Three-dimensional regions-of-interest-based intra-operative four-dimensional soft tissue perfusion imaging using a standard x-ray system with no gantry rotation: A simulation study for a proof of concept

Volumetric soft tissue perfusion assessment on a region basis from x-ray angiography images: Motion compensation

BACKGROUND

Assessing the soft tissue perfusion quantitatively in interventional suites before, during, and after interventional procedures is desired. The method, if possible, has to assess the perfusion volumetrically and quantitatively, be robust against lesion overlaps and patient motion, require no additional radiation dose, be quick (possibly in real-time), and fit to the clinical workflow well. We have developed a method called IPEN (for Intra-operative PErfusion assessment with No gantry rotation) that has potential to accomplish all of the desired goals except for the patient motion. The innovation with IPEN is not to reconstruct volumetric images, but to estimate enhancement of multiple three-dimensional regions-of-interest directly from x-ray projections acquired at one angle.

PURPOSE

To further develop the IPEN method such that it can compensate for patient motion when the patient moves quickly during the angiography scan but stays still otherwise.

METHODS

The proposed motion-compensating IPEN (MCI) consists of the following three steps: (Step 1) The time segment is broken into multiple segments, that is, a set of rapid motion segments and a set of stationary segments; (Step 2) the MCI estimates ROI enhancement within each stationary segment; and (Step 3) MCI connects segments. The performance of the proposed MCI and the original IPEN were assessed using the digital perfusion phantom, simulating 13 ischemic stroke "patients." The head moved within 0.6 s each time, and seven times during 16-s scans; motion magnitude parameter a (for ± a mm and ± a degrees) was 0.0 (no motion), 0.5, 2.0, 5.0, and 25.0 for each scan. The accuracy of time-enhancement curves (TECs) and calculated perfusion-like parameter ("max-slope" for the maximum of slope of TEC; similar to Patlak plot analysis) was assessed. In addition, the effect of the motion segments on the accuracy of the estimated TEC has been studied systematically.

RESULTS

Head motion induced very severe inconsistency and artifact in synthesized digital subtraction angiography images. The original IPEN had disjoint TECs, and the correlation coefficients (r) against the true values decreased from 0.475 at a = 0.5 to 0.023 at a = 25.0. The proposed MCI provided smooth and accurate TECs with r = 0.995 at a = 0.5 and r = 0.989 at a = 25.0. The 𝓁2-norm of the error vectors of the max-slope values was 5.6-64.2 (d.l.) for the original IPEN, whereas it was < 0.1 for the MCI for the motion magnitudes investigated. There was an strong linear relationship between the non-linearity of the derivative of TECs and biases in TEC: r was 0.999. MCI would have a significant bias when a lengthy motion occurs when an ROI enhancement changes non-linearly during the time.

CONCLUSION

The proposed MCI can compensate for the patient motion very effectively and accurately when the motion is not continuous and the ROI enhancement does not change non-linearly and significantly during the motion segment.

Intraprocedural C-arm dual-phase cone-beam enhancement patterns correlate with tumor absorbed dose after radioembolization

BACKGROUND

Recent studies have shown a clear relationship between absorbed dose and tumor response to treatment after hepatic radioembolization. These findings help to create more personalized treatment planning and dosimetry. However, crucial to this goal is the ability to predict the dose distribution prior to treatment. The microsphere distribution is ultimately determined by (i) the hepatic vasculature and the resulting blood flow dynamics and (ii) the catheter position.

PURPOSE

To show that pretreatment, intra-procedural imaging of blood flow patterns, as quantified by catheter-directed intra-arterial contrast enhancement, correlate with posttreatment microsphere accumulation and, consequently, absorbed dose.

MATERIALS AND METHODS

Patients who participated in a clinical trial (NCT01177007) and for whom both a pretreatment dual-phase contrast-enhanced cone-beam CT (CBCT) and a posttreatment 90Y PET/CT scan were available were included in this retrospective study. Tumors and perfused volumes were manually delineated on the CBCT by an experienced radiologist. The mean, sum, and standard deviation of the voxels in each volume were recorded. The delineations were transferred to the PET-based absorbed dose maps by coregistration of the corresponding CTs. Linear multiple regression was used to correlate pretreatment CBCT enhancement to posttreatment 90Y PET/CT-based absorbed dose in each region. Leave-one-out cross-validation and Bland-Altman analyses were performed on the predicted versus measured absorbed doses.

RESULTS

Nine patients, with a total of 23 tumors were included. All presented with hepatocellular carcinoma (HCC). Visually, all patients had a clear correspondence between CBCT enhancement and absorbed dose. The correlation between CBCT enhancement and posttherapy absorbed tumor dose based was strong (R2 = 0.91), and moderate for the non-tumor liver tissue (R2 = 0.61). Limits of agreement were approximately ±55 Gray for tumor tissue.

CONCLUSION

There is a linear relationship between pretreatment blood dynamics in HCC tumors and posttreatment absorbed dose, which, if shown to be generalizable, allows for pretreatment tumor absorbed dose prediction.