Clinician's guide to the basic principles of MRI.

MRI is an important and widely used imaging modality for clinical diagnosis. This article provides a concise discussion of the basic principles of MRI physics for non-radiology clinicians, with a general explanation of the fundamentals of signal generation and image contrast mechanisms. Common pulse sequences, tissue suppression techniques and use of gadolinium contrast with relevant clinical applications are presented. Knowledge of these concepts would provide an appreciation of how MR images are acquired and interpreted to facilitate interdisciplinary understanding between radiologists and referring clinicians.

Artificial Intelligence Predictive Analytics in the Management of Outpatient MRI Appointment No-Shows.

OBJECTIVE. Outpatient appointment no-shows are a common problem. Artificial intelligence predictive analytics can potentially facilitate targeted interventions to improve efficiency. We describe a quality improvement project that uses machine learning techniques to predict and reduce outpatient MRI appointment no-shows. MATERIALS AND METHODS. Anonymized records from 32,957 outpatient MRI appointments between 2016 and 2018 were acquired for model training and validation along with a holdout test set of 1080 records from January 2019. The overall no-show rate was 17.4%. A predictive model developed with XGBoost, a decision tree-based ensemble machine learning algorithm that uses a gradient boosting framework, was deployed after various machine learning algorithms were evaluated. The simple intervention measure of using telephone call reminders for patients with the top 25% highest risk of an appointment no-show as predicted by the model was implemented over 6 months. RESULTS. The ROC AUC for the predictive model was 0.746 with an optimized F1 score of 0.708; at this threshold, the precision and recall were 0.606 and 0.852, respectively. The AUC for the holdout test set was 0.738 with an optimized F1 score of 0.721; at this threshold, the precision and recall were 0.605 and 0.893, respectively. The no-show rate 6 months after deployment of the predictive model was 15.9% compared with 19.3% in the preceding 12-month preintervention period, corresponding to a 17.2% improvement from the baseline no-show rate (p < 0.0001). The no-show rates of contactable and noncontactable patients in the group at high risk of appointment no-shows as predicted by the model were 17.5% and 40.3%, respectively (p < 0.0001). CONCLUSION. Machine learning predictive analytics perform moderately well in predicting complex problems involving human behavior using a modest amount of data with basic feature engineering, and they can be incorporated into routine workflow to improve health care delivery.

Multiple spontaneous tendon ruptures from enthesis failure in primary hyperparathyroidism: a case report and review of imaging findings.

Cases of spontaneous tendon ruptures have been previously reported in the literature. Although both renal failure and hyperparathyroidism have been implicated as separate aetiologies, their frequent co-existence has confounded analysis. We report a case of a young man with primary hyperparathyroidism presenting with multiple acute spontaneous tendon ruptures. This case affords an opportunity to evaluate the imaging features of acute spontaneous tendon ruptures in the context of primary hyperparathyroidism, and in conjunction with a review of previous literature reports, an imaging-based hypothesis on the pathophysiology and aetiology of spontaneous tendon ruptures is proposed.

Reporting of CT cervical spine after office hours by radiology trainees-analysis of discrepancy rates and RADPEER scores.

PURPOSE: To review the errors made by radiology trainees in the reporting of cervical spine CTs (CCT) and to compare the discrepancy rates between the stages of training. METHODS: All CCTs reported by trainees after office hours between January 2015 and December 2015 were retrospectively reviewed by a team of five musculoskeletal consultants with experience ranging between 7 and 15 years. Discrepancies between the provisional report by the trainee and the findings by the musculoskeletal consultants were graded according to the RADPEER scoring system. Sensitivity and specificity of the trainees were assessed. RESULTS: Of 254 CCT provisional reports, there were 12 (4.7%) discrepancies, of which 5 (2.0%) discrepancies were likely to be clinically significant. We found a clinically significant difference between the stage of training of the trainee and RADPEER score (P = 0.023). The sensitivity and specificity of the senior radiology trainees were 97.0 and 98.1%, respectively, and that of the junior radiology trainees were 80 and 98.0% respectively (P = 0.039). Conditions misinterpreted as fractures include degenerative changes (n = 2) and nutrient vessel (n = 1). Other missed abnormalities include ossification of the posterior longitudinal ligament (n = 1), fracture of the foramen transversarium (n = 2), vertebral body fractures (n = 2), articular facet fractures (n = 2), and transverse process fractures (n = 2). CONCLUSION: Cervical spine CTs performed after office hours can be safely interpreted by senior radiology trainees to a reasonable degree, although a targeted intervention to improve diagnostic performance of junior radiology trainees may be of clinical benefit.

Comparison of acetabular version angle measurements between prone and reformatted supine computed tomography images.

PURPOSE: To compare acetabular version angle measurements of CT scans in the prone and reformatted supine positions. CT acetabular version angle measurements have previously been done in the prone position to correct for pelvic tilt. With the advent of multidetector CT, recent studies have evaluated acetabular version angles measured in the supine position. To our knowledge, a comparison between these two approaches has not been performed. STUDY DESIGN: Case series in which consecutive CT urography studies of 49 adult patients performed in both prone and supine positions were retrospectively reviewed, and acetabular version angles of both hips measured. METHOD: Retrospective review of 49 consecutive CT urography studies performed in both prone and supine positions was done, and acetabular version angles of both hips were measured. Two radiologists measured the acetabular version angles independently. Multiplanar reformation of the supine CT images was performed to compensate for pelvic tilt and rotation prior to angle measurements. RESULTS: There was excellent interobserver agreement between the two readers (ICC = 0.90). Acetabular version angle measurements from the prone CT images were larger compared to reformatted supine images (24.0 and 21.3°, respectively, p < 0.0001), with greater angles found in women. There was strong correlation between supine and prone acetabular version angle measurements with a Pearson correlation coefficient of 0.743. CONCLUSIONS: Acetabular version angles measured from prone and reformatted supine CT images show strong correlation but are significantly different with larger angles obtained from the former and in women; clinical implications of these findings may require further study in other to determine the best method of version angle measurement. CT acetabular version angle measurement is also reliable with excellent interobserver correlation.

Bone bruise patterns in knee injuries: where are they found?

PURPOSE: Bone bruise represents an entity of occult bone lesions that can occur in the knee, causing knee pain and tenderness clinically. The aim of this study was to investigate the incidence and pattern of bone bruising seen in the anterior cruciate ligament (ACL) injury cohort, the non-ACL injury cohort, and between both cohorts. METHODS: We reviewed 710 knee magnetic resonance imagings performed over a 6-month period. Eighty-eight patients with prior history of a knee injury were identified. The mechanism of injury and other clinical findings was noted. RESULTS: Among these 88 patients, 58 patients had an associated ACL injury (31 had isolated ACL injuries; 27 had combined ACL and other ligamentous injuries). Among the 30 who had non-ACL injuries, 15 had either an MCL, LCL, or PCL injury. The remaining 15 patients had no associated ligament injury. With an ACL injury, the most common bone bruise sites are the lateral femur (74%) and lateral tibia (64%). Without an ACL injury, the pattern of bruising was more common in the lateral femur (69%) and medial tibia (37%). CONCLUSION: Bone bruises are important as previous studies have shown that they can cause persistent knee pain. Our study has shown that there are differences in pattern of bone bruising in knee injuries with or without ACL injuries.

Morphometric Analysis of the Calcaneus in a Southeast Asian Population.

Introduction The calcaneus is the most commonly fractured tarsal bone, accounting for up to 60% of tarsal bone fractures and 2% of all fractures in the body. With the calcaneus playing an important role in maintaining a stable and efficient bipedal gait, the sequelae of these injuries have also been associated with potential long-term disability or discomfort, especially if improperly managed. Incorrectly sized implants similarly cause their own set of complications, such as poor fixation, impingement, or implant prominence. This potentially increases the need for revision surgery or implant removal, with increased morbidity for the patient. As such, a thorough understanding of calcaneal morphology is vital to ensure optimal conservative and surgical management of calcaneal pathology. CT imaging has become an indispensable tool in the evaluation of such a complex three-dimensional structure and allows us to accurately map out calcaneal morphology. This study aims to evaluate calcaneal morphology in the Southeast Asian population using CT imaging and to determine if morphological differences exist between male and female patients. Methods Calcaneus measurements were taken from CT scans of 100 patients with intact calcanei, consisting of 34 female and 66 male patients. Patients who have had fractures or previous calcaneus surgery were excluded. IBM SPSS Statistics for Windows, Version 28.0 (Released 2021; IBM Corp., Armonk, NY, USA) was used for statistical calculations. Mean values were calculated, and t-tests were performed to establish any significant differences between measurements taken from male and female patients. Results were deemed to have a significant difference if the p-value was less than 0.05. Results Males had larger calcanei measurements than females in all parameters included. Calcaneal length in females measured on CT axial views was 66.2 mm, compared to 75.2 mm in males (p < 0.001). Calcaneal height, measured at the medial wall, was 28.2 mm in females and 33.9 mm in males (p < 0.001). Calcaneal height measured at the lateral wall was 33.3 mm and 38.1 mm in females and males, respectively (p > 0.001). Calcaneal width was 33.0 mm in females and 36.9 mm in males (p < 0.001). The mean dimensions measured in the total sample were an axial length of 72.1 mm, a medial wall height of 32.0 mm, a lateral wall height of 36.4 mm, and a width of 35.6 mm. Conclusion There is a significant difference in calcaneal morphology on CT imaging between male and female patients in the Southeast Asian population, which is an important consideration for surgical planning and the selection of appropriately sized implants.

Persistent Bilateral Atypical Femoral Fractures in an Antiresorptive-Naïve Singaporean Chinese Patient with Graves' Disease.

Atypical femoral fractures (AFFs) are rare adverse effects of bisphosphonate therapy. We report an unusual case of bilateral diaphyseal AFFs in an antiresorptive-naïve Singaporean Chinese female with Graves' disease. She presented with complete right AFF requiring surgical fixation, and persistent left incomplete AFF for over four years. Femoral bowing, varus femoral geometry, and ethnic influence likely contributed to the AFFs' formation. This case may provide insights into the pathogenesis of AFFs in high-risk Asian populations.

Cost-effectiveness analysis of phone reminders for outpatient magnetic resonance imaging (MRI) appointments in Singapore.

INTRODUCTION: Due to long wait times, rising demand and limited resources for Magnetic Resonance Imaging (MRI) services, phone call reminders were implemented as an intervention to increase scanner utilisation and improve non-attendance at the radiology department in Changi General Hospital, Singapore. AIM: This study aims to evaluate the impact of phone reminders on outpatient MRI non-attendance rate as well as the operational efficiency and savings of this intervention through cost-effectiveness analysis. METHODS: MRI outpatient records from January to December 2020 (pre-intervention period) and January to December 2021 (post-intervention period) were retrospectively obtained from the hospital systems. Non-attendance rates, costs and savings following the intervention were compared. RESULTS: Outpatient appointment non-attendance rates reduced from 12.85% to 8.93% after intervention. Following the phone reminders, 2,953 patients (21.69%) decided to cancel or reschedule their appointments. Based on the 91.07% attendance rate (100% - 8.93%), another 2689 slots were recovered from the cancellation of these appointments and were given to other patients. The reduction in non-attendance rates (3.92%) after the intervention translates to an increase in attendance of 533 patients while the net revenue generation with the phone reminder intervention was $387,179. CONCLUSION: Cost analysis indicates that phone reminders provide an inexpensive, easily implemented and personalised method to help increase adherence and improve appointment attendance. Reminding patients by phone calls two day before their appointments also leads to better optimization of appointment slots from cancelations and re-scheduling that can be used to allocate these appointments to other patients.

The iPad tablet computer for mobile on-call radiology diagnosis? Auditing discrepancy in CT and MRI reporting.

Tablet computers such as the iPad, which have a large format, improved graphic display resolution and a touch screen interface, may have an advantage compared to existing mobile devices such as smartphones and laptops for viewing radiological images. We assessed their potential for emergency radiology teleconsultation by reviewing multi-image CT and MRI studies on iPad tablet computers compared to Picture Archival and Communication Systems (PACS) workstations. Annonymised DICOM images of 79 CT and nine MRI studies comprising a range of common on-call conditions, reported on full-featured diagnostic PACS workstation by one Reporting Radiologist, were transferred from PACS to three iPad tablet computers running OsiriX HD v 2.02 DICOM software and viewed independently by three reviewing radiologists. Structured documentation was made of major findings (primary diagnosis or other clinically important findings), minor findings (incidental findings), and user feedback. Two hundred and sixty four readings (88 studies read by three reviewing radiologists) were compared, with 3.4 % (nine of 264) major discrepancies and 5.6 % (15 of 264) minor discrepancies. All reviewing radiologists reported favorable user experience but noted issues with software stability and limitations of image manipulation tools. Our results suggest that emergency conditions commonly encountered on CT and MRI can be diagnosed using tablet computers with good agreement with dedicated PACS workstations. Shortcomings in software and application design should be addressed if the potential of tablet computers for mobile teleradiology is to be fully realized.

Pitfalls in multidetector computed tomography imaging of traumatic spinal injuries.

The advent of multidetector computed tomography (MDCT) has largely supplanted plain radiography as the recommended primary imaging modality for the evaluation of acute spinal injuries. Although MDCT is highly sensitive and specific for bony injuries, errors in diagnosis can still occur. Knowledge of the possible imaging pitfalls on MDCT, leading to either misdiagnosis of fractures or missed fractures, is vital in ensuring an accurate diagnosis. This paper serves to highlight conditions that can mimic or reduce the sensitivity for the detection of acute spinal injuries, as well as demonstrate imaging findings which aid in the detection and diagnosis of subtle spinal injuries. Review areas for clinically relevant extra-spinal findings in the context of trauma will also be discussed.

3D MRI with CT-like bone contrast - An overview of current approaches and practical clinical implementation.

CT is the imaging modality of choice for assessment of 3D bony morphology but incurs the penalty of ionizing radiation. Improving the ability of 3D MRI to provide high-resolution images of cortical bone with CT-like bone contrast has been a focus of recent research. The ability of 3D MRI to deliver cortical bone information with similar diagnostic performance to CT would complement assessment of soft tissues and medullary bone from a single MRI examination, simplifying evaluation and obviating radiation exposure from additional CT. This article presents an overview of current 3D MRI approaches for imaging cortical bone with CT-like bone contrast including ultrashort echo time, zero echo time, T1-weighted gradient recalled echo, susceptibility-weighted imaging and deep learning techniques. We also discuss clinical implementation of an optimized stack-of-stars 3D gradient recalled echo pulse sequence (3D-Bone) on commercially available MRI scanners for rendering 3D MRI with CT-like bone contrast in our institutional practice.

Incidence of Atypical Femoral Fracture and Its Mortality in a Single Center in Singapore.

Bisphosphonates (BP) are the most commonly prescribed effective form of osteoporosis treatment with adverse effects associated with prolonged use such as atypical femoral fractures (AFF). Asians have an elevated risk of AFF at 5 to 6 times those of whites and Hispanics. In this study, we characterize factors associated with AFF and its mortality in a single center in Singapore. We conducted a cohort study of subjects older than 50 years admitted to Changi General Hospital (CGH), Singapore, with fragility subtrochanteric femoral fractures from 2009 to 2015. Using the ASBMR 2014 criteria, fractures are classified into atypical and typical subtrochanteric femoral fractures. CGH uses a nationalized electronic health record that allows review of information on patients' demographics, clinical history and previous investigations. Mortality was assessed as of December 31, 2019. Between 2009 and 2015, there were 3097 hip fractures, of which 393 were subtrochanteric femoral fractures and 69 were classified as AFF by ASBMR 2014 criteria. A total of 52.2% of AFF occurred with BP exposure of median duration 56.5 (28 to 66) months. Multivariate regression showed that BP exposure was associated with the highest risk of AFF (odds ratio [OR] = 6.65 [2.35-18.9]). AFF patients had higher 5-year survival (0.85 versus 0.62, p = 0.001) compared with typical subtrochanteric fracture patients. However, after adjusting for variables, the type of subtrochanteric femoral fractures were no longer significantly associated with progression to death, whereas older age, higher mean Charlson comorbidity score, and Malay ethnicity were the strongest predictors of death. AFF constitutes a small proportion of hip and femoral fractures with prolonged BP use being the highest risk factor for its development. There is no evidence of increased mortality or morbidity in patients with AFF compared with the typical subtrochanteric fracture. The fear of AFF should not impede treatment of typical osteoporotic fractures in this population. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Validation of cartilage thickness calculations using indentation analysis.

Different methods have been used to cross-validate cartilage thickness measurements from magnetic resonance images (MRIs); however, a majority of these methods rely on interpolated data points, regional mean and/or maximal thickness, or surface mean thickness for data analysis. Furthermore, the accuracy of MRI cartilage thickness measurements from commercially available software packages has not necessarily been validated and may lead to an under- or overestimation of cartilage thickness. The goal of this study was to perform a matching point-to-point validation of indirect cartilage thickness calculations using a magnetic resonance (MR) image data set with direct cartilage thickness measurements using biomechanical indentation testing at the same anatomical locations. Seven bovine distal femoral condyles were prepared and a novel phantom filled with dilute gadolinium solution was rigidly attached to each specimen. High resolution MR images were acquired, and thickness indentation analysis of the cartilage was performed immediately after scanning. Segmentation of the MR data and cartilage thickness calculation was performed using semi-automated software. Registration of MR and indentation data was performed using the fluid filled phantom. The inter- and intra-examiner differences of the measurements were also determined. A total of 105 paired MRI-indentation thickness data points were analyzed, and a significant correlation between them was found (r=0.88, p<0.0001). The mean difference (+/-std. dev.) between measurement techniques was 0.00+/-0.23 mm, with Bland-Altman limits of agreement of 0.45 mm and -0.46 mm. The intra- and inter-examiner measurement differences were 0.03+/-0.22 mm and 0.05+/-0.24 mm, respectively. This study validated cartilage thickness measurements from MR images with thickness measurements from indentation by using a novel phantom to register the image-based and laboratory-based data sets. The accuracy of the measurements was comparable to previous cartilage thickness validation studies in literature. The results of this study will aid in validating a tool for clinical evaluation of in-vivo cartilage thickness.

Correlation of magnetic resonance imaging and histologic examination of physeal bars in a rabbit model.

BACKGROUND: The formation of a physeal bony bridge, or bar, is frequently observed in pediatric patients after trauma and is visualized using magnetic resonance imaging (MRI). No study to date has validated the indirect MRI bar area measurements with direct measurements. PURPOSE: To create a physeal bar using a radiofrequency (RF) ablation technique in a rabbit model and to validate an indirect measurement of the bar area from MRIs with direct histologic measurements. METHODS: An epiphysiodesis procedure was performed on the proximal tibial growth plates of 15 skeletally immature rabbit knees using radiofrequency ablation. The rabbits were euthanized 6 weeks postoperatively and volumetric ex vivo MRIs of the knees were acquired. The physeal bar area was calculated from a 3-dimensional reconstruction of the segmented MRIs and from matching histologic sections of the tibia. RESULTS: A physeal bar was successfully created in all the rabbits. A strong correlation, r=0.83 (P=0.0001), was found between the MRI and histologic surface area measurements. The mean bar area from MRI measurements was 35.0 ± 20.8 mm² (mean ± SD), and the mean bar area from histologic measurements was 29.8 ± 16.1 mm². CONCLUSIONS: This study found excellent correlation between the MRI and histologic physeal bar area measurements. The measurement differences that were found may be attributed to histologic specimen preparation and the geometry chosen to model the physis. CLINICAL RELEVANCE: The results of this study allow for the quantitative evaluation of in vivo human physes in future studies and development of predictive models for limb length discrepancy.

REACT - A novel flow-independent non-gated non-contrast MR angiography technique using magnetization-prepared 3D non-balanced dual-echo dixon method: Preliminary clinical experience.

Flow-independent relaxation-based non-contrast MR angiography techniques yield good signal-to-noise ratio and high blood-tissue contrast, complementing non-contrast flow-dependent and contrast-enhanced MR angiography techniques in the assessment of vascular disorders. However, these techniques often suffer from imaging artifacts at high magnetic field strengths or across large fields-of-view. Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) is a recently introduced flow-independent non-gated non-contrast three-dimensional MR angiography technique that has been developed to mitigate some of these issues. We present our initial experience with the clinical applications of REACT in imaging disorders of the central and peripheral vascular systems.

Dual-energy X-ray absorptiometry bone densitometry and pitfalls in the assessment of osteoporosis: a primer for the practicing clinician.

A guide to the clinician on the use of dual-energy x-ray absorptiometry bone densitometry for the management of osteoporosis and the importance of recognizing its pitfalls. PURPOSE: Osteoporosis is a major risk factor for severe fractures in the aging population worldwide, posing a serious public health issue. Dual-energy X-ray absorptiometry (DXA) is and remains the main tool for screening of osteoporosis and monitoring of osteoporosis treatment through quantitative measurement of bone mineral density (BMD). Employing DXA to measure BMD is not without pitfalls. We set out to analyze and classify the potential pitfalls of DXA acquisitions and BMD measurements encountered in clinical practice in our institution. METHODS: Technical inaccuracies and discrepancies in BMD interpretation in the history of our department were analyzed and classified into different categories of pitfalls. RESULTS: We found that major pitfalls of BMD acquisition and interpretation using DXA can be classified into technical, patient, and interpretive factors. These are illustrated with case examples. CONCLUSION: Good technical understanding of BMD measurements using DXA and recognition of potential pitfalls allow for greater technical and interpretive accuracy, which together hopefully increases the precision of osteoporosis management when practiced in accordance with established clinical guidelines.

Free-breathing non-contrast-enhanced flow-independent MR angiography using magnetization-prepared 3D non-balanced dual-echo Dixon method: A feasibility study at 3 Tesla.

In this work we aimed to investigate the feasibility of using a new pulse sequence called Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) for free-breathing non-contrast-enhanced MR angiography (NCE-MRA) for multiple anatomies on 3T. Two magnetization-preparation pulses were incorporated with a three-dimensional dual-echo Dixon sequence. A T2-prep pulse, followed by a non-selective inversion pulse with a short inversion time, together suppressed tissue with short T1 and T2, while enhancing the signal of native blood with long T1 and T2. A two-point non-balanced gradient-echo Dixon method, based on dual-echo acquisition with semi-flexible echo times for water-fat separation, was used for improved fat suppression over a large field of view. General image quality, vasculature visibility, and clinical indications of the proposed method were investigated in healthy subjects and patients in both torso and extremities based on visual inspection. Preliminary results from REACT obtained in free-breathing with no cardiac triggering showed uniform suppression of background tissue over the field of view and robust blood-to-tissue contrast over multiple anatomies. Future clinical studies are warranted for further investigation of its diagnostic performance and limitations.

Computed Tomography Urography: Comparison of Image Quality and Radiation Dose between Single- and Split-Bolus Techniques.

INTRODUCTION: In this study, we aimed to compare the split-bolus and single-bolus computerised tomography (CT) urography and determine if this offers a reduction in radiation dose without compromising image quality. MATERIALS AND METHODS: A retrospective evaluation was performed on 88 patients undergoing split-bolus CT urography and this was compared to a control group of 101 consecutive patients undergoing single-bolus CT urography. A radiation dose analysis was performed on each subject. Subjects with urinary bladder lesions, hydronephrosis, renal masses or cysts >3 cm in diameter were excluded. All images were classified according to image quality by 2 consultant radiologists. RESULTS: Opacification of  the renal parenchyma, pelvicalyceal system, proximal ureters and urinary bladder were comparable between the 2 techniques, whilst image quality of the middle and distal third of the ureters was better using the split-bolus technique. The mean dose length product (DLP) for the single-bolus technique was 1324.1 mGy-cm, whilst that of  the split-bolus technique was 885.7 mGy-cm. The mean effective dose reduction was calculated to be 31.1% between the 2 groups. CONCLUSION: The split-bolus technique gives a reduced radiation dose without compromising image quality. The associated reduction in images is beneficial for data storage and reporting efficiency. As such, our department will adopt the split-bolus technique for young, low-risk patients.

Anatomical Variants of Lister's Tubercle: A New Morphological Classification Based on Magnetic Resonance Imaging.

OBJECTIVE: Lister's tubercle is used as a standard anatomical landmark in hand surgery and arthroscopy procedures. In this study, we aimed to evaluate and propose a classification for anatomical variants of Lister's tubercle. MATERIALS AND METHODS: Between September 2011 and July 2014, 360 MRI examinations for wrists performed using 1.5T scanners in a single institution were retrospectively evaluated. The prevalence of anatomical variants of Lister's tubercle based on the heights and morphology of its radial and ulnar peaks was assessed. These were classified into three distinct types: radial peak larger than ulnar peak (Type 1), similar radial and ulnar peaks (Type 2) and ulnar peak larger than radial peak (Type 3). Each type was further divided into 2 subtypes (A and B) based on the morphology of the peaks. RESULTS: The proportions of Type 1, Type 2, and Type 3 variants in the study population were 69.2, 21.4, and 9.5%, respectively. For the subtypes, the Type 1A variant was the most common (41.4%) and conformed to the classical appearance of Lister's tubercle; whereas, Type 3A and 3B variants were rare configurations (6.4% and 3.1%, respectively) wherein the extensor pollicis longus tendon coursed along the radial aspect of Lister's tubercle. CONCLUSION: Anatomical variations of Lister's tubercle have potential clinical implications for certain pathological conditions and pre-procedural planning. The proposed classification system facilitates a better understanding of these anatomical variations and easier identification of at-risk and rare variants.