Implementation and evaluation of a protocol management system for automated review of CT protocols.

Protocol review is important to decrease the risk of patient injury and increase the consistency of CT image quality. A large volume of CT protocols makes manual review labor-intensive, error-prone, and costly. To address these challenges, we have developed a software system for automatically managing and monitoring CT proto-cols on a frequent basis. This article describes our experiences in the implementation and evaluation of this protocol monitoring system. In particular, we discuss various strategies for addressing each of the steps in our protocol-monitoring workflow, which are: maintaining an accurate set of master protocols, retrieving protocols from the scanners, comparing scanner protocols to master protocols, reviewing flagged differences between the scanner and master protocols, and updating the scanner and/or master protocols. In our initial evaluation focusing only on abdo-men and pelvis protocols, we detected 309 modified protocols in a 24-week trial period. About one-quarter of these modified protocols were determined to contain inappropriate (i.e., erroneous) protocol parameter modifications that needed to be corrected on the scanner. The most frequently affected parameter was the series description, which was inappropriately modified 47 times. Two inappropriate modifications were made to the tube current, which is particularly important to flag as this parameter impacts both radiation dose and image quality. The CT protocol changes detected in this work provide strong motivation for the use of an automated CT protocol quality control system to ensure protocol accuracy and consistency.

Personalized image-based radiation dosimetry for routine clinical use in peptide receptor radionuclide therapy: pretherapy experience.

Patient-specific dose calculations are not routinely performed for targeted radionuclide therapy procedures, partly because they are time consuming and challenging to perform. However, it is becoming widely recognized that a personalized dosimetry approach can help plan treatment and improve understanding of the dose-response relationship. In this chapter, we review the procedures and essential elements of an accurate internal dose calculation and propose a simplified approach that is aimed to be practical for use in a busy nuclear medicine department.

Preclinical PET Imaging and Toxicity Study of a 68Ga-Functionalized Polymeric Cardiac Blood Pool Agent.

Cardiac blood pool imaging is currently performed almost exclusively with 99mTc-based compounds and SPECT/CT imaging. Using a generator-based PET radioisotope has a few advantages, including not needing nuclear reactors to produce it, obtaining better resolution in humans, and potentially reducing the radiation dose to the patient. When the shortlived radioisotope 68Ga is used, it can be applied repeatedly on the same day-for example, for the detection of bleeding. Our objective was to prepare and evaluate a long-circulating polymer functionalized with gallium for its biodistribution, toxicity, and dosimetric properties. A 500 kDa hyperbranched polyglycerol was conjugated to the chelator NOTA and radiolabeled rapidly at room temperature with 68Ga. It was then injected intravenously into a rat, and gated imaging allowed us to easily observe wall motion and cardiac contractility, confirming the suitability of this radiopharmaceutical for cardiac blood pool imaging. Internal radiation dose calculations showed that the radiation doses that patients would receive from the PET agent would be 2.5× lower than those from the 99mTc agent. A complete 14-day toxicology study in rats concluded that there were no gross pathology findings, changes in body or organ weights, or histopathological events. This radioactive-metal-functionalized polymer might be a suitable non-toxic agent to advance for clinical application.

Selection of optimal tube potential settings for dual-energy CT virtual mono-energetic imaging of iodine in the abdomen.

PURPOSE: To determine the appropriate tube potential settings for dual-source, dual-energy data acquisition across a range of phantom sizes, and to determine the optimal photon energies for virtual mono-energetic imaging. METHODS: Water phantoms (15-50-cm wide) containing an iodine test object were scanned on a third-generation dual-source CT scanner using all available tube potential pairs. Virtual mono-energetic images at 40, 50, 60, and 70 keV were produced using Mono-energetic Plus. To determine the practical operating parameters for the evaluated CT system, data exclusions were made based on water CT number accuracy, artifacts, and using a noise constraint. Image quality metrics were measured and compared. RESULTS: Excluded tube potential pairs were identified; these were generally at low tube potentials for the low-energy beam and low photon energies. For non-excluded conditions, the highest CNR was obtained using the 70/150Sn setting in phantoms ≤35 cm at 40 keV. CONCLUSIONS: 70/150Sn provided optimal iodine CNR below 40 cm lateral phantom width at 40 keV, while 90/150Sn allowed acceptable image quality in phantoms >40-cm wide at or above 60 keV.

Technical Note: Improved CT number stability across patient size using dual-energy CT virtual monoenergetic imaging.

PURPOSE: The purpose of this study was to evaluate, over a wide range of phantom sizes, CT number stability achieved using two techniques for generating dual-energy computed tomography (DECT) virtual monoenergetic images. METHODS: Water phantoms ranging in lateral diameter from 15 to 50 cm and containing a CT number test object were scanned on a DSCT scanner using both single-energy (SE) and dual-energy (DE) techniques. The SE tube potentials were 70, 80, 90, 100, 110, 120, 130, 140, and 150 kV; the DE tube potential pairs were 80/140, 70/150Sn, 80/150Sn, 90/150Sn, and 100/150Sn kV (Sn denotes that the 150 kV beam was filtered with a 0.6 mm tin filter). Virtual monoenergetic images at energies ranging from 40 to 140 keV were produced from the DECT data using two algorithms, monoenergetic (mono) and monoenergetic plus (mono+). Particularly in large phantoms, water CT number errors and/or artifacts were observed; thus, datasets with water CT numbers outside ±10 HU or with noticeable artifacts were excluded from the study. CT numbers were measured to determine CT number stability across all phantom sizes. RESULTS: Data exclusions were generally limited to cases when a SE or DE technique with a tube potential of less than 90 kV was used to scan a phantom larger than 30 cm. The 90/150Sn DE technique provided the most accurate water background over the large range of phantom sizes evaluated. Mono and mono+ provided equally improved CT number stability as a function of phantom size compared to SE; the average deviation in CT number was only 1.4% using 40 keV and 1.8% using 70 keV, while SE had an average deviation of 11.8%. CONCLUSIONS: The authors' report demonstrates, across all phantom sizes, the improvement in CT number stability achieved with mono and mono+ relative to SE.

The influence of focal spot blooming on high-contrast spatial resolution in CT imaging.

PURPOSE: The objective of this work was to investigate focal spot blooming effects on the spatial resolution of CT images and to evaluate an x-ray tube that uses dynamic focal spot control for minimizing focal spot blooming. METHODS: The influence of increasing tube current at a fixed tube potential of 80 kV on high-contrast spatial resolution of seven different CT scanner models (scanners A-G), including one scanner that uses dynamic focal spot control to reduce focal spot blooming (scanner A), was evaluated. Spatial resolution was assessed using a wire phantom for the modulation transfer function (MTF) calculation and a copper disc phantom for measuring the slice sensitivity profile (SSP). The impact of varying the tube potential was investigated on two scanner models (scanners A and B) by measuring the MTF and SSP and also by using the resolution bar pattern module of the ACR CT phantom. The phantoms were scanned at 70-150 kV on scanner A and 80-140 kV on scanner B, with tube currents from 100 mA up to the maximum tube current available on each scanner. The images were reconstructed using a slice thickness of 0.6 mm with both smooth and sharp kernels. Additionally, focal spot size at varying tube potentials and currents was directly measured using pinhole and slit camera techniques. RESULTS: Evaluation of the MTF and SSP data from the 7 CT scanner models evaluated demonstrated decreased focal spot blooming for newer scanners, as evidenced by decreasing deviations in MTF and SSP as tube current varied. For scanners A and B, where focal spot blooming effects as a function of tube potential were assessed, the spatial resolution variation in the axial plane was much smaller on scanner A compared to scanner B as tube potential and current changed. On scanner A, the 50% MTF never decreased by more than 2% from the 50% MTF measured at 100 mA. On scanner B, the 50% MTF decreased by as much as 19% from the 50% MTF measured at 100 mA. Assessments of the SSP, the bar patterns in the ACR phantom and the pinhole and slit camera measurements were consistent with the MTF calculations. CONCLUSIONS: Focal spot blooming has a noticeable effect on spatial resolution in CT imaging. The focal spot shaping technology of scanner A greatly reduced blooming effects.

Comparison of internal dose estimates obtained using organ-level, voxel S value, and Monte Carlo techniques.

PURPOSE: The authors' objective was to compare internal dose estimates obtained using the Organ Level Dose Assessment with Exponential Modeling (OLINDA/EXM) software, the voxel S value technique, and Monte Carlo simulation. Monte Carlo dose estimates were used as the reference standard to assess the impact of patient-specific anatomy on the final dose estimate. METHODS: Six patients injected with 99mTc-hydrazinonicotinamide-Tyr3-octreotide were included in this study. A hybrid planar/SPECT imaging protocol was used to estimate 99mTc time-integrated activity coefficients (TIACs) for kidneys, liver, spleen, and tumors. Additionally, TIACs were predicted for 131I, 177Lu, and 90Y assuming the same biological half-lives as the 99mTc labeled tracer. The TIACs were used as input for OLINDA/EXM for organ-level dose calculation and voxel level dosimetry was performed using the voxel S value method and Monte Carlo simulation. Dose estimates for 99mTc, 131I, 177Lu, and 90Y distributions were evaluated by comparing (i) organ-level S values corresponding to each method, (ii) total tumor and organ doses, (iii) differences in right and left kidney doses, and (iv) voxelized dose distributions calculated by Monte Carlo and the voxel S value technique. RESULTS: The S values for all investigated radionuclides used by OLINDA/EXM and the corresponding patient-specific S values calculated by Monte Carlo agreed within 2.3% on average for self-irradiation, and differed by as much as 105% for cross-organ irradiation. Total organ doses calculated by OLINDA/EXM and the voxel S value technique agreed with Monte Carlo results within approximately ±7%. Differences between right and left kidney doses determined by Monte Carlo were as high as 73%. Comparison of the Monte Carlo and voxel S value dose distributions showed that each method produced similar dose volume histograms with a minimum dose covering 90% of the volume (D90) agreeing within ±3%, on average. CONCLUSIONS: Several aspects of OLINDA/EXM dose calculation were compared with patient-specific dose estimates obtained using Monte Carlo. Differences in patient anatomy led to large differences in cross-organ doses. However, total organ doses were still in good agreement since most of the deposited dose is due to self-irradiation. Comparison of voxelized doses calculated by Monte Carlo and the voxel S value technique showed that the 3D dose distributions produced by the respective methods are nearly identical.

JADA: a graphical user interface for comprehensive internal dose assessment in nuclear medicine.

PURPOSE: The main objective of this work was to design a comprehensive dosimetry package that would keep all aspects of internal dose calculation within the framework of a single software environment and that would be applicable for a variety of dose calculation approaches. METHODS: Our MATLAB-based graphical user interface (GUI) can be used for processing data obtained using pure planar, pure SPECT, or hybrid planar/SPECT imaging. Time-activity data for source regions are obtained using a set of tools that allow the user to reconstruct SPECT images, load images, coregister a series of planar images, and to perform two-dimensional and three-dimensional image segmentation. Curve fits are applied to the acquired time-activity data to construct time-activity curves, which are then integrated to obtain time-integrated activity coefficients. Subsequently, dose estimates are made using one of three methods. RESULTS: The organ level dose calculation subGUI calculates mean organ doses that are equivalent to dose assessment performed by OLINDA/EXM. Voxelized dose calculation options, which include the voxel S value approach and Monte Carlo simulation using the EGSnrc user code DOSXYZnrc, are available within the process 3D image data subGUI. CONCLUSIONS: The developed internal dosimetry software package provides an assortment of tools for every step in the dose calculation process, eliminating the need for manual data transfer between programs. This saves times and minimizes user errors, while offering a versatility that can be used to efficiently perform patient-specific internal dose calculations in a variety of clinical situations.

The accuracy and reproducibility of SPECT target volumes and activities estimated using an iterative adaptive thresholding technique.

OBJECTIVE: Our aim was to design a practical and reproducible image segmentation method for calculations of total absorbed doses in organs and tumours for internally delivered radioisotopes. We have built upon our previously proposed use of two separate thresholds and employed an iterative technique for semiautomatic selection of background regions for segmenting an object of interest using thresholds that depend on the source-to-background ratio of activity concentrations. METHODS: The parameters of curves relating volume and activity thresholds to source-to-background ratio were established using phantoms with 20 different inserts. The accuracy of our technique was validated using a second phantom experiment, whereas the reproducibility of volume, activity and dose estimates of organs and tumours was investigated using 13 patient studies. The accuracy and reproducibility of segmentations achieved were assessed using images reconstructed with three different methods that ranged from a standard clinical reconstruction to an advanced quantitative reconstruction approach. RESULTS: In the validation phantom experiment, bottle volumes and activities measured using iterative adaptive thresholding agreed on average with the true values to within 4%, regardless of the reconstruction method used. In the patient studies, volumes and activities estimated from the single-photon emission computed tomography images reconstructed with clinical software agreed with the volumes and activities estimated using the advanced reconstruction approach to within 6%, whereas the corresponding doses agreed to within 4%. CONCLUSION: The proposed iterative adaptive thresholding technique can accurately determine object volume and activity, which allows standard clinical reconstructions to generate absorbed dose estimates that are similar to those values obtained using more advanced reconstruction methods.

Patient-specific radiation dosimetry of 99mTc-HYNIC-Tyr3-octreotide in neuroendocrine tumors.

UNLABELLED: (99m)Tc-hydrazinonicotinamide-Tyr(3)-octreotide ((99m)Tc-HYNIC-TOC) is increasingly gaining acceptance as a new radiopharmaceutical for the diagnosis of pathologic lesions overexpressing somatostatin receptors. However, little information has been published about the radiation dosimetry of this agent. The aim of this study was to assess the biodistribution and radiation dosimetry of commercially available (99m)Tc-HYNIC-TOC. A dose calculation procedure designed to be feasible to implement in a busy clinical environment was used. METHODS: Twenty-eight patients were imaged for suspected neuroendocrine tumors using a series of whole-body planar, dynamic planar, and SPECT/CT studies, after injection with (99m)Tc-HYNIC-TOC. Patient-specific dosimetry was performed using the OLINDA/EXM software with time-integrated activity coefficients estimated from a hybrid planar/SPECT technique. A phantom experiment was performed to establish adaptive thresholds for determination of source region volumes and activities. RESULTS: Pathologic uptake, diagnosed as due to neuroendocrine tumors, was observed in 12 patients. Normal organs with significant uptake included the kidneys, liver, and spleen. The mean effective dose after (99m)Tc-HYNIC-TOC injection was 4.6 ± 1.1 mSv. Average normal-organ doses were 0.030 ± 0.012, 0.021 ± 0.007, and 0.012 ± 0.005 mGy/MBq for the spleen, kidneys, and liver, respectively. The interpatient kidney dose ranged from 0.011 to 0.039 mGy/MBq, whereas the range of tumor doses varied from 0.003 to 0.053 mGy/MBq. The ratio of tumor to kidney dose ranged from 0.13 to 2.9. The optimal thresholds for recovery of true activity in the phantom study were significantly lower than those used for volume determination. CONCLUSION: The patient-specific 3-dimensional dosimetry protocol used in this study is a clinically feasible technique that has been applied to demonstrate large dose variations in tumors and normal organs between patients imaged with (99m)Tc-HYNIC-TOC.