Uh oh, the boot drive on the computer at home has decided to disappear. I don’t know if it was something I did when I put in a new DVD drive, or if it just happened to be a coincidence. BIOS claims there’s nothing attached to any of the on-board IDE channels, so it’s either a problem with the cabling, the drive or the motherboard is pooched. Computer POSTs fine, so I don’t think it’s the motherboard. I may have knocked something loose putting in the drive.
Time to crack the case open again and check things out.
Maybe it’ll still get accepted
Got my hands on a copy of the paper that beat mine to publication.
The end result they come up with is the same as mine, although their work was done on just one gamma camera and had a little more focus on image quality than mine did. I was able to do some cross-camera comparisons with my data and had a little more analysis on the core question (is T1/2 the same between collimators). I think mine still has a good chance of being published. Hopefully the reviewers will also think it’s a worthy addition to this other paper. I just won’t have first post bragging rights.
Journal Club: Simultaneous Acquisition of Multislice PET and MR Images: Initial Results with a MR-Compatible PET Scanner
Today’s journal club article comes from JNM and talks about some new bleeding-edge tech alluded to in the previous journal club article: PET and MRI.
The technology presented in the paper is pretty bleeding edge and represents 2 years of instrumentation and development work. They present a prototype PET unit for use in a small animal MR magnet operating at 7T. Their solution to solving the problem of detecting light from the scintillator crystals was to use position sensitive photodiodes, which are less prone to distortions from magnetic field effects. In order to reduce electrical noise in the detectors, the authors used a cold nitrogen gas to cool the detectors. This is understandably a significant limitation for real world clinical work, but not insurmountable. Several interesting effects were noted with using the photodiodes and fiberoptic coupling and are nicely illustrated with sample images.
Some very interesting development work here that shows a lot of potential. It’s not the first PET/MRI hybrid unit developed or the only one being worked on, but the design and implementation the authors have come up with has the potential of retrofitting existing MR scanners with the capability rather than having to get a new magnet. Obviously it’s still several years away from any kind of implementation for human use, but in the meantime a working unit for small animal imaging would probably yield some very useful information for researchers.
Ciprian Catana, Yibao Wu, Martin S. Judenhofer, Jinyi Qi, Bernd J. Pichler and Simon R. Cherry, “Simultaneous Acquisition of Multislice PET and MR Images: Initial Results with a MR-Compatible PET Scanner“, J Nucl Med 47: 1968-1976
Abstract:
PET and MRI are powerful imaging techniques that are largely complementary in the information they provide. We have designed and built a MR-compatible PET scanner based on avalanche photodiode technology that allows simultaneous acquisition of PET and MR images in small animals.
Methods: The PET scanner insert uses magnetic field-insensitive, position-sensitive avalanche photodiode (PSAPD) detectors coupled, via short lengths of optical fibers, to arrays of lutetium oxyorthosilicate (LSO) scintillator crystals. The optical fibers are used to minimize electromagnetic interference between the radiofrequency and gradient coils and the PET detector system. The PET detector module components and the complete PET insert assembly are described. PET data were acquired with and without MR sequences running, and detector flood histograms were compared with the ones generated from the data acquired outside the magnet. A uniform MR phantom was also imaged to assess the effect of the PET detector on the MR data acquisition. Simultaneous PET and MRI studies of a mouse were performed ex vivo.
Results: PSAPDs can be successfully used to read out large numbers of scintillator crystals coupled through optical fibers with acceptable performance in terms of energy and timing resolution and crystal identification. The PSAPD-LSO detector performs well in the 7-T magnet, and no visible artifacts are detected in the MR images using standard pulse sequences.
Conclusion: The first images from the complete system have been successfully acquired and reconstructed, demonstrating that simultaneous PET and MRI studies are feasible and opening up interesting possibilities for dual-modality molecular imaging studies.
The perils of procrastinating
So it seems a group of people at Ottawa Hospital in Ontario has just had a paper published in JNMT that covers pretty much the same material I worked on and just submitted to the same journal. My contact at GSK told me it was something they also sponsored (like my project), but wasn’t aware they had submitted it for publication.
Trying to get my hands on a copy of the article so I can read it and see what they looked at. Fortunately they come up with the same conclusions and results I did. From the abstract it seems like some of the things they investigated were different from what I looked at, so hopefully it’s different enough from mine that the reviewers decide it’s still worthy of publication.
My abstract:
Objective: Residence time measurements obtained by serial whole body conjugate view imaging are commonly used in patient specific dosimetry for radioimmunotherapy (RIT) applications. In order to determine the effect of collimator selection on residence time measurements for 131I, the accuracy of 131I half-life measurements using multiple gamma camera and collimator combinations was investigated. Method: Serial anterior and posterior whole body images were acquired over a period of 15 days using 4 different gamma cameras with medium and/or high energy collimators. Background corrected geometric mean counts from the images were fitted to a mono-exponential curve to determine the half-life of 131I for the different gamma camera/collimator combinations. Results: An average half-life of 8.15 days with a standard deviation (SD) of 0.07 days was obtained from all camera/collimator combinations. A half life of 8.12 days (SD 0.11 d) was obtained for the high energy collimators, and 8.18 d (SD 0.04 d) for the medium energy collimators. These values are all very close to the 8.02 day 131I physical half-life and were not found to be statistically different (p=0.44). Similar results were also obtained for the measured half-life for single head gamma camera configurations (mean half life 8.15 d, SD 0.12 d). The therapeutic 131I-tositumomab dose resulting from the differences in measured half-life ranged between 2.58–2.6 GBq (69.8–70.4 mCi). Conclusion: There is no significant difference in 131I half-life and residence time measurements made using medium or high energy collimators in dual head or single head imaging configurations.
Their abstract:
131I-Tositumomab has been used in treating patients with non-Hodgkin’s lymphoma. It is generally recommended that high-energy collimators be used to image patients before they receive 131I-tositumomab therapy, to determine the effective half-life for therapeutic dose and gross biodistribution. Because many nuclear medicine departments do not possess high-energy collimators, this study was designed to assess the suitability of using medium-energy collimators. The effect of scanning speed was also investigated, in an attempt to optimize the acquisition time. Methods: Measurements were taken using an elliptic anthropomorphic torso phantom and an organ-scanning phantom fitted with fillable spheres (1-5 cm in diameter) and organ inserts. Three phantom studies were performed with differing initial 131I concentrations in the organs, the spheres, and the thoracic and abdominal chambers. Images were acquired with both high-energy and medium-energy collimators and at acquisition speeds of 20 and 100 cm/min. The half-life for each combination (study/collimator/speed) was calculated from a linear fit of the data. The contrast of the tumor sphere was assessed using 2 identical regions, placed on and beside the sphere, and averaged over several time points. Biodistribution and image quality were visually assessed by 2 independent observers. Results: Measured half-life values and visual assessment of biodistribution showed no significant difference between the 2 collimators (P = 0.32) or acquisition speeds (P = 0.85). A significant difference in the contrast of the tumor spheres was observed between the 2 collimators (P < 0.01) but not between acquisition speeds. Visual assessment of the images showed increased noise on the image acquired at 100 cm/min, although this noise did not affect lesion detectability. Conclusion: Measured half-life is not significantly different between the 2 collimators; hence, calculation of the residence time would be nearly the same. Medium-energy collimators can be used to accurately calculate the 131I-tositumomab therapeutic dose and detect alterations in biodistribution.
Food meme
Nabbed from Heather who nabbed it from Mike
Favorite food to crunch: Corn nuts
Favorite comfort food: Rice porridge (congee)
Food that makes the best noise: Anything that sizzles on a hot pan
Favorite picnic lunch: Sammiches
Favorite food scene in a movie: The segment in Eat Drink Man Woman where the dad spends the whole morning making up dim sum dishes
Favorite food lyrics: Peaches by Presidents of the USA
Least favorite food lyrics: Can’t think of any
Best food smell memory: The smells inside a real Chinese restaurant (not the cheesy Chinese buffet places).
Favorite summer snack: Strawberries
Food that reminds me of the ocean: Anything fish.
Favorite winter snack: Hot chocolate.
Most likely Favorite thing to eat for lunch: Chili and fries
Least likely to eat for lunch: Liver and onions in the cafeteria.
Makes me gag: Cilantro
Food tradition I don’t like: Anything made with bean paste
Saturday night food: Don’t really have any regular saturday night foods.
Favorite wild foods: Any kind of Pacific Salmon
Favorite medicinal food: Honey
Food that reflects my heritage: Dim sum
Food most like me: Chocolate. Simple, sweet and melts when warm.
Favorite raw food smell: Does chocolate count as a raw food?