Fractional Flow Reserve Estimated at Coronary CT Angiography in Intermediate Lesions: Comparison of Diagnostic Accuracy of Different Methods to Determine Coronary Flow Distribution.

Purpose To compare the diagnostic accuracy of different computed tomographic (CT) fractional flow reserve (FFR) algorithms for vessels with intermediate stenosis. Materials and Methods This cross-sectional HIPAA-compliant and human research committee-approved study applied a four-step CT FFR algorithm in 61 patients (mean age, 69 years ± 10; age range, 29-89 years) with a lesion of intermediate-diameter stenosis (25%-69%) at CT angiography who underwent FFR measurement within 90 days. The per-lesion diagnostic performance of CT FFR was tested for three different approaches to estimate blood flow distribution for CT FFR calculation. The first two, the Murray law and the Huo-Kassab rule, used coronary anatomy; the third used contrast material opacification gradients. CT FFR algorithms and CT angiography percentage diameter stenosis (DS) measurements were compared by using the area under the receiver operating characteristic curve (AUC) to detect FFRs of 0.8 or lower. Results Twenty-five lesions (41%) had FFRs of 0.8 or lower. The AUC of CT FFR determination by using contrast material gradients (AUC = 0.953) was significantly higher than that of the Huo-Kassab (AUC = 0.882, P = .043) and Murray law models (AUC = 0.871, P = .033). All three AUCs were higher than that for 50% or greater DS at CT angiography (AUC = 0.596, P < .001). Correlation of CT FFR with FFR was highest for gradients (Spearman ρ = 0.80), followed by the Huo-Kassab rule (ρ = 0.68) and Murray law (ρ = 0.67) models. All CT FFR algorithms had small biases, ranging from -0.015 (Murray) to -0.049 (Huo-Kassab). Limits of agreement were narrowest for gradients (-0.182, 0.147), followed by the Huo-Kassab rule (-0.246, 0.149) and the Murray law (-0.285, 0.256) models. Conclusion Clinicians can perform CT FFR by using a four-step approach on site to accurately detect hemodynamically significant intermediate-stenosis lesions. Estimating blood flow distribution by using coronary contrast opacification variations may improve CT FFR accuracy. © RSNA, 2017 Online supplemental material is available for this article.

Three-dimensional printing of MRI-visible phantoms and MR image-guided therapy simulation.

PURPOSE: To demonstrate the use of anatomic MRI-visible three-dimensional (3D)-printed phantoms and to assess process accuracy and material MR signal properties. METHODS: A cervical spine model was generated from computed tomography (CT) data and 3D-printed using an MR signal-generating material. Printed phantom accuracy and signal characteristics were assessed using 120 kVp CT and 3 Tesla (T) MR imaging. The MR relaxation rates and diffusion coefficient of the fabricated phantom were measured and 1 H spectra were acquired to provide insight into the nature of the proton signal. Finally, T2 -weighted imaging was performed during cryoablation of the model. RESULTS: The printed model produced a CT signal of 102 ± 8 Hounsfield unit, and an MR signal roughly 1/3rd that of saline in short echo time/short repetition time GRE MRI (456 ± 36 versus 1526 ± 121 arbitrary signal units). Compared with the model designed from the in vivo CT scan, the printed model differed by 0.13 ± 0.11 mm in CT, and 0.62 ± 0.28 mm in MR. The printed material had T2 ∼32 ms, T2*∼7 ms, T1 ∼193 ms, and a very small diffusion coefficient less than olive oil. MRI monitoring of the cryoablation demonstrated iceball formation similar to an in vivo procedure. CONCLUSION: Current 3D printing technology can be used to print anatomically accurate phantoms that can be imaged by both CT and MRI. Such models can be used to simulate MRI-guided interventions such as cryosurgeries. Future development of the proposed technique can potentially lead to printed models that depict different tissues and anatomical structures with different MR signal characteristics. Magn Reson Med 77:613-622, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Multicomponent T2 relaxation studies of the avian egg.

PURPOSE: To investigate the tissue-like multiexponential T2 signal decays in avian eggs. METHODS: Transverse relaxation studies of raw, soft-boiled and hard-boiled eggs were performed at 3 Tesla using a three-dimensional Carr-Purcell-Meiboom-Gill imaging sequence. Signal decays over a TE range of 11 to 354 ms were fitted assuming single- and multicomponent signal decays with up to three separately decaying components. Fat saturation was used to facilitate spectral assignment of observed decay components. RESULTS: Egg white, yolk and the centrally located latebra all demonstrate nonmonoexponential T2 decays. Specifically, egg white exhibits two-component decays with intermediate and long T2 times. Meanwhile, yolk and latebra are generally best characterized with triexponential decays, with short, intermediate and very long T2 decay times. Fat saturation revealed that the intermediate component of yolk could be attributed to lipids. Cooking of the egg profoundly altered the decay curves. CONCLUSION: Avian egg T2 decay curves cover a wide range of decay times. Observed T2 components in yolk and latebra as short as 10 ms, may prove valuable for testing clinical sequences designed to measure short T2 components, such as myelin-associated water in the brain. Thus we propose that the egg can be a versatile and widely available MR transverse relaxation phantom.

Computer-Based Vertebral Tumor Cryoablation Planning and Procedure Simulation Involving Two Cases Using MRI-Visible 3D Printing and Advanced Visualization.

OBJECTIVE: We report the development and use of MRI-compatible and MRI-visible 3D printed models in conjunction with advanced visualization software models to plan and simulate safe access routes to achieve a theoretic zone of cryoablation for percutaneous image-guided treatment of a C7 pedicle osteoid osteoma and an L1 lamina osteoblastoma. Both models altered procedural planning and patient care. CONCLUSION: Patient-specific MRI-visible models can be helpful in planning complex percutaneous image-guided cryoablation procedures.

Medical 3D Printing for the Radiologist.

While use of advanced visualization in radiology is instrumental in diagnosis and communication with referring clinicians, there is an unmet need to render Digital Imaging and Communications in Medicine (DICOM) images as three-dimensional (3D) printed models capable of providing both tactile feedback and tangible depth information about anatomic and pathologic states. Three-dimensional printed models, already entrenched in the nonmedical sciences, are rapidly being embraced in medicine as well as in the lay community. Incorporating 3D printing from images generated and interpreted by radiologists presents particular challenges, including training, materials and equipment, and guidelines. The overall costs of a 3D printing laboratory must be balanced by the clinical benefits. It is expected that the number of 3D-printed models generated from DICOM images for planning interventions and fabricating implants will grow exponentially. Radiologists should at a minimum be familiar with 3D printing as it relates to their field, including types of 3D printing technologies and materials used to create 3D-printed anatomic models, published applications of models to date, and clinical benefits in radiology. Online supplemental material is available for this article.

Avian egg latebra as brain tissue water diffusion model.

PURPOSE: Simplified models of non-monoexponential diffusion signal decay are of great interest to study the basic constituents of complex diffusion behavior in tissues. The latebra, a unique structure uniformly present in the yolk of avian eggs, exhibits a non-monoexponential diffusion signal decay. This model is more complex than simple phantoms based on differences between water and lipid diffusion, but is also devoid of microscopic structures with preferential orientation or perfusion effects. METHODS: Diffusion scans with multiple b-values were performed on a clinical 3 Tesla system in raw and boiled chicken eggs equilibrated to room temperature. Diffusion encoding was applied over the ranges 5-5,000 and 5-50,000 s/mm(2). A low read-out bandwidth and chemical shift was used for reliable lipid/water separation. Signal decays were fitted with exponential functions. RESULTS: The latebra, when measured over the 5-5,000 s/mm(2) range, exhibited independent of preparation clearly biexponential diffusion, with diffusion parameters similar to those typically observed in in vivo human brain. For the range 5-50,000 s/mm(2), there was evidence of a small third, very slow diffusing water component. CONCLUSION: The latebra of the avian egg contains membrane structures, which may explain a deviation from a simple monoexponential diffusion signal decay, which is remarkably similar to the deviation observed in brain tissue.

Immobilized contrast-enhanced MRI: Gadolinium-based long-term MR contrast enhancement of the vein graft vessel wall.

An implantable MR contrast agent that can be covalently immobilized on tissue during surgery has been developed. The rationale is that a durable increase in tissue contrast using an implantable contrast agent can enhance postsurgical tissue differentiation using MRI. For small-vessel (e.g., vein graft) MRI, the direct benefit of such permanent "labeling" of the vessel wall by modification of its relaxation properties is to achieve more efficient imaging. This efficiency can be realized as either increased contrast leading to more accurate delineation of vessel wall and lesion tissue boundaries, or, faster imaging without penalizing contrast-to-noise ratio, or a combination thereof. We demonstrate, for the first time, stable long-term MRI enhancement using such an exogenous contrast mechanism based on immobilizing a modified diethylenetriaminepentaacetic acid gadolinium(3+) dihydrogen complex on a human vein using a covalent amide bond. Signal enhancement due to the covalently immobilized contrast agent is demonstrated for excised human vein specimens imaged at 3 T, and its long-term stability is demonstrated during a 4-month incubation period.

Coronary enhancement for prospective ECG-gated single R-R axial 320-MDCT angiography: comparison of 60- and 80-mL iopamidol 370 injection.

OBJECTIVE: The objective of our study was to evaluate the difference in coronary enhancement provided by 60 versus 80 mL of contrast medium (370 mg I/mL) for prospectively ECG-gated single-heartbeat axial 320-MDCT. MATERIALS AND METHODS: We retrospectively evaluated 108 consecutive 320-MDCT angiography studies. Group 1 (n = 36) received 60 mL of an iodinated contrast medium and group 2 (n = 72), 80 mL. All patients were imaged with a standardized protocol: iopamidol 370 followed by 40 mL of saline, both administered at a rate of 6 mL/s. Two imagers subjectively assessed image quality throughout the coronary arteries. Region-of-interest attenuation (HU) measurements were performed in the aorta plus the proximal and distal coronary arteries. RESULTS: Subjective analysis of all coronary segments showed slightly better image quality for group 2. Patients in group 1 had significantly (p < 0.05) lower mean attenuation values for the individual coronary vessels. Nevertheless, 96.7% of all coronary segments in the group 1 patients had an attenuation of greater than 300 HU; when analysis was limited to group 1 patients with a body mass index of greater than 30, 92.8% of the segments were more than 300 HU, and all segments measured more than 250 HU. CONCLUSION: An injection protocol based on 60 mL of iopamidol (370 mg I/mL) for prospectively ECG-gated wide-area detector single-heartbeat coronary CT angiography (CTA) has less coronary enhancement than a protocol based on 80 mL. However, using 60 mL, more than 96% of coronary segments had sufficient enhancement (i.e., > 300 HU), supporting the general use of 60-mL protocols for clinical wide-area detector coronary CTA.

In vivo differentiation of two vessel wall layers in lower extremity peripheral vein bypass grafts: application of high-resolution inner-volume black blood 3D FSE.

Lower extremity peripheral vein bypass grafts (LE-PVBG) imaged with high-resolution black blood three-dimensional (3D) inner-volume (IV) fast spin echo (FSE) MRI at 1.5 Tesla possess a two-layer appearance in T1W images while only the inner layer appears visible in the corresponding T2W images. This study quantifies this difference in six patients imaged 6 months after implantation, and attributes the difference to the T(2) relaxation rates of vessel wall tissues measured ex vivo in two specimens with histologic correlation. The visual observation of two LE-PVBG vessel wall components imaged in vivo is confirmed to be significant (P < 0.0001), with a mean vessel wall area difference of 6.8 +/- 2.7 mm(2) between contrasts, and a ratio of T1W to T2W vessel wall area of 1.67 +/- 0.28. The difference is attributed to a significantly (P < 0.0001) shorter T(2) relaxation in the adventitia (T(2) = 52.6 +/- 3.5 ms) compared with the neointima/media (T(2) = 174.7 +/- 12.1 ms). Notably, adventitial tissue exhibits biexponential T(2) signal decay (P < 0.0001 vs monoexponential). Our results suggest that high-resolution black blood 3D IV-FSE can be useful for studying the biology of bypass graft wall maturation and pathophysiology in vivo, by enabling independent visualization of the relative remodeling of the neointima/media and adventitia.

Diagnostic performance of on-site computed CT-fractional flow reserve based on fluid structure interactions: comparison with invasive fractional flow reserve and instantaneous wave-free ratio.

AIMS: We evaluated diagnostic accuracy of CT-fractional flow reserve (CT-FFR) computed on-site with a new vendor workstation, against invasive FFR as the reference standard. METHODS AND RESULTS: Retrospective analyses compared CT-FFR of 104 vessels with 30-90% diameter stenosis in 75 patients imaged using single-rotation 320 detector-row coronary CT angiography (CCTA) with invasive FFR performed within 90 days. Prospective ECG-gated CCTA included exposure of 70-99% of the R-R interval. CT-FFR was computed on-site within the same physical space as the CT scanner and reading room. The diagnostic accuracy of CCTA >50% and CT-FFR ≤0.8 to detect hemodynamically significant stenosis, defined as FFR ≤0.8, was determined, as was the correlation of CT-FFR to FFR and instantaneous wave-free ratio (iFR). Forty-four vessels (42.3%) had an invasive FFR ≤0.8. The sensitivity, specificity, positive, and negative predictive value of CT-FFR ≤0.8 vs. CCTA >50% to detect hemodynamically significant stenosis defined as FFR ≤0.8 were 90.9% vs. 70.5%, 78.3% vs. 43.3%, 75.5% vs. 47.7%, and 92.2% vs. 66.7%, respectively. Area under the curve of CT-FFR was significantly higher than CCTA >50% [0.85, 95% confidence interval (CI): 0.76-0.91 vs. 0.57, 95% CI: 0.47-0.67; P < 0.0001]. The correlation coefficient between CT-FFR and iFR was r = 0.62 (95% CI: 0.40-0.77, P < 0.0001) and that between CT-FFR and invasive FFR was r = 0.52 (95% CI: 0.28-0.70, P = 0.0001). CT-FFR inter- and intra-observer correlations were excellent (r = 0.83 and r = 0.82, respectively). CONCLUSION: Locally computed CT-FFR based on fluid structure interaction has excellent diagnostic accuracy to detect a significant FFR ≤0.8 compared with conventional CCTA and high reproducibility.

Fast, exact k-space sample density compensation for trajectories composed of rotationally symmetric segments, and the SNR-optimized image reconstruction from non-Cartesian samples.

A recently developed method for exact density compensation of non uniformly arranged samples relies on the analytically known cross-correlations of Fourier basis functions corresponding to the traced k-space trajectory. This method produces a linear system whose solution represents compensated samples that normalize the contribution of each independent element of information that can be expressed by the underlying trajectory. Unfortunately, linear system-based density compensation approaches quickly become computationally demanding with increasing number of samples (i.e., image resolution). Here, it is shown that when a trajectory is composed of rotationally symmetric interleaves, such as spiral and PROPELLER trajectories, this cross-correlations method leads to a highly simplified system of equations. Specifically, it is shown that the system matrix is circulant block-Toeplitz so that the linear system is easily block-diagonalized. The method is described and demonstrated for 32-way interleaved spiral trajectories designed for 256 image matrices; samples are compensated non iteratively in a few seconds by solving the small independent block-diagonalized linear systems in parallel. Because the method is exact and considers all the interactions between all acquired samples, up to a 10% reduction in reconstruction error concurrently with an up to 30% increase in signal to noise ratio are achieved compared to standard density compensation methods.

The transluminal attenuation gradient in coronary CT angiography for the detection of hemodynamically significant disease: can all arteries be treated equally?

OBJECTIVE: Results of the use of the transluminal attenuation gradient (TAG) at coronary CT angiography (CCTA) to predict hemodynamically significant disease vary widely. This study tested whether diagnostic performance of TAG to predict fractional flow reserve (FFR) ≤ 0.8 is improved when applied separately to subsets of coronary arteries that carry similar physiological flow. METHODS: 28 patients with 64 × 0.5 mm CCTA and invasive FFR in ≥1 major coronary artery were retrospectively evaluated. Two readers assessed TAG in each artery. The receiver operating characteristic (ROC) area under the curve (AUC) was used to assess the diagnostic performance of TAG to detect hemodynamically significant disease following a clinical use rule [negative: FFR > 0.8 or ≤ 25% diameter stenosis (DS) at invasive catheter angiography; positive: FFR ≤ 0.8 or ≥ 90% DS at invasive catheter angiography]. ROC AUC was compared for all arteries pooled together, vs separately for arteries carrying similar physiological flow (Group 1: all left anterior descending plus right-dominant left circumflex; Group 2: right-dominant RCA plus left/co-dominant left circumflex). RESULTS: Of the 84 arteries, 30 had FFR measurements, 30 had ≤25% DS and 13 had ≥90% DS. 11 arteries with 26-89% DS and no FFR measurement were excluded. TAG interobserver reproducibility was excellent (Pearson r = 0.954, Bland-Altman bias: 0.224 Hounsfield unit cm-1). ROC AUC to detect hemodynamically significant disease was higher when considering arteries separately (Group 1 AUC = 0.841, p = 0.039; Group 2 AUC = 0.840, p = 0.188), than when pooling all arteries together (AUC = 0.661). CONCLUSION: Incorporating information on the physiology of coronary flow via the particular vessel interrogated and coronary dominance may improve the accuracy of TAG, a simple measurement that can be quickly performed at the time of CCTA interpretation to detect hemodynamically significant stenosis in individual coronary arteries. Advances in knowledge: The interpretation of TAG may benefit by incorporating information regarding which coronary artery is being interrogated.

Strategies for inner volume 3D fast spin echo magnetic resonance imaging using nonselective refocusing radio frequency pulses.

Fast spin echo (FSE) trains elicited by nonselective "hard" refocusing radio frequency (RF) pulses have been proposed as a means to enable application of FSE methods for high-resolution 3D magnetic resonance imaging (MRI). Hard-pulse FSE (HPFSE) trains offer short (3-4 ms) echo spacings, but are unfortunately limited to imaging the entire sample within the coil sensitivity thus requiring lengthy imaging times, consequently limiting clinical application. In this work we formulate and analyze two general-purpose combinations of 3D HPFSE with inner volume (IV) MR imaging to circumvent this limitation. The first method employs a 2D selective RF excitation followed by the HPFSE train and focuses on required properties of the spatial excitation profile with respect to limiting RF pulse duration in the 5-6 ms range. The second method employs two orthogonally selective 1D RF excitations (a 90x degrees - 180y degrees pair) to generate an echo from magnetization within the volume defined by their intersection. Subsequent echoes are formed via the HPFSE train, placing the focus of the method on (a) avoiding spurious echoes that may arise from transverse magnetization located outside the slab intersection when it is unavoidably affected by the nonselective refocusing pulses and (b) avoiding signal losses due to the necessarily different spacing (in time) of the RF pulse applications. The performance of each method is experimentally measured using Carr-Purcell-Meiboom-Gill (CPMG) multi-echo imaging, enabling examination of the magnetization evolution throughout the echo train. The methods as implemented achieve 95% to 97% outer volume signal suppression, and higher suppression appears to be well within reach, by further refinement of the selective RF excitations. Example images of the human brain and spine are presented with each technique. We conclude that the SNR efficiency of volume imaging in conjunction with the short echo spacing afforded by hard pulse trains enables high-resolution 3D HPFSE MRI of a small field-of-view (FOV) with minimal aliasing artifact.

Enhancing the acquisition efficiency of fast magnetic resonance imaging via broadband encoding of signal content.

Current efficient magnetic resonance imaging (MRI) methods such as parallel-imaging and k-t methods encode MR signals using a set of effective encoding functions other than the Fourier basis. This work revisits the proposition of directly manipulating the set of effective encoding functions at the radiofrequency excitation step in order to increase MRI efficiency. This approach, often termed "broadband encoding," enables the application of algebraic matrix factorization technologies to extract efficiency by representing and encoding MR signal content in a compacted form. Broadband imaging equivalents of fast multiecho, parallel and k-t MRI are developed and analyzed. The potential of these techniques to increase the time efficiency of data acquisition is experimentally verified on a commercial MRI scanner using simple spin-echo imaging. A three-dimensional gradient-echo dynamic imaging application that demonstrates the potential benefits of this approach compared to the present state of the art for certain applications is also presented.

Applications of 3D printing in cardiovascular diseases.

3D-printed models fabricated from CT, MRI, or echocardiography data provide the advantage of haptic feedback, direct manipulation, and enhanced understanding of cardiovascular anatomy and underlying pathologies. Reported applications of cardiovascular 3D printing span from diagnostic assistance and optimization of management algorithms in complex cardiovascular diseases, to planning and simulating surgical and interventional procedures. The technology has been used in practically the entire range of structural, valvular, and congenital heart diseases, and the added-value of 3D printing is established. Patient-specific implants and custom-made devices can be designed, produced, and tested, thus opening new horizons in personalized patient care and cardiovascular research. Physicians and trainees can better elucidate anatomical abnormalities with the use of 3D-printed models, and communication with patients is markedly improved. Cardiovascular 3D bioprinting and molecular 3D printing, although currently not translated into clinical practice, hold revolutionary potential. 3D printing is expected to have a broad influence in cardiovascular care, and will prove pivotal for the future generation of cardiovascular imagers and care providers. In this Review, we summarize the cardiovascular 3D printing workflow, from image acquisition to the generation of a hand-held model, and discuss the cardiovascular applications and the current status and future perspectives of cardiovascular 3D printing.

Cardiothoracic Applications of 3-dimensional Printing.

Medical 3-dimensional (3D) printing is emerging as a clinically relevant imaging tool in directing preoperative and intraoperative planning in many surgical specialties and will therefore likely lead to interdisciplinary collaboration between engineers, radiologists, and surgeons. Data from standard imaging modalities such as computed tomography, magnetic resonance imaging, echocardiography, and rotational angiography can be used to fabricate life-sized models of human anatomy and pathology, as well as patient-specific implants and surgical guides. Cardiovascular 3D-printed models can improve diagnosis and allow for advanced preoperative planning. The majority of applications reported involve congenital heart diseases and valvular and great vessels pathologies. Printed models are suitable for planning both surgical and minimally invasive procedures. Added value has been reported toward improving outcomes, minimizing perioperative risk, and developing new procedures such as transcatheter mitral valve replacements. Similarly, thoracic surgeons are using 3D printing to assess invasion of vital structures by tumors and to assist in diagnosis and treatment of upper and lower airway diseases. Anatomic models enable surgeons to assimilate information more quickly than image review, choose the optimal surgical approach, and achieve surgery in a shorter time. Patient-specific 3D-printed implants are beginning to appear and may have significant impact on cosmetic and life-saving procedures in the future. In summary, cardiothoracic 3D printing is rapidly evolving and may be a potential game-changer for surgeons. The imager who is equipped with the tools to apply this new imaging science to cardiothoracic care is thus ideally positioned to innovate in this new emerging imaging modality.

The residual STL volume as a metric to evaluate accuracy and reproducibility of anatomic models for 3D printing: application in the validation of 3D-printable models of maxillofacial bone from reduced radiation dose CT images.

BACKGROUND: The effects of reduced radiation dose CT for the generation of maxillofacial bone STL models for 3D printing is currently unknown. Images of two full-face transplantation patients scanned with non-contrast 320-detector row CT were reconstructed at fractions of the acquisition radiation dose using noise simulation software and both filtered back-projection (FBP) and Adaptive Iterative Dose Reduction 3D (AIDR3D). The maxillofacial bone STL model segmented with thresholding from AIDR3D images at 100 % dose was considered the reference. For all other dose/reconstruction method combinations, a "residual STL volume" was calculated as the topologic subtraction of the STL model derived from that dataset from the reference and correlated to radiation dose. RESULTS: The residual volume decreased with increasing radiation dose and was lower for AIDR3D compared to FBP reconstructions at all doses. As a fraction of the reference STL volume, the residual volume decreased from 2.9 % (20 % dose) to 1.4 % (50 % dose) in patient 1, and from 4.1 % to 1.9 %, respectively in patient 2 for AIDR3D reconstructions. For FBP reconstructions it decreased from 3.3 % (20 % dose) to 1.0 % (100 % dose) in patient 1, and from 5.5 % to 1.6 %, respectively in patient 2. Its morphology resembled a thin shell on the osseous surface with average thickness <0.1 mm. CONCLUSION: The residual volume, a topological difference metric of STL models of tissue depicted in DICOM images supports that reduction of CT dose by up to 80 % of the clinical acquisition in conjunction with iterative reconstruction yields maxillofacial bone models accurate for 3D printing.

Carr-Purcell-Meiboom-Gill imaging of prostate cancer: quantitative T2 values for cancer discrimination.

Quantitative, apparent T(2) values of suspected prostate cancer and healthy peripheral zone tissue in men with prostate cancer were measured using a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence in order to assess the cancer discrimination potential of tissue T(2) values. The CPMG imaging sequence was used to image the prostates of 18 men with biopsy-proven prostate cancer. Whole gland coverage with nominal voxel volumes of 0.54 x 1.1 x 4 mm(3) was obtained in 10.7 min, resulting in data sets suitable for generating high-quality images with variable T(2)-weighting and for evaluating quantitative T(2) values on a pixel-by-pixel basis. Region-of-interest analysis of suspected healthy peripheral zone tissue and suspected cancer, identified on the basis of both T(1)- and T(2)-weighted signal intensities and available histopathology reports, yielded significantly (P<.0001) longer apparent T(2) values in suspected healthy tissue (193+/-49 ms) vs. suspected cancer (100+/-26 ms), suggesting potential utility of this method as a tissue specific discrimination index for prostate cancer. We conclude that CPMG imaging of the prostate can be performed in reasonable scan times and can provide advantages over T(2)-weighted fast spin echo (FSE) imaging alone, including quantitative T(2) values for cancer discrimination as well as proton density maps without the point spread function degradation associated with short effective echo time FSE sequences.

High-resolution peripheral vein bypass graft wall studies using high sampling efficiency inner volume 3D FSE.

A 3D inner-volume fast spin echo (3D IV-FSE) sequence was developed for ECG-gated, black-blood, T1- and T2-weighted vessel wall imaging of peripheral vein bypass grafts (PVBG). The sequence utilizes nonselective refocusing excitations to minimize echo spacings and a highly selective IV excitation scheme to minimize the need for oversampling of z-encode slice selections. The method was tested in eight PVBG patients who also underwent 2D FSE graft imaging. High-quality 3D imaging was achieved in all subjects, with significant spatial resolution and volume coverage gains compared to the more conventional 2D FSE sequences normalized for signal-to-noise ratios (SNRs) and scan times. Compared to previously proposed 3D IV-FSE methods, nonselective refocusing resulted in a more than 20% FSE echo train sampling efficiency increase while the use of highly selective IV excitation resulted in a 30% improvement in slice oversampling efficiency.

Basis function cross-correlations for robust k-space sample density compensation, with application to the design of radiofrequency excitations.

The problem of k-space sample density compensation is restated as the normalization of the independent information that can be expressed by the ensemble of Fourier basis functions corresponding to the trajectory. Specifically, multiple samples (complex exponential functions) may be contributing to each independent information element (independent basis function). Normalization can be accomplished by solving a linear system based on the cross-correlation matrix of the underlying Fourier basis functions. The solution to this system is straightforward and can be obtained without resorting to discretization since the cross-correlations of Fourier basis functions are analytically known. Furthermore, no restrictions are placed on the k-space trajectory and its point-spread function. Additionally, the linear system can be used to elucidate key trade-offs involved in k-space trajectory design. The approach can be used to compensate samples acquired for image reconstruction or designed for low flip angle radiofrequency (RF) excitation. Here it is demonstrated for the latter application, using reversed spiral trajectories. In this case the linear system approach enables one to easily incorporate additional constraints such as smoothness to the solution. For typical RF excitation durations (<20 ms) it is shown that density compensation can even be achieved without numerical iteration.