CASE REPORT
Decreased Subject Contrast and Summation Artifact An Explanation for a Nearly Imperceptible Bullet by X-ray Examination Eric W. Graham, BS,* Alexander M. Tawadros, MD,† and Joseph A. Prahlow, MD‡ Abstract: X-ray examination is used to detect foreign bodies during forensic autopsy of a suspected gunshot wound case. There are several previously described situations in which a projectile is not immediately localized by radiography. In this report, we present a case of a metal bullet lodged near the atlanto-occipital junction, where it was present but not readily apparent on radiograph. Although computed tomography is ideal for detecting such objects, many forensic pathologists must still rely on x-ray only. To our knowledge, the forensics literature does not contain a case where a lead bullet was rendered nearly imperceptible by x-ray examination. We describe 2 concepts of radiation physics—poor x-ray penetration and summation artifact—which can cause a radiopaque object such as a bullet to seem much less so. The difference between best practices in hospital and forensic radiology may explain how this occurred. This case serves to caution the pathologist that forensic radiographs may not completely depict the type or quantity of projectiles present in a gunshot wound case. Key Words: forensic autopsy, radiography, x-ray, gunshot wound (Am J Forensic Med Pathol 2014;35: 249–252)
T
he forensic autopsy has included radiography for more than 100 years.1 A primary purpose is to localize foreign bodies, such as projectiles, and assist in describing their path through the body.2 Commonly, these present with an easily distinguishable metallic density.3 Several scenarios have been described in which a projectile from a gunshot wound is not easily detected on initial radiograph.4–9 In this report, we present an autopsy case where a typical lead-core bullet near the base of the skull was not readily apparent on the radiograph. Only after careful inspection of the x-ray was a faint outline of the bullet evident, even after adjusting the digital x-ray image and consulting with a radiologist.
CASE REPORT A 39-year-old obese African-American man was found dead. A coroner's autopsy was performed in a hospital autopsy facility by a board-certified forensic pathologist. External examination revealed 7 gunshot wound complexes. Anterior/posterior (AP) radiographs of the skull, neck, chest, abdomen, pelvis, humerus, and femur were obtained by certified radiologic technologists via a portable General Electric AMX4 x-ray machine using an AGFA computed radiography detector (without attached viewing monitor). The radiographs were initially interpreted by the forensic pathologist (hard copies of films delivered to the autopsy room and viewed on a rated light box) and a radiologist (digital films
Manuscript received May 12, 2014; accepted July 19, 2014. From the *Indiana University School of Medicine-South Bend, South Bend; †Radiology, Inc, Mishawaka; and ‡South Bend Medical Foundation, Indiana University School of Medicine-South Bend, South Bend, IN. The authors report no conflicts of interest. Reprints: Joseph A. Prahlow, MD, South Bend Medical Foundation, Indiana University School of Medicine-South Bend, 530 N Lafayette Blvd, South Bend, IN 46601. E-mail: [email protected]. Copyright © 2014 by Lippincott Williams & Wilkins ISSN: 0195-7910/14/3504–0249 DOI: 10.1097/PAF.0000000000000121
Am J Forensic Med Pathol • Volume 35, Number 4, December 2014
viewed via PACS on a high-resolution monitor) to contain no radiopaque foreign bodies. Before internal examination, it was surmised that, of the 7 wounds, five were perforating, and one was graze type. Because there was no associated exit wound, the seventh entrance wound was considered to likely represent a penetrating wound, with the entrance in the left back (Fig. 1); however, no bullet was evident on x-rays of the head/neck (Fig. 2) or trunk regions. Careful examination of the scalp, facial orifices, and skin folds revealed no hidden exit wound. As the forensic pathologist was considering calling the x-ray technicians back to look for a possible bullet embolus, a more careful evaluation of the head/neck x-ray revealed the faint outline of what seemed to be a bullet, near the base of the skull (Fig. 3), although its apparent density on x-ray was much less than the gold necklace, which was readily apparent on the same film. Consultation with the radiologist was immediately made; however, the presumed bullet remained indistinct (Fig. 4). Despite this fact, the official radiology report was amended to mention the presence of a bullet, and subsequent internal examination at autopsy was confirmatory. The bullet perforated the posterior left chest wall and ribs 4, 3, 2, and 1. It then perforated the left neck and posterolateral aspect of the second cervical vertebral body, transected the cervical spinal cord, perforated the anterior aspect of the first cervical vertebral body, and entered the soft tissues immediately anterior and adjacent to the atlanto-occipital junction. A minimally deformed, jacketed, medium-caliber bullet was recovered from this location (Fig. 5). Casings at the scene revealed that the bullet was a Fiocchi 38 Special (Lecco, Italy).
DISCUSSION In a gunshot wound case, radiographs are commonly used to detect metallic fragments, bullets, or jacketing present within the body at autopsy. A “bullet rule”10 has been described, in which the sum of bullet wounds (entrance and exit) and projectiles found on imaging should always be an even number. When this is not initially true, the pathologist must consider several possibilities. Misidentification of the presumed entrances and exits may have occurred, or the pathologist may have initially missed an entrance or exit wound. There may have been intracorporeal fragmentation, leading to multiple exit wounds from a single entrance. Wounds may be “hidden” in hair, skin folds, or a body orifice. Another common reason that the “wound plus x-ray projectile” might not equal an even number is when the x-ray examinations initially “miss” a projectile. Even experienced radiologists may miss a projectile on imaging through the “professional blinkers phenomenon.”4 The apparent angle of entry does not necessarily correlate with the final resting location of the projectile or fragments. Bullets may change angle within the body when encountering a bone5 or may embolize to distant areas outside the view of the initial radiographs.6 Further exploration may be necessary. Shotgun wadding is nonmetallic and thus not readily apparent by x-ray.7 Nonradiopaque plastic or rubber bullets are rarely used but can be seen in law enforcement settings.8 In addition, ammunition with aluminum jacketing exists; if the jacketing separates from the bullet core, the jacket, which is www.amjforensicmedicine.com
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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Graham et al
FIGURE 1. Gunshot entrance wound of the left upper midback region.
radiolucent, may not be visualized on x-ray.9 Furthermore, not all suspect densities seen in gunshot wound radiographs are actually projectiles. Bullet mimics may include other internal foreign bodies,11 bony fragments,12 or external items such as zippers.13 Multidetector computed tomography (MDCT) has been suggested as superior to standard imaging for the detection of projectile fragments.14 A comparison study by Harcke et al15 demonstrated that full-body digital radiography successfully identified all metal fragments also found by MDCT, although MDCT was superior in 3-dimensional localization. For many forensic pathologists, such imaging is simply not available at their facility. In the current case, a lead-core bullet was not clearly visualized on AP imaging initially. Only after careful reexamination of the x-ray did it become apparent that a bullet was actually present within the victim's upper neck region, near the base of the skull. Although a lateral skull study is essential in an emergent gunshot
wound of the head or neck,16 it is not always performed in autopsy cases. Often, the initial autopsy evaluation includes only a single AP image. Reasons for not universally performing an additional lateral view initially may include difficult patient positioning, limited technologist availability in a hospital setting, or increased cost. In the ideal setting, a lateral film would be performed and, in this case, would likely have been beneficial in detecting the obscured bullet.
FIGURE 2. The AP radiograph of the head and neck, with no obviously visible projectile. Note that the gold necklace is readily visible.
FIGURE 4. An “enhanced” x-ray image, attempting to better visualize the bullet. Note that, compared with the gold necklace, the bullet remains nearly imperceptible.
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FIGURE 3. A closer view of the x-ray depicted in Figure 2, with an arrow indicating the location of the supposed bullet.
© 2014 Lippincott Williams & Wilkins
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Am J Forensic Med Pathol • Volume 35, Number 4, December 2014
FIGURE 5. The bullet recovered from the victim at autopsy.
This case provides an example of 2 phenomena of radiography understood in the radiation physics literature, but, to our knowledge, undescribed in the forensic pathology literature: poor penetration (leading to decreased subject contrast) and summation artifact. With radiography, x-rays pass through the patient onto a cassette, forming an image. Each tissue encountered by the x-rays attenuates the beam according to its density and thickness, which leads to the contrast visualized on a radiograph. Detection is based on 2 principles. Object contrast is the inherent difference in density between a lesion and its surrounding structures, and subject contrast is the difference in x-ray transmission.17,18 The x-ray tube produces x-rays across a continuum of energy levels, measured in kilovoltage. Higher energy x-rays are better able to penetrate tissues. Lower energy x-rays are preferentially absorbed when they encounter tissues, increasing the effective energy level of remaining x-rays. Commonly, kilovoltage is indicated by the kilovoltage peak (kVp), which describes the highest energy level produced. The kVp is responsible for penetration of tissues, and an inappropriately low kVp will lead to incomplete penetrance and decreased subject contrast.18 The AP skull film was performed at 70 kVp and 3.2 mA s with an exposure rating of 1.86 log median exposure. The film was slightly underexposed, with company recommendations for log median exposure between 1.9 and 2.5 on AGFA systems.19 However, the primary concern with this case is incomplete penetration of the anatomy, leading to poor visualization of all structures and masking the deeply situated bullet. A better-penetrated image will have longer grayscale and will provide finer anatomical detail. Use of a higher kVp, such as 80, would have significantly improved penetration of the bony skull and mandible and facilitated differentiation of the bullet.18 Patient radiation dose is not a primary concern for the deceased, and every effort should be made to provide sufficient anatomical detail with appropriate exposure levels. In addition, the jaw, teeth, cervical spine, and deep soft tissues of the neck significantly sheltered the bullet, which was deeply situated. These dense tissues and the depth of the bullet preferentially attenuated low-energy x-rays so that x-rays reaching the bullet had a better chance of being transmitted. Thus, although there was a significant density difference between them, this decreased the subject contrast between the lead bullet and surrounding tissues. This masking is termed summation artifact. The metal necklace was denser and less sheltered, thus appearing as expected for a metal object. We rely on the assistance of the corresponding hospital radiology department to obtain forensic radiographs and often overlook the challenges faced because of the differences between © 2014 Lippincott Williams & Wilkins
Decreased Subject Contrast and Summation Artifact
forensic and typical radiography. First, one of the most common themes in imaging is to decrease radiation dose to as low as reasonably achievable. Although this principle does not apply in the setting of imaging deceased patients, the emphasis on decreasing dose in the rest of radiology may make typical practices less than ideal for autopsy purposes. Second, many radiology technologists have little experience working with autopsies. The lack of experience as well as the potential stress of dealing with the deceased may keep the technologist from using best practices. In addition, a hospital's radiology department may be quite large, with numerous technologists. If the number of autopsy cases requiring x-ray examination is relatively small, it is likely that each individual technologist's experience with autopsy radiography will be quite limited. The pathologist should be aware of these issues when using forensic radiography. The present case illustrates the potential for a projectile to be masked on radiography to a point where it is nearly invisible, depending on location and imaging technique. This should be an additional consideration when the bullet rule seems not to hold on initial evaluation. The pathologist should be aware of the several possibilities in which radiographs may not completely depict foreign bodies in a gunshot wound case, including lead projectiles. Although CT imaging is ideal in any foreign body investigation, many forensic pathologists do not have access to this technology. In the absence of readily available CT imaging or other body scan x-ray technology, many pathologists must rely on standard radiography at autopsy. For those forensic pathologists who must use hospital-based radiology services, several additional obstacles may exist in obtaining and interpreting autopsy x-rays. Inadequate penetration and summation artifact represent an explanation for why an otherwise radiopaque object, such as a bullet, may become much less radiopaque in appearance on routine x-ray. The forensic pathologist and radiographic operator must recognize that technical factors can significantly mask the appearance of foreign bodies and take care to perform an adequate study.
REFERENCES 1. Brogdon BM, Lichtenstein J. Forensic radiology in historical perspective. In: Brogdon BM, ed. Forensic Radiology. Boca Raton, FL: CRC Press; 1998:13–34. 2. Choi CH, Pritchard J, Richard J. Path of bullet and injuries determined by radiography. Am J Forensic Med Pathol. 1990;11:244–245. 3. Wilson AJ. Gunshot injuries: what does a radiologist need to know? RadioGraphics. 1999;19:1358–1368. 4. Bajanowski T, Karger B, Brinkmann B. Scratched pustule or gunshot wound? A medical odyssey. Int J Legal Med. 2001;114(4–5):267–268. 5. Engels PT, Tien HC. The lucky penny: an illustration of the bullet rule. CMAJ. 2012;184:63–65. 6. Slobodan S, Slobodan N, Djordje A. Popliteal artery bullet embolism in a case of homicide: a case report and review of the tangible literature. Forensic Sci Int. 2004;139:27–33. 7. Beverly MC, Pring DJ, Coombs RR. Radiolucent plastic in gunshot wounds. Injury. 1985;16:461–463. 8. Hollerman JJ, Fackler ML, Coldwell DM, et al. Gunshot wounds: 2. Radiology. AJR Am J Roentgenol. 1990;155:691–702. 9. Conradi SE. New aluminum-jacketed bullets: the case of the “invisible” jacket. Am J Forensic Med Pathol. 1982;3:153–155. 10. Westreich M. The odd or even bullet. Injury. 1986;17:45–46. 11. Cina SJ, Gelven PL, Nichols CA. A rock in a hard place. A brief case report. Am J Forensic Med Pathol. 1995;16:333–335.
www.amjforensicmedicine.com
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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Graham et al
12. Geary UM, Ritchie DA, Luke LC. Occult gunshot injury of the temporal bone. J Accid Emerg Med. 1997;14:185–186. 13. Dodd GD, Budzik RF. Identification of retained firearm projectiles on plain radiographs. AJR Am J Roentgenol. 1990;154:471–475. 14. Harcke HT, Levy AD, Getz JM, et al. MDCT analysis of projectile injury in forensic investigation. AJR Am J Roentgenol. 2008;190:W106–W111. 15. Harcke HT, Levy AD, Abbot RM. Autopsy radiography: digital radiographs (DR) vs multidetector computed tomography (MDCT) in high-velocity gunshot-wound victims. Am J Forensic Med Pathol. 2007;28:13–19.
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16. Pinto A, Brunese L, Scaglione M, et al. Gunshot injuries in the neck area: ballistics elements and forensic issues. Semin Ultrasound CT MR. 2009;30:215–220. 17. Huda W, Sloane R. Review of Radiology Physics. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2003. 18. Carroll QB. Practical Radiographic Imaging. 8th ed. Springfield, IL: Charles B. Thomas; 2007. 19. Carlton RR, Adler AM. Principles of Radiographic Imaging: An Art and a Science. Clifton Park, NY: Delmar Learning; 2005.
© 2014 Lippincott Williams & Wilkins
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Decreased Subject Contrast and Summation Artifact An Explanation for a Nearly Imperceptible Bullet by X-ray Examination Eric W. Graham, BS,* Alexander M. Tawadros, MD,† and Joseph A. Prahlow, MD‡ Abstract: X-ray examination is used to detect foreign bodies during forensic autopsy of a suspected gunshot wound case. There are several previously described situations in which a projectile is not immediately localized by radiography. In this report, we present a case of a metal bullet lodged near the atlanto-occipital junction, where it was present but not readily apparent on radiograph. Although computed tomography is ideal for detecting such objects, many forensic pathologists must still rely on x-ray only. To our knowledge, the forensics literature does not contain a case where a lead bullet was rendered nearly imperceptible by x-ray examination. We describe 2 concepts of radiation physics—poor x-ray penetration and summation artifact—which can cause a radiopaque object such as a bullet to seem much less so. The difference between best practices in hospital and forensic radiology may explain how this occurred. This case serves to caution the pathologist that forensic radiographs may not completely depict the type or quantity of projectiles present in a gunshot wound case. Key Words: forensic autopsy, radiography, x-ray, gunshot wound (Am J Forensic Med Pathol 2014;35: 249–252)
T
he forensic autopsy has included radiography for more than 100 years.1 A primary purpose is to localize foreign bodies, such as projectiles, and assist in describing their path through the body.2 Commonly, these present with an easily distinguishable metallic density.3 Several scenarios have been described in which a projectile from a gunshot wound is not easily detected on initial radiograph.4–9 In this report, we present an autopsy case where a typical lead-core bullet near the base of the skull was not readily apparent on the radiograph. Only after careful inspection of the x-ray was a faint outline of the bullet evident, even after adjusting the digital x-ray image and consulting with a radiologist.
CASE REPORT A 39-year-old obese African-American man was found dead. A coroner's autopsy was performed in a hospital autopsy facility by a board-certified forensic pathologist. External examination revealed 7 gunshot wound complexes. Anterior/posterior (AP) radiographs of the skull, neck, chest, abdomen, pelvis, humerus, and femur were obtained by certified radiologic technologists via a portable General Electric AMX4 x-ray machine using an AGFA computed radiography detector (without attached viewing monitor). The radiographs were initially interpreted by the forensic pathologist (hard copies of films delivered to the autopsy room and viewed on a rated light box) and a radiologist (digital films
Manuscript received May 12, 2014; accepted July 19, 2014. From the *Indiana University School of Medicine-South Bend, South Bend; †Radiology, Inc, Mishawaka; and ‡South Bend Medical Foundation, Indiana University School of Medicine-South Bend, South Bend, IN. The authors report no conflicts of interest. Reprints: Joseph A. Prahlow, MD, South Bend Medical Foundation, Indiana University School of Medicine-South Bend, 530 N Lafayette Blvd, South Bend, IN 46601. E-mail: [email protected]. Copyright © 2014 by Lippincott Williams & Wilkins ISSN: 0195-7910/14/3504–0249 DOI: 10.1097/PAF.0000000000000121
Am J Forensic Med Pathol • Volume 35, Number 4, December 2014
viewed via PACS on a high-resolution monitor) to contain no radiopaque foreign bodies. Before internal examination, it was surmised that, of the 7 wounds, five were perforating, and one was graze type. Because there was no associated exit wound, the seventh entrance wound was considered to likely represent a penetrating wound, with the entrance in the left back (Fig. 1); however, no bullet was evident on x-rays of the head/neck (Fig. 2) or trunk regions. Careful examination of the scalp, facial orifices, and skin folds revealed no hidden exit wound. As the forensic pathologist was considering calling the x-ray technicians back to look for a possible bullet embolus, a more careful evaluation of the head/neck x-ray revealed the faint outline of what seemed to be a bullet, near the base of the skull (Fig. 3), although its apparent density on x-ray was much less than the gold necklace, which was readily apparent on the same film. Consultation with the radiologist was immediately made; however, the presumed bullet remained indistinct (Fig. 4). Despite this fact, the official radiology report was amended to mention the presence of a bullet, and subsequent internal examination at autopsy was confirmatory. The bullet perforated the posterior left chest wall and ribs 4, 3, 2, and 1. It then perforated the left neck and posterolateral aspect of the second cervical vertebral body, transected the cervical spinal cord, perforated the anterior aspect of the first cervical vertebral body, and entered the soft tissues immediately anterior and adjacent to the atlanto-occipital junction. A minimally deformed, jacketed, medium-caliber bullet was recovered from this location (Fig. 5). Casings at the scene revealed that the bullet was a Fiocchi 38 Special (Lecco, Italy).
DISCUSSION In a gunshot wound case, radiographs are commonly used to detect metallic fragments, bullets, or jacketing present within the body at autopsy. A “bullet rule”10 has been described, in which the sum of bullet wounds (entrance and exit) and projectiles found on imaging should always be an even number. When this is not initially true, the pathologist must consider several possibilities. Misidentification of the presumed entrances and exits may have occurred, or the pathologist may have initially missed an entrance or exit wound. There may have been intracorporeal fragmentation, leading to multiple exit wounds from a single entrance. Wounds may be “hidden” in hair, skin folds, or a body orifice. Another common reason that the “wound plus x-ray projectile” might not equal an even number is when the x-ray examinations initially “miss” a projectile. Even experienced radiologists may miss a projectile on imaging through the “professional blinkers phenomenon.”4 The apparent angle of entry does not necessarily correlate with the final resting location of the projectile or fragments. Bullets may change angle within the body when encountering a bone5 or may embolize to distant areas outside the view of the initial radiographs.6 Further exploration may be necessary. Shotgun wadding is nonmetallic and thus not readily apparent by x-ray.7 Nonradiopaque plastic or rubber bullets are rarely used but can be seen in law enforcement settings.8 In addition, ammunition with aluminum jacketing exists; if the jacketing separates from the bullet core, the jacket, which is www.amjforensicmedicine.com
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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Am J Forensic Med Pathol • Volume 35, Number 4, December 2014
Graham et al
FIGURE 1. Gunshot entrance wound of the left upper midback region.
radiolucent, may not be visualized on x-ray.9 Furthermore, not all suspect densities seen in gunshot wound radiographs are actually projectiles. Bullet mimics may include other internal foreign bodies,11 bony fragments,12 or external items such as zippers.13 Multidetector computed tomography (MDCT) has been suggested as superior to standard imaging for the detection of projectile fragments.14 A comparison study by Harcke et al15 demonstrated that full-body digital radiography successfully identified all metal fragments also found by MDCT, although MDCT was superior in 3-dimensional localization. For many forensic pathologists, such imaging is simply not available at their facility. In the current case, a lead-core bullet was not clearly visualized on AP imaging initially. Only after careful reexamination of the x-ray did it become apparent that a bullet was actually present within the victim's upper neck region, near the base of the skull. Although a lateral skull study is essential in an emergent gunshot
wound of the head or neck,16 it is not always performed in autopsy cases. Often, the initial autopsy evaluation includes only a single AP image. Reasons for not universally performing an additional lateral view initially may include difficult patient positioning, limited technologist availability in a hospital setting, or increased cost. In the ideal setting, a lateral film would be performed and, in this case, would likely have been beneficial in detecting the obscured bullet.
FIGURE 2. The AP radiograph of the head and neck, with no obviously visible projectile. Note that the gold necklace is readily visible.
FIGURE 4. An “enhanced” x-ray image, attempting to better visualize the bullet. Note that, compared with the gold necklace, the bullet remains nearly imperceptible.
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www.amjforensicmedicine.com
FIGURE 3. A closer view of the x-ray depicted in Figure 2, with an arrow indicating the location of the supposed bullet.
© 2014 Lippincott Williams & Wilkins
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Am J Forensic Med Pathol • Volume 35, Number 4, December 2014
FIGURE 5. The bullet recovered from the victim at autopsy.
This case provides an example of 2 phenomena of radiography understood in the radiation physics literature, but, to our knowledge, undescribed in the forensic pathology literature: poor penetration (leading to decreased subject contrast) and summation artifact. With radiography, x-rays pass through the patient onto a cassette, forming an image. Each tissue encountered by the x-rays attenuates the beam according to its density and thickness, which leads to the contrast visualized on a radiograph. Detection is based on 2 principles. Object contrast is the inherent difference in density between a lesion and its surrounding structures, and subject contrast is the difference in x-ray transmission.17,18 The x-ray tube produces x-rays across a continuum of energy levels, measured in kilovoltage. Higher energy x-rays are better able to penetrate tissues. Lower energy x-rays are preferentially absorbed when they encounter tissues, increasing the effective energy level of remaining x-rays. Commonly, kilovoltage is indicated by the kilovoltage peak (kVp), which describes the highest energy level produced. The kVp is responsible for penetration of tissues, and an inappropriately low kVp will lead to incomplete penetrance and decreased subject contrast.18 The AP skull film was performed at 70 kVp and 3.2 mA s with an exposure rating of 1.86 log median exposure. The film was slightly underexposed, with company recommendations for log median exposure between 1.9 and 2.5 on AGFA systems.19 However, the primary concern with this case is incomplete penetration of the anatomy, leading to poor visualization of all structures and masking the deeply situated bullet. A better-penetrated image will have longer grayscale and will provide finer anatomical detail. Use of a higher kVp, such as 80, would have significantly improved penetration of the bony skull and mandible and facilitated differentiation of the bullet.18 Patient radiation dose is not a primary concern for the deceased, and every effort should be made to provide sufficient anatomical detail with appropriate exposure levels. In addition, the jaw, teeth, cervical spine, and deep soft tissues of the neck significantly sheltered the bullet, which was deeply situated. These dense tissues and the depth of the bullet preferentially attenuated low-energy x-rays so that x-rays reaching the bullet had a better chance of being transmitted. Thus, although there was a significant density difference between them, this decreased the subject contrast between the lead bullet and surrounding tissues. This masking is termed summation artifact. The metal necklace was denser and less sheltered, thus appearing as expected for a metal object. We rely on the assistance of the corresponding hospital radiology department to obtain forensic radiographs and often overlook the challenges faced because of the differences between © 2014 Lippincott Williams & Wilkins
Decreased Subject Contrast and Summation Artifact
forensic and typical radiography. First, one of the most common themes in imaging is to decrease radiation dose to as low as reasonably achievable. Although this principle does not apply in the setting of imaging deceased patients, the emphasis on decreasing dose in the rest of radiology may make typical practices less than ideal for autopsy purposes. Second, many radiology technologists have little experience working with autopsies. The lack of experience as well as the potential stress of dealing with the deceased may keep the technologist from using best practices. In addition, a hospital's radiology department may be quite large, with numerous technologists. If the number of autopsy cases requiring x-ray examination is relatively small, it is likely that each individual technologist's experience with autopsy radiography will be quite limited. The pathologist should be aware of these issues when using forensic radiography. The present case illustrates the potential for a projectile to be masked on radiography to a point where it is nearly invisible, depending on location and imaging technique. This should be an additional consideration when the bullet rule seems not to hold on initial evaluation. The pathologist should be aware of the several possibilities in which radiographs may not completely depict foreign bodies in a gunshot wound case, including lead projectiles. Although CT imaging is ideal in any foreign body investigation, many forensic pathologists do not have access to this technology. In the absence of readily available CT imaging or other body scan x-ray technology, many pathologists must rely on standard radiography at autopsy. For those forensic pathologists who must use hospital-based radiology services, several additional obstacles may exist in obtaining and interpreting autopsy x-rays. Inadequate penetration and summation artifact represent an explanation for why an otherwise radiopaque object, such as a bullet, may become much less radiopaque in appearance on routine x-ray. The forensic pathologist and radiographic operator must recognize that technical factors can significantly mask the appearance of foreign bodies and take care to perform an adequate study.
REFERENCES 1. Brogdon BM, Lichtenstein J. Forensic radiology in historical perspective. In: Brogdon BM, ed. Forensic Radiology. Boca Raton, FL: CRC Press; 1998:13–34. 2. Choi CH, Pritchard J, Richard J. Path of bullet and injuries determined by radiography. Am J Forensic Med Pathol. 1990;11:244–245. 3. Wilson AJ. Gunshot injuries: what does a radiologist need to know? RadioGraphics. 1999;19:1358–1368. 4. Bajanowski T, Karger B, Brinkmann B. Scratched pustule or gunshot wound? A medical odyssey. Int J Legal Med. 2001;114(4–5):267–268. 5. Engels PT, Tien HC. The lucky penny: an illustration of the bullet rule. CMAJ. 2012;184:63–65. 6. Slobodan S, Slobodan N, Djordje A. Popliteal artery bullet embolism in a case of homicide: a case report and review of the tangible literature. Forensic Sci Int. 2004;139:27–33. 7. Beverly MC, Pring DJ, Coombs RR. Radiolucent plastic in gunshot wounds. Injury. 1985;16:461–463. 8. Hollerman JJ, Fackler ML, Coldwell DM, et al. Gunshot wounds: 2. Radiology. AJR Am J Roentgenol. 1990;155:691–702. 9. Conradi SE. New aluminum-jacketed bullets: the case of the “invisible” jacket. Am J Forensic Med Pathol. 1982;3:153–155. 10. Westreich M. The odd or even bullet. Injury. 1986;17:45–46. 11. Cina SJ, Gelven PL, Nichols CA. A rock in a hard place. A brief case report. Am J Forensic Med Pathol. 1995;16:333–335.
www.amjforensicmedicine.com
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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Graham et al
12. Geary UM, Ritchie DA, Luke LC. Occult gunshot injury of the temporal bone. J Accid Emerg Med. 1997;14:185–186. 13. Dodd GD, Budzik RF. Identification of retained firearm projectiles on plain radiographs. AJR Am J Roentgenol. 1990;154:471–475. 14. Harcke HT, Levy AD, Getz JM, et al. MDCT analysis of projectile injury in forensic investigation. AJR Am J Roentgenol. 2008;190:W106–W111. 15. Harcke HT, Levy AD, Abbot RM. Autopsy radiography: digital radiographs (DR) vs multidetector computed tomography (MDCT) in high-velocity gunshot-wound victims. Am J Forensic Med Pathol. 2007;28:13–19.
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16. Pinto A, Brunese L, Scaglione M, et al. Gunshot injuries in the neck area: ballistics elements and forensic issues. Semin Ultrasound CT MR. 2009;30:215–220. 17. Huda W, Sloane R. Review of Radiology Physics. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2003. 18. Carroll QB. Practical Radiographic Imaging. 8th ed. Springfield, IL: Charles B. Thomas; 2007. 19. Carlton RR, Adler AM. Principles of Radiographic Imaging: An Art and a Science. Clifton Park, NY: Delmar Learning; 2005.
© 2014 Lippincott Williams & Wilkins
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
