Research ArticleImaging

Blanching Defects at Pressure Points: Observations from Dynamic Total-Body PET/CT Studies

Yasser G. Abdelhafez, Kristin McBride, Edwin K. Leung, Heather Hunt, Benjamin A. Spencer, Javier E. Lopez, Kwame Atsina, Elizabeth J. Li, Guobao Wang, Simon R. Cherry, Ramsey D. Badawi, Fatma Sen and Lorenzo Nardo
Journal of Nuclear Medicine Technology December 2022, 50 (4) 327-334; DOI: https://doi.org/10.2967/jnmt.122.263905

Article Figures & Data

Figures

  • Figure
  • FIGURE 1.
    FIGURE 1.

    Example of complete (A) and partial (B) blanching defects. (A) Images from 29-y-old healthy woman weighing 81 kg and 165 cm tall, injected with 18F-FDG (369 MBq). PET image (left) demonstrates bilateral posterior parietooccipital scalp defects, complete on left side (arrow) and partial on right side (arrowhead). 18F-FDG PET/CT image (middle) shows no CT abnormality. Lung window (right) outlines head support setup (arrows). (B) Images from 43-y-old healthy woman weighing 53 kg and 160 cm tall, injected with 18F-FDG (18.5 MBq). PET image (left) demonstrates relative photopenia at right posterior parietal scalp region (arrowhead), representing partial blanching defect. Contralateral side (left side) shows no abnormality. 18F-FDG PET/CT image (middle) shows no CT abnormality at site of partial defect. Lung window (right) outlines head position within support setup (arrows) and demonstrates minimal tilting of skull toward side of partial defect (arrowhead). Color version of this figure is available as supplemental file at http://tech.snmjournals.org.

  • FIGURE 2.
    FIGURE 2.

    Examples of partial and complete restoration of uptake within complete blanching defects seen at pressure points, from left to right, against skull and scapulae bilaterally, sacrum, and left calcaneus. (A–D) PET images from last 20 min of dynamic 60-min acquisition (A), their respective 20-min static acquisition at 90 min (C), and corresponding PET/CT images (B and D) in lung window, to demonstrate relationship with positioning setup and scanner table. Sites with complete defects on dynamic images are marked with arrowheads, and sites with partial restoration at 90-min time point are marked with arrows. Blanching defects against skull showed complete restoration on right side and partial restoration on left side, and those against scapulae and sacrum showed complete restoration, whereas defects opposite heel showed partial restoration on delayed 90-min image. Color version of this figure is available as supplemental file at http://tech.snmjournals.org.

  • FIGURE 3.
    FIGURE 3.

    Changes in pattern of blanching defects against calcaneus in same subject across 2 dynamic scans, baseline (A) and follow-up (B), separated by 2 wk. Shown are representative images from 74-y-old man with genitourinary cancer weighing 74 kg and 170 cm tall. 18F-FDG PET images demonstrate bilateral complete blanching defects opposite calcaneus (A, arrowheads), with no corresponding abnormality in PET/CT image (middle). Follow-up dynamic PET scan in same subject shows unilateral partial defect on left foot (B, arrowhead). CT images with lung window (right) outline positioning setup demonstrating relationship of heels with respect to knee cushion (top) and table couch (bottom) during respective scan time points. Color version of this figure is available as supplemental file at http://tech.snmjournals.org.

  • FIGURE 4.
    FIGURE 4.

    Examples of other nonsystematic blanching defects (arrowheads). (A) Absence of skin and subcutaneous 18F-fluciclovine uptake opposite cervicodorsal vertebrae at site of transition between head support and scanner table, as might be caused by pressure against prominent spinous processes. (B) Absence of 18F-FDG uptake at dorsum of foot at site of tightened immobilization belt. (C) Reduced-to-absent 18F-fluciclovine uptake opposite medial and lateral epicondyles of right humerus at site of wrapped immobilization belt around elbows. (D) A few additional patterns of blanching defects in lower limb: at distal third of calf as it is pressing against end of knee cushion (left), opposite calcaneus although silicon pad was placed to minimize pressure (middle), and again opposite calcaneus at end of knee/leg cushion, where heels do not touch scanner table (right). Color version of this figure is available as supplemental file at http://tech.snmjournals.org.

Tables

  • TABLE 1.

    General Characteristics of Study Participants

    Characteristic18F-FDG dose (n = 47)Fluciclovine (standard dose)
    LowIntermediateStandard
    Age (y)45 ± 11.1 (26–62)51.7 ± 9.3 (39–66)55.1 ± 15 (26–78)71.0 ± 8.3 (54.1–89)
    Weight (kg)78.4 ± 16.1 (53.1–102.5)95 ± 17.9 (77–131.7)81.8 ± 15.1 (53–113)91.0 ± 16.7 (68.4–148)
    Height (cm)173.6 ± 10.5 (157.5–195.6)170.6 ± 12.4 (152.4–193)171.1 ± 8.3 (157.5–185.4)178.1 ± 7.8 (165.1–195.6)
    BMI (kg/m2)25.8 ± 3.4 (20.4–32.2)32.6 ± 4.5 (26.8–40.4)28 ± 5.3 (19.4–37)28.7 ± 5.4 (19.4–46.8)
    Injected dose (MBq)19.6 ± 1.7 (17.2–23.5)188.4 ± 8.6 (175.7–196.7)372.3 ± 17.0 (331.9–393.8)314.6 ± 19.7 (287.2–389.6)
    Fasting duration (h)9.2 ± 3.0 (6–15)11.4 ± 3.4 (6–18)11 ± 2.9 (6–20)6.9 ± 3.4 (4–16)
    Blood glucose (mg/dL)90.7 ± 19.2 (39–113)94.3 ± 12.7 (76–113)97.9 ± 21.8 (65–154)Not applicable
    Sex
     Female7290
     Male881330
    Disease
     Cancer00730
     Cardiovascular01000
    Healthy150150
    Imaging time points
     Dynamic and delayed1510150
     Dynamic only00730
    Arms position
     Above head00029
     To sides1510221
    Attenuation-corrected CT dose
     Ultralow (5 mAs)1510150
     Low (50 mAs)00730
    PET/CT misregistration
     No1081725
     Yes5255

    • Qualitative data are number; continuous data are mean and range.

  • TABLE 2.

    κ-Agreement on Defect Detection/Laterality and Grade between 2 Readers According to Scan Time Point and Evaluated Pressure Points

    Scan timing and evaluated pressure pointsAgreement
    Detection*Grade of defect
    Dynamic only0.81 (0.75–0.88)0.81 (0.75–0.83)
    90-min only0.66 (0.44–0.88)0.70 (0.49–0.91)
    Skull0.76 (0.62–0.89)0.75 (0.60–0.89)
    Scapulae0.84 (0.74–0.95)0.88 (0.80–0.95)
    Sacrum0.72 (0.55–0.89)0.74 (0.60–0.89)
    Calcaneus0.78 (0.66–0.90)0.82 (0.73–0.92)

    • ↵* Agreement figures on detection also include agreement on laterality.

    • Data in parentheses are 95% CI.

  • TABLE 3.

    Distribution of Blanching Defects According to Anatomic Site, Laterality, and Grade on Dynamic and Delayed Imaging

    Blanching defectDynamic (n = 77)Delayed static (n = 40)*
    SkullScapulaeSacrumCalcaneusSkullScapulaeSacrumCalcaneus
    Absent534358937373832
    Present243419473326
     One or unilateral
      Partial82811223
      Complete531170000
     Two or bilateral
      Partial38NA421NA3
      Complete†821NA3500NA0
    Outside field of view000210002

    • ↵* 37 of original 77 participants did not undergo 90-min imaging.

    • ↵† In presence of bilateral defects with different defect grades, higher grade was recorded for that pressure point.

    • NA = not applicable because sacrum was evaluated as single pressure point.

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