Biomedical subjects

R Jason Stafford

Publications and source records attributed to R Jason Stafford.

10 recordsLinked to original sources

PubMed2006

Specimen radiography in confirmation of MRI-guided needle localization and surgical excision of breast lesions.

OBJECTIVE: Confirmation of lesion retrieval after MRI-guided needle localization and surgical excision of breast lesions are difficult because the targeted lesion is not enhanced ex vivo. The aim of this study was to determine the feasibility of using specimen radiography to verify lesion removal after MRI-guided needle localization and surgical excision. CONCLUSION: To our knowledge, our study was the first to examine the use of specimen radiography in the localization and excision of breast lesions. Specimen radiography is a reliable, cost-effective alternative to repeated dynamic contrast-enhanced MRI for confirming lesion removal after surgery. Specimen radiography has the additional advantage of facilitating immediate assessment of surgical margins.

Biopsy, Needle↗

PubMed2005

A fast spin echo two-point Dixon technique and its combination with sensitivity encoding for efficient T2-weighted imaging.

A fast spin echo two-point Dixon (fast 2PD) technique was developed for efficient T2-weighted imaging with uniform water and fat separation. The technique acquires two interleaved fast spin echo images with water and fat in-phase and 180 degrees out-of-phase, respectively, and generates automatically separate water and fat images for each slice. The image reconstruction algorithm uses an improved and robust region-growing scheme for phase correction and achieves consistency in water and fat identification between different slices by exploiting the intrinsic correlation between the complex images from two neighboring slices. To further lower the acquisition time to that of a regular fast spin echo acquisition with a single signal average, we combined the fast 2PD technique with sensitivity encoding (SENSE). Phantom experiments show that the fast 2PD and SENSE are complementary in scan efficiency and signal-to-noise ratio (SNR). In vivo data from scanning of clinical patients demonstrate that T2-weighted imaging with uniform and consistent fat separation, including breath-hold abdominal examinations, can be readily performed with the fast 2PD technique or its combination with SENSE.

Abdomen↗

PubMed2005

Partially parallel imaging with phase-sensitive data: Increased temporal resolution for magnetic resonance temperature imaging.

Magnetic resonance temperature imaging can be used to monitor the progress of thermal ablation therapies, increasing treatment efficacy and improving patient safety. High temporal resolution is important when therapies rapidly heat tissue, but many approaches to faster image acquisition compromise image resolution, slice coverage, or phase sensitivity. Partially parallel imaging techniques offer the potential for improved temporal resolution without forcing such concessions. Although these techniques perturb image phase, relative phase changes between dynamically acquired phase-sensitive images, such as those acquired for MR temperature imaging, can be reliably measured through partially parallel imaging techniques using reconstruction filters that remain constant across the series. Partially parallel and non-accelerated phase-difference-sensitive data can be obtained through arrays of surface coils using this method. Average phase differences measured through partially parallel and fully Fourier encoded images are virtually identical, while phase noise increases with g(sqrt)L as in standard partially parallel image acquisitions..

Animals↗

PubMed2004

Silicone-specific imaging using an inversion-recovery-prepared fast three-point Dixon technique.

PURPOSE: To demonstrate a new hybrid magnetic resonance imaging (MRI) technique capable of simultaneously generating water-specific and silicone-specific images in a single acquisition. MATERIALS AND METHODS: This technique combines short TI inversion-recovery (STIR) technique for robust fat suppression with an efficient fast spin-echo-based three-point Dixon technique for robust separation of remaining water and silicone in the presence of field inhomogeneities. Images demonstrating the feasibility of the technique were acquired with a 1.5-Tesla scanner in a phantom and in a volunteer with both saline and silicone implants in vivo. RESULTS: The new technique provided water-specific and silicone-specific images of diagnostic quality. Separation of the water and silicone chemical species was complete and satisfactory. Compared with a chemical shift-selective technique, the new technique does not rely heavily on field homogeneity and requires the same or even less scan time to acquire images with similar scan parameters, resolution, and signal-to-noise ratio (SNR). CONCLUSION: The feasibility and potential application of the new technique were demonstrated via imaging a phantom and a silicone breast prosthesis in vivo, and it may be used for more consistent imaging of the silicone implants without compromising the image quality or overall scan time.

Adipose Tissue↗

PubMed2004

Interleaved echo-planar imaging for fast multiplanar magnetic resonance temperature imaging of ultrasound thermal ablation therapy.

PURPOSE: To develop a multiplanar magnetic resonance temperature imaging (MRTI) technique based on interleaved gradient-echo echo-planar imaging (EPI), verify in phantom, develop software tools to process and display data on a clinical scanner in near real-time, and demonstrate feasibility to monitor ultrasound thermal ablation therapy in vivo. MATERIALS AND METHODS: Temperature estimation used complex phase-difference subtraction of the EPI MRTI data to indirectly measure the temperature-dependent water proton-resonance-frequency shift. Software tools were developed to run on a clinical 1.5-T MR scanner that processed and displayed relevant temperature and thermal dosimetry data during the course of thermal ablation treatments in canine brain and prostate in vivo. RESULTS: EPI MRTI provided multi-planar acquisitions and increased temperature sensitivity and lipid suppression. Relative to a single-plane fast gradient-echo MRTI sequence at comparable spatial and temporal resolutions in phantom, EPI MRTI demonstrated a three-fold increase in sensitivity and slice coverage per TR. In vivo monitoring of ultrasound thermal ablation therapy in canine brain and prostate demonstrated the usefulness of the temperature and thermal dose information. CONCLUSION: Multi-planar MRTI allowed progression of thermal damage to be monitored and treatment parameters adjusted in near real-time (less than five second delay). EPI MRTI is an effective multi-planar monitoring method during ultrasound thermal ablation procedures.

Animals↗

PubMed2003

Dynamic gadolinium uptake in thermally treated canine brain tissue and experimental cerebral tumors.

RATIONALE AND OBJECTIVES: Thermal coagulation of cerebral tumors induces reactive changes within adjacent brain tissue, which appear as Gd-DTPA enhancement in MR images. This makes assessment of therapeutic success difficult to establish radiographically because the reactive changes can mimic residual tumor. Dynamic Gd-DTPA uptake curves in reactive tissue and tumor were investigated to assess the utility of contrast enhanced (CE)-dynamic MRI to distinguish reactive changes from residual tumor in a canine model. MATERIALS AND METHODS: Cerebral thermal necrosis was induced using a 980 nm laser in 11 dogs with intracerebral transmissible venereal tumors (TVTs). A fast spin-echo T1-weighted imaging sequence was used for CE-dynamic MRI. Gd-DTPA uptake data were acquired with 10-second temporal resolution and for untreated TVTs for reactive tissue using a sigmoidal-exponential model. RESULTS: Characteristic gadolinium uptake curves were measured and characterized for reactive brain tissue, and untreated and treated TVTs. Both early and delayed dynamic responses were significantly different in reactive brain tissue compared with TVT. CONCLUSION: Reactive thermal changes in otherwise normal brain tissue can be distinguished from residual tumor after cerebral thermal therapy using CE-dynamic MRI.

Animals↗

PubMed2002

Magnetic resonance imaging-guided focused ultrasound thermal therapy in experimental animal models: correlation of ablation volumes with pathology in rabbit muscle and VX2 tumors.

PURPOSE: To further investigate the use of magnetic resonance-guided focused ultrasound therapy (MRgFUS) as a noninvasive alternative to surgery in the local control of soft-tissue tumors by ablating prescribed volumes of VX2 rabbit tumors and comparing with ablation of normal tissue volumes. MATERIALS AND METHODS: Small, ellipsoidal ablations at shallow depth were created using 5- to 15-second sonication pulses at radio frequency (RF) powers of 50-125 W using a spherical, air-backed transducer operating at 1.463 MHz under MR guidance in a 1.5-T clinical scanner. RESULTS: Excellent correlation was observed between prescribed treatment volumes, MR thermal dosimetry, post-treatment verification MRI, and histopathology. Multifocal ablations of VX2 tumors in rabbits at depths of up to 2.5 cm resulted in complete ablation of the prescribed treatment volume. CONCLUSION: MRgFUS is an effective technique for treating tumors in vivo. Techniques developed for treatments in homogeneous tissue volumes are applicable in the more complicated tumor environment if MR temperature feedback is available to modify treatment delivery parameters.

Animals↗

PubMed2002

MRI-guided thermal therapy of transplanted tumors in the canine prostate using a directional transurethral ultrasound applicator.

PURPOSE: To evaluate MRI-based techniques for visual guidance, thermal monitoring, and assessment during transurethral ultrasound thermal therapy of implanted tumors in an in vivo canine prostate model. MATERIALS AND METHODS: Transmissible venereal tumors (TVT) were grown in the right lobe of the prostate in four dogs. High-temperature thermal therapy was selectively applied to the tumor-bearing lobe using a transurethral ultrasound applicator with a 180 degrees directional heating pattern. Temperature-sensitive MRI (MRTI) using a fast interleaved gradient-echo echo-planar (iGE-EPI) imaging sequence was used for cumulative thermal dose calculations in multiple image planes during the treatment. The results from MRTI-based dose maps and post-treatment MRI were compared to those from histologic analysis. RESULTS: MRTI monitoring in multiple planes across the prostate guided the use and control of a directive ultrasound applicator for the selective ablation of the sections of the prostate that contained implanted tumors. Findings in gadolinium enhanced MRI obtained immediately after thermal therapy slightly underestimated the size of tissue necrosis after treatment, as verified by histopathologic analysis. CONCLUSION: The use of multiplanar MRTI with a transurethral ultrasound applicator shows significant potential for selective thermal ablation of prostate tumor and tissue.

Animals↗

PubMed2002

Multiplanar MR temperature-sensitive imaging of cerebral thermal treatment using interstitial ultrasound applicators in a canine model.

PURPOSE: To study the feasibility of an interleaved gradient-echo, echo-planar imaging (iGE-EPI) sequence for multiplanar magnetic resonance temperature imaging (MRTI) to monitor intracerebral thermal treatment three-dimensionally using multielement ultrasound applicators. MATERIALS AND METHODS: Transmissible venereal tumor (TVT) fragments were injected into the right cerebral hemisphere of five dogs. Guided by MRI, an interstitial ultrasound applicator was inserted into the tumor or normal brain tissue. The iGE-EPI sequence was used to estimate temperature changes by computing the complex phase-difference induced by temperature-dependent shifts in the proton resonance frequency of water. The thermal dose maps were updated every 6-8 seconds for five to seven image planes during treatment. The results of MRTI were compared with those of post-treatment MRI and histologic analysis. RESULTS: The multiplanar MRTI monitored temperature and thermal dose distributions in tumor and normal brain tissue over the entire user-defined treatment volume. The ultrasound applicators produced contiguous areas of coagulative necrosis, resulting in 1.5-4.0 cm(3) volumes of tissue necrosis. MRTI-based assessments of thermal-dose distributions were consistent with the results of post-treatment MRI and histologic analysis. CONCLUSION: Multiplanar MRTI is feasible for measuring necrosing thermal doses during intracerebral thermal delivery by interstitial ultrasound applicators.

Animals↗

PubMedDate not supplied

Optimizing heat shock protein expression induced by prostate cancer laser therapy through predictive computational models.

Thermal therapy efficacy can be diminished due to heat shock protein (HSP) induction in regions of a tumor where temperatures are insufficient to coagulate proteins. HSP expression enhances tumor cell viability and imparts resistance to chemotherapy and radiation treatments, which are generally employed in conjunction with hyperthermia. Therefore, an understanding of the thermally induced HSP expression within the targeted tumor must be incorporated into the treatment plan to optimize the thermal dose delivery and permit prediction of the overall tissue response. A treatment planning computational model capable of predicting the temperature, HSP27 and HSP70 expression, and damage fraction distributions associated with laser heating in healthy prostate tissue and tumors is presented. Measured thermally induced HSP27 and HSP70 expression kinetics and injury data for normal and cancerous prostate cells and prostate tumors are employed to create the first HSP expression predictive model and formulate an Arrhenius damage model. The correlation coefficients between measured and model predicted temperature, HSP27, and HSP70 were 0.98, 0.99, and 0.99, respectively, confirming the accuracy of the model. Utilization of the treatment planning model in the design of prostate cancer thermal therapies can enable optimization of the treatment outcome by controlling HSP expression and injury.

Animals↗