Regional Strain Analysis with Multidetector CT in a Swine Cardiomyopathy Model: Relationship to Cardiac MR Tagging and Myocardial Fibrosis.

PURPOSE: To investigate the use of cine multidetector computed tomography (CT) to detect changes in myocardial function in a swine cardiomyopathy model. MATERIALS AND METHODS: All animal protocols were in accordance with the Principles for the Utilization and Care of Vertebrate Animals Used in Testing Research and Training and approved by the University of Missouri Animal Care and Use Committee. Strain analysis of cine multidetector CT images of the left ventricle was optimized and analyzed with feature-tracking software. The standard of reference for strain was harmonic phase analysis of tagged cardiac magnetic resonance (MR) images at 3.0 T. An animal model of cardiomyopathy was imaged with both cardiac MR and 320-section multidetector CT at a temporal resolution of less than 50 msec. Three groups were evaluated: control group (n = 5), aortic-banded myocardial hypertrophy group (n = 5), and aortic-banded and cyclosporine A- treated cardiomyopathy group (n = 5). Histologic samples of the myocardium were obtained for comparison with strain results. Dunnett test was used for comparisons of the concentric remodeling group and eccentric remodeling group against the control group. RESULTS: Collagen volume fraction ranged from 10.9% to 14.2%; lower collagen fraction values were seen in the control group than in the cardiomyopathy groups (P < .05). Ejection fraction and conventional metrics showed no significant differences between control and cardiomyopathy groups. Radial strain for both cardiac MR and multidetector CT was abnormal in both concentric (cardiac MR 25.1% ± 4.2; multidetector CT 28.4% ± 2.8) and eccentric (cardiac MR 23.2% ± 2.0; multidetector CT 24.4% ± 2.1) remodeling groups relative to control group (cardiac MR 18.9% ± 1.9, multidetector CT 22.0% ± 1.7, P < .05, all comparisons). Strain values for multidetector CT versus cardiac MR showed better agreement in the radial direction than in the circumferential direction (r = 0.55, P = .03 vs r = 0.40, P = .13, respectively). CONCLUSION: Multidetector CT strain analysis has potential to identify regional wall-motion abnormalities in cardiomyopathy that is not otherwise detected using conventional metrics of myocardial function.

Noninvasive imaging of myocardial extracellular matrix for assessment of fibrosis.

PURPOSE OF REVIEW: Myocardial fibrosis is a common feature of many cardiomyopathies, including hypertrophic cardiomyopathy. Myocardial fibrosis has been shown to be reversible and treatable with timely intervention. Although early detection and assessment of fibrosis is crucial, adequate diagnostics are still in development. Recent studies have shown progress on noninvasive imaging methods of fibrosis using cardiovascular magnetic resonance (CMR) and nuclear imaging modalities. RECENT FINDINGS: T1 mapping and extracellular volume mapping (ECV) combined with CMR imaging are cutting edge methods that have the potential to assess interstitial myocardial fibrosis. Recent findings show that ECV measurement can be correlated to the extent of diffuse fibrosis. Comparatively, molecular imaging targets specific biomarkers in the fibrosis formation pathway and provides enhanced sensitivity for imaging early disease. Biomarkers include molecules involved in angiogenesis, ventricular remodeling, and fibrotic tissue formation, whereas collagen targeted agents can directly identify fibrotic tissue in the heart. SUMMARY: This review introduces novel methods of fibrosis imaging that utilize properties of extracellular matrix and its biomarkers. Changes in characteristics and cellular biomarkers of the extracellular space can provide significant information regarding fibrosis formation and its role in cardiomyopathy. Ultimately, these findings may improve detection and monitoring of disease and improve efficiency and effectiveness of the treatment.

NCI Rectal-Anal Task Force consensus recommendations for design of clinical trials in rectal cancer.

The optimal management of locally advanced rectal cancer is rapidly evolving. The National Cancer Institute Rectal-Anal Task Force convened an expert panel to develop consensus on the design of future clinical trials of patients with rectal cancer. A series of 82 questions and subquestions, which addressed radiation and neoadjuvant therapy, patient perceptions, rectal cancer populations of special interest, and unique design elements, were subject to iterative review using a Delphi analytical approach to define areas of consensus and those in which consensus is not established. The task force achieved consensus on several areas, including the following: 1) the use of total neoadjuvant therapy with long-course radiation therapy either before or after chemotherapy, as well as short-course radiation therapy followed by chemotherapy, as the control arm of clinical trials; 2) the need for greater emphasis on patient involvement in treatment choices within the context of trial design; 3) efforts to identify those patients likely, or unlikely, to benefit from nonoperative management or minimally invasive surgery; 4) investigation of the utility of circulating tumor DNA measurements for tailoring treatment and surveillance; and 5) the need for identification of appropriate end points and recognition of challenges of data management for patients who enter nonoperative management trial arms. Substantial agreement was reached on priorities affecting the design of future clinical trials in patients with locally advanced rectal cancer.

Cardiac and Respiratory Motion Correction for Simultaneous Cardiac PET/MR.

Cardiac PET is a versatile imaging technique providing important diagnostic information about ischemic heart diseases. Respiratory and cardiac motion of the heart can strongly impair image quality and therefore diagnostic accuracy of cardiac PET scans. The aim of this study was to investigate a new cardiac PET/MR approach providing respiratory and cardiac motion-compensated MR and PET images in less than 5 min. Methods: Free-breathing 3-dimensional MR data were acquired and retrospectively binned into multiple respiratory and cardiac motion states. Three-dimensional cardiac and respiratory motion fields were obtained with a nonrigid registration algorithm and used in motion-compensated MR and PET reconstructions to improve image quality. The improvement in image quality and diagnostic accuracy of the technique was assessed in simultaneous 18F-FDG PET/MR scans of a canine model of myocardial infarct and was demonstrated in a human subject. Results: MR motion fields were successfully used to compensate for in vivo cardiac motion, leading to improvements in full width at half maximum of the canine myocardium of 13% ± 5%, similar to cardiac gating but with a 90% ± 57% higher contrast-to-noise ratio between myocardium and blood. Motion correction led to an improvement in MR image quality in all subjects, with an increase in sharpness of the canine coronary arteries of 85% ± 72%. A functional assessment showed good agreement with standard MR cine scans with a difference in ejection fraction of -2% ± 3%. MR-based respiratory and cardiac motion information was used to improve the PET image quality of a human in vivo scan. Conclusion: The MR technique presented here provides both diagnostic and motion information that can be used to improve MR and PET image quality. Reliable respiratory and cardiac motion correction could make cardiac PET results more reproducible.

Automatic high-resolution infarct detection using volumetric multiphase dual-energy CT.

OBJECTIVES: Late contrast enhancement CT (LCE-CT) visualizes the presence of myocardial infarcts. Differentiation of the contrast-enhanced infarct from blood pool is challenging. We developed a novel method using data from first pass CT angiography (CTA) imaging to enable automatic infarct detection. MATERIALS AND METHODS: A canine model of myocardial infarction was produced in 11 animals. Two months later, first pass CTA (90 kVp) and LCE-CT (dual energy 90 kVp/150 kVp tin filtered) were performed. Late gadolinium enhancement MRI was used as reference standard. The CTA and LCE-CT were co-registered using a fully automatic non-rigid method based on curved B-splines. The method allowed for limited elastic deformation and the considerable differences in attenuation between first-pass and delayed image. The blood pool was easily identified on the CTA image by high attenuation. Because CTA and LCE-CT were registered, the blood pool segmentation can be directly transferred to the LCE-CT - thereby solving the key problem of infarct/blood pool differentiation. The remaining segmentation of infarcted vs. noninfarcted myocardium was performed using a threshold. Automatic and MRI-guided expert segmentations of LCE-CT infarcts were compared to each other on volume and area basis (intraclass correlation coefficient, ICC) and on voxel basis (dice similarity coefficient, DSC between automatic and expert CT segmentation). CT infarct volumes were compared with the reference standard MRI. RESULTS: The infarcts were mainly subendocardial (81%) and relatively small (median MRI infarct mass 7.4 g). The automatic segmentation showed excellent agreement with expert segmentation on volume and area measurements (ICC = 0.96 and 0.87, respectively). DSC showed moderately good agreement (DSC = 0.47). Compared to MRI there was modest agreement (ICC = 0.62) and excellent correlation (R = 0.9). Manual interaction was less than 1 min per exam. CONCLUSION: We propose an automatic method for infarct segmentation on LCE-CT using multiphase CT information, which showed excellent agreement with expert readers and favorable correlation with MRI.

Optimized energy of spectral CT for infarct imaging: Experimental validation with human validation.

OBJECTIVES: Late contrast enhancement visualizes myocardial infarction, but the contrast to noise ratio (CNR) is low using conventional CT. The aim of this study was to determine if spectral CT can improve imaging of myocardial infarction. MATERIALS AND METHODS: A canine model of myocardial infarction was produced in 8 animals (90-min occlusion, reperfusion). Later, imaging was performed after contrast injection using CT at 90 kVp/150 kVpSn. The following reconstructions were evaluated: Single energy 90 kVp, mixed, iodine map, multiple monoenergetic conventional and monoenergetic noise optimized reconstructions. Regions of interest were measured in infarct and remote regions to calculate contrast to noise ratio (CNR) and Bhattacharya distance (a metric of the differentiation between regions). Blinded assessment of image quality was performed. The same reconstruction methods were applied to CT scans of four patients with known infarcts. RESULTS: For animal studies, the highest CNR for infarct vs. myocardium was achieved in the lowest keV (40 keV) VMo images (CNR 4.42, IQR 3.64-5.53), which was superior to 90 kVp, mixed and iodine map (p = 0.008, p = 0.002, p < 0.001, respectively). Compared to 90 kVp and iodine map, the 40 keV VMo reconstructions showed significantly higher histogram separation (p = 0.042 and p < 0.0001, respectively). The VMo reconstructions showed the highest rate of excellent quality scores. A similar pattern was seen in human studies, with CNRs for infarct maximized at the lowest keV optimized reconstruction (CNR 4.44, IQR 2.86-5.94). CONCLUSIONS: Dual energy in conjunction with noise-optimized monoenergetic post-processing improves CNR of myocardial infarct delineation by approximately 20-25%.

Dual-contrast agent photon-counting computed tomography of the heart: initial experience.

To determine the feasibility of dual-contrast agent imaging of the heart using photon-counting detector (PCD) computed tomography (CT) to simultaneously assess both first-pass and late enhancement of the myocardium. An occlusion-reperfusion canine model of myocardial infarction was used. Gadolinium-based contrast was injected 10 min prior to PCD CT. Iodinated contrast was infused immediately prior to PCD CT, thus capturing late gadolinium enhancement as well as first-pass iodine enhancement. Gadolinium and iodine maps were calculated using a linear material decomposition technique and compared to single-energy (conventional) images. PCD images were compared to in vivo and ex vivo magnetic resonance imaging (MRI) and histology. For infarct versus remote myocardium, contrast-to-noise ratio (CNR) was maximal on late enhancement gadolinium maps (CNR 9.0 ± 0.8, 6.6 ± 0.7, and 0.4 ± 0.4, p < 0.001 for gadolinium maps, single-energy images, and iodine maps, respectively). For infarct versus blood pool, CNR was maximum for iodine maps (CNR 11.8 ± 1.3, 3.8 ± 1.0, and 1.3 ± 0.4, p < 0.001 for iodine maps, gadolinium maps, and single-energy images, respectively). Combined first-pass iodine and late gadolinium maps allowed quantitative separation of blood pool, scar, and remote myocardium. MRI and histology analysis confirmed accurate PCD CT delineation of scar. Simultaneous multi-contrast agent cardiac imaging is feasible with photon-counting detector CT. These initial proof-of-concept results may provide incentives to develop new k-edge contrast agents, to investigate possible interactions between multiple simultaneously administered contrast agents, and to ultimately bring them to clinical practice.

64Cu-DOTA as a surrogate positron analog of Gd-DOTA for cardiac fibrosis detection with PET: pharmacokinetic study in a rat model of chronic MI.

OBJECTIVES: The aim of this study was to investigate the pharmacokinetics of (64)Cu-DOTA (1,4,7,10-azacyclododecane-N,N',N'',N'''-tetraacetic acid), a positron surrogate analog of the late gadolinium (Gd)-enhancement cardiac magnetic resonance agent, Gd-DOTA, in a rat model of chronic myocardial infarction (MI) and its microdistribution in the cardiac fibrosis by autoradiography. METHODS: DOTA was labeled with (64)Cu-acetate. CD rats (n=5) with MI by left anterior descending coronary artery ligation and normal rats (n=6) were injected intravenously with (64)Cu-DOTA (18.5 MBq, 0.02 mmol DOTA/kg). Dynamic PET imaging was performed for 60 min after injection. (18)F-Fluorodeoxyglucose ([(18)F]-FDG) PET imaging was performed to identify the viable myocardium. For the region of interest analysis, the (64)Cu-DOTA PET image was coregistered to the [(18)F]-FDG PET image. To validate the PET images, slices of heart samples from the base to the apex were analyzed using autoradiography and by histological staining with Masson's trichrome. RESULTS: (64)Cu-DOTA was rapidly taken up in the infarct area. The time-activity curves demonstrated that (64)Cu-DOTA concentrations in the blood, fibrotic tissue, and perfusion-rich organs peaked within a minute post injection; thereafter, it was rapidly washed out in parallel with blood clearance and excreted through the renal system. The blood clearance curve was biphasic, with a distribution half-life of less than 3 min and an elimination half-life of ∼21.8 min. The elimination half-life of (64)Cu-DOTA from the focal fibrotic tissue (∼22.4 min) and the remote myocardium (∼20.1 min) was similar to the blood elimination half-life. Consequently, the uptake ratios of focal fibrosis-to-blood and remote myocardium-to-blood remained stable for the time period between 10 and 60 min. The corresponding ratios obtained from images acquired from 30 to 60 min were 1.09 and 0.59, respectively, indicating that the concentration of (64)Cu-DOTA in the focal fibrosis was 1.85 (1.09/0.59) times greater than that in the remote myocardium. Thus, this finding indicates that the extracellular volume fraction was 1.85 times greater in the focal fibrosis than in the remote myocardium. The accumulation of (64)Cu-DOTA in fibrotic tissue was further supported by autoradiography and histology images. The autoradiography images of (64)Cu-DOTA in the fibrotic tissues were qualitatively superimposed over the histology images of the fibrotic tissues. The histology images of the infarct areas were characterized by a heterogeneous distribution of thin bands of fibrotic collagen, myocytes, and expanded extracellular space. CONCLUSION: (64)Cu-DOTA is a useful surrogate positron analog of Gd-DOTA, enabling quantitative measurement of the uptake values in fibrotic tissues by dynamic PET imaging and calculation of the extracellular volume fractions of the fibrotic tissues. At a microscopic level, the distribution of (64)Cu-DOTA is nonuniform, corresponding to the heterogeneous distribution of expanded extracellular space in the setting of MI.

Pharmacokinetics and microbiodistribution of 64Cu-labeled collagen-binding peptides in chronic myocardial infarction.

OBJECTIVES: The aim of the study is to evaluate the pharmacokinetics and microbiodistribution of Cu-labeled collagen-binding peptides. METHODS: The affinity constant (KD), association (ka), and dissociation rate constant (kd) for the peptide collagelin or its analog (named CRPA) binding to collagen were measured by biolayer interferometric analysis. Rats (n=4-5) with myocardial infarction or normal were injected intravenously with the Cu-labeled peptides or Cu-DOTA as a control. Dynamic PET imaging was performed for 60 min at 7-8 weeks after infarct. Fluorine-18 fluorodeoxyglucose PET imaging was performed to identify the viable myocardium. To validate the PET images, slices of heart samples from the base to the apex were analyzed using autoradiography and histology. RESULT: The peptides bound to collagen with a KD of ∼0.9 µmol/l. The Cu-peptides and Cu-DOTA accumulated in the infarct area (confirmed by autoradiography and histology images) within 1 min of injection and were excreted rapidly through the renal system. The blood clearance curves were biphasic with elimination half-lives of 21.9±2.4, 26.2±4.6, and 21.2±2.1 min for Cu-CRPA, Cu-collagelin, and the control Cu-DOTA, respectively. The clearance half-lives from the focal fibrotic tissue (24.1±1.5, 25.6±8.0, and 21.4±1.3 min, respectively) and remote myocardium (20.8±0.7, 21.0±5.5, and 19.1±2.4 min, respectively) were not significantly different. The uptake ratios of infarct-to-remote myocardium (1.93±0.18, 2.15±0.38, and 1.88±0.08, respectively) for Cu-CRPA, Cu-collagelin, and Cu-DOTA remained stable for the time period between 10 and 60 min. CONCLUSION: The distribution of the Cu-collagelin probes corresponds to the heterogeneous distribution of expanded extracellular space in the setting of myocardial infarction. The overall washout rate from the fibrous tissue was determined by the slow washout rate (t1/2≥20 min) of the peptides from the extracellular space to the vasculature, not by the dissociation rate (t1/2<2 min) of the Cu-peptides from collagen.

Albumin-binding domain conjugate for near-infrared fluorescence lymphatic imaging.

PURPOSE: The aim of this study was to develop and characterize a novel peptide imaging agent for noninvasive near-infrared fluorescence imaging of protein transport by the lymphatics. An imaging agent consisting of a cyclic albumin-binding domain (cABD) peptide, with sequence, Arg-Leu-Ile-Glu-Asp-Ile-Cys-Leu-Pro-Arg-Trp-Gly-Cys-Leu-Trp-Glu-Asp-Asp-Lys, was conjugated to a near-infrared fluorophore, IRDye800CW, allowing for enhanced vascular uptake, retention, and fluorescence imaging. PROCEDURE: Characterization of the cABD-IRDye800 peptide conjugate was performed using fluorescence spectroscopy to assess optical properties and SDS-PAGE and Biacore binding assays to determine binding affinity and specificity. Fluorescence imaging of normal C57BL/6 mice was conducted to monitor lymphatic uptake and retention. RESULTS: cABD-IRDye800 exhibited approximately six times greater fluorescent yield and greater stability than indocyanine green, an agent previously used in humans to image lymphatic vasculature. The agent exhibited affinity for albumin with IC(50) and Kd in the nanomolar range and demonstrated superior retention characteristics within mouse lymphatics when compared with IRDye800CW. CONCLUSIONS: cABD-IRDye800 has utility for assessing lymphatic function in mouse models of human lymphatic disease and the potential for use in clinical diagnostic imaging of the lymphatic vasculature.