Parametric response mapping of CT images provides early detection of local bone loss in a rat model of osteoporosis

Vascular Deformation Mapping for CT Surveillance of Thoracic Aortic Aneurysm Growth

Background Aortic diameter measurements in patients with a thoracic aortic aneurysm (TAA) show wide variation. There is no technique to quantify aortic growth in a three-dimensional (3D) manner. Purpose To validate a CT-based technique for quantification of 3D growth based on deformable registration in patients with TAA. Materials and Methods Patients with ascending and descending TAA with two or more CT angiography studies between 2006 and 2020 were retrospectively identified. The 3D aortic growth was quantified using vascular deformation mapping (VDM), a technique that uses deformable registration to warp a mesh constructed from baseline aortic anatomy. Growth assessments between VDM and clinical CT diameter measurements were compared. Aortic growth was quantified as the ratio of change in surface area at each mesh element (area ratio). Manual segmentations were performed by independent raters to assess interrater reproducibility. Registration error was assessed using manually placed landmarks. Agreement between VDM and clinical diameter measurements was assessed using Pearson correlation and Cohen κ coefficients. Results A total of 38 patients (68 surveillance intervals) were evaluated (mean age, 69 years ± 9 [standard deviation]; 21 women), with TAA involving the ascending aorta (n = 26), descending aorta (n = 10), or both (n = 2). VDM was technically successful in 35 of 38 (92%) patients and 58 of 68 intervals (85%). Median registration error was 0.77 mm (interquartile range, 0.54-1.10 mm). Interrater agreement was high for aortic segmentation (Dice similarity coefficient = 0.97 ± 0.02) and VDM-derived area ratio (bias = 0.0, limits of agreement: -0.03 to 0.03). There was strong agreement (r = 0.85, P < .001) between peak area ratio values and diameter change. VDM detected growth in 14 of 58 (24%) intervals. VDM revealed growth outside the maximally dilated segment in six of 14 (36%) growth intervals, none of which were detected with diameter measurements. Conclusion Vascular deformation mapping provided reliable and comprehensive quantitative assessment of three-dimensional aortic growth and growth patterns in patients with thoracic aortic aneurysms undergoing CT surveillance. Published under a CC BY 4.0 license Online supplemental material is available for this article. See also the editorial by Wieben in this issue.

Potential of electrical impedance spectroscopy to differentiate between healthy and osteopenic bone

Osteoporosis involves loss of structural stability of bone due to an increase in bone porosity. Dual energy X-ray absorptometry is used to evaluate bone in terms of quantity. However, it does not give an evaluation of the patient's bone quality. For this, present study has been carried out to assess the structural deterioration of bone using electrical impedance spectroscopy.

METHODS

Electrical Impedance Spectroscopy has been applied to evaluate the structural and compositional changes of cortical bone in the frequency range of 50 Hz to 5 MHz for the ovariectomized rat model. Initially, bone resorption in the ovariectomized group has been confirmed by estimating tartaric resistant acid phosphatase levels; morphometric parameters; bone matrix components, hydroxyapatite crystallite size and bone micro architecture. The mid diaphyseal regions from the femora and tibiae of sixty days post ovariectomy and control rats were used for the measurement of dielectric parameters. A dispersion model based analysis has been developed by a complex least square fitting of the dielectric data.

FINDINGS

Increased tartaric resistant acid phosphatase levels, altered bone matrix components, hydroxyapatite crystallite size and disturbed microarchitecture in the ovariectomized group give us the confirmation of increased bone resorption following estrogen deficiency. These changes were shown to be reflected by single dispersion model based fitted parameters which shows the considerable change in all the parameters of ovariectomized group compared to the control.

INTERPRETATION

It has been demonstrated that the parameters of the dispersion model can reflect the bone structural and compositional changes.

Age and Small Airway Imaging Abnormalities in Subjects with and without Airflow Obstruction in SPIROMICS

RATIONALE

Aging is associated with reduced FEV₁ to FVC ratio (FEV₁/FVC), hyperinflation, and alveolar enlargement, but little is known about how age affects small airways.

OBJECTIVES

To determine if chest computed tomography (CT)-assessed functional small airway would increase with age, even among asymptomatic individuals.

METHODS

We used parametric response mapping analysis of paired inspiratory/expiratory CTs to identify functional small airway abnormality (PRM^FSA) and emphysema (PRM^EMPH) in the SPIROMICS (Subpopulations and Intermediate Outcome Measures in COPD Study) cohort. Using adjusted linear regression models, we analyzed associations between PRM^FSA and age in subjects with or without airflow obstruction. We subdivided participants with normal spirometry based on respiratory-related impairment (6-minute-walk distance <350 m, modified Medical Research Council ≥2, chronic bronchitis, St. George's Respiratory Questionnaire >25, respiratory events requiring treatment [antibiotics and/or steroids or hospitalization] in the year before enrollment).

MEASUREMENTS AND MAIN RESULTS

Among 580 never- and ever-smokers without obstruction or respiratory impairment, PRM^FSA increased 2.7% per decade, ranging from 3.6% (ages 40-50 yr) to 12.7% (ages 70-80 yr). PRM^EMPH increased nonsignificantly (0.1% [ages 40-50 yr] to 0.4% [ages 70-80 yr]; P = 0.34). Associations were similar among nonobstructed individuals with respiratory-related impairment. Increasing PRM^FSA in subjects without airflow obstruction was associated with increased FVC (P = 0.004) but unchanged FEV₁ (P = 0.94), yielding lower FEV₁/FVC ratios (P < 0.001). Although emphysema was also significantly associated with lower FEV₁/FVC (P = 0.04), its contribution relative to PRM^FSA in those without airflow obstruction was limited by its low burden.

CONCLUSIONS

In never- and ever-smokers without airflow obstruction, aging is associated with increased FVC and CT-defined functional small airway abnormality regardless of respiratory symptoms.

Potential for Early Fracture Risk Assessment in Patients with Metastatic Bone Disease using Parametric Response Mapping of CT Images

Pathologic vertebral compression fractures (PVCFs) cause significant morbidity in patients with metastatic bone disease. Limitations in existing clinical biomarkers leave clinicians without reliable metrics for predicting PVCF, thus impeding efforts to prevent this severe complication. To establish the feasibility of a new method for defining the risk of a PVCF, we retrospectively analyzed serial computed tomography (CT) scans from 5 breast cancer patients using parametric response mapping (PRM) to quantify dynamic bone miniral density (BMD) changes that preceded an event. Vertebrae segmented from each scan were registered to the same spatial frame and voxel classification was accomplished using a predetermined threshold of change in Hounsfield units (HU), resulting in relative volumes of increased (PRM_HU+), decreased (PRM_HU−), or unchanged (PRM_HU0) attenuation. A total of 7 PVCFs were compared to undiseased vertebrae in each patient serving as controls. A receiver operator curve (ROC) analysis identified optimal imaging times for group stratification. BMD changes were apparent by an elevated PRM_HU+ as early as 1 year before fracture. ROC analysis showed poor performance of PRM_HU− in stratifying PVCFs versus controls. As early as 6 months before PVCF, PRM_HU+ was significantly larger (12.9 ± 11.6%) than control vertebrae (2.3 ± 2.5%), with an area under the curve of 0.918 from an ROC analysis. Mean HU changes were also significant between PVCF (26.8 ± 26.9%) and control (−2.2 ± 22.0%) over the same period. A PRM analysis of BMD changes using standard CT imaging was sensitive for spatially resolving changes that preceded structural failure in these patients.

Integrated multimodal imaging of dynamic bone-tumor alterations associated with metastatic prostate cancer

Bone metastasis occurs for men with advanced prostate cancer which promotes osseous growth and destruction driven by alterations in osteoblast and osteoclast homeostasis. Patients can experience pain, spontaneous fractures and morbidity eroding overall quality of life. The complex and dynamic cellular interactions within the bone microenvironment limit current treatment options thus prostate to bone metastases remains incurable. This study uses voxel-based analysis of diffusion-weighted MRI and CT scans to simultaneously evaluate temporal changes in normal bone homeostasis along with prostate bone metatastsis to deliver an improved understanding of the spatiotemporal local microenvironment. Dynamic tumor-stromal interactions were assessed during treatment in mouse models along with a pilot prospective clinical trial with metastatic hormone sensitive and castration resistant prostate cancer patients with bone metastases. Longitudinal changes in tumor and bone imaging metrics during delivery of therapy were quantified. Studies revealed that voxel-based parametric response maps (PRM) of DW-MRI and CT scans could be used to quantify and spatially visualize dynamic changes during prostate tumor growth and in response to treatment thereby distinguishing patients with stable disease from those with progressive disease (p<0.05). These studies suggest that PRM imaging biomarkers are useful for detection of the impact of prostate tumor-stromal responses to therapies thus demonstrating the potential of multi-modal PRM image-based biomarkers as a novel means for assessing dynamic alterations associated with metastatic prostate cancer. These results establish an integrated and clinically translatable approach which can be readily implemented for improving the clinical management of patients with metastatic bone disease.

Parametric response mapping of dynamic CT as an imaging biomarker to distinguish viability of hepatocellular carcinoma treated with transcatheter arterial chemoembolization

PURPOSE

Accurate assessment of viability of hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE) is important for therapy planning. The purpose of this study is to determine the diagnostic value of a novel image analysis method called parametric response mapping (PRM) in predicting viability of tumor in HCC treated with TACE for dynamic CT images.

METHODS

35 patients who had 35 iodized-oil defect areas (IODAs) in HCCs treated with TACE were included in our study. These patients were divided into two groups, one group with viable tumors (n = 22) and the other group with non-viable tumors (n = 13) in the IODA. All patients were followed up using triple-phase dynamic CT after the treatment. We compared (a) manual analysis, (b) using PRM results, and (c) using PRM results with automatic classifier to distinguish between two tumor groups based on dynamic CT images from two longitudinal exams. Two radiologists performed the manual analysis. The PRM approach was implemented using prototype software. We adopted an off-the-shelf k nearest neighbor (kNN) classifier and leave-one-out cross-validation for the third approach. The area under the curve (AUC) values were compared for three approaches.

RESULTS

Manual analysis yielded AUC of 0.74, using PRM results yielded AUC of 0.84, and using PRM results with an automatic classifier yielded AUC of 0.87.

CONCLUSIONS

We improved upon the standard manual analysis approach by adopting a novel image analysis method of PRM combined with an automatic classifier.

Image registration for quantitative parametric response mapping of cancer treatment response

Imaging biomarkers capable of early quantification of tumor response to therapy would provide an opportunity to individualize patient care. Image registration of longitudinal scans provides a method of detecting treatment associated changes within heterogeneous tumors by monitoring alterations in the quantitative value of individual voxels over time, which is unattainable by traditional volumetric-based histogram methods. The concepts involved in the use of image registration for tracking and quantifying breast cancer treatment response using parametric response mapping (PRM), a voxel-based analysis of diffusion-weighted magnetic resonance imaging (DW-MRI) scans, are presented. Application of PRM to breast tumor response detection is described, wherein robust registration solutions for tracking small changes in water diffusivity in breast tumors during therapy are required. Methodologies that employ simulations are presented for measuring expected statistical accuracy of PRM for response assessment. Test-retest clinical scans are used to yield estimates of system noise to indicate significant changes in voxel-based changes in water diffusivity. Overall, registration-based PRM image analysis provides significant opportunities for voxel-based image analysis to provide the required accuracy for early assessment of response to treatment in breast cancer patients receiving neoadjuvant chemotherapy.

Rapid healing of femoral defects in rats with low dose sustained BMP2 expression from PEGDA hydrogel microspheres

Current strategies for bone regeneration after traumatic injury often fail to provide adequate healing and integration. Here, we combined the poly (ethylene glycol) diacrylate (PEGDA) hydrogel with allogeneic "carrier" cells transduced with an adenovirus expressing BMP2. The system is unique in that the biomaterial encapsulates the cells, shielding them and thus suppressing destructive inflammatory processes. Using this system, complete healing of a 5 mm-long femur defect in a rat model occurs in under 3 weeks, through secretion of 100-fold lower levels of protein as compared to doses of recombinant BMP2 protein used in studies which lead to healing in 2-3 months. New bone formation was evaluated radiographically, histologically, and biomechanically at 2, 3, 6, 9, and 12 weeks after surgery. Rapid bone formation bridged the defect area and reliably integrated into the adjacent skeletal bone as early as 2 weeks. At 3 weeks, biomechanical analysis showed the new bone to possess 79% of torsional strength of the intact contralateral femur. Histological evaluation showed normal bone healing, with no infiltration of inflammatory cells with the bone being stable approximately 1 year later. We propose that these osteoinductive microspheres offer a more efficacious and safer clinical option over the use of rhBMP2.