowel inflammation from fibrotic disease in patients with Crohn's disease (CD). Materials and Methods MRI studies of 81 patients (mean age, 43 years; range, 22–77 years; M:F ratio 33:48) had T2W and T1W imaging including SPAIR-SSH and delayed Gd-3DGRE. The ability to assess disease activity in bowel segments affected were retrospectively evaluated by a grading scheme based on subjective analysis of signal intensities. These results were compared against the standard clinical parameters of disease activity. Results SPAIR-SSH images correlated better (r = 0.74, P < 0.0001) with activity than delayed Gd-3DGRE (r = 0.39, P = 0.0003), with a significant difference between the two techniques (P < 0.0001). SPAIR-SSH images showed higher specificity in detection of severely active disease in per patient (98%) and segmental (98%) analysis compared to Gd-3DGRE (57%, 70%). Gd-3DGRE technique showed significantly higher sensitivity (P = 0.01) in identifying active disease in per patient (83%) and segmental (85%) analysis compared to SPAIR-SSH (70%, 64%). Conclusion SPAIR-SSH detects actively diseased CD bowel segments with a high level of specificity. Noninflammatory bowel fibrosis corresponds to abnormal uptake on delayed phase Gd-3DGRE images but without associated elevated abnormal signal on SPAIR-SSH. J. Magn. Reson. Imaging 2008;28:1133–1140. © 2008 Wiley-Liss, Inc.

Purpose To assess a possible correlation between active acute hepatitis and the development of abnormal liver perfusion demonstrated as heterogeneous enhancement on arterial phase gadolinium-enhanced MRI. Dynamically-enhanced MRI of the liver can detect reversible perfusion abnormalities that correlate with acute hepatitis. Materials and Methods Six patients presenting with symptoms and clinical findings in keeping with transient acute hepatitis underwent serial MRI of the liver throughout the course of the disease. Serial liver enzyme analysis was performed for all six patients, and histopathology was assessed for three patients. Imaging included gadolinium-enhanced arterial and venous-phase gradient-echo sequences. Results Arterial phase gadolinium-enhanced MRI showed abnormal irregular liver perfusion in the setting of acute hepatitis, and the degree of irregularity, as well as the persistence of irregular enhancement into the venous phase, correlated with the clinical severity of the disease. Conclusion Acute hepatitis can cause irregular enhancement of the liver on arterial-phase, gadolinium-enhanced, gradient-echo MRI, a reversible finding that improves with clinical improvement of the disease. J. Magn. Reson. Imaging 2004;20:838–842. © 2004 Wiley-Liss, Inc.

Purpose To evaluate peripancreatic signal changes on fat-suppressed T1-weighted spoiled gradient echo images associated with acute pancreatitis and investigate potential utility in regards to relationship to clinical outcome. Materials and Methods The abdominal MR images in 31 patients with acute pancreatitis were reviewed, and evaluated for the presence of elevated signal intensity within the peripancreatic fat on fat-suppressed T1-weighted spoiled gradient echo images; the degree of signal changes was graded as mild, moderate, or severe. Results Ten of 31 patients demonstrated abnormal high signal intensity in the peripancreatic fat on fat-suppressed T1-weighted images. The degree of signal change was mild in three patients, moderate in one, and severe in six patients. All six patients with severe elevated peripancreatic soft tissue signal died within seven to 68 days (mean, 47 days) of their admission. All 21 patients without elevated peripancreatic fat signal survived without any complications. The correlation between the presence and severity of elevated peripancreatic MR signal and patient outcome was significant (P < 0.05). Conclusion Elevated peripancreatic signal on fat-suppressed T1-weighted images is associated progressively with poor outcome in patients with acute pancreatitis, and may represent a simplified method for prognostic cross-sectional imaging. J. Magn. Reson. Imaging 2003;18:49–58. © 2003 Wiley-Liss, Inc.

We sought to evaluate dynamic post–gadolinium contrast enhanced magnetic resonance (MR) imaging characteristics of adrenal adenomas with comparison to those of malignant adrenal tumors. MR images, including in- and out-of-phase spoiled gradient echo (SGE) and dynamic gadolinium enhancement, of 35 adrenal adenomas in 34 patients, and 12 malignant adrenal tumors in 12 patients, were reviewed retrospectively. MR images were assessed for the presence of a capillary blush on immediate postgadolinium SGE images, and for rapid washout of contrast on 45-second postgadolinium SGE images. Thirty-five adrenal adenomas (mean size, 3.1 cm) and 12 malignant adrenal tumors (mean size, 7.4 cm) were assessed. Of 35 adrenal adenomas, 25 (71%) showed a homogeneous capillary blush on immediate postgadolinium images. Thirty-three (94%) adrenal adenomas demonstrated rapid washout on 45-second postgadolinium images (P < 0.001). Of 35 adrenal adenomas, 30 (86%) showed diminished signal intensity (SI) on out-of-phase images. Of 12 malignant adrenal tumors, none showed a homogeneous capillary blush on immediate postgadolinium images. Six (50%) malignant tumors showed negligible enhancement, four (33%) showed irregular patchy enhancement, and two (17%) showed peripheral enhancement (P < 0.001). On 45-second postgadolinium images, 11 (92%) of 12 malignant adrenal tumors showed irregular enhancement. In the majority of adrenal adenomas, an initial homogeneous capillary blush and rapid washout are demonstrated on gadolinium-enhanced dynamic MR imaging. Our preliminary results suggest that this may provide useful complementary information to the appearance of adrenal masses on in- and out-of-phase images. J. Magn. Reson. Imaging 2001;13:242–248. © 2001 Wiley-Liss, Inc.

The aim of this study was to describe the magnetic resonance (MR) appearances of diseases of the stomach using combined T1-weighted spoiled gradient-echo, T2-weighted single-shot echo train spin-echo and gadolinium-enhanced spoiled gradient-echo sequences. All patients with gastric diseases who underwent combined T2-weighted single-shot echo train spin-echo and gadolinium-enhanced conventional and fat-suppressed spoiled gradient-echo imaging between October 1, 1996 and March 1, 1999, and who had histological or other imaging proof of disease, were included in this study. This patient population was comprised of 40 patients with subsequently proven gastric abnormalities, including malignant tumors (25) or benign disease (15). The MRI sequences included T1-weighted, T2-weighted, and early and late gadolinium-enhanced spoiled gradient-echo (SGE) images. Evaluation was made of the following parameters: a) the ability to detect the disease process on MRI, by comparing the original prospective MR reports with the records of the pathology department; b) the MR appearance of a variety of gastric diseases; and c) the sequences that most clearly demonstrated abnormalities by retrospective review of the MR studies. MR images demonstrated 22 of 25 malignant tumors. Evaluation of the extent of the tumor was correctly shown in 22 of 25 tumors. Small-volume tumor (one patient with gastric adenocarcinoma, and one patient with lymphoma) and coexistent infiltrative adenocarcinoma and gastritis (one patient) rendered demonstration of tumor poor on MR images in three patients. Tumors were mildly hypointense on T1-weighted images and mildly hyperintense on T2-weighted images. Tumors enhanced in a heterogeneous fashion compared with background stomach wall, but they ranged from hypointense to hyperintense on early and late post-gadolinium SGE images. Regarding benign diseases, the changes of gastritis were evident in three of four cases. Gastritis appeared as increased mucosal enhancement that ranged from moderate to intense on early and late post-gadolinium SGE images. Imaging findings of the various entities are described in greater detail in the text. MR findings in a variety of neoplastic and non-neoplastic diseases of the stomach are described. Neoplastic diseases were consistently observed in most cases; however, small tumors and tumors coexistent with inflammatory changes were poorly evaluated. The changes of gastritis were demonstrated as increased enhancement of the gastric wall. J. Magn. Reson. Imaging 10:950–960, 1999. © 1999 Wiley-Liss, Inc.

Many transplantation programs utilize noninvasive abdominal and pelvic imaging in the pre-operative evaluation of recipient candidates. Practice patterns vary, and consensus guidelines addressing the risks and benefits of computed tomography (CT) and magnetic resonance imaging (MRI) in the pre-transplant evaluation process do not currently exist. In this single-center study, we examined the frequency, clinical significance, and associated costs of CT and MRI findings during the pre-transplant evaluation of renal transplant recipients. A retrospective chart review of 3041 adult patients who underwent a CT/CTA or MRI/MRA of the abdomen and pelvis for pre-transplant evaluation between 2005 and 2010 was performed. Pre-transplant imaging with MRI offered a more sensitive evaluation in comparison with CT, with the notable exception of abnormalities in which calcium was detected. Patients imaged with CT had a significantly greater proportion of subsequent clinical actions arising from imaging findings. The total financial cost of MRI was greater than that of CT. No cases of nephrogenic systemic fibrosis (NSF) in patients who received MultiHance gadolinium contrast were reported. In conclusion, the risks, benefits, and costs of CT/CTA and MRI/MRA must be carefully considered to optimize the pre-operative evaluation of renal transplant recipients.

Purpose: To develop an accurate patient‐specific PET attenuation coefficients map to be used in hybrid MRI‐PET systems for braintumorimaging. The attenuation maps are obtained by warping a general (atlas) CT dataset to the patient‐specific MRI dataset using a deformable registration model.Method and Materials: Patient MR images and the atlas CTimages are registered using a B‐Spline deformable model and the Mattes formulation of the mutual information metric as registration criterion. The registration establishes a voxel‐to‐voxel correspondence that maps each voxel in the CT atlas voxels to the MRI dataset, creating an artificial, individualized CT scan of the patient's anatomy as observed in the MRI dataset. To evaluate the accuracy of the deformable‐based attenuation correction, ten clinical braintumor cases are studied with MR‐CT image sets. For each case an artificial CT is computed by warping the atlas to the MRI datasets. This artificial CT is compared to the true patient's CT in terms of geometrical accuracy of the deformation module as well as a voxel‐to‐voxel comparison of HU units. Results: In all cases, mapping form the atlas CT to the individual MR was achieved with great geometrical accuracy as visually judged using the qualitative visual inspection tools. The mean distance between the artificial and true CT's external contour and bony anatomy was 1 mm and 1.5 mm, respectively. In terms of HU unit comparison, the mean voxel‐to‐voxel difference was less than 5%. Conclusion: Attenuation correction for hybrid MRI‐PET scanners can be easily achieved by individualizing an atlas CT to the MRI dataset using the BSpline deformable model, with no user interaction required. The method provides clinical accuracy while eliminating the need for an additional CT scan for PET attenuation correction.

Introduction: Diagnostic imaging techniques using fluoro‐deoxy‐glucose (FDG) — positron emission tomography(PET) and magnetic resonance imaging(MRI) offer tumor‐specific imaging capabilities for breast cancerimaging. Combining PET‐MRI systems may provide synergistic information on abnormal soft tissue processes useful for discriminating tumor from other soft tissue abnormalities that may mimic tumor. We propose a deformable image registration method able to align MRI series over an FDG‐PET dataset which may improve metastatic for breast cancerimaging.Method: To more precisely replicate presentation of FDG‐PET when analyzing FDG‐PET/MRI, a deformable registration method was devised to correct locally defined posture changes. To mathematically represent the deformations, we use a BSpline model whose coefficients are iteratively calculated in small steps using a gradient‐based optimization algorithm under the guidance of a mutual information metric. The deformable BSpline approach technique was evaluated using checkerboard views and compared to a rigid body registration. Results: Comparison of rigid versus deformable registration of checkerboard FDG‐PET and MRIimages revealed superior results for deformable registration. The deformable registration was feasible and showed exact anatomical correlation between FDG‐PET and MRimages in a checkerboard. Increased activity from the FDG‐PET scan clearly corresponded to anatomical structures on the MRimages. Clinically, the deformable registration of FDG‐PET and MRI revealed the complimentary information. Regions of increased FDG activity on PET‐CT, which was initially rated as possible tumor disease, were evaluated based on the additional soft tissue information available from the MRI. In one patient case, MRI revealed a benign uterine fibroid which was not definitive on PET‐CT. Conclusion: Deformable image registration of PET‐CT and MRI using a BSpline algorithm is feasible for metastatic breast cancer detection.