Journal of Indira Gandhi Institute Of Medical Sciences

REVIEW ARTICLE
Year
: 2022  |  Volume : 8  |  Issue : 2  |  Page : 105--108

A novel black bone magnetic resonance imaging − An alternative to ionizing radiation in oral and maxillofacial imaging


Prarthana Govil1, Abhishek Tayal2,  
1 Department of Oral Medicine and Radiology, Babu Banarsi Das University of Dental Sciences, Jhunjhunu, Rajasthan, India
2 Department of Internal Medicine, Singhania University, Jhunjhunu, Rajasthan, India

Correspondence Address:
Prarthana Govil
Department of Oral Medicine and Radiology, Babu Banarsi Das University of Dental Sciences, Lucknow, Uttar Pradesh
India

Abstract

Over the decades, potential harmful effects of ionizing radiation continue to be a serious discussion among the researchers. Especially in the field of oral and maxillofacial imaging, the technique to reduce radiation doze to the humans has witnessed substantial advancement. The development of “BLACK BONE magnetic resonance imaging (MRI)” signifies dawn of new era in the head-and-neck imaging of the cortical bone, where this can be used as a replacement for computed tomography which is one of ionizing imaging modality used globally. Black bone MRI is a low flip angle MRI sequence which provides a high image contrast between bone and other tissues but reduces the contrast between the individual soft tissues thus enhancing bone soft-tissue boundary. This MRI sequence will eradicate radiation burden to the patient mainly pediatrics diagnosis and adult screening of benign and malignant lesions affecting the craniofacial region. This article explores this breadth of scientific discovery and its development.



How to cite this article:
Govil P, Tayal A. A novel black bone magnetic resonance imaging − An alternative to ionizing radiation in oral and maxillofacial imaging.J Indira Gandhi Inst Med Sci 2022;8:105-108


How to cite this URL:
Govil P, Tayal A. A novel black bone magnetic resonance imaging − An alternative to ionizing radiation in oral and maxillofacial imaging. J Indira Gandhi Inst Med Sci [serial online] 2022 [cited 2022 Nov 26 ];8:105-108
Available from: http://www.jigims.co.in/text.asp?2022/8/2/105/355314


Full Text



 Introduction



In 1985, when X-rays were discovered what followed not only was a scientific discovery but also a health hazard. Radiology has developed a lot since then. Exposure time has reduced from hours to minutes to milliseconds; radiography has changed from the analog to digital and further the development of imaging from 2D to three-dimensional (3D) thus enhancing the image quality. Scientist since then has come a long way of this miraculous discovery but what cannot be changed are the potential harmful effects of these ionizing radiations in the long run. 3D imaging (e.g., computed tomography [CT] and magnetic resonance imaging [MRI]) the recent milestone in radiology has resulted in more accurate diagnosis and thus accurate treatment plan.

There are about 3000 scanners throughout India, and therefore, the potential of this modality is so high that within the next 10 years, it will not be surprising, if the quantity doubles.[1] By its nature, CT involves larger radiation doses than the more common, conventional X-ray imaging procedures.[2] Hounsfield, also in his 1973 paper on CT, stated that “the exposure of the patient to X-Rays must be restricted.” We however, continue to fall short of Hounsefield's advice because of increased imaging demands. The superior quality of bony imaging on CT and also the ability to make 3D rendered images of the craniofacial skeleton has maintained CT, the gold standard for this region. The consensus among radiology professionals is that steps should be taken to reverse, or at least minimize radiation exposure from CT, yet for maxillo-craniofacial imaging this has largely consisted of radiation reduction techniques and therefore there is introduction of cone-beam CT.[3] MRI is also increasingly used in the imaging of pathological conditions, but its relatively poor details of hard tissue remain its limitations in cases of hard-tissue pathology. Hence, to find an alternative of this ionizing radiation CT, nonionizing radiation technique “Black Bone MRI” is been recently researched and reported. This technique utilizes a low flip angle, with short repetition and echo times, to produce uniform contrast of the soft tissue, with densely packed cortical bone.[4] In this article, we summarize concise information on this nonionizing radiation which is a potential alternative to ionizing radiation.

 What is Black Bone Magnetic Resonance Imaging??



That is a question which arises from the beginning, to make it in concise form it is − an imaging technique which uses repetition time of 8.6 ms and echo time of 4.2 ms and flip angle 5° which enables the differentiation of bone from almost uniform contrast of the soft tissues. It offers greatest potential in imaging benign conditions of the facial skeleton [Table 1].{Table 1}

 Principle of Image Formation in Black Bone Magnetic Resonance Imaging



The principle for black bone MRI and conventional MRI is the same. The patient is placed inside a large magnet called phantom. A magnetic field is applied which causes the nuclei of many atoms, specifically hydrogen, to align with the magnetic field. The scanner directs a radiofrequency pulse into the patient, causing some hydrogen nuclei to absorb the energy. When the RF pulse is turned off, the stored energy is released from the body and detected as a signal in coil in the scanner. This signal is used to construct the MR image.[5]

 Mechanism of Black Bone Magnetic Resonance Imaging



Siemens developed susceptibility-weighted imaging (SWI).[6] Calcification being diamagnetic decreases the magnetization in bone in comparison with the applied magnetic field. This reduces the Larmor frequency where there's calcium and causes heterogeneity within the localized force field that results in intra-and intervoxel dephasing thus causing signal drop-out within the voxel containing calcium; moreover, as adjacent voxels, a phenomenon remarked as “blooming.” The technique gives high contrast between bone and soft tissues, but low contrast between different soft tissues, thus the low signal bone is well distinguished from the encompassing soft tissues. [Figure 1] and [Figure 2] Thus, the SWI sequence will be used for black bone imaging.[7]{Figure 1}{Figure 2}

Henceforth, it increases bone and soft tissue contrast provide low contrast between different soft tissues, thus the low signal bone is easily distinguished from the surrounding soft tissues, can also be reformatted into three reconstructions because, although the sequence is two dimensional, the slice thickness is small and does not cause significant step artifact. The sequence is best run immediately after routine half fourier acquisition single shot turbo–spin echo.

Flip angle

Standard ideal angle is the principal parameter in black bone MRI sequence. The flip angle is important as it suppress signal from both fat and water to provide a uniform soft-tissue contrast, and therefore, enhances bone soft-tissue contrast. The flip angle is 5° which adequately suppress signal from both fat and water to obtain a uniform soft tissue background. The ability to clearly identify bone is therefore optimized in areas where bone is enveloped within soft tissue, such as mandibular region.[8]

Image contrast

It is principally controlled by the extrinsic parameters such as echo time and repetition time which can be adjusted as required.

 Applications



Alternative to CT and cone-beam CT which uses ionizing radiation for examining dental pathology.

In cephalometric analysisAssessment of skeletal dysplasia's, which is the most common indication for fetal CTEvaluation of the skull base and craniofacial skeleton in certain congenital anomalies, for example, evaluation of the mandible, hard palate, and petrous bones in Goldenhar or Treacher Collins syndromes, pyriform sinus stenosis in single midline median central incisor and for choanal atresia and also the petrous bones in coloboma, heart defects, atresia choanae, retardation, genital anomalies, and ear anomalies syndromeTo exclude and identify the fractures of the facial skeleton and benign and malignant infiltrating tumorsUtilized to produce 3D models of the craniofacial skeleton in both adults and an infantDistinction between normal and prematurely fused suturesImaging of arteries, including those of head and neck to examine occlusion, aneurysms, or arteriovenous malformationAssessment of spinal abnormalities, bony abnormalities in myelomeningocele, scoliosis, segmentation anomalies and sacrococcygeal teratoma[9]Pelvimetry.

Advantages

Nonionizing methodOf great value to young, fetus and pregnant women.

Disadvantages

Increased cost and scanning time associated with MRI compared with CTExclusion of those patients with significant metal foreign bodies (e.g., pacemakers)Those who cannot tolerate MRI due to claustrophobia or increased body mass index.

Limitation

The key limitation of the technique is in areas where “black bone” abuts black air, such as the sinuses, which makes separation of the two particularly challenging.

 Conclusion



Potential benefits of “Black Bone MRI” when imaging a maxillofacial region are still under research. We have discussed each aspect of this imaging modality which makes it an accurate alternative to the ionizing radiation. A shift from CT to “black bone” worldwide will require lot of awareness among clinician and open acceptance to this new technique. The potential adverse consequences of repeated radiation exposure of the head and neck have been well documented.[10],[11] The risk is greater for children, who are inherently more radiosensitive and have more remaining years of life during which a radiation induced cancer can develop.[2] Hence, practical implication for worldwide radiation protection is the need of the hour.

As discussed “black bone,” MRI avoids radiation exposure adds advantage to this technique with the limitations. The “black bone” MRI sequence adds approximately 5 min to the examination time, but may eliminate the costs of a second examination in the form of a CT, which is commonly utilized in head-and-neck imaging.[4] Researchers continue investigate about this technique but every clinician must have knowledge about this new seed in the field of radiology so that familiarity to each and everyone can be adopted and applied in the daily practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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