Jeffrey H. Yanof

CT and Ultrasound Guided Stereotactic High Intensity Focused Ultrasound (HIFU)

To demonstrate the feasibility of CT and B‐mode Ultrasound (US) targeted HIFU, a prototype coaxial focused ultrasound transducer was registered and integrated to a CT scanner. CT and diagnostic ultrasound were used for HIFU targeting and monitoring, with the goals of both thermal ablation and non‐thermal enhanced drug delivery. A 1 megahertz coaxial ultrasound transducer was custom fabricated and attached to a passive position‐sensing arm and an active six degree‐of‐freedom robotic arm via a CT stereotactic frame. The outer therapeutic transducer with a 10 cm fixed focal zone was coaxially mounted to an inner diagnostic US transducer (2–4 megahertz, Philips Medical Systems). This coaxial US transducer was connected to a modified commercial focused ultrasound generator (Focus Surgery, Indianapolis, IN) with a maximum total acoustic power of 100 watts. This pre‐clinical paradigm was tested for ability to heat tissue in phantoms with monitoring and navigation from CT and live US. The feasibility of navigatio...

Is coronary stent assessment improved with spectral analysis of dual energy CT

RATIONALE AND OBJECTIVES The aims of this study were to distinguish stents from iodinated contrast on the basis of spectral characteristics on dual-energy computed tomographic (DECT) imaging and to determine whether DECT imaging might provide a more accurate measurement of true stent lumen. MATERIALS AND METHODS Three stainless steel stents and one cobalt chromium stent were scanned using a multidetector, single-source DECT scanner. Stents 2.5, 3.5, and 4.0 mm in diameter were filled with iodinated contrast, submerged in water, and scanned. Spectral analysis was performed to assess the separation of stents from iodinated contrast. Two independent reviewers measured stent lumen diameter and strut thickness on low-energy (L(0)), high-energy (L(1)), and combined-energy (L(c)) images. Dual-energy full-width half-maximum edge detection analysis was used to provide an independent assessment of stent luminal diameter and strut thickness. RESULTS Two-dimensional graphical plots of computed tomographic attenuation for the L(0) and L(1) images did not demonstrate a sharp separation between the absorption characteristics of stents and iodinated contrast material. Stent lumens were underestimated by approximately 50% on L(c) images. Observer measurements on L(1) images demonstrated a 24% decrease in strut thickness and a 25% increase in stent luminal diameter compared to L(0) images (P < .0001). Full-width half-maximum measurements did not demonstrate significant changes in stent luminal diameters or strut thicknesses between L(0) and L(1) images. CONCLUSIONS Spectral analysis did not clearly distinguish stents from iodinated contrast with the DECT system used in this study. The larger stent lumens visualized by the high-energy components of the x-ray spectrum were not related to improved computed tomographic delineation of stent thickness.

Individualized radiation dose control in 256-slice CT coronary angiography (CTCA) in retrospective ECG-triggered helical scans: Using a measure of body size to adjust tube current selection

PURPOSE To reduce radiation dose for retrospective ECG-triggered helical 256-slice CTCA by determining an optimal body size index to prospectively adjust tube current. METHODS 102 consecutive patients with suspected CAD underwent retrospective ECG-triggered CTCA using 256-slice CT scanner. Six body size indexes including BMI, nipple level (NL) bust, thoracic anteroposterior diameter at NL, chest circumference (CC) at NL, left main and right coronary artery (RCA) origin level were measured and their correlation with noise was evaluated using linear regression. An equation was developed to use this index to adjust tube current. Additional 102 consecutive patients were scanned with the index-based mAs adjustment. A t-test for independent samples was used to compare radiation dose levels with and without the index-based mAs selection method. RESULTS Linear regression indicated that CC RCA had the best correlation with noise (R2=0.603). Effective radiation dose was reduced from 16.6±0.9 to 9.8±2.7 mSv (p<0.01), i.e. 40.9% lower dose with the CC RCA-adapted tube current method. The image quality scores indicated no significant difference with and without the size-based mAs selection method. CONCLUSION An accessible measure of body size, such as CC RCA, can be used to adapt tube current for individualized radiation dose control.

CT Radiation Dose: Philips Perspective

Fulfilling the demand for effective diagnostic and therapeutic information has led to a steady increase in the use of computed tomography (CT). With this trend, CT departments strive to scan with the “As Low As Reasonably Achievable” (ALARA) principle; however, its practice varies significantly among sites and scanners servicing an ever-widening range of clinical indications and patient populations. Philips strategies for simplifying CT dose management are described. Multiple components of the Philips CT imaging chain have been designed to increase volume imaging speed, dose efficiency, and image quality, thereby enabling opportunities for lower dose scan protocols and helping to achieve doses ALARA. In addition, nine seamlessly integrated protocol-driven and patient-adaptive technologies including DoseRight Automatic Current Selection, DoseRight dose modulation, DoseRight Cardiac, Step & Shoot, IntelliBeam Filters, SmartShape Wedge (bowtie) Filters, Eclipse DoseRight collimator, and iDose4 Iterative Reconstruction Technique are described. These combined technologies automatically use the quantity and quality of radiation where and when needed, leading to image quality improvements and dose reductions. Combining Philips’ dose optimized CT imaging chain with automatic dose optimization tools begins a new era where expanding multi-detector CT will be fueled not only by increasing clinical benefits, but also by easily lowering dose to levels not previously possible for broader patient populations.

Image-Guided Therapy (IGT): New CT and Hybrid Imaging Technologies

Integrated multi-modality IGT prototypes are described for IR and OR suites of the future including procedures guided with CT and hybrid imaging devices. Radiofrequency Ablation (RFA) is an exemplary application, and the prototypes can be adapted to other procedures. To investigate pre-planning 1 , a software prototype enables virtual electrode placement. Intra-procedurally, a CT-integrated robot aligns its laser to planned trajectories. Interventional tools and mini-imaging devices are registered to imagers and 3-D data sets by attaching them as robot hands, or by tracking them with electromagnetic or optical systems. Tissue response is monitored with new 3-D real-time imaging. The ultimate goal is to simplify treatment and provide benefit to the patient.