Instrumentation quality assurance and performance

Operational and Performance Experience with uMI550 Digital PET-CT during Routine Quality Control Procedures

Introduction  The quality control (QC) procedures for positron emission tomography (PET) scanners are covered by National Electrical Manufacturers Association and International Electrotechnical Commission. QC must be carried out at regular intervals according to the specifications of the scanner manufacturer. Daily and weekly QC plays a valuable role in monitoring positron emission tomography (PET) scanner performance changes. This study shares operational and performance experience of QC procedures that do not require a radioactive Ge-68 source to perform daily QC and experience with fluorodeoxyglucose F18 ( 18 F-FDG) as a substitute for germanium-68/sodium-22 (Ge-68/Na-22) source for weekly QC. Method  This study was performed on an uMI550 digital positron emission tomography-computed tomography (PET-CT) scanner. In this scanner daily QC checks system temperature and humidity, system count rate, data link status, and voltage. QC was performed at the console control, the position of the scanner table was in the home position pulled out from the gantry, and the room was closed during the quick QC. Weekly full QC check items include look-up table drift, energy drift, time-of-flight status, C-map status, temperature and humidity, and voltage. Weekly full QC was performed with a 18 F-FDG source in a rod phantom source. Results  Over 200 daily QC tests without a radioactive source Ge-68 phantom and 50 full weekly QC tests using a 18 F-FDG rod phantom were performed with this scanner according to the manufacturer's instructions and a test report was generated. No daily QC errors or warnings were observed during this period. Conclusion  The new approach for the daily PET QC does not expose operators to radiation. This translates into commercial and operational merits with consistent performance and results. Implications for Practice  Reduction in radiation exposure to operating staff during QC procedure in PET-CT scanner.

Diagnostic accuracy of high-resolution attenuation-corrected Anger-camera SPECT in the detection of coronary artery disease

BACKGROUND

There is limited data on diagnostic accuracy of recently introduced high-resolution Anger (HRA) SPECT incorporating attenuation correction (AC), noise reduction, and resolution recovery algorithms. We therefore studied 54 consecutive patients (excluding those with prior MI or cardiomyopathy) who had HRA-AC SPECT and coronary angiography (CA) ≤ 30 days and no change in symptoms.

METHODS

The HRA-AC studies were acquired in 128 × 128 matrix (3.2 mm pixel) format with simultaneous Gd-153 line-source AC. Measured variables were image quality, interpretive certainty, sensitivity and specificity for any CAD, sensitivity for single- and multivessel CAD, and the influence of gender, body mass index (BMI), and stress modality.

RESULTS

The mean age of the patients was 66 ± 11 years with a BMI of 32 ± 7 kg·m(-2). Mean interpretive certainty score was 2.7 on a 3-point scale and mean image quality score was 3.3 on a 4-point scale. Stress perfusion defects were detected in 34 of 38 patients with obstructive CAD [sensitivity 89%, 95% confidence interval (CI) 76%-95%]. The specificity was 75% (CI 51%-90%) and overall diagnostic accuracy was 85% (CI 73%-92%). Accuracy did not differ for females vs males, for BMI ≤30 vs >30, or for pharmacologic vs exercise SPECT. Sensitivity for single-vessel disease was 88% (CI 69%-96%) and for multivessel disease was 93% (CI 69%-99%).

CONCLUSION

New Anger technology incorporating innovative improvements results in high image quality with excellent interpretive certainty and high diagnostic accuracy.

Attenuation of the side effect profile of regadenoson: a randomized double-blind placebo-controlled study with aminophylline in patients undergoing myocardial perfusion imaging and have severe chronic kidney disease--the ASSUAGE-CKD trial

A subgroup analysis of the ASSUAGE trial suggested that the standardized intravenous aminophylline administration following regadenoson-stress leads to substantial attenuation of regadenoson adverse-effects in patients with severe chronic kidney disease (CKD). In a randomized, double-blinded, placebo-controlled clinical trial of patients with stage 4 and 5 CKD, we compared the frequency and severity of regadenoson adverse-effects in those who received 75 mg of intravenous aminophylline versus a matching placebo administered 90 s post-radioisotope injection. Consecutive 300 patients with severe CKD (36% women; 86% end-stage renal disease; age 55 (±13) years) were randomized to receive aminophylline (n = 150) or placebo (n = 150). In the aminophylline arm, there was 65% reduction in the incidence of the primary endpoint of diarrhea (9 (6.0%) vs. 26 (17.3%), P = 0.002), 51% reduction in the secondary endpoint of any regadenoson adverse-effect (47 (31.3%) vs. 96 (64%), P < 0.001) and 70% reduction in headache (16 (10.7%) vs. 54 (36%), P < 0.001). The stress protocol was better tolerated in the aminophylline group (P = 0.008). The quantitative summed difference score, as a measure of stress-induced ischemic burden, was similar between the study groups (P = 0.51). In conclusion, the routine standardized administration of intravenous aminophylline in patients with severe CKD substantially reduces the frequency and severity of the adverse-effects associated with regadenoson-stress without changing the ischemic burden. [NCT01336140].

Attenuation of the side effect profile of regadenoson: a randomized double-blinded placebo-controlled study with aminophylline in patients undergoing myocardial perfusion imaging. "The ASSUAGE trial"

BACKGROUND

It is unknown whether the standardized intravenous aminophylline administration following regadenoson-stress can prevent the gastrointestinal and other adverse effects associated with regadenoson.

METHODS

In a randomized, double-blinded, placebo-controlled clinical trial we compared the frequency and severity of regadenoson adverse effects in those who received 75 mg of intravenous aminophylline versus a matching placebo administered 2 minutes after regadenoson or 90 seconds post-radioisotope injection.

RESULTS

248 patients [44.8% women, mean age 62.2 (± 13.3) years] were randomized to receive aminophylline (124) or placebo (124). In the aminophylline arm, there was 50% reduction in the incidence of the primary endpoint of diarrhea and abdominal discomfort [11 (8.9%) vs 22 (17.7%), P = .04] and 70% reduction in the incidence of diarrhea [4 (3.2%) vs 13 (10.5%), P = .02]. Additionally, aminophylline use was associated with 34% reduction in the secondary endpoint of any regadenoson adverse effects [55 (44.4%) vs 83 (66.9%), P < .001] and 71% reduction in headache [9 (7.3%) vs 31 (25%), P < .001]. The stress protocol was better tolerated in the aminophylline group (P = .007). The quantitative summed difference score was similar in both study groups (P = .92). There were no excess adverse events in the aminophylline arm.

CONCLUSIONS

This trial supports the routine administration of IV-aminophylline to reduce the frequency and severity of adverse effects associated with regadenoson-stress.

Image-based biomarkers in clinical practice

The growth of functional and metabolically informative imaging is eclipsing anatomic imaging alone in clinical practice. The recognition that magnetic resonance (MR) and positron emission tomography (PET)-based treatment planning and response assessment are essential components of clinical practice and furthermore offer the potential of quantitative analysis being important. Extracting the greatest benefit from these imaging techniques will require refining the best combinations of multimodality imaging through well-designed clinical trials that use robust image-analysis tools and require substantial computer based infrastructure. Through these changes and enhancements, image-based biomarkers will enhance clinical decision making and accelerate the progress that is made through clinical trial research.

A multicenter evaluation of a new post-processing method with depth-dependent collimator resolution applied to full-time and half-time acquisitions without and with simultaneously acquired attenuation correction

BACKGROUND

The field of nuclear cardiology is limited by image quality and length of procedure. The use of depth-dependent resolution recovery algorithms in conjunction with iterative reconstruction holds promise to improve image quality and reduce acquisition time. This study compared the Astonish algorithm employing depth-dependent resolution recovery and iterative reconstruction to filtered backprojection (FBP) using both full-time (FTA) and half-time (HTA) data. Attenuation correction including scatter correction in conjunction with the Astonish algorithm was also evaluated.

METHODS

We studied 187 consecutive patients (132 with cardiac catheterization and 55 with low likelihood for CAD) from three nuclear cardiology laboratories who had previously undergone clinically indicated rest/stress Tc-99m sestamibi or tetrofosmin SPECT. Acquisition followed ASNC guidelines (64 projections, 20-25 seconds). Processing of the full-time data sets included FBP and Astonish (FTA). A total of 32 projection data sets were created by stripping the full-time data sets and processing with Astonish (HTA). Attenuation correction was applied to both full-time and half-time Astonish-processed images (FTA-AC and HTA-AC, respectively). A consensus interpretation of three blinded readers was performed for image quality, interpretative certainty, and diagnostic accuracy, as well as severity and reversibility of perfusion and functional parameters.

RESULTS

Full-time and half-time Astonish processing resulted in a significant improvement in image quality in comparison with FBP. Stress and rest perfusion image quality (excellent or good) were 85%/80% (FBP), 98%/95% (FTA), and 95%/92% (HTA), respectively (p < 0.001). Interpretative certainty and diagnostic accuracy were similar with FBP, FTA, and HTA. Left ventricular functional data were not different despite a slight reduction in half-time gated image quality. Application of attenuation correction resulted in similar image quality and improved normalcy (FTA vs. FTA-AC: 76% vs. 95%; HTA vs. HTA-AC: 76% vs. 100%) and specificity (FTA vs. FTA-AC: 62% vs. 78%; HTA vs. HTA-AC: 63% vs. 84%) (p < 0.01 for all comparisons).

CONCLUSION

Astonish processing, which incorporates depth-dependent resolution recovery, improves image quality without sacrificing interpretative certainty or diagnostic accuracy. Application of simultaneously acquired attenuation correction, which includes scatter correction, to full-time and half-time images processed with this method, improves specificity and normalcy while maintaining high image quality.

A practical, automated quality assurance method for measuring spatial resolution in PET

The use of different scanners, acquisition protocols, and reconstruction algorithms has been identified as a problem that limits the use of PET in multicenter trials. The aim of this project was to aid standardization of data collection by developing a quality assurance method for measuring the spatial resolution achieved with clinical imaging protocols.

METHODS

A commercially available (68)Ge cylinder phantom (diameter, 20 cm) with a uniform activity concentration was positioned in the center of the PET field of view, and an image was acquired using typical clinical parameters. Spatial resolution was measured by artificially generating an object function (O) with uniform activity within a 20-cm-diameter cylinder, assuming no noise and perfect spatial resolution, centered on the original image (I); dividing F[I] by F[O], where F indicates a 2-dimensional Fourier transform, to produce a modulation transfer function; and taking the inverse Fourier transform of the modulation transfer function to produce a point-spread function in image space. The method was validated using data acquired on 4 different commercial PET systems.

RESULTS

Spatial resolution on the Discovery LS was measured at 5.75 +/- 0.58 mm, compared with 5.54 +/- 0.19 mm from separate point source measurements. Variability of the resolution measurements differed between scanners and protocols, but the typical SD was approximately 0.15 mm when iterative reconstruction was used. The potential for predicting resolution recovery coefficients for small objects was also demonstrated.

CONCLUSION

The proposed method does not require elaborate phantom preparation and is practical to perform, and data analysis is fully automated. This approach is useful for evaluating clinical reconstruction protocols across varying scanners and reconstruction algorithms and should greatly aid standardization of data collection between centers.

Diagnostic performance of fusion of myocardial perfusion imaging (MPI) and computed tomography coronary angiography

BACKGROUND

We evaluated the incremental diagnostic value of fusion images of coronary computed tomography angiography (CTA) and myocardial perfusion imaging (MPI) over MPI alone or MPI and CTA side-by-side to identify obstructive coronary artery disease (CAD > 50% stenosis) using invasive coronary angiography (ICA) as the gold standard.

METHODS

50 subjects (36 men; 56 +/- 11 years old) underwent rest-stress MPI and CTA within 12-26 days of each other. CTAs were performed with multi-detector CT-scanners (31 on 64-slice; and 19 on 16-slice). 37 patients underwent ICA while 13 subjects did not because of low (<5%) pre-test likelihood (LLK) of disease. Three blinded readers scored the images in sequential sessions using (1) MPI alone (2) MPI and CTA side-by-side, (3) fused CTA/MPI images.

RESULTS

One or more critical stenoses during ICA were found in 28 patients and non-critical stenoses were found in 9 patients. MPI, side-by-side MPI-CTA, and fused CTA/MPI showed the same normalcy rate (NR:13/13) in LLK subjects. The fusion technique performed better than MPI and MPI and CTA side-by-side for the presence of CAD in any vessel (overall area under the curve (AUC) for fused images: 0.89; P = .005 vs MPI, P = .04 vs side-by-side MPI-CTA) and for localization of CAD to the left anterior descending coronary artery (AUC: 0.82, P < .001 vs MPI; P = .007 vs side-by-side MPI-CTA). There was a non-significant trend for better detection of multi-vessel disease with fusion.

CONCLUSIONS

Using ICA as the gold standard, fusion imaging provided incremental diagnostic information compared to MPI alone or side-by-side MPI-CTA for the diagnosis of obstructive CAD and for localization of CAD to the left anterior descending coronary artery.

Routine quality control of clinical nuclear medicine instrumentation: a brief review

This article reviews routine quality-control (QC) procedures for current nuclear medicine instrumentation, including the survey meter, dose calibrator, well counter, intraoperative probe, organ ("thyroid") uptake probe, gamma-camera, SPECT and SPECT/CT scanner, and PET and PET/CT scanner. It should be particularly useful for residents, fellows, and other trainees in nuclear medicine, nuclear cardiology, and radiology. The procedures described and their respective frequencies are presented only as general guidelines.

Cost of preimplantation cardiac imaging in patients referred for a primary-prevention implantable cardioverter-defibrillator

Recent guidelines have focused on ejection fraction cut-off values to determine eligibility for primary-prevention implantable cardioverter-defibrillators (ICDs). Clinical trials that led to the guidelines used varying techniques for ejection fraction assessment, including echocardiography and multigated acquisition (MUGA) scan. A prospective cohort study to determine the economic attractiveness of repeated echocardiography and MUGA scanning during the evaluation process of patients referred for consideration of a primary-prevention ICD was undertaken. From January 2005 to December 2006, data were collected for patients aged >18 years with ejection fraction <30% referred for a primary-prevention ICD based on referral assessment of heart function in any form. Costs based on the 2006 Ontario Health Insurance Plan fee schedule were determined for clinical assessment, echocardiography, MUGA scanning, and ICD implantation in patients who remained eligible based on MUGA ejection fraction. The 100 patients (age 61.1 +/- 10.2 years; 78 men) assessed for primary-prevention ICD implantation had an ejection fraction of 28.9 +/- 12.3% using MUGA scan. Thirty-one of 100 patients (31%) had an ejection fraction >30% and were no longer eligible for an ICD. Although imaging increased preimplantation cost from dollars 130 to dollars 536 per patient, averted inappropriate ICDs decreased the overall per-patient cost from dollars 20,914 to dollars 14,877. Despite an additional testing cost of dollars 40,599, the overall cost savings was dollars 603,722 in the 100 patients, with a cost savings of dollars 6,037 per patient. In conclusion, verification of ejection fraction identified a significant proportion of patients who were not eligible for an ICD.