Computerized planning of prostate cryosurgery using variable cryoprobe insertion depth.

The current study presents a computerized planning scheme for prostate cryosurgery using a variable insertion depth strategy. This study is a part of an ongoing effort to develop computerized tools for cryosurgery. Based on typical clinical practices, previous automated planning schemes have required that all cryoprobes be aligned at a single insertion depth. The current study investigates the benefit of removing this constraint, in comparison with results based on uniform insertion depth planning as well as the so-called "pullback procedure". Planning is based on the so-called "bubble-packing method", and its quality is evaluated with bioheat transfer simulations. This study is based on five 3D prostate models, reconstructed from ultrasound imaging, and cryoprobe active length in the range of 15-35 mm. The variable insertion depth technique is found to consistently provide superior results when compared to the other placement methods. Furthermore, it is shown that both the optimal active length and the optimal number of cryoprobes vary among prostate models, based on the size and shape of the target region. Due to its low computational cost, the new scheme can be used to determine the optimal cryoprobe layout for a given prostate model in real time.

Computerized Planning of Cryosurgery Using Bubble Packing: An Experimental Validation on a Phantom Material.

The current study focuses on experimentally validating a planning scheme based on the so-called bubble-packing method. This study is a part of an ongoing effort to develop computerized planning tools for cryosurgery, where bubble packing has been previously developed as a means to find an initial, uniform distribution of cryoprobes within a given domain; the so-called force-field analogy was then used to move cryoprobes to their optimum layout. However, due to the high quality of the cryoprobes' distribution, suggested by bubble packing and its low computational cost, it has been argued that a planning scheme based solely on bubble packing may be more clinically relevant. To test this argument, an experimental validation is performed on a simulated cross-section of the prostate, using gelatin solution as a phantom material, proprietary liquid-nitrogen based cryoprobes, and a cryoheater to simulate urethral warming. Experimental results are compared with numerically simulated temperature histories resulting from planning. Results indicate an average disagreement of 0.8 mm in identifying the freezing front location, which is an acceptable level of uncertainty in the context of prostate cryosurgery imaging.

Cryosurgery planning using bubble packing in 3D.

As part of an ongoing project to develop automated tools for cryosurgery planning, the current study focuses on the development of a 3D bubble packing method. A proof-of-concept for the new method is demonstrated on five prostate models, reconstructed from ultrasound images. The new method is a modification of an established method in 2D. Ellipsoidal bubbles are packed in the volume of the prostate in the current study; such bubbles can be viewed as a first-order approximation of a frozen region around a single cryoprobe. When all cryoprobes are inserted to the same depth, optimum planning was found to occur at about 60% of the length of the prostate (measured from its apex), which leads to cooling of approximately 75% of the prostate volume below a specific temperature threshold of - 22 degrees C. Bubble packing has the potential to dramatically reduce the run time for automated planning.

Computerized planning of prostate cryosurgery with pullback operation.

This study is a part of an ongoing project to develop computerized tools for cryosurgery planning. Prostate cryosurgery is frequently performed as a two-stage process in which the first-stage targets are frozen with the cryoprobes at a greater insertion depth, while the second stage of freezing is performed after some cryoprobes are pulled back to new locations, this process being known as the pullback procedure. This paper proposes a method to generate computationally a preferred cryoprobe layout for the pullback operation, using a previously proposed bubble-packing method for cryosurgery planning. For this purpose, additional constraints are imposed to align packed bubbles along the same insertion path between the different stages, and to vary the number of bubbles at each stage. The method is demonstrated on 3D patient models from four individuals, using cryoprobes with a diameter of 1.5 mm and an active length of 15 mm. Results are verified with bioheat transfer simulations, and compared with the non-pullback operations using cryoprobes with longer (25 mm) active lengths. When compared with results of the non-pullback procedure, results with pullback suggest some improvement in freezing in the apex region of the prostate, with a slight increase in overall freezing damage to surrounding healthy tissues.

An efficient numerical technique for bioheat simulations and its application to computerized cryosurgery planning.

As a part of ongoing efforts to develop computerized planning tools for cryosurgery, the current study focuses on developing an efficient numerical technique for bioheat transfer simulations. Our long-term goal is to develop a planning tool for cryosurgery that takes a 3D reconstruction of a target region, and suggests the best cryoprobe layout. Toward that goal, a planning algorithm, termed "force-field analogy," has been recently presented, based on a sequence of bioheat transfer simulations, which are by far the most computationally expensive part of the planning method. The objective in the current study is to develop a finite difference numerical scheme for bioheat transfer simulations, which reduces the overall run time of computerized planning, thereby making it clinically relevant. While the general concept of variable grid size and time intervals is not new, its application to the phase change problem of cryosurgery is the unique contribution of the current study.

Bubble packing application in computerized planning of cryosurgery.

Among many factors, the effectiveness of the cryoprocedure is determined by the quality of the cryoprobes layout. A computerized planning tool for optimizing this layout has the potential of improving the outcome of cryosurgery, reducing post-operative complications, and reducing the cost of the clinical operation. As part of an ongoing effort to develop planning tools for cryosurgery, the current study takes a novel approach, based on bubble-packing method. This study shows that the application of bubble-packing shortens runtime by an order of magnitude. In this study, the bubble-packing method is integrated with bioheat transfer simulations to demonstrate the quality of planning.

Towards intra-operative computerized planning of prostate cryosurgery.

BACKGROUND: As part of ongoing efforts to develop computerized planning tools for cryosurgery, the current study provides a comparison between two recently developed methods for planning, known as bubble packing and force-field analogy. METHODS: For the purpose of comparison, four 3D prostate models were reconstructed from ultrasound imaging. The quality of planning for each method was evaluated based on bioheat transfer simulations. RESULTS: Both methods are shown to be robust planning tools in 3D. Typical results show at least 75% of the target region volume having temperatures below a target temperature isotherm for planning. While the force-field analogy method yields superior planning results, it comes at the expense of an order of magnitude longer run time, with only moderate improvement. CONCLUSIONS: Due to time constraints in a clinical setup, bubble packing alone may be considered adequate for computerized planning. Furthermore, only bubble packing is demonstrated to be adequate for intra-operative planning.

Two-phase computerized planning of cryosurgery using bubble-packing and force-field analogy.

BACKGROUND: Cryosurgery is the destruction of undesired tissues by freezing, as in prostate cryosurgery, for example. Minimally invasive cryosurgery is currently performed by means of an array of cryoprobes, each in the shape of a long hypodermic needle. The optimal arrangement of the cryoprobes, which is known to have a dramatic effect on the quality of the cryoprocedure, remains an art held by the cryosurgeon, based on the cryosurgeon's experience and "rules of thumb." An automated computerized technique for cryosurgery planning is the subject matter of the current paper, in an effort to improve the quality of cryosurgery. METHOD OF APPROACH: A two-phase optimization method is proposed for this purpose, based on two previous and independent developments by this research team. Phase I is based on a bubble-packing method, previously used as an efficient method for finite element meshing. Phase II is based on a force-field analogy method, which has proven to be robust at the expense of a typically long runtime. RESULTS: As a proof-of-concept, results are demonstrated on a two-dimensional case of a prostate cross section. The major contribution of this study is to affirm that in many instances cryosurgery planning can be performed without extremely expensive simulations of bioheat transfer, achieved in Phase I. CONCLUSIONS: This new method of planning has proven to reduce planning runtime from hours to minutes, making automated planning practical in a clinical time frame.

Three-dimensional computer graphics for surgical procedure learning: Web three-dimensional application for cleft lip repair.

OBJECTIVE: In surgical procedures for cleft lip, surgeons attempt to use various skin incisions and small flaps to achieve a better and more natural shape postoperatively. They must understand the three-dimensional (3D) structure of the lips. However, they may have difficulty learning the surgical procedures precisely from normal textbooks with two-dimensional illustrations. Recent developments in 3D computed tomography (3D-CT) and laser stereolithography have enabled surgeons to visualize the structures of cleft lips from desired viewpoints. However, this method cannot reflect the advantages offered by specific surgical procedures. To solve this problem, we used the benefits offered by 3D computer graphics (3D-CG) and 3D animation. DESIGN AND RESULTS: By using scanning 3D-CT image data of patients with cleft lips, 3D-CG models of the cleft lips were created. Several animations for surgical procedures such as incision designs, rotation of small skin flaps, and sutures were made. This system can recognize the details of an operation procedure clearly from any viewpoint, which cannot be acquired from the usual textbook illustrations. This animation system can be used for developing new skin-flap design, understanding the operational procedure, and using tools in case presentations. The 3D animations can also be uploaded to the World Wide Web for use in teleconferencing.