Supervising the Supervisors—Procedural Training and Supervision in Internal Medicine Residency

At teaching hospitals, bedside procedures (paracentesis, thoracentesis, lumbar puncture, arthrocentesis and central venous catheter insertion) are performed by junior residents and supervised by senior peers. Residents’ perceptions about supervision or how often peer supervision produces unsafe clinical situations are unknown. To examine the experience and practice patterns of residents performing bedside procedures. Cross-sectional e-mail survey of 653 internal medicine (IM) residents at seven California teaching hospitals. Surveys asked questions in three areas: (1) resident experience performing procedures: numbers of procedures performed and whether they received other (e.g., simulator) training; (2) resident comfort performing and supervising procedures; (3) resident reports of their current level of supervision doing procedures, experience with complications as well as perceptions of factors that may have contributed to complications. Three hundred sixty-seven (56%) of the residents responded. Most PGY1 residents had performed fewer than five of any of the procedures, but most PGY-3 residents had performed at least ten by the end of their training. Resident comfort for each procedure increased with the number of procedures performed (p < 0.001). Although residents reported that peer supervision happened often, they also reported high rates of supervising a procedure before feeling comfortable with proper technique. The majority of residents (64%) reported at least one complication and did not feel supervision would have prevented complications, even though many reported complications represented technique- or preparation-related problems. Residents report low levels of comfort and experience with procedures, and frequently report supervising prior to feeling comfortable. Our findings suggest a need to examine best practices for procedural supervision of trainees

A Method for Determination of the Timing Stability of PET Scanners

Abstract—We report on the timing resolution and stability of the MicroPET R4 PET scanner. Its detectors have energy resolutions in the range of 25 % and previously reported timing resolutions 3.2 ns. Our preliminary evaluation of this instrument showed that artefact-free normalization sinograms could only be obtained with a timing window of 10 ns or more in spite of a timing resolution of 3.2 ns. This instrument uses high-speed electronics albeit with 2-ns timing clock. We performed sham transmission scans with nothing in the field of view, and a range of timing windows from 2 to 14 ns and used a 14-ns timing blank scan to generate effective attenuation sinograms as a function of timing window. These showed trues count-rates which fit well to a ERF @ A function. However, the effective attenuation value, which should be 1.0, changes from block to block and becomes very high in some blocks ( 3.5 at 6 ns) suggesting the need for timing alignment. A method was devised to measure the timing stability to a precision better than the timing bin width of 2 ns. Index Terms—Positron emission tomography, timing alignment, timing stability, time-of-flight. I

Do Epilepsy Patients with Cognitive Impairment Have Alzheimer’s Disease-like Brain Metabolism?

Although not classically considered together, there is emerging evidence that Alzheimer’s disease (AD) and epilepsy share a number of features and that each disease predisposes patients to developing the other. Using machine learning, we have previously developed an automated fluorodeoxyglucose positron emission tomography (FDG-PET) reading program (i.e., MAD), and demonstrated good sensitivity (84%) and specificity (95%) for differentiating AD patients versus healthy controls. In this retrospective chart review study, we investigated if epilepsy patients with/without mild cognitive symptoms also show AD-like metabolic patterns determined by the MAD algorithm. Scans from a total of 20 patients with epilepsy were included in this study. Because AD diagnoses are made late in life, only patients aged ≥40 years were considered. For the cognitively impaired patients, four of six were identified as MAD+ (i.e., the FDG-PET image is classified as AD-like by the MAD algorithm), while none of the five cognitively normal patients was identified as MAD+ (χ2 = 8.148, p = 0.017). These results potentially suggest the usability of FDG-PET in prognosticating later dementia development in non-demented epilepsy patients, especially when combined with machine learning algorithms. A longitudinal follow-up study is warranted to assess the effectiveness of this approach

Evaluation of very highly pixellated crystal blocks with SiPM readout as candidates for PET/MR detectors in a small animal PET insert

Arrays of silicon photo-multipliers (SiPMs) are good candidates for the readout of detectors in PET MR inserts due to their high packing density, efficiency, low bias voltage and insensitivity to magnetic fields. In this study we report the readout performance of SensL SiPM arrays in terms of their ability to resolve all elements of pixellated lutetium oxyorthosilicate (LYSO) crystals their energy resolution, and coincidence response function. Two SensL SPMarray-4 were used as light sensors. Two LYSO crystal blocks consisting of a arrays of 8 78 1.2 mm 7 1.2 mm 7 6.0 mm crystals on the lower layer and 7 77 1.2 mm 7 1.2 mm 7 4.0 mm crystals on the upper layer (which is offset by 1/2 the crystal width) were mounted on the SensL arrays. A second study was performed with single layer arrays of 8 78 1.2 mm 7 1.2 mm 7 10.0 mm crystals. All of the crystals in the dual layer block were easily identified with a peak to valley ratio of 7.2 while the single layer blocks had a peak to valley ratio of 11.2. The crystal dots were more uniformly spaced in the dual layer arrays suggesting that the inter-layer connection affords some useful light sharing. The average energy resolution for all 113 crystals was 16.3\ub12.3%. The coincidence response to a 0.25 mm Na-22 source in plastic was 0.97 \ub10.12 mm for normally incident gamma rays with the detectors 120 mm apart. These results indicate that it should be possible to achieve a spatial resolution of about one millimetre near the center of the field of view. \ua9 2012 IEEE.Peer reviewed: YesNRC publication: Ye

Simulation guided optimization of Dual Layer Offset detector design for use in small animal PET

A small animal PET insert for use inside of a small MR bore is currently in the design phase. The small diameter of the tomograph results in an increased need to collect Depth of Interaction (DOI) information to mitigate the parallax error. The tomograph will use a Dual Layer Offset block design to collect DOI information. Of critical importance to the design of the block is the depth into the block where the front layer is separated from the back layer. With the total thickness of scintillating crystal limited to 10 mm, GATE simulations with a single block were run with the front layer thickness ranging from 1 mm to 10 mm (single layer). These simulations characterized the block's ability to accurately locate the radial coordinate of the first interaction location of a `single'. It was found that a split between front and back that is roughly even minimized the mispositioning of the radial coordinate of first interaction. To estimate the reconstructed resolution and resolution uniformity obtainable with this block design, coincidence data from a full tomograph were simulated. Data were reconstructed using Filtered Back Projection. Data were also reconstructed with the DOI information discarded to estimate the improvement in resolution uniformity obtained with this block design.Peer reviewed: YesNRC publication: Ye

Evaluation of high density pixilated crystal blocks with SiPM readout as candidates for PET/MR detectors in a small animal PET insert

Arrays of silicon photo-multipliers (SiPMs) are good candidates for the readout of detectors in PET/MR inserts due to their high packing density, efficiency, low bias voltage and insensitivity to magnetic fields. We tested individual dual-layer blocks of pixilated lutetium oxy-orthosilicate (LYSO) coupled to SensL 4 74 SiPM arrays in terms of their ability to resolve all elements using resolvability index (RI) defined by the FWHM of the crystal response function divided by the separation. Our crystal blocks had 49 1.67 7 1.67 7 6.0 mm\ub3 crystals on the bottom layer and 36 1.67 7 1.67 7 4.0 mm\ub3 crystals in the top layer which was offset by \ubd of the crystal pitch. All 85 crystals were well resolved: RI=0.46 compared with RI=.41 for a conventional pre-clinical PET scanner's block with 40% lower crystal density. A pair of crystal blocks mounted on translation stages scanned a 0.25 mm \ub2\ub2Na source in 60 0.25 mm steps with the detectors angulated as if there were 16 blocks in a ring. The FWHM near the centre of the field of view was 1.31 mm and FWTM was 2.7 mm.Peer reviewed: YesNRC publication: Ye

Development of a PET Scanner for Simultaneously Imaging Small Animals with MRI and PET

Recently, positron emission tomography (PET) is playing an increasingly important role in the diagnosis and staging of cancer. Combined PET and X-ray computed tomography (PET-CT) scanners are now the modality of choice in cancer treatment planning. More recently, the combination of PET and magnetic resonance imaging (MRI) is being explored in many sites. Combining PET and MRI has presented many challenges since the photo-multiplier tubes (PMT) in PET do not function in high magnetic fields, and conventional PET detectors distort MRI images. Solid state light sensors like avalanche photo-diodes (APDs) and more recently silicon photo-multipliers (SiPMs) are much less sensitive to magnetic fields thus easing the compatibility issues. This paper presents the results of a group of Canadian scientists who are developing a PET detector ring which fits inside a high field small animal MRI scanner with the goal of providing simultaneous PET and MRI images of small rodents used in pre-clinical medical research. We discuss the evolution of both the crystal blocks (which detect annihilation photons from positron decay) and the SiPM array performance in the last four years which together combine to deliver significant system performance in terms of speed, energy and timing resolution.Medicine, Faculty ofScience, Faculty ofNon UBCPhysics and Astronomy, Department ofRadiology, Department ofReviewedFacult

Assessment of three techniques for delivering stem cells to the heart using PET and MR imaging

Background: Stem cell therapy has a promising potential for the curing of various degenerative diseases, including congestive heart failure (CHF). In this study, we determined the efficacy of different delivery methods for stem cell administration to the heart for the treatment of CHF. Both positron emission tomography (PET) and magnetic resonance imaging (MRI) were utilized to assess the distribution of delivered stem cells. Methods: Adipose-derived stem cells of male rats were labeled with super-paramagnetic iron oxide (SPIO) and 18 F-fluorodeoxyglucose (FDG). The left anterior descending coronary artery (LAD) of the female rats was occluded to induce acute ischemic myocardial injury. Immediately after the LAD occlusion, the double-labeled stem cells were injected into the ischemic myocardium (n = 5), left ventricle (n = 5), or tail vein (n = 4). In another group of animals (n = 3), the stem cells were injected directly into the infarct rim 1 week after the LAD occlusion. Whole-body PET images and MR images were acquired to determine biodistribution of the stem cells. After the imaging, the animals were euthanized and retention of the stem cells in the vital organs was determined by measuring the cDNA specific to the Y chromosome. Results: PET images showed that retention of the stem cells in the ischemic myocardium was dependent on the cell delivery method. The tail vein injection resulted in the least cell retention in the heart (1.2% \ub1 0.6% of total injected cells). Left ventricle injection led to 3.5% \ub1 0.9% cell retention and direct myocardial injection resulted in the highest rate of cell retention (14% \ub1 4%) in the heart. In the animals treated 1 week after the LAD occlusion, rate of cell retention in the heart was only 4.5% \ub11.1%, suggesting that tissue injury has a negative impact on cell homing. In addition, there was a good agreement between the results obtained through PET-MR imaging and histochemical measurements. Conclusion: PET-MR imaging is a reliable technique for noninvasive tracking of implanted stem cells in vivo. Direct injection of stem cells into the myocardium is the most effective way for cell transplantation to the heart in heart failure models.Peer reviewed: YesNRC publication: Ye