MRI-guided needle localization: technique

Deep learning-based automatic pipeline for 3D needle localization on intra-procedural 3D MRI

PURPOSE

Accurate and rapid needle localization on 3D magnetic resonance imaging (MRI) is critical for MRI-guided percutaneous interventions. The current workflow requires manual needle localization on 3D MRI, which is time-consuming and cumbersome. Automatic methods using 2D deep learning networks for needle segmentation require manual image plane localization, while 3D networks are challenged by the need for sufficient training datasets. This work aimed to develop an automatic deep learning-based pipeline for accurate and rapid 3D needle localization on in vivo intra-procedural 3D MRI using a limited training dataset.

METHODS

The proposed automatic pipeline adopted Shifted Window (Swin) Transformers and employed a coarse-to-fine segmentation strategy: (1) initial 3D needle feature segmentation with 3D Swin UNEt TRansfomer (UNETR); (2) generation of a 2D reformatted image containing the needle feature; (3) fine 2D needle feature segmentation with 2D Swin Transformer and calculation of 3D needle tip position and axis orientation. Pre-training and data augmentation were performed to improve network training. The pipeline was evaluated via cross-validation with 49 in vivo intra-procedural 3D MR images from preclinical pig experiments. The needle tip and axis localization errors were compared with human intra-reader variation using the Wilcoxon signed rank test, with p < 0.05 considered significant.

RESULTS

The average end-to-end computational time for the pipeline was 6 s per 3D volume. The median Dice scores of the 3D Swin UNETR and 2D Swin Transformer in the pipeline were 0.80 and 0.93, respectively. The median 3D needle tip and axis localization errors were 1.48 mm (1.09 pixels) and 0.98°, respectively. Needle tip localization errors were significantly smaller than human intra-reader variation (median 1.70 mm; p < 0.01).

CONCLUSION

The proposed automatic pipeline achieved rapid pixel-level 3D needle localization on intra-procedural 3D MRI without requiring a large 3D training dataset and has the potential to assist MRI-guided percutaneous interventions.

A 20-gauge active needle design with thin-film printed circuitry for interventional MRI at 0.55T

PURPOSE

This work aims to fabricate RF antenna components on metallic needle surfaces using biocompatible polyester tubing and conductive ink to develop an active interventional MRI needle for clinical use at 0.55 Tesla.

METHODS

A custom computer numeric control-based conductive ink printing method was developed. Based on electromagnetic simulation results, thin-film RF antennas were printed with conductive ink and used to fabricate a medical grade, 20-gauge (0.87 mm outer diameter), 90-mm long active interventional MRI needle. The MRI visibility performance of the active needle prototype was tested in vitro in 1 gel phantom and in vivo in 1 swine. A nearly identical active needle constructed using a 44 American Wire Gauge insulated copper wire-wound RF receiver antenna was a comparator. The RF-induced heating risk was evaluated in a gel phantom per American Society for Testing and Materials (ASTM) 2182-19.

RESULTS

The active needle prototype with printed RF antenna was clearly visible both in vitro and in vivo under MRI. The maximum RF-induced temperature rise of prototypes with printed RF antenna and insulated copper wire antenna after a 3.96 W/kg, 15 min. long scan were 1.64°C and 8.21°C, respectively. The increase in needle diameter was 98 µm and 264 µm for prototypes with printed RF antenna and copper wire-wound antenna, respectively.

CONCLUSION

The active needle prototype with conductive ink printed antenna provides distinct device visibility under MRI. Variations on the needle surface are mitigated compared to use of a 44 American Wire Gauge copper wire. RF-induced heating tests support device RF safety under MRI. The proposed method enables fabrication of small diameter active interventional MRI devices having complex geometries, something previously difficult using conventional methods.

MRI-guided needle localization: Indications, tips, tricks, and review of the literature

We describe the history of, indications for, and techniques involved in MRI-guided needle localization (MRI-NL). MRI-NL continues to be a safe, effective method of sampling lesions that are only detected with MRI, particularly for anatomically challenging lesions such as those near the chest wall, the nipple, the skin, and/or in close proximity to implants.

MRI guided needle localization in a patient with recurrence pleomorphic sarcoma and post-operative scarring

MRI-guided wire localization is commonly used for surgical localization of breast lesions. Here we introduce an alternative use of this technique to help with surgical resection of a recurrent pleomorphic sarcoma embedded in extensive post-treatment scar tissue. We describe a case of recurrent pleomorphic soft tissue sarcoma in the thigh after treatment with neoadjuvant therapy, surgery, and radiation. Due to the distortion of the normal tissue architecture and formation of extensive scar tissue from prior treatment, wire localization under MRI was successfully used to assist the surgeon in identifying the recurrent tumor for removal.

Photoacoustic imaging of breast microcalcifications: a preliminary study with 8-gauge core-biopsied breast specimens

Background

We presented the photoacoustic imaging (PAI) tool and to evaluate whether microcalcifications in breast tissue can be detected on photoacoustic (PA) images.

Methods

We collected 21 cores containing microcalcifications (n = 11, microcalcification group) and none (n = 10, control group) in stereotactic or ultrasound (US) guided 8-gauge vacuum-assisted biopsies. Photoacoustic (PA) images were acquired through ex vivo experiments by transmitting laser pulses with two different wavelengths (700 nm and 800 nm). The presence of microcalcifications in PA images were blindly assessed by two radiologists and compared with specimen mammography. A ratio of the signal amplitude occurring at 700 nm to that occurring at 800 nm was calculated for each PA focus and was called the PAI ratio.

Results

Based on the change of PA signal amplitude between 700 nm and 800 nm, 10 out of 11 specimens containing microcalcifications and 8 out of 10 specimens without calcifications were correctly identified on blind review; the sensitivity, specificity, accuracy, positive predictive and negative predictive values of our blind review were 90.91%, 80.0%, 85.71%, 83.33% and 88.89%. The PAI ratio in the microcalcification group was significantly higher than that in the control group (the median PAI ratio, 2.46 versus 1.11, respectively, P = .001). On subgroup analysis in the microcalcification group, neither malignant diagnosis nor the number or size of calcification-foci was proven to contribute to PAI ratios.

Conclusion

Breast microcalcifications generated distinguishable PA signals unlike breast tissue without calcifications. So, PAI, a non-ionizing and non-invasive hybrid imaging technique, can be an alternative in overcoming the limitations of conventional US imaging.

US-guided vacuum-assisted biopsy of microcalcifications in breast lesions and long-term follow-up results

OBJECTIVE

To evaluate the diagnostic accuracy of the use of an ultrasonography (US)-guided vacuum-assisted biopsy for microcalcifications of breast lesions and to evaluate the efficacy of the use of US-guided vacuum-assisted biopsy with long-term follow-up results.

MATERIALS AND METHODS

US-guided vacuum-assisted biopsy cases of breast lesions that were performed between 2002 and 2006 for microcalcifications were retrospectively reviewed. A total of 62 breast lesions were identified where further pathological confirmation was obtained or where at least two years of mammography follow-up was obtained. These lesions were divided into the benign and malignant lesions (benign and malignant group) and were divided into underestimated group and not-underestimated lesions (underestimated and not-underestimated group) according to the diagnosis after a vacuum-assisted biopsy. The total number of specimens that contained microcalcifications was analyzed and the total number of microcalcification flecks as depicted on specimen mammography was analyzed to determine if there was any statistical difference between the groups.

RESULTS

There were no false negative cases after more than two years of follow-up. Twenty-nine lesions were diagnosed as malignant (two invasive carcinomas and 27 carcinoma in situ lesions). Two of the 27 carcinoma in situ lesions were upgraded to invasive cancers after surgery. Among three patients diagnosed with atypical ductal hyperplasia, the diagnosis was upgraded to a ductal carcinoma in situ after surgery in one patient. There was no statistically significant difference in the number of specimens with microcalcifications and the total number of microcalcification flecks between the benign group and malignant group of patients and between the underestimated group and not-underestimated group of patients.

CONCLUSION

US-guided vacuum-assisted biopsy can be an effective alternative to stereotactic-guided vacuum-assisted biopsy in cases where microcalcifications are visible with the use of high-resolution US.

Missed Breast Cancers at US-guided Core Needle Biopsy: How to Reduce Them

Ultrasonographically (US) guided core needle biopsy is currently recognized as a reliable alternative to surgical biopsy for the histopathologic diagnosis of breast lesions. However, despite advances in biopsy devices and techniques, false-negative diagnoses are unavoidable and may delay the diagnosis and treatment of breast cancer. The most common reasons for false-negative diagnosis are (a) technical or sampling errors, (b) failure to recognize or act on radiologic-histologic discordance, and (c) lack of imaging follow-up after a benign biopsy result. Technical difficulties (eg, poor lesion or needle visualization, deeply located lesions, dense fibrotic tissue) cause inaccurate sampling but can be reduced by using modified standard techniques. Radiologic-histologic correlation is also of critical importance in US-guided core needle biopsy. Radiologic-histologic discordance occurs when the histologic results do not provide a sufficient explanation for the imaging features and indicates that the lesion may not have been sampled adequately, so that repeat biopsy is warranted. Appropriate follow-up imaging is invaluable; even patients with concordant benign findings after US-guided core needle biopsy are directed to undergo follow-up imaging because there may be delays in the recognition of false-negative findings. Optimization of technique, radiologic-histologic correlation, and postbiopsy follow-up protocols are recommended to reduce the occurrence of false-negative diagnosis at US-guided core needle biopsy performed by radiologists.

Numerical simulations of intra-voxel dephasing effects and signal voids in gradient echo MR imaging using different sub-grid sizes

Signal void artifacts in gradient echo imaging are caused by the intra-voxel dephasing of the spins. Intra-voxel dephasing can be estimated by computing the field distribution on a sub-grid inside each picture element, followed by integration of all magnetization components. The strategy of computing the artifacts based on the integration of the sub-voxel signal components is presented here for different sub-grids. The coarseness of the sub-grid is directly related to computational effort. The possibility to save memory space and computing time for the dipole model by computing the field only on a sub-grid is addressed in the presented article. It is investigated as to how far computational time and memory space can be reduced by using an appropriate sub-grid. Numerical results for a model of a partially diamagnetically coated needle shaft are compared to experimental findings. In the case of a pure titanium needle, it is shown as being sufficient to compute the field distribution on a sub-grid that is at least four times coarser in each direction than the grid used to discretize the object in the related MR image. Due to three nested loops over the 3D grid, the need for memory space and time is saved by a factor 64. Deviations between measurements and simulations for the broad side of the artifact (uncompensated) and for the small side of the artifact (compensated) were 15.5%, respectively, 19.1% for orientation parallel to the exterior field, and 22.7%, respectively, 23.1% for orientation perpendicular to the exterior field.

Contrast-enhanced MRI in breast cancer patients eligible for breast-conserving therapy: complementary value for subgroups of patients

The aim of this study was to identify patients prior to breast-conserving therapy (BCT) who have complementary value of contrast-enhanced magnetic resonance imaging (MRI) over conventional imaging in the assessment of tumor extent. All patients were eligible for BCT according to conventional imaging, and underwent preoperative MRI as part of this study. One hundred and sixty-five patients (166 tumors) were included. MRI was defined to have complementary value if conventional imaging underestimated or overestimated tumor extent (by more than 10 mm compared to histology) and MRI assessed the extent accurately. Logistic regression was employed to identify characteristics that are predictive of the complementary value of preoperative MRI. MRI had complementary value in 39 cases (23%). Patients <58 years old with irregular lesion margins at mammography and discrepancy in tumor extent by more than 10 mm between mammography and ultrasonography had a 3.2x higher chance of accurate assessment at MRI (positive predictive value 50%, negative predictive value 84%, p=0.0002). Preoperative MRI in patients eligible for BCT is more accurate than conventional imaging in the assessment of tumor extent in approximately one out of four patients. Subgroups of patients in whom MRI has complementary value may be defined by the differences in clinical and imaging features.

Method for rapid MRI needle tracking

A new method for MRI needle tracking within a given two-dimensional (2D) image slice is presented. The method is based on k-space investigation of the difference image between the current dynamic frame and a reference frame. Using only a few central k-lines of the difference image and a nonlinear optimization procedure, one can resolve the parameters that define the 2D sinc function that best characterizes the needle in k-space. The spatial location and orientation of the needle are determined from these parameters. Rapid needle tracking is obtained by repeated acquisitions of the same set of several central k-lines (as in a "keyhole" protocol) and repeated computation of these parameters. The calculated needle tip is depicted on the reference image by means of a graphic overlay. The procedure was tested in computer simulations and in actual MRI scans (the computations were done offline). It was demonstrated that six k-lines out of 128 usually suffice to locate the needle. The refresh rate of the needle location depends on the time required to sample the subset of k-lines, calculate the current needle location, and refresh the reference image.

The development and evaluation of a three-dimensional ultrasound-guided breast biopsy apparatus

We have designed a prototype three-dimensional ultrasound guidance (3D USB) apparatus to improve the breast biopsy procedure. Features from stereotactic mammography and free-hand US-guided biopsy have been combined with 3D US imaging. This breast biopsy apparatus accurately guides a needle into position for the sampling of target tissue. We have evaluated this apparatus in three stages. First, by testing the placement accuracy of a needle in a tissue mimicking phantom. Second, with tissue mimicking phantoms that had embedded lesions for biopsy. Finally, by comparison to free-hand US-guided biopsy, using chicken breast phantoms. The first two stages of evaluation quantified the mechanical biases in the 3D USB apparatus. Compensating for these, a 96% success rate in targeting 3.2 mm "lesions" in chicken breast phantoms was achieved when using the 3D USB apparatus. The expert radiologists performing biopsies with free-hand US guidance achieved a 94.5% success rate. This has proven an equivalence between our apparatus, operated by non-experts, and free-hand biopsy performed by expert radiologists, for 3.2 mm lesions in vitro, with a 95% confidence.

MR-guided interventional breast procedures considering vacuum biopsy in particular

Histologic work-up of just MR-detected breast lesions has become essential with increasing use of contrast-enhanced MR imaging. In the present article an overview is given about the different MR-guided breast interventions, performed since 1990. Presently, for reasons of costs and image quality closed magnets are most widely used. The following approaches have been described: MR-guided freehand localization in supine position, stereotaxic localization in supine position and most frequently used localization in the prone position by means of a compression device that immobilises the breast to prevent tissue shift during intervention. Only limited experience exists with interventions on open magnets. MR-guided wire localization is a well-established procedure. Recently, percutaneous vacuum biopsy of enhancing breast lesions has become possible under MR guidance. The new system allows accurate and safe access to lesions in any location of the breast and direct check-up of representative excision by visualisation of the cavity. Thus reliable histologic evaluation of lesions smaller than 10 mm is possible with this approach.