Deborah Tout

Assessment of a protocol for routine simultaneous myocardial blood flow measurement and standard myocardial perfusion imaging with rubidium-82 on a high count rate positron emission tomography system.

ObjectivesHigh count rate positron emission tomography (PET) systems offer the potential for accurate myocardial blood flow (MBF) quantification during first-pass dynamic imaging in conjunction with standard rubidium-82 (Rb-82) PET myocardial perfusion imaging (MPI). We investigate the feasibility of this using a Siemens Biograph mCT. Materials and methodsCurrent routine clinical PET MPI is performed with 1480 MBq (40 mCi) Rb-82. Dynamic first-pass images from 217 consecutive patients were reviewed for evidence of detector saturation, indicating that count rate limits had been exceeded. Phantom acquisitions in the presence of high count rates were performed to assess the effect of detector saturation on quantitative accuracy. ResultsAccurate MBF quantification and perfusion imaging using current protocols was successful in 85% of clinical cases. Detector block saturation was observed in 15% of cases, and phantom acquisitions indicate that saturation may have an adverse effect on quantitative accuracy. Visualization of transit or pooling of Rb-82 in the vessels in the axilla was the most consistent feature when saturation occurred. Reduction of administered activity to 1110 MBq (30 mCi) and subsequent evaluation of 159 patients ensured successful MBF quantification while maintaining good diagnostic quality perfusion imaging in 99% of cases. ConclusionMBF quantification and good-quality standard perfusion imaging can be performed on a high count rate PET system using a single-acquisition protocol. The administered activity requires optimization and we recommend 1110 MBq for PET MPI with a Biograph mCT.

Quantitative relationship between coronary artery calcium and myocardial blood flow by hybrid rubidium-82 PET/CT imaging in patients with suspected coronary artery disease

BackgroundWe assessed the relationship between coronary artery calcium (CAC) score, myocardial blood flow (MBF) and coronary flow reserve (CFR) in patients undergoing hybrid 82Rb positron emission tomography (PET)/computed tomography (CT) imaging for suspected CAD. We also evaluated if CAC score is able to predict a reduced CFR independently from conventional coronary risk factors.MethodsA total of 637 (mean age 58 ± 13 years) consecutive patients were studied. CAC score was measured according to the Agatston method and patients were categorized into 4 groups (0, 0.01-99.9, 100-399.9, and ≥400). Baseline and hyperemic MBF were automatically quantified. CFR was calculated as the ratio of hyperemic to baseline MBF and it was considered reduced when <2.ResultsGlobal CAC score showed a significant inverse correlation with hyperemic MBF and CFR (both P < .001), while no correlation between CAC score and baseline MBF was found. At multivariable logistic regression analysis age, diabetes and CAC score were independently associated with reduced CFR (all P < .001). The addition of CAC score to clinical data increased the global chi-square value for predicting reduced CFR from 81.01 to 91.13 (P < .01). Continuous net reclassification improvement, obtained by adding CAC score to clinical data, was 0.36.ConclusionsCAC score provides incremental information about coronary vascular function over established CAD risk factors in patients with suspected CAD and it might be helpful for identifying those with a reduced CFR.

Accurate markerless respiratory tracking for gated whole body PET using the Microsoft Kinect

The motion due to respiration is responsible for greatly reducing image quality of whole body positron emission tomography, PET. A simple method to produce a respiratory signal to enable gating of PET listmode data using the Microsoft Kinect, a consumer grade 3D scanner, is presented. Phantom data produced by a sinusoidally oscillating phantom being tracked by an existing commercially available respiratory monitoring system and a Kinect based contactless tracking system shows that the Kinect system outperforms the Varian RPM tracking by producing higher resolution traces. When testing the Kinect using human subjects, the collected surface trace is sensitive enough to detect the patients heart rate. This has potential for improving motion correction of whole body imaging by including extra surface information provided by the Kinect, in addition to the basic respiratory signal.

Myocardial perfusion scintigraphy using rubidium-82 positron emission tomography

INTRODUCTION Myocardial perfusion scintigraphy (MPS) is an established non-invasive technique for the diagnosis and management of patients with suspected or known coronary artery disease. Because of the wealth of prognostic data, MPS single photon emission computed tomography (SPECT) is the most commonly used functional test to detect inducible ischaemia. However, the increasing availability of positron emission tomography (PET) scanners for oncology along with the introduction of the generator-produced PET tracer rubidium-82 (⁸²Rb) has helped the growth of MPS PET. SOURCES OF DATA Relevant review articles, primary literature and clinical guidelines identified through medical literature search engines. AREAS OF AGREEMENT PET offers advantages over SPECT, including increased patient throughput because of rapid scanning protocols, reduced radiation exposure to patients and the ability to quantify tracer distribution accurately and hence measure myocardial perfusion in millilitre per gram per minute and hence myocardial perfusion reserve (MPR). AREAS OF CONTROVERSY Although PET has advantages over SPECT, there are no large-scale prognostic or cost-effectiveness data to support it use as the primary MPS technique. GROWING POINTS A wider use of absolute measurements of perfusion has the potential to improve diagnostic accuracy and to add prognostic value over relative assessment of myocardial perfusion. AREAS TIMELY FOR DEVELOPING RESEARCH Assessment of absolute myocardial perfusion may provide insight into the effects of traditional risk factors on perfusion reserve and the impact of risk factor modifications on progression of coronary artery disease.

Computed tomography automatic exposure control techniques in 18F-FDG oncology PET-CT scanning.

ObjectivesComputed tomography (CT) automatic exposure control (AEC) systems are now used in all modern PET-CT scanners. A collaborative study was undertaken to compare AEC techniques of the three major PET-CT manufacturers for fluorine-18 fluorodeoxyglucose half-body oncology imaging. Materials and methodsAn audit of 70 patients was performed for half-body CT scans taken on a GE Discovery 690, Philips Gemini TF and Siemens Biograph mCT (all 64-slice CT). Patient demographic and dose information was recorded and image noise was calculated as the SD of Hounsfield units in the liver. A direct comparison of the AEC systems was made by scanning a Rando phantom on all three systems for a range of AEC settings. ResultsThe variation in dose and image quality with patient weight was significantly different for all three systems, with the GE system showing the largest variation in dose with weight and Philips the least. Image noise varied with patient weight in Philips and Siemens systems but was constant for all weights in GE. The z-axis mA profiles from the Rando phantom demonstrate that these differences are caused by the nature of the tube current modulation techniques applied. The mA profiles varied considerably according to the AEC settings used. ConclusionCT AEC techniques from the three manufacturers yield significantly different tube current modulation patterns and hence deliver different doses and levels of image quality across a range of patient weights. Users should be aware of how their system works and of steps that could be taken to optimize imaging protocols.

A comparison between upright and supine myocardial perfusion imaging with attenuation correction.

ObjectiveThe Digirad Cardius XACT is an upright myocardial perfusion imaging (MPI) single photon emission computed tomography system offering low-dose computed tomography for attenuation correction (AC). This study compares patient acceptability and image appearance for both non-AC and AC images on the XACT with supine MPI performed on a GE Infinia Hawkeye. Patients and methodsA total of 47 patients [29 male patients; mean (range) BMI, 29.1 (21.0–57.5) kg/m2] referred for routine MPI underwent rest and stress MPI on the XACT and Infinia. Non-AC and AC bullseye plots were created and uptake scores were recorded in each of five segments. All studies were reported by an experienced observer with clinical details available. A patient questionnaire was used to determine the relative comfort with the two systems. ResultsPerfusion patterns on upright and supine non-AC images were significantly different and displayed a notable distinction between sexes. Perfusion patterns on upright and supine AC images were similar for both male and female patients, although some discrepancies between diagnostic reports still existed. A strong preference for upright imaging was demonstrated by the patient questionnaire. ConclusionChanges in soft-tissue and diaphragmatic attenuation between upright and supine MPI can be overcome with the addition of AC. However, clinicians should still ensure that they are aware of typical artefacts produced by upright and supine imaging.

Basic Principles of PET-CT Imaging

PET-CT imaging has become a very powerful tool in cancer imaging; it utilises the detection of the radiation emitted from radionuclides that decay by positron (β+) emission. This chapter looks into the physical principles of this technique, factors that affect the quality of the images produced and some of the artefacts and problems that may be encountered.

PET time-of-flight performance using analytic modeling and offset point-sources measurements

We present initial findings from performance testing of a time-of-flight (TOF) PET scanner with respect to the scanners TOF discriminatory power when compared with a theoretical model. A 2-D geometric model was produced to provide the difference in distance-of-flight of the two photons from a point source to the detector ring. The effectiveness of the discriminatory power was quantified by the percentage of events that were correctly assigned to the sinogram associated with the difference in TOF of the photons.