Spectral analysis of non-contrast fluoroscopy for evaluation of pulmonary perfusion: Feasibility and sensitivity testing with a phantom.

BACKGROUND: Oscillating x-ray attenuation in the lungs provides an opportunity to evaluate pulmonary perfusion without contrast. Recent intensity-based methods have been compared to pulmonary scintigraphy and CT angiography but lack rigorous phantom studies. PURPOSE: A new method to quantify the periodic signal amplitude was employed using spectral analysis. Performance was characterized using a water phantom capable of creating an oscillating x-ray attenuation at physiologic amplitudes. Feasibility in detecting abnormal perfusion was performed on a volunteer with pulmonary vascular disease and compared to pulmonary angiography, the clinical gold standard. METHODS: For each fluoroscopic acquisition, the normalized temporal signal from each pixel was decomposed into its frequency components using Fourier transformation, and the spectral amplitude, defined as the x-ray pulsatility index (XPI), was determined at the desired frequency using a band-pass filter. XPI was displayed as a pixel-wise parametric colormap. Based on XPI maps generated using two human volunteers, a water bath phantom was constructed with a fluctuating fluid height and a 1 cm diameter pulsatility defect. Contrast-to-noise (CNR) of the defect was measured using fluoroscopy images acquired at variable fluid height fluctuation (0.1-1.9 mm) and oscillation frequency (30-60 bpm). Various sampling frame rates (3-30 fps) and acquisition durations (1.8-8 s) using truncated datasets were reconstructed from full datasets. Fluoroscopic images were obtained in a patient just prior to pulmonary angiography in the same projection. RESULTS: XPI maps in human subjects showed high signal to background contrast with high central XPI measuring up to 0.5. Phantom experiments revealed CNR was linearly correlated to fluid height change (r2  = 0.998). CNR is proportional to increasing sampling frame rate and increasing acquisition duration as expected with Fourier analysis. XPI map displayed multifocal perfusion defects in good agreement with pulmonary angiography. CONCLUSION: Spectral analysis is an accurate and sensitive method to detect small changes in periodic x-ray attenuation using a short fluoroscopic acquisition. This method demonstrated good agreement to pulmonary angiography and shows promise for clinical imaging of pulmonary perfusion using standard fluoroscopic methods.

Predictive Dosimetry and Outcomes of Hepatocellular Carcinoma Treated by Yttrium-90 Resin Microsphere Radioembolization: A Retrospective Analysis Using Technetium-99m Macroaggregated Albumin Single Photon Emission CT/CT and Planning Software.

PURPOSE: To characterize estimated mean absorbed tumor dose (ADT), objective response (OR), and estimated target dose of hepatocellular carcinoma (HCC) after resin microsphere yttrium-90 (90Y) radioembolization using partition dosimetry. MATERIALS AND METHODS: In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving 90Y radioembolization between October 2015 and June 2022 was performed using a commercial software package and pretreatment technetium-99m macroaggregated albumin single photon emission computed tomography (SPECT)/computed tomography (CT). In total, 101 patients with HCC underwent 102 treatments of 127 index tumors. Patients underwent imaging every 2-3 months after treatment to determine best response per modified Response Evaluation Criteria in Solid Tumors (mRECIST). Best response was defined as the greatest response category per mRECIST and categorized as OR or nonresponse (NR). A Cox proportional hazards model evaluated the probability of tumor OR and progression-free survival using ADT. RESULTS: The median follow-up period was 148 days (interquartile range [IQR], 92-273 days). The median ADT of OR was 141.9 Gy (IQR, 89.4-215.8 Gy) compared with the median ADT of NR treatments of 70.8 Gy (IQR, 42.0-135.3 Gy; P < .001). Only ADT was predictive of response (hazard ratio = 2.79 [95% confidence interval {CI}: 1.44-5.40]; P = .003). At 6 months, an ADT of 157 Gy predicted 90.0% (95% CI: 41.3%-98.3%) probability of OR. At 1 year, an ADT of 157 Gy predicted 91.6% (95% CI: 78.3%-100%) probability of progression-free survival. Partition modeling and delivered activity were predictive of progression (P = .021 and P = .003, respectively). CONCLUSIONS: For HCC treated with resin microspheres, tumors receiving higher ADT exhibited higher rates of OR. An ADT of 157 Gy predicted 90.0% OR at 6 months.

A Pilot Nonrandomized Controlled Trial Examining the Use of Artificial Tears on the Radioactivity of Tears After Radioactive Iodine Treatment for Thyroid Cancer.

Background: Nasolacrimal duct obstruction (NLDO) is an adverse effect of high dose radioactive iodine (RAI) therapy for thyroid carcinoma. There are currently no established preventive measures. This study assesses whether preservative free artificial tears (PFATs) can decrease the 131I sodium iodide (131I) activity in the tears of patients following RAI therapy for thyroid carcinoma, and potentially serve as a preventive measure for RAI-associated NLDO. Methods: This non-randomized prospective pilot clinical trial recruited contact-lens wearing patients undergoing RAI therapy for thyroid cancer to self-administer PFATs into the right eye for four days starting on the day of RAI ingestion. Left eyes were the controls. While wearing contacts, patients self-administered PFATs per the following-Day 1: every 15 minutes for 2 hours, then every 30 minutes until bedtime, day 2: every hour for at least 12 hours, day 3: four times a day, and day 4: two times a day. Contact lenses were changed daily, and all lenses were collected one week later. Levels of 131I activity were measured by a well counter, decay-corrected, and converted to units of becquerel. Statistical analyses were performed to compare the 131I activities of the experimental and control eyes. Results: Sixteen eyes of eight patients treated with an average of 145.7 mCi (range 108-159) of 131I for papillary thyroid cancer were included. On day 1, artificial tears decreased the geometric mean 131I activity by 26% in the experimental eyes (p = 0.008). Artificial tears also decreased the geometric mean area under the curve over four days by 23% (p = 0.002). Conclusions: 131I is present in the tears following RAI therapy for thyroid carcinoma. Frequent PFATs starting on the day of RAI ingestion may decrease the level of 131I in the tears. This finding could have implications for lowering the risk of NLDO. Future multi-center clinical trials are needed to determine whether the use of artificial tears after RAI therapy may decrease the risk of NLDO. Clinical Trial Registration: NCT04327999.

Partition Dosimetry and Outcomes of Metastatic Neuroendocrine Tumors after Yttrium-90 Resin Microsphere Radioembolization.

PURPOSE: To characterize estimated mean tumor-absorbed dose (ADT) and objective response of metastatic neuroendocrine tumor (NET) after resin microsphere yttrium-90 (90Y) hepatic radioembolization using partition dosimetry. MATERIALS AND METHODS: In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving 90Y radioembolization between 2013 and 2022 involved the use of Sureplan (MIM Software, Cleveland, Ohio) and technetium-99m macroaggregated albumin single photon emission computed tomography (SPECT) combined with computed tomography. Thirty-six patients with NET underwent treatment of 56 index tumors. Patients underwent imaging every 3-6 months after treatment to determine best response per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and modified RECIST (mRECIST) criteria. Responses were categorized as objective response (OR) or nonresponse (NR). Wilcoxon rank sum test evaluated differences in continuous variables, and Pearson χ2 test evaluated differences in categorical variables. RESULTS: Median follow-up was 582 days (IQR, 187-1,227 days). Per RECIST 1.1, 27 patients (75%) experienced OR and 9 patients experienced (25%) NR. Of the 36 patients, 33 (92%) showed hypervascular, mRECIST-evaluable tumors. Among them, 28 patients (85%) showed mRECIST OR and 5 patients (15%) showed NR. The mRECIST OR group received a higher ADT than the NR group (median, 107 Gy; IQR, 95.1-154 Gy vs median, 70.4 Gy; IQR, 62.9-87.6 Gy; P = .048). All tumors receiving at least 120 Gy showed mRECIST OR. CONCLUSIONS: In hypervascular metastatic NET treated by 90Y resin microsphere radioembolization, higher tumor dose was associated with better tumor response per mRECIST. Doses of ≥120 Gy led to OR.

Predictive Partition Dosimetry and Outcomes after Yttrium-90 Resin Microsphere Radioembolization of Colorectal Cancer Metastatic to the Liver: A Retrospective Analysis.

PURPOSE: To characterize estimated absorbed tumor dose (ADT), objective response (OR), and estimated target dose of liver metastatic colorectal cancer (mCRC) after resin microsphere yttrium-90 (90Y) radioembolization using partition dosimetry. MATERIALS AND METHODS: In this retrospective, single-center study, multicompartment dosimetry of index tumors undergoing 90Y radioembolization from October 2013 to July 2022 was performed using MIM SurePlan and pretreatment technetium-99m macroaggregated albumin infusion data. Thirty-eight patients with mCRC underwent treatments for 59 index tumors. Patients were imaged every 2-3 months after treatment and then every 3-6 months after disease control to determine the best response per Response Evaluation Criteria in Solid Tumors 1.1. Responses were categorized as OR or nonresponse (NR). A Cox proportional hazards model evaluated the probability of tumor OR and local progression-free survival (LPFS) based on ADT. RESULTS: Patients had a median follow-up of 116 days (interquartile range [IQR], 69-231 days). The ADT was higher for OR patients than for NR patients (median, 130.8 [IQR, 85.6-239.0] vs 40.6 [IQR, 26.0-66.3] Gy; P < .001). A greater percentage of OR than NR patients were treated with activities calculated by partition modeling (54% vs 12%; P = .005). Only ADT predicted response (P = .032). At 6 months, an ADT of 120 Gy predicted a 55% (95% CI, 0.0%-89%) probability of OR. Only ADT (P = .010) and female sex (P = .014) predicted LPFS. At 1 year, an ADT of 120 Gy predicted a 70% (95% CI, 35%-100%) probability of LPFS. CONCLUSIONS: Tumor dose was the strongest predictor of OR for mCRC. Administration of an estimated 120 Gy to mCRC predicted 55% OR with 90Y resin microspheres at 6 months.

Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least-squares curve fitting.

Measuring transverse relaxation rate (R2* = 1/T2*) via MRI allows for noninvasive evaluation of multiple clinical parameters, including liver iron concentration (LIC) and fat fraction. Both fat and iron contribute to diffuse liver disease when stored in excess in the liver. This liver damage leads to fibrosis and cirrhosis with an increased risk of developing hepatocellular carcinoma. Liver iron concentration is linearly related to R2* measurements using MRI. A phantom was constructed to assess R2* quantification variability on 1.5 and 3 T MRI systems. Quantification was executed using least-squares curve fitting techniques. The phantom was created using readily available, low-cost materials. It contains four vials with R2* values that cover a clinically relevant range (100 to 420 Hz at 1.5 T). Iron content was achieved using ferric chloride solutions contained in glass vials, each affixed in a three-dimensional (3D)-printed polylactide (PLA) structure, surrounded by distilled water, all housed in a sealed acrylic cylinder. Multiple phantom stands were also 3D-printed using PLA for precise orientation of the phantom with respect to the direction of the static magnetic field. Acquisitions at different phantom angles, across multiple MRI systems, and with different pulse sequence parameters were evaluated. The variability between any two R2* measurements, taken in the same vial under these various acquisition conditions, on a 1.5 T MRI system, was <7% for each of the four vials. For 3 T MRI systems, variability was less than 14% in all cases. Variability was <6% for both 1.5 and 3 T acquisitions when unchanged pulse sequence parameters were used. The phantom can be used to mimic a range of clinically relevant levels of R2* relaxation rates, as measured using MRI. These measurements were found to be reproducible relative to the gold-standard method, liver biopsy, across several different image acquisition conditions.

Radiation Exposure During Operative Fixation of Pediatric Supracondylar Humerus Fractures: Is Lead Shielding Necessary?

BACKGROUND: Factors that impact radiation exposure during operative fixation of pediatric supracondylar humerus (SCH) fractures have been investigated; however, no studies have measured the equivalent dose at the patient's radiosensitive organs. Our hypothesis was that intraoperative fluoroscopy exposes pediatric patients to a significant radiation load and lead shielding of radiosensitive organs is important. The goal of the study was to quantify the patient's radiation exposure during the procedure by measuring the radiation load at the thyroid and gonads. METHODS: A prospective quality improvement project of radiation exposure during percutaneous fixation of isolated SCH fractures was performed over a 4-week period. The c-arm image intensifier was used as the operating table and radiation dosimeters were positioned over the thyroid and gonadal lead shields. Fluoroscopy times were recorded, doses were calculated, and the dosimeters were analyzed. To assure that the prospective cohort was representative of a larger population of SCH fractures, demographics and fluoroscopy time of the prospective cohort were compared with a 12-month retrospective cohort in which dosimetry was not performed. RESULTS: Prospective cohort-18 patients with type 2 (8) and type 3 (10) fractures were prospectively studied with intraoperative measurement of thyroid and gonadal radiation equivalent doses. Mean age was 4.9 years (1.9 to 9.5 y) and mean weight was 21.4 kg (13.1 to 33.5 kg). Mean fluoroscopy time was 65.0 seconds (25.3 to 168.4 s), and absorbed skin dose at the elbow was 0.47 mGy (0.18 to 1.21 mGy). The radiation dosimeters overlying the thyroid and gonads measured minimal radiation indicating equivalent doses of <0.01 mSv for all patients in the prospective cohort.Retrospective cohort-163 patients with type 2 (60) and type 3 (103) fractures were retrospectively studied. The mean age was 5.5 years (0.02 to 13.7 y) and weight was 21.6 kg (2.0 to 71.9 kg). Mean fluoroscopy time was 74.1 seconds (10.2 to 288.9 s), and absorbed skin dose at the elbow was 0.53 mGy (0.07 to 2.07 mGy).There were no statistically significant differences between the cohorts. CONCLUSIONS: The smaller prospective cohort had fluoroscopy times and radiation doses that were not statistically different from the larger retrospective cohort, suggesting that the dosimeter measurements are representative of intraoperative radiation exposure during fixation of pediatric SCH fractures. The equivalent dose to the thyroid and gonads was minimal and approximates daily background radiation. Shielding of radiosensitive organs is appropriate when practical to minimize cumulative lifetime radiation exposure, particularly in smaller patients and when longer fluoroscopy times are anticipated. LEVEL OF EVIDENCE: Level 2.