أفضل التصوير بالرنين المغناطيسي (انظر. التصوير بالرنين المغناطيسي لمنطقة واحدة) أطباء الجهاز الهضمي في أنقرة - توب -12 أطباء

الأستاذ المشارك الدكتور يوسف أجكجوز
التخصص: طب الأورام

تعليم:

• 2004-2011: كلية الطب بجامعة إينونو
• 2011-2016: مستشفى أنقرة نوموني للتدريب والبحث، الطب الباطني
• 2017-2022: جامعة العلوم الصحية، قسم الأورام الطبية

الخبرة المهنية:

• 2016-2017: مستشفى مدينة بينجول، الطب الباطني
• 2021-2022: جامعة العلوم الصحية، قسم الأورام الطبية
• 2022-2023: مستشفى كاستامونو للتعليم والبحث، قسم الأورام الطبية
• 2023-2024: جامعة ولاية أوهايو، قسم الأورام الطبية
• 2024-حتى الآن: جامعة لقمان حكيم، قسم الأورام الطبية، مستشفى أنقرة

التجارب السريرية، الدورات، الشهادات:

التجارب السريرية:

• 2017-2021: المرحلة الثالثة، دراسة CheckMate-649 (باحث مساعد)
• 2022-حتى الآن: المرحلة الثالثة، دراسة Fortitude-101 (باحث مساعد)

الدورات:

• 2018: برنامج تدريبي في الإحصاء الحيوي الأساسي والمتقدم من Medicres (جاري)، إسطنبول-فيينا
• 2019: دورة تعليمية في علم الأورام المناعي، 1-2 مارس 2019، فيينا، مجموعة الأورام التعاونية لأوروبا الوسطى (CECOG)
• 2018: شهادة الممارسة السريرية الجيدة، 7-8 أبريل 2018، أنقرة، جامعة العلوم الصحية
• 2017: برنامج تدريب أساسيات علم الأورام، 25-26 نوفمبر 2017، أضنة، جمعية علم الأورام السريرية
• 2016: دورة الموجات فوق الصوتية الأساسية (10 ساعات نظرية + 10 ساعات عملية)، 24-25 سبتمبر 2016، أنقرة، جمعية طب الطوارئ التركية

الشهادات:

• جاري: شهادة ECFMG
• 2024: السلوك المسؤول في الأبحاث في CITI (جامعة ولاية أوهايو)
• 2024: CITI IACUC-أبحاث الحيوانات المعملية (جامعة ولاية أوهايو)
• 2024: حماية الأشخاص الخاضعين للتجارب من خلال CITI (جامعة ولاية أوهايو)
• 2024: ممارسات CITI السريرية الجيدة (جامعة ولاية أوهايو)
• 2023: اختبار اللغة الإنجليزية المهنية (OET)
• 2019: نظام اختبار اللغة الإنجليزية الدولي (IELTS)، مجموع النقاط: 6.5، 26 مايو 2019، أنقرة، المجلس الثقافي البريطاني
• 2017: امتحان USMLE Step 2 CK؛ النتيجة: 244، 7 فبراير 2017
• 2016: امتحان USMLE الخطوة 1؛ النتيجة: 215، 25 أغسطس 2016

العضويات:

• الجمعية الأمريكية لعلم الأورام السريري (ASCO) - 2022
• الجمعية التركية لعلم الأورام الطبية - 2020

PEER‐REVIEWED PUBLICATIONS
1. Bal E, Bozkurt I “Santral Sinir Sistemi Tümörlerinde Epidemiyoloji ve Klinik Epidemiology and Clinic in Central
Nervous System – a review” Türkiye Klinikleri J Med Oncol-Special Topics 2013;6(1):1-5
2. Bozkurt I, Ozveren MF, Ayberk G “Tricks in shortening spinal column reconstruction through posterior approach –
Letter to editor” Arch Orthop Trauma Surg. 2014 Apr 6. PMID: 24705509
3. Dumanli Ozcan AT, Aksoy M, Erkılıç E, Özcan E, Bozkurt I, Bal E “Anesthesia Management During Biopsy With
Stereotactic Neurosurgery Intervention” Turk Med J. 2016; 8(2): 65-68
4. Senturk S, Gurcay AG, Bozkurt I, Gurcan O, Eroglu H, Turkoglu OF, Bodur E, Bavbek M “Effects of tadalafil—TypeV phosphodiesterase enzyme inhibitor—On rats with spinal trauma” British Journal of Neurosurgery, Online on
November 7, 2014. doi:10.3109/02688697.2014.976174.
5. Gurcay AG, Gurcan O, Kazanci O, Bozkurt I, Senturk S, Bodur E, Turkoglu OF, Bavbek M “Comparative biochemical
and motor function analysis of Alpha Lipoic Acid and N-Acetyl Cysteine treatment on rats with experimental spinal
cord injury” Turkish Neurosurgery 2016;26(1):119-26. doi: 10.5137/1019-5149.JTN.14594-15.0.
6. Kazanci A, Gurcan O, Gurcay AG, Bozkurt I, Algin O, Turkoglu OF, Bavbek M. “A simple, safe and effective surface
marking and targeting method combined with intraoperative ultrasonography for small subcortical intracranial
lesions.” J Neurosurg Sci. 2015 Jul 14. PMID: 26173480
7. Gurcan O, Gurcay AG, Kazanci A, Senturk S , Bozkurt I “Extended Lumbar Laminectomy: A Safe And Swift
Technique / Uzatılmış Lomber Laminektomi: Güvenli Ve Hızlı Bir Teknik” The Journal of Turkish Spinal
Surgery, Volume: 27, Issue: 2, 2016, pp: 117-120.
8. Gurcay AG, Kazanci A, Gurcan O, Bozkurt I, Onder E, Altınel F, Bavbek M. “Evaluation of Topical Application of
Polysaccharide Hemostat and Oxidized Regenerated Cellulose on Epidural Fibrosis in Rats”, Journal of
Neurological Sciences (Turkish) 2016, Volume 33, Number 2, 278-85.
9. Gurcay AG, Bozkurt I, Senturk S, Kazanci A, Gurcan O, Turkoglu OF, Beskonakli E. “Diagnosis, treatment, and
management strategy of meningioma during pregnancy,” Asian J Neurosurg, ahead of print, DOI:10.4103/1793-
5482.181115
10. Gurcay AG, Gurcan O, Kazanci A, Bozkurt I, Senturk S, Ferat M, Turkoglu OF, Beskonakli E, Orhun Yavuz H S.
“Xanthogranuloma of the sellar region.” Neurol India 2016;64:1075-9, DOI: 10.4103/0028-3886.190238
11. Turkoglu OF, Bozkurt I. “The Use of Hemostatic Matrix with Thrombin in an Adjacent Segment Disease patient
using ASA,” Turkiye Klinikleri Gold J 2017;2(1):5-7 Article Language: TR
12. Gurcan O, Kazanci A, Gurcay AG, Kucukyildiz HC, Bozkurt I, Turkoglu OF, Bavbek M. “Occipital Aneurysmal Bone
Cysts in an Adult Patient: A Rare Case and Review of Literature.” Med J Islamic World Acad Sci. doi:
10.5505/ias.2016.27146 2016;24(4):123-126
13. Bal E, Bozkurt I, Akıncı C, Yılmaz N. “Metopic Suture Synostosis (Trigonocephaly): A Case Report.” Med J Islamic
World Acad Sci. 2016; 24(2): 69-72. DOI: 10.5505/ias.2016.15921
3
14. Atasoy F, Sen B, Nar F, Bozkurt I. “Improvement of Radial basis Function Interpolation Performance on Cranial
Implant Design” International Journal of Advanced Computer Science and Applications(IJACSA), 8(8), 2017.
http://dx.doi.org/10.14569/IJACSA.2017.080811
15. Ozturk Y, Bozkurt I, Yaman ME, Guvenc Y, Tolunay T, Bayram P, Hayirli N, Billur D, Erbay FK, Senturk S, Bozkurt G.
“Histopathologic Analysis of Tamoxifen on Epidural Fibrosis.” World Neurosurg. 2018 Mar;111:e941-e948. doi:
10.1016/j.wneu.2018.01.004.
16. Senturk S, Yaman ME, Aydin HE, Guney G, Bozkurt I, Paksoy K, Abdioglu AA. Effects of Resveratrol on
Inflammation and Apoptosis After Experimental Spinal Cord Injury. Turk Neurosurg. 2018;28(6):889-896. doi:
10.5137/1019-5149.JTN.21829-17.3. PMID: 29368318.
17. Tezel G, Timur SS, Bozkurt I, Turkoglu OF, Eroglu I, Nemutlu E, Oner L, Eroglu H. “A Snapshot on the Current Status
of Alzheimer's Disease, Treatment Perspectives, in-Vitro and in-Vivo Research Studies and Future Opportunities,”
Chem Pharm Bull (Tokyo). 2019 Oct 1;67(10):1030-1041. doi: 10.1248/cpb.c19-00511.
18. Bozkurt I, Chaurasia B. “Attitudes of Neurosurgeons Toward Social Media: A Multi-Institutional Study.” World
Neurosurg. 2020 Dec 21:S1878-8750(20)32634-6. doi: 10.1016/j.wneu.2020.12.067.
19. Bozkurt I. “Meralgia Paresthetica Caused By Thoracolumbar Brace in Conservatively Treated Thoracolumbar
Fractures.” J Turk Spinal Surg 2021; 32: 80-83. DOI: 10.4274/jtss.galenos.2021.54264
20. Ismail Bozkurt, Atilla Kazanci, Oktay Gurcan, Ahmet G. Gurcay, Ata T. Arikok & Murad Bavbek (2021) “Spinal
epidural fibrosis following hemostatic agent employment,” British Journal of Neurosurgery, DOI:
10.1080/02688697.2021.1950627
21. İsmail BOZKURT, Ebru KARAKOÇ (2021).Spine Surgery During The Covid-19 Pandemic: One Trauma Center
Experience In Central Anatolia. Osmangazi Tıp Dergisi. Doi: 10.20515/otd.957550
22. Ozturk Y, Bozkurt I, Guvenc Y, et al. Modafinil attenuates the neuroinflammatory response after experimental
traumatic brain injury [published online ahead of print, 2021 Sep 21]. J Neurosurg Sci. 2021;10.23736/S0390-
5616.21.05382-0. doi:10.23736/S0390-5616.21.05382-0
23. Bozkurt I, Umana HE, Deora H, Wellington J, Karakoc E, Chaurasia B. “Factors Affecting Neurosurgeons’ Decisions
to Forgo Life-Sustaining Treatments after Traumatic Brain Injury.” World Neurosurgery Available online 18
December 2021 In Press, Journal Pre-proof. https://doi.org/10.1016/j.wneu.2021.12.056
24. Bozkurt I, Ozturk Y, Guney G, Arslan B, Gulbahar O, Guvenc Y, Senturk S, Yaman ME. “Effects of pirfenidone on
experimental head injury in rats.” Int J Clin Exp Pathol 2022;15(1):20-28. ISSN:1936-2625/IJCEP0138062
25. Bozkurt I, Yasar B, Uslu MB, Bozdogan N. “A Primary Sacral Melanoma of Unknown Origin: A Case Report.”
Oncologie 2022; 24(1), 163–171. DOI: 10.32604/oncologie.2022.019263
26. Paksoy K, Şentürk S, Akyoldas G, Bozkurt İ, Yaman ME, Sezgin Y. “Radyological Comparison of Lumbar Nerve Root
Thickness in Patients with Lumbar Disc Herniation.” Genel Tıp Derg. 2022; 32(3): 335-338. doi:
10.54005/geneltip.1034311
27. Alvarez Aquino A, Ramirez M, Bozkurt I, et al. “Treatment of Intracranial Tumors With Stereotactic Radiosurgery:
Short-Term Results From Cuba.” Cureus. 2022 Oct;14(10): e29955. doi:10.7759/cureus.29955
28. Lavadi RS, Bozkurt I, Harikar MM, Umana GE, Chaurasia B. “The Role of Social Media on the Research Productivity
of Neurosurgeons During the COVID-19 Pandemic.” World Neurosurg. 2022 Sep 16:S1878-8750(22)01328-6. doi:
10.1016/j.wneu.2022.09.051.
29. Ferini G, Palmisciano P, Scalia G, Haider AS, Bin-Alamer O, Sagoo NS, Bozkurt I, Deora H, Priola SM, Aoun SG,
Umana GE. “The role of radiation therapy in the treatment of spine metastases from hepatocellular carcinoma: a
systematic review and meta-analysis.” Neurosurg Focus. 2022 Nov;53(5):E12. doi: 10.3171/2022.8.FOCUS2255.
PMID: 36321286.
30. Hernandez C L, Díaz S M, Nurmukhametov R, Goncharov E, Ramirez MJE, Bozkurt I, Ramirez Pena IJ. “A Case
Report of a Sacral Giant Cell Tumor Treated With Block Resection and Lumbo-Pelvic Fixation.” Cureus. 2022
Nov;14(11): e31224. doi:10.7759/cureus.31224
4
31. Bozkurt I, Senturk S, Yaman ME, Guvenc Y, Ozturk Y, Guney G, Cingirt M, Gulbahar O. “Effect of sumatriptan
following simulated traumatic brain injury in rats.” Cesk Slov Neurol N 2022; 85(5): 389-396. doi:
10.48095/cccsnn2022389
32. Türkmen C, Özcan A, Karahan Z, Bozkurt İ. “Reciprocal activation changes of lower extremity muscles caused by
the abdominal hollowing maneuver in patients with unilateral lumbar disc herniation: an EMG study.” J Health Sci
Med / JHSM. 2023; 6(1): 59-65. doi: 10.32322/jhsm.1193371
33. Pahwa B, Chaurasia B, Garg K, Bozkurt I, Deora H. “Factors Affecting the Choice of Neurosurgery Subspecialty: A
Geographical and Gender-wise Analysis.” World Neurosurgery, 2023. doi: 10.1016/j.wneu.2023.01.012 
 

Sema Yılmaz was born on July 30, 1965. She received her undergraduate degree from Istanbul University Cerrahpaşa Medical Faculty and completed her medical residency training at the Department of Pediatrics at Zeynep Kamil Women's and Children's Health and Diseases Hospital. She also completed her medical subspecialty training in Pediatric Hematology/Oncology at Cukurova University. Her medical residency thesis was titled "The Relationship Between Morning First Urine Density and Nocturnal Enuresis in Children Aged 3-6 Years", and her medical subspecialty thesis was titled "Comparison of Sphingosine 1-phosphate Receptor 4 Gene Expression in Healthy Children and Neuroblastoma Patients". She started her medical career as a general practitioner. After working as a general practitioner for 4 years, she worked as a doctor researcher at Zeynep Kamil Women's and Children's Health and Diseases Training and Research Hospital for 5 years. She then served as a specialist doctor, assistant professor, and associate professor at various institutions. She worked at Houston MD Anderson, North Carolina-UNC, Boston-Harvard University in the USA. Additionally, she conducted research on cell therapies. She received the title of professor in Pediatric Hematology/Oncology at Usak Medical Faculty. She is a member of the Turkish Pediatric Oncology Group, European Association for Cancer Research (EACR), Turkish Medical Association, Turkish National Pediatrics Association, Turkish Pediatrics Association, Pediatrics Specialty Academy Association (PUADER), Turkish Immunology Association, Turkish Hematology Association, and Molecular Oncology Association (MOKAD). She currently serves her patients at Koru Hospital. Her medical interests include:

Cell therapies in childhood cancers

Cancer immunology

Investigation of genetic pathways responsible for cancer and metastasis

Pulmonary microbiota

BAL transplantation

Prof. Dr. Gülşah Bademci is a physician specialized in the field of brain, nerve, spine, and spinal cord surgery. She graduated as the fourth-ranked student from Ankara University Faculty of Medicine in 1993. She obtained her title as a brain and nerve surgeon from the Ankara University Faculty of Medicine Department of Brain and Nerve Surgery in 2001. In 2008, she became an associate professor at the Kırıkkale University Faculty of Medicine, and in 2021, she became a professor at the Yüksek İhtisas University Faculty of Medicine. She has contributed to numerous international publications, serving as a research and clinical fellow at the University of Arkansas Medical Sciences with Prof. Dr. M. Gazi Yaşargil, and as a research fellow at Yale University School of Medicine. She holds ECFMG America Board Step 1 and EANS European Board certificates. She speaks advanced-level English and has awards in tennis and swimming. She also pursues professional-level caricature art and medical illustration. In her 30-year career, she has performed numerous surgeries as a brain and nerve surgery specialist, particularly in spinal canal stenosis surgery, lumbar and cervical disc herniations, brain tumors, hydrocephalus surgery, and nerve compressions.

Prof. Dr. Osman İLHAN graduated from Ankara University Faculty of Medicine in 1978. After completing his internal medicine residency at the same faculty in 1982, he served as a senior resident at the GATA Hematology Clinic during his military service. After completing his mandatory service at SSK Ulus Hospital, he returned to Ankara University Faculty of Medicine for a subspecialty. In 1990, he became an associate professor of hematology. He worked in Genoa, Italy to increase his knowledge and experience in leukemia. He was part of the team that performed the first bone marrow stem cell transplant in Turkey. In 1996, he went to the MD Anderson Cancer Center in the USA to work on "Stem Cell Mobilization, Cryopreservation, and Transplantation." In 1996, he became a professor of hematology. In 1999, he was elected as the regional president of ESFH (European Society for Hemapheresis). Dr. İlhan, who was the founder and president of the Hemapheresis Society in 2000, joined the World Apheresis Association (WAA) in 2001. He became the President of the Turkish Hematology Association in October 2001. Dr. İlhan, who is an active member of the European Hematology Association (EHA), was a member of the accreditation committee (ECAH) for education. He played a role in the accreditation of Turkish hematologists in CME credits by participating in the accreditation of congresses and courses held in Turkey as a Provider Status. He served as the founding president of the Cellular Therapy and Regenerative Medicine Association established in 2008. He became the founding president of the Geriatric Hematology Association in 2011. He is the Honorary President of the World Apheresis Congress (WAA) held in 2012. Dr. İlhan, who previously served on drug licensing and ethics committees at the Ministry of Health, has also served as the Chairman of the Photopheresis-Apheresis Commission and the Scientific Committee for Bone Marrow Transplantation, as well as the Chairman of the National Organ Tissue Cell Coordination Board, the Scientific Board of Cord Blood, and the Stem Cell Research Board. He is the founding president of the STEM CELL FOUNDATION and has played an important role in the establishment of TURKOK (Turkish Stem Cell Donor Bank). Dr. İlhan has over 300 publications in journals registered in PubMed and more than 5000 citations. He holds the Platinum CME certificate from the European Hematology Association. He owns four brands/patents named “Kökten Çözüm (Deep Solution), Telehematoloji (Telehematology), Hemaferez (Hemapheresis), Kanser Kök Hücresi (Cancer Stem Cell)”. He is currently the President of the Ankara Medical Association. Prof. Dr. Osman İlhan, who served at Ankara University Faculty of Medicine for 50 years, began working at Özel Koru Ankara Hospital as of January 1, 2023.

His medical interests include:

Hematopoietic Stem Cell Transplantation (Autologous, Allogeneic)

Acute Leukemia

Chronic Leukemia Treatments

Hodgkin Lymphoma

Non-Hodgkin Lymphoma Treatments

Multiple Myeloma Treatments, MDS

Aplastic Anemia

ITP

TTP Treatments

Hypercoagulability

Hereditary Thrombophilia Treatments

Therapeutic Apheresis

Photopheresis

Geriatric Hematology Diseases.

Prof. Dr. Süleyman Bülent Bektaşer was born in Kayseri in 1968. He graduated from Hacettepe University Faculty of Medicine in 1992. In 1997, he completed his specialization training in Orthopedics and Traumatology at Ankara Dr. Muhittin Ülker Emergency and Traumatology Hospital with a thesis on "Total Knee Arthroplasty Applications and Early Results". Between 1997 and 2000, he worked as a specialist doctor at the Orthopedics and Traumatology Clinic of the same hospital, and between 2000 and 2004, he served as a chief resident at the same hospital. Between 2004 and 2013, he worked as a chief resident in the Orthopedics and Traumatology Clinic at Ankara Atatürk Training and Research Hospital of the Ministry of Health. He became an associate professor in 2004 and worked as a lecturer at Ankara Atatürk Training and Research Hospital between 2014 and 2016. He was appointed as a full professor at Yüksek İhtisas University in 2018. Throughout his academic career, he has published numerous scientific articles. He currently works at Koru Ankara Hospital and his medical interests include:

Hip, knee, shoulder arthroplasty (prosthetic surgery, robotic knee prosthesis surgery)

Extremity traumas (fractures and muscle/tendon tears)

Orthopedic oncology surgeries

Sports injuries and arthroscopy

Hand surgery

Shoulder and elbow surgery.

Prof. M.D. Yusuf Serdar Sakin was born in Nevşehir in 1978. After completing his primary and secondary education in Ankara, he graduated from the Faculty of Medicine at Gülhane Military Medical Academy in 2002.
Following his graduation, he served in Gole/Ardahan for two years. He started his internal medicine training at the Department of Internal Medicine, Gülhane Faculty of Medicine.
After completing his training, he worked as an internal medicine specialist in Ankara. A year later, he began additional training in the Department of Gastroenterology at Gülhane Faculty of Medicine and completed his training in 2014.
After graduation, Yusuf Serdar Sakin continued to work in the same department. He also received advanced endoscopy and Motility training at AMC Center in the Netherlands in 2017.
After obtaining the title of Associate Professor in 2017, he became a Professor in 2023.
He currently provides medical services to patients at Koru Ankara Hospital. His areas of medical interest include:

-Endoscopic retrograde cholangiopancreatography (ERCP)
-Push enteroscopy
-Endoscopic mucosal resection
-High-resolution manometry
-pH/pH-impedance metry analysis
-Advanced endoscopic procedures (stenting, dilation, etc.)
-Gastrointestinal motility disorders
-Gastroesophageal reflux disease
-Inflammatory bowel diseases
-Advanced endoscopic procedures and pancreatitis.

Kürşat Fidancı is a medical doctor who graduated from GATA Faculty of Medicine in 1999. Between 2000 and 2002, he served as the Chief Physician of the Şırnak Çakırsöğüt Commando Brigade. He completed his residency in Pediatrics from 2002 to 2006 at Istanbul GATA Haydarpaşa Training and Research Hospital. He worked as a Pediatrician at Ankara Beytepe Military Hospital between 2006 and 2009. He completed his subspecialty training in Paediatric Cardiology at GATA Faculty of Medicine Pediatric Cardiology Department from 2010 to 2013. He became an Assistant Professor in 2014 and obtained the title of Associate Professor in April 2016. He worked as a faculty member in the Department of Pediatric Cardiology at GATA Faculty of Medicine between September 2014 and December 2021. As a pediatric cardiologist, Dr. Kürşat Fidancı has seen numerous patients and his medical interests include Fetal Echocardiography, Congenital Heart Diseases, Rheumatic Heart Diseases, Rhythm Disorders, and Athlete's Heart Health and Follow-up.

Dr. Abdurrahim Gözen, born in 1982 in Gercüş, Batman, is a specialist in Orthopedics and Traumatology with a focus on pediatric orthopedics, trauma, arthroscopy, and arthroplasty. After graduating from Istanbul University Medical Faculty, he completed his residency at Yüzüncü Yıl University. With over six years of professional experience in both state and private hospitals, Dr. Gözen is an active member of associations like TOTBİD and TUSYAD. He has participated in numerous national and international conferences, consistently enhancing his expertise in orthopedic surgery and advancing patient care practices.

Assoc. Dr. İsmail Gülşen is a distinguished neurosurgeon serving at Lokman Hekim Van Hospital in Turkey. With extensive expertise in advanced brain and spine surgery, he has contributed significantly to the field through innovative techniques and patient-focused care. Dr. Gülşen specializes in diagnosing and treating complex neurological conditions, offering cutting-edge surgical interventions. His commitment to excellence is reflected in his continuous pursuit of medical advancements and personalized treatment strategies. For further details on his qualifications and professional achievements contact lokman hekim health group.

الدكتور بلال أرجول هو رائد في مجال أمراض الجهاز الهضمي.

لقد غيرت بروتوكولات العلاج المبتكرة التي ابتكرها حياة العديد من المرضى، بما في ذلك حالة رائعة حيث نجح في علاج مريض باستخدام جراحة بضع العضلة بالمنظار عن طريق الفم (POEM).

يقول الدكتور بلال أرجول في كثير من الأحيان: "الشفاء لا يقتصر على علاج حالة معينة؛ بل يتعلق باستعادة الأمل وتحسين الحياة". وتتجلى هذه الفلسفة في كل جانب من جوانب عمله، مما يجعل منه وفريقه شخصية ملهمة حقًا في المجتمع الطبي".
لقد ألف حوالي 100 بحث في مواضيع أكاديمية مختلفة