The proton resonance frequency (PRF) shift provides a means of measuring temperature changes during minimally invasive thermotherapy. However, conventional PRF thermometry relies on the subtraction of baseline images, which makes it sensitive to tissue motion and frequency drift during the course of treatment. In this study, a new method is presented that eliminates these problems by estimating the background phase from each acquired image phase. In this referenceless method, a polynomial is fit to the background phase outside the heated region in a weighted least-squares fit. Extrapolation of the polynomial to the heated region serves as the background phase estimate, which is then subtracted from the actual phase. Minimally invasive thermal therapy is a promising treatment for a variety of cancers. It is desirable to monitor temperature during such a procedure by magnetic resonance proton resonance frequency (PRF) shift thermometry (1,2) because it provides quantitative temperature information in near real time. This method uses changes in the phase of gradient-recalled echo (GRE) images to estimate the relative temperature change ⌬T, as given bywhere ␣ ϭ -0.01 ppm/°C is the PRF change coefficient for aqueous tissue, ␥ is the gyromagnetic ratio, B 0 is the main magnetic field, TE is the echo time, and baseline is the initial phase before heating. In conventional PRF shift thermometry, phase images acquired prior to heating (i.e., baseline or reference images) are subtracted from phase images acquired during heating. However, when tissue motion is present, images acquired during heating are not registered to the baseline images, and the background magnetic field changes nonuniformly, resulting in erroneous baseline phase elimination and inaccurate temperature measurements. Many of the target areas for thermotherapy are in the abdomen, where motion is ubiquitous. For example, motion of the liver has an average amplitude of 1.3 cm during normal breathing (3). Because thermal therapy treatments require several minutes to perform, they cannot be performed in a single breath-hold. Furthermore, it is difficult to use multiple breath-holds, because reproducible breathholding is hard to achieve. Even without respiratory motion, displacement between images can occur. Thermal coagulation leads to structural changes and deformation of the tissue (4,5), which can even be observed ex vivo without any other contribution to motion. This heating-induced tissue motion is frequently not a simple displacement, and, unlike respiration, it cannot be corrected by a reregistration scheme. Swelling caused by the formation of edema can also contribute to tissue displacement (6), as can changes in bowel-filling and the state of muscles. For example, we have measured shifts in the canine prostate of Ͼ5 mm over the course of a 48-min ablation experiment.In recent studies, investigators have used conventional respiratory gating in animals under general anesthesia and mechanical respiration (7,8) to overcome the problem of motion in thermal...

Transurethral ultrasound applicators with highly directional energy deposition and rotational control were investigated for precise treatment of benign prostatic hyperplasia (BPH) and adenocarcinoma of the prostate (CaP). Two types of catheter-based applicators were fabricated, using either 90 degrees sectored tubular (3.5 mm OD x 10 mm) or planar transducers (3.5 mm x 10 mm). They were constructed to be MRI compatible, minimally invasive and allow for manual rotation of the transducer array within a 10 mm cooling balloon. In vivo evaluations of the applicators were performed in canine prostates (n = 3) using MRI guidance (0.5 T interventional magnet). MR temperature imaging (MRTI) utilizing the proton resonance frequency shift method was used to acquire multiple-slice temperature overlays in real time for monitoring and guiding the thermal treatments. Post-treatment T1-weighted contrast-enhanced imaging and triphenyl tetrazolium chloride stained tissue sections were used to define regions of tissue coagulation. Single sonications with the 90 degrees tubular applicator (9-15 W, 12 min, 8 MHz) produced coagulated zones covering an 80 degrees wedge of the prostate extending from 1-2 mm outside the urethra to the outer boundary of the gland (16 mm radial coagulation). Single sonications with the planar applicator (15-20 W, 10 min, approximately 8 MHz) generated thermal lesions of approximately 30 degrees extending to the prostate boundary. Multiple sequential sonications (sweeping) of a planar applicator (12 W with eight rotations of 30 degrees each) demonstrated controllable coagulation of a 270 degrees contiguous section of the prostate extending to the capsule boundary. The feasibility of using highly directional transurethral ultrasound applicators with rotational capabilities to selectively coagulate regions of the prostate while monitoring and controlling the treatments with MRTI was demonstrated in this study.

Split-bolus MDCT urography detected all proven cases of tumors of the upper urinary tract, yielding high sensitivity and specificity. The split-bolus technique has the potential to reduce both radiation dose and the number of images generated by MDCT urography.

The catheter-based ultrasound devices can produce spatially selective regions of thermal destruction in prostate. The MR thermal imaging and thermal dose maps, obtained in multiple slices through the target volume, are useful for controlling therapy delivery (rotation, power levels, duration). Contrast-enhanced T1-weighted MRI and diffusion-weighted imaging are useful tools for assessing treatment.

Despite extensive research on sexual dysfunction after gynecological cancer, uncertainty remains regarding the nature and extent of sexual problems following surgery for early cervical cancer. This study investigated whether radical hysterectomy for stage IB cancer of the cervix without adjuvant treatment entails short- or long-term sexual difficulties. Twenty patients with stage IB cervical cancer undergoing radical hysterectomy (CG), 18 women treated with hysterectomy for a benign gynecological condition (BG), and 20 gynecologically healthy women (HG) were studied. At 0, 4, and 8 months postoperatively, data were prospectively gathered using standardized questionnaires and specifically developed scales. Sexual functioning was covered in 15 specifically designed items and analyzed using Fisher's exact tests. For all other variables, group comparisons were computed using analysis of variance (ANOVA) or nonparametric statistical equivalents. Nonsignificant trends, consistent across time and groups, resulted for most of the sexual variables. Preoperatively, cancer patients exhibited slightly better sexual functioning than the other two groups, but over time this decreased slightly. Conversely, sexual functioning among the patients with benign disease showed steady improvement. These results indicate that radical hysterectomy for stage IB cervical cancer does not entail major sexual sequelae. Because of the limited sample size of our study, conclusions must be drawn cautiously.

Thermal therapy offers a minimally invasive option for treating benign prostatic hyperplasia (BPH) and localized prostate cancer. In this study we investigated a transurethral ultrasound applicator design utilizing curvilinear, or slightly focused, transducers to heat prostatic tissue rapidly and controllably. The applicator was constructed with two independently powered transducer segments operating at 6.5 MHz and measuring 3.5 mm x 10 mm with a 15 mm radius of curvature across the short axis. The curvilinear applicator was characterized by acoustic efficiency measurements, acoustic beam plots, biothermal simulations of human prostate, ex vivo heating trials in bovine liver, and in vivo heating trials in canine prostate (n=3). Each transducer segment was found to emit a narrow acoustic beam (max width <3 mm), which extended the length of the transducer, with deeper penetration than previously developed planar or sectored tubular transurethral ultrasound applicators. Acoustic and biothermal simulations of human prostate demonstrated three treatment schemes for the curvilinear applicator: single shot (10 W, 60 s) schemes to generate narrow ablation zones (13 x 4 mm, 52 degrees C at the lesion boundary), incremental rotation (10 W, 10 degrees/45 s) to generate larger sector-shaped ablation zones (16 mm x 180 degrees sector), and rotation with variable sonication times (10 W, 10 degrees/15-90 s) to conform the ablation zone to a predefined boundary (9-17 mm x 180 degrees sector, 13 min total treatment time). During in vivo canine prostate experiments, guided by MR temperature imaging, single shot sonications (6 W/transducer, 2-3 min) with the curvilinear applicator ablated 20 degree sections of tissue to the prostate boundary (9-15 mm). Multiple adjacent sonications ("sweeping") ablated large sections of the prostate (180 degrees) by using the MR temperature imaging to adjust the power (4-6.4 W/transducer) and sonication time (30-180 s) at each 10 degrees rotation such that the periphery of the prostate reached 52 degrees C before the next rotation. The conclusion of this study was that the curvilinear applicator produces a narrow and penetrating ultrasound beam that, when combined with image guidance, can provide a precise technique for ablating target regions with a contoured outer boundary, such as the prostate capsule, by rotating in small steps while dynamically adjusting the net applied electrical power and sonication time at each position.

Referenceless proton resonance frequency (PRF) shift thermometry provides a means to measure temperature changes during minimally invasive thermotherapy that is inherently robust to motion and tissue displacement. However, if the referenceless method is used to determine temperature changes during prostate ablation, phase gaps between water and fat in image regions used to determine the background phase can confound the phase estimation. We demonstrate an extension to referenceless thermometry which eliminates this problem by allowing background phase estimation in the presence of phase discontinuities between aqueous and fatty tissue. In this method, images are acquired with a multiecho sequence and binary water and fat maps are generated from a Dixon reconstruction. For the background phase estimation, water and fat regions are treated separately and the phase offset between the two tissue types is determined. The method is demonstrated feasibile in phantoms and during in vivo thermal ablation of canine prostate.

The feasibility of MRI-guided interstitial ultrasound thermal therapy of the prostate was evaluated in an in vivo canine prostate model. MRI compatible, multielement interstitial ultrasound applicators were developed using 1.5 mm diameter cylindrical piezoceramic transducers (7 to 8 MHz) sectored to provide 180 degrees of angular directional heating. Two in vivo experiments were performed in canine prostate. The first using two interstitial ultrasound applicators, the second using three ultrasound applicators in conjunction with rectal and urethral cooling. In both experiments, the applicators were inserted transperineally into the prostate with the energy directed ventrally, away from the rectum. Electrical power levels of 5-17 W per element (approximately 1.6-5.4 W acoustic output power) were applied for heating periods of 18 and 48 min. Phase-sensitive gradient-echo MR imaging was used to monitor the thermal treatment in real-time on a 0.5 T interventional MRI system. Contrast-enhanced T1-weighted images and vital-stained serial tissue sections were obtained to assess thermal damage and correlate to real-time thermal contour plots and calculated thermal doses. Results from these studies indicated a large volume of ablated (nonstained) tissue within the prostate, extending 1.2 to 2.0 cm from the applicators to the periphery of the gland, with the dorsal margin of coagulation well-defined by the applicator placement and directionality. The shape of the lesions correlated well to the hypointense regions visible in the contrast-enhanced T1-weighted images, and were also in good agreement with the contours of the 52 degrees C threshold temperature and t43 > 240 min. This study demonstrates the feasibility of using directional interstitial ultrasound in conjunction with MRI thermal imaging to monitor and possibly control thermal coagulation within a targeted tissue volume while potentially protecting surrounding tissue, such as rectum, from thermal damage.