This diagnostic imaging figure displays 18F-Florbetapir Positron Emission Tomography (PET) scans of the brain, comparing amyloid-negative (A) and amyloid-positive (B) findings. Both panels include axial, coronal, and sagittal views. In Panel A (Negative scans), the radiotracer is primarily localized within the white matter, maintaining a clear visual contrast between the radiolabeled white matter and the darker, non-binding gray matter. This pattern represents the absence of significant beta-amyloid plaque deposition. In Panel B (Positive scans), there is a marked increase in tracer uptake within the cortical gray matter across the frontal, parietal, and temporal lobes, as well as the posterior cingulate cortex. This increased tracer intensity results in a loss of the normal gray-white matter contrast, as the cortical uptake matches or exceeds white matter levels. These findings are clinically significant for the pathological identification of amyloid deposition associated with Alzheimer's disease. The comparison highlights the shift from a white-matter-only distribution to a global cortical uptake pattern used in diagnostic neurology.

Multi-modal diagnostic imaging of the brain in the axial plane demonstrating findings consistent with neurodegenerative parkinsonism. Image (a) is a 123I-ioflupane DAT SPECT scan showing bilaterally decreased radiotracer uptake in the striatal structures of the basal ganglia, particularly affecting the putaminal regions, giving the remaining uptake an oval appearance. An asymmetric pattern is noted with a more pronounced deficit in the left basal ganglion. Image (b) presents a side-by-side comparison of an 18F-FDG PET scan and a T1-weighted MR image. The FDG-PET reveals relatively increased glucose metabolism in the bilateral putaminal regions, which serves as a metabolic marker for Parkinson's disease. The corresponding T1-weighted MRI shows normal anatomical structures without specific pathological changes or volume loss in the cerebral cortex. This comparison illustrates the clinical significance of functional imaging (SPECT and PET) over structural imaging (MRI) in the early diagnosis of dopamine transporter deficiency and metabolic shifts associated with Parkinsonian syndromes.

This diagnostic comparison image presents axial brain scans from two different functional imaging modalities: 18F-Fluoro-L-dopa (FDOPA) PET (row a) and 123I-FPCIT (DATSCAN) SPECT (row b). The images illustrate the neurochemical profile of patients with advanced dementia with Lewy bodies (DLB). Both rows demonstrate a characteristic reduction in radiotracer uptake within the basal ganglia, specifically the striatum (caudate nucleus and putamen). In row (a), the FDOPA PET scans show diminished metabolic activity in the dopaminergic system, indicated by the reduced intensity and area of the warm colors (yellow/red) compared to healthy controls. In row (b), the DATSCAN SPECT images reveal a severe decrease in dopamine transporter (DAT) availability, represented by the restricted and weakened signal in the striatal regions. The surrounding cortical and subcortical brain tissue displays low, uniform background uptake in both modalities, primarily in cooler blue and green tones. This visual comparison highlights the integrated role of PET and SPECT imaging in identifying presynaptic dopaminergic deficits, a core diagnostic feature for differentiating alpha-synucleinopathies like DLB from other dementias such as Alzheimer’s disease.

This diagnostic image displays a series of F-18 fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) axial slices of a human brain from a 56-year-old female. The montage represents a normal baseline scan conducted at rest, showcasing 28 sequential cross-sectional slices from the cerebellum and skull base through the vertex. The radiotracer distribution is characterized by symmetrical, physiological uptake throughout the cerebral cortex and subcortical structures. Consistent metabolic activity is observed in the frontal, parietal, temporal, and occipital lobes, as well as the basal ganglia and thalamus. There is a high grey-to-white matter contrast, which is normal for FDG PET imaging. No focal areas of pathological hypometabolism or hypermetabolism are present, indicating preserved glucose metabolism across all neuroanatomical regions. This imaging modality is used in neurology and nuclear medicine to evaluate regional cerebral metabolic rates of glucose (rCMRglu), serving as a reference for diagnosing conditions like epilepsy, neurodegenerative diseases, or focal brain lesions.

This Comparison Chart features a series of transaxial 18F-flortaucipir PET/CT fusion images of the brain, demonstrating tau protein deposition patterns. The image is organized into two rows: 'Normal' (top) representing a healthy elderly individual and 'Abnormal' (bottom) representing a patient with Alzheimer’s Disease (AD). The color scale on the right indicates radiotracer intensity, with green and yellow representing high retention. In the 'Normal' row, the brain shows minimal cortical radiotracer uptake, with some physiological off-target binding in deep brain structures and the retina. In contrast, the 'Abnormal' row displays marked, bilateral radiotracer retention across several cortical regions, specifically the inferior lateral temporal lobes, temporoparietal junctions, and the posterior cingulate cortex. These findings correlate with advanced Braak staging of tau pathology in AD. The image serves as a diagnostic reference for identifying neurodegenerative tauopathies and illustrates the clinical utility of tau-specific PET imaging in geriatric neurology.

This diagnostic comparison image displays axial brain scans from two different functional imaging modalities, [123I]FP-CIT SPECT (top row) and [18F]FE-PE2I PET/CT (bottom row), across two clinical states: Non-Parkinsonian Syndrome (Non-PS, left) and Parkinsonian Syndrome (PS, right). The primary focus is the radiotracer uptake within the dopaminergic pathways of the striatum, specifically the caudate nucleus and putamen. In the Non-PS columns, both SPECT and PET/CT show intense, symmetrical, comma-shaped tracer binding, reflecting normal dopamine transporter (DAT) density. In the PS columns, there is a visible reduction in tracer uptake, particularly in the posterior striatum (putamen), which appears shorter or fainter compared to the Non-PS state. The PET/CT row provides enhanced anatomical localization by fusing high-resolution molecular data with structural CT data. This comparison illustrates the clinical utility of molecular imaging in identifying neurodegenerative changes associated with Parkinsonian syndromes, highlighting the loss of striatal dopaminergic innervation.

This diagnostic image displays Fluorodeoxyglucose (FDG) PET/CT brain imaging of a 68-year-old male presenting with personality changes, characteristic of Frontotemporal Dementia (FTD). Panel (a) shows an axial view and panel (b) shows a sagittal view using a rainbow color scale to map metabolic activity. These views demonstrate marked hypometabolism (purple/blue) in the frontal and temporal lobes, while metabolic activity is relatively preserved (green/yellow/red) in the parietal and occipital lobes, including the precuneus and posterior cingulate cortex (PCC). Panel (c) presents Single-Subject Statistical Parametric Mapping (ss-SPM) results. This analysis highlights significant negative deviation from control mean uptake values, visualized as blue and purple clusters overlaying brain templates across multiple slices (sagittal, axial, and coronal). The ss-SPM confirms a characteristic FTD pattern: predominant hypometabolism in the anterior cingulate and frontal regions compared to the posterior cingulate. This imaging profile serves as an educational example of how FDG-PET and quantitative SPM analysis can differentiate FTD from other neurodegenerative conditions like Alzheimer's disease.

This diagnostic comparison chart displays neuroimaging results for Alzheimer’s disease (AD) and Frontotemporal Lobar Degeneration (FTLD) relative to healthy controls. The image utilizes statistical parametric mapping overlaid on brain templates in sagittal, coronal, and axial views. Red clusters indicate glucose hypometabolism (FDG-PET), blue clusters represent cortical atrophy (structural MRI), and violet regions show where atrophy and hypometabolism overlap. The upper panel (AD < Controls) demonstrates a characteristic pattern of hypometabolism in the parieto-mesial cortex, specifically the precuneus and posterior cingulate, with bilateral involvement of the lateral temporal and inferior parietal regions. The lower panel (FTLD < Controls) shows a distinct distribution concentrated in the fronto-median and fronto-lateral cortex, as well as the insula, with a marked lateralization to the left hemisphere. This visualization highlights the differential topographical patterns of neurodegeneration used to distinguish these two common forms of dementia through functional and structural imaging modalities.

This diagnostic image set consists of 30 transversal slices from an FDG-PET (Fluorodeoxyglucose Positron Emission Tomography) scan of a patient with Alzheimer's disease. The color-coded metabolic map uses orange/red to represent high glucose metabolism and purple/blue for low metabolism (hypometabolism). The scans demonstrate a classic neurodegenerative pattern: marked hypometabolism is visible in the posterior cingulate cortex and the posterior temporoparietal association cortex. In contrast, the frontal lobes and primary motor/sensory cortices show relatively preserved metabolic activity, indicated by the higher intensity orange regions. This visual disparity between the hypoactive posterior regions and the normally active frontal regions is a key diagnostic hallmark used to differentiate Alzheimer's disease from other forms of dementia, such as frontotemporal dementia. The series provides a comprehensive view of global cerebral glucose utilization from the base of the brain through the vertex.

This diagnostic image set consists of axial [123I]FP-CIT SPECT (DaTscan) slices of a human brain, used to evaluate presynaptic dopamine transporter (DAT) density. The scans demonstrate a bilateral reduction in tracer uptake within the striatum, particularly affecting the posterior putamen. In a normal scan, the striatal uptake typically appears as a bright, comma-shaped or 'comma-like' signal representing the caudate nucleus and putamen. In these images, the signal is markedly diminished and more 'period-shaped,' indicating loss of dopaminergic neurons. There is a visible asymmetry in the signal intensity, with the left side showing a more pronounced deficit compared to the right, consistent with asymmetric neurodegeneration typical of Parkinson's disease. The color-coded heat map shows the highest concentration of DAT in the red/yellow regions, which are noticeably restricted in this patient. These findings are clinically significant for confirming presynaptic dopamine transporter loss to support a diagnosis of Parkinsonian syndrome in patients presenting with movement disorders like bradykinesia and tremors.

Diagnostic [123I]ioflupane (DaTSCAN) brain SPECT images in the axial plane, focusing on striatal dopamine transporter (DAT) activity. The image set is organized into two rows. The top row displays striatal phantom scans comparing 'clinical' (left) and 'research' (right) reconstruction algorithms; the clinical version shows smoother, more symmetrical bilateral high-intensity signals, while the research reconstruction exhibits higher granularity and sharper signal localization. The bottom row presents comparative clinical cases: the left image shows a healthy subject with normal, symmetrical, 'comma-shaped' tracer uptake in the caudate nucleus and putamen bilaterally. The right image shows a patient with Parkinson's disease, demonstrating a significant dopaminergic deficit characterized by marked asymmetry, reduced signal intensity, and a 'period-shaped' appearance due to the characteristic loss of uptake in the posterior putamen. These images illustrate the diagnostic utility of DAT imaging in differentiating healthy dopaminergic function from the neurodegenerative changes associated with Parkinsonian syndromes.

This composite diagnostic image illustrates the longitudinal effects of N-acetylcysteine (NAC) on dopamine transporter (DaT) availability in a Parkinson's disease patient. Section A displays two axial DaTscan (SPECT) images: 'pre-NAC' (left) and 'post-NAC' (right). The color-coded intensity maps show a transition from yellow/green to deep red in the striatum (caudate and putamen), indicated by arrows, signifying a substantial increase in dopamine transporter binding following treatment. Section B presents statistical parametric mapping (SPM8) results from a group-level paired t-test. Significant clusters (p < 0.05) are overlaid on axial T1-weighted MRI templates across three slices. These areas of significantly greater binding post-treatment are localized to the bilateral basal ganglia and are rendered in an orange-to-red color scale corresponding to T-values (0 to 6+). The visualization demonstrates both individual qualitative improvement in dopaminergic function and collective statistical significance in regional tracer uptake, relevant to clinical research in neurodegenerative disease management.

This Comparison Chart displays axial brain PET (Positron Emission Tomography) scans using three different amyloid-targeting radiopharmaceuticals: Florbetaben (FBB, panels a/d), Flutemetamol (FMM, panels b/e), and Florbetapir (FPN, panels c/f). The images are arranged to compare negative scans (upper row: a, b, c) with positive scans (lower row: d, e, f) using a rainbow color scale where warmer colors (red, orange, yellow) indicate higher radiopharmaceutical uptake and cooler colors (green, blue) indicate lower uptake. In the negative amyloid scans, tracer uptake is primarily localized to the white matter, maintaining a clear distinction from the cortical gray matter, which appears cool-toned. Notably, the FPN negative scan (c) shows higher striatal uptake compared to the others. In the positive scans, there is a diffuse, widespread increase in tracer uptake throughout the cortical regions (frontal, temporal, and parietal lobes), leading to a loss of the normal gray-white matter differentiation. This series illustrates the diagnostic visual markers for amyloid plaque deposition in Alzheimer's disease assessment across different PET tracers.

This diagnostic image series presents six sagittal Positron Emission Tomography (PET) scans of the human brain, illustrating the uptake patterns of various Amyloid-beta (A̢) radiotracers in patients with Alzheimer’s disease. The tracers shown include [11C]PiB, [18F]Florbetaben, [18F]Flutemetamol, [18F]Florbetapir, [18F]Flutafuranol, and [18F]FIBT. The images use a pseudo-color scale where red/orange represents high signal intensity (higher plaque burden) and blue/green represents lower intensity. Most tracers demonstrate significant cortical uptake, particularly in the frontal, parietal, and temporal lobes, as well as the cingulate cortex. Variations in signal distribution are visible: [11C]PiB and [18F]Florbetapir show broad cortical involvement, whereas [18F]FIBT displays a more heterogeneous and localized distribution with lower overall intensity. This comparison highlights the differences in binding affinity, specificity, and pharmacokinetics among FDA-approved and experimental A̢ imaging agents, which are essential for the diagnosis and longitudinal monitoring of neurodegenerative amyloidopathies.

This composite educational graphic presents diagnostic imaging and quantitative analysis from a pre-clinical Parkinson’s disease study using mouse models. Panels A–D display coregistered coronal [18F]FDOPA PET/CT images of the brain across four experimental groups: (A) non-transgenic control, (B) hLRRK2 wild-type, (C) hLRRK2 R1441G hemizygous (HEM), and (D) hLRRK2 R1441G homozygous (HOM). The heatmaps represent the distribution of tracer uptake, where vibrant red/orange hotspots in the striatum indicate robust dopamine synthesis and storage in groups A and B. In contrast, groups C and D show a marked reduction in signal intensity in these regions, visualized as cooler yellow and green tones. Panel E is a dot plot with mean bars quantifying the average [18F]FDOPA uptake (SUV) in the striatum. Statistical significance markers (**, ***, ****) indicate that both the HEM and HOM R1441G transgenic groups have significantly lower striatal uptake compared to the hLRRK2 wild-type group. This visual content demonstrates nigrostriatal dopaminergic dysfunction associated with the LRRK2 R1441G mutation, serving as an educational resource for studying neurodegenerative disease biomarkers and metabolic imaging.

This medical illustration depicts a dopaminergic synapse within the brain, focusing on molecular targets for Positron Emission Tomography (PET) radiotracers used in diagnosing Parkinson's disease. The diagram is divided into presynaptic and postsynaptic components. The presynaptic section illustrates dopamine synthesis (Tyrosine to L-DOPA via TH, then to Dopamine via AADC), vesicular storage mediated by VMAT2, synaptic release, and reuptake via the dopamine transporter (DAT). Corresponding PET tracers are listed: 18F-DOPA for AADC activity; 11C-DTBZ and 18F-FP-(+)-DTBZ for VMAT2 availability; and 11C-CFT for DAT availability. The postsynaptic section identifies D2 and D3 receptors as primary targets, with listed tracers including 18F-fallypride, 11C-FLB457, 11C-RAC, and 11C-PHNO. A sagittal brain diagram provides anatomical context, highlighting the midbrain/striatal region as the focus of these neuroimaging techniques. The educational focus is on the in vivo assessment of dopaminergic terminal integrity and receptor status.

This diagnostic image provides a split-view MRI assessment of a knee joint following a double-bundle anterior cruciate ligament (ACL) reconstruction. The left panel shows a coronal view, highlighting the femoral condyles, the tibial plateau, and the intra-articular space where the graft is positioned. A linear measurement of 32.0 mm is applied to the graft structure within the intercondylar notch. The right panel displays a sagittal or oblique view focused on the tibial and femoral tunnel placement. Critical surgical planning or post-operative measurements are visible, including a tunnel length of 66.5 mm, a tibial width measurement of 57.0 mm, and a graft inclination angle indicated as 61.2 degrees. The imaging demonstrates the anatomical relationship between the distal femur, proximal tibia, and the reconstructed ligamentous tissue, which is essential for evaluating graft tension and tunnel positioning in sports medicine and orthopedic surgery.

This diagnostic image is a T2-weighted sagittal MRI scan of a human knee joint, captured six months post-Anterior Cruciate Ligament (ACL) reconstruction. The image provides a detailed view of the femoral condyles, the tibial plateau, and the joint space with visible articular cartilage layers. A primary focus is the femoral bone tunnel and the reconstructed ACL graft, which are being assessed for postoperative outcomes. Superimposed on the anatomical scan is a grid of numbered, diagonal white dotted lines (ranging from labels 5.50 to 14). These lines represent the planning of cross-sectional scan layers, oriented perpendicular to the long axis of the femoral bone tunnel. This specialized imaging plane is used for the precise measurement of bone tunnel enlargement and to evaluate the integration of the graft. The image demonstrates key concepts in orthopedic radiology, including postoperative graft assessment, tunnel positioning, and MRI slice acquisition planning for musculoskeletal analysis.

**Imaging Modality:** Oblique coronal proton density-weighted (PDW) magnetic resonance imaging (MRI). **Anatomical Region:** Right knee joint focusing on the intercondylar notch and proximal tibia. **Observed Pathology/Post-operative Status:** Status post-anterior cruciate ligament (ACL) reconstruction. The image demonstrates the morphology of the surgical tunnels and the ACL graft. **Characteristic Visual Features:** * **Femoral Tunnel:** An anteromedial (AM) femoral tunnel is visible with a conical, widened morphology, measured at a diameter of 12.01 mm. * **Tibial Tunnel:** An evenly narrowed tibial AM tunnel is observed, measured at 7.50 mm. * **ACL Graft:** A continuous, low-signal intensity band representing the ACL graft is seen traversing the joint space between the femoral and tibial tunnels. * **Hardware:** A white arrow indicates the position of an interference screw within the tibial tunnel, partially obscured by susceptibility artifact. **Differentiating Features:** The image highlights tunnel widening (conical femoral tunnel) versus uniform tunnel maintenance (tibial tunnel), which is critical for assessing post-operative graft stability and potential tunnel osteolysis.

This anterior-posterior (AP) radiograph of a human right knee demonstrates a post-operative assessment of an anterior cruciate ligament (ACL) reconstruction. The image focuses on the evaluation of the tibial tunnel position using the Romano method. Key anatomical structures visible include the distal femur, proximal tibia, fibula, and the knee joint space. A radiolucent tibial tunnel is clearly visible, demarcated by dashed lines, following an oblique trajectory from the medial aspect of the proximal tibia toward the intercondylar eminence. Lettered annotations (A, B, and C) facilitate the measurement of the tunnel's exit point relative to the tibial plateau's width (B-C). Specifically, point A indicates the center of the tunnel's articular exit near the medial tibial spine. Surgical hardware, likely representing metallic staples or sutures, is faintly visible near the joint line and lateral femoral cortex. This diagnostic image is used in orthopedic surgery to ensure anatomical tunnel placement, which is critical for graft isometricity and preventing post-operative graft impingement or failure.

This diagnostic image is a coronal CT reconstruction of the human knee joint, specifically the distal femur and proximal tibia/fibula. The image illustrates a radiological assessment of femoral tunnel positioning following Anterior Cruciate Ligament (ACL) reconstruction, utilizing the method described by Hoser et al. (2005). Visible landmarks include the medial and lateral femoral condyles, the intercondylar notch, and the tibial plateau. A clear surgical femoral tunnel appears as a dark, circular lucency within the lateral femoral condyle near the notch roof. Superimposed red reference lines facilitate measurement: one horizontal line tangent to the most distal points of the femoral condyles and a perpendicular vertical line extending from the intracondylar roof to the distal condylar line. This vertical line is labeled with '0%' at the roof and '100%' at the distal level, serving as a coordinate system to quantify the tunnel's proximal-distal position. This clinical imaging is used in orthopedics to evaluate surgical accuracy and graft placement stability.

This diagnostic image displays two side-by-side sagittal T2-weighted MRI scans of a human knee joint, illustrating the methodology for assessing Anterior Cruciate Ligament (ACL) graft maturation. The images demonstrate the placement of Regions of Interest (ROIs) used to measure signal intensity. In the left panel, three circular ROIs are color-coded along the intra-articular course of the ACL graft: red for the proximal third (near the femoral tunnel), green for the middle third, and blue for the distal third (near the tibial tunnel). In the right panel, a yellow circular ROI labeled 'P' is placed on the mid-substance of the Posterior Cruciate Ligament (PCL), which serves as a hypointense reference point for signal normalization. The visual focuses on the 'A/P ratio'—a quantitative metric comparing graft signal (A) to the PCL signal (P)—to track ligamentization post-reconstruction. This clinical imaging tool is used in sports medicine and orthopedics to evaluate the biological healing of hamstring tendon grafts within the joint environment.

Two sagittal proton-density (PD) intermediate-weighted MRI scans of the knee (labeled A and B) demonstrating regions of interest (ROI) for measuring signal intensity of an anterior cruciate ligament (ACL) autograft. Image A shows three 4 mm circular ROIs along the intraarticular course of the ACL graft: proximal (red), mid-substance (yellow), and distal (green). Image B identifies internal reference points used for signal normalization: the mid-substance of the posterior cruciate ligament (PCL, blue circle) and the medial head of the gastrocnemius muscle (white circle). The images illustrate a standardized method for calculating the ACL/PCL signal ratio (APR) and the ACL/muscle ratio (AMR) to monitor the graft maturation and ligamentization process postoperatively. The primary anatomical structures visible include the femoral condyle, tibial plateau, reconstructed ACL, intact PCL, and posterior musculature.

A diagnostic MRI image of a sagittal oblique PD-STIR section of a stifle (knee) joint, illustrating the methodology for calculating the signal-to-noise quotient (SNQ) to assess graft maturation. The image displays three specific Regions of Interest (ROIs): a blue circular ROI positioned over the intra-articular ligament graft, a green circular ROI placed over the posterior cruciate ligament (PCL) to serve as an internal reference, and an orange circular ROI located cranial to the skin edge to measure background signal intensity. Quantitative data overlays at the top of the image provide detailed pixel intensity statistics for each ROI, including area (mm²), mean, median, standard deviation, and range. This radiological technique is used in orthopedic research to objectively quantify the signal intensity of an ACL or similar graft relative to healthy ligamentous tissue and background noise, where a lower SNQ value indicates more advanced ligamentization and graft healing.

This composite educational figure illustrates the clinical imaging and histopathology of a cyclops lesion (localized arthrofibrosis) following anterior cruciate ligament (ACL) reconstruction. Panel A shows a sagittal T2-weighted or proton density-weighted MRI of the knee. An arrow highlights the pathognomonic cyclops lesion: a well-defined, low-to-intermediate signal intensity nodule situated within the anterior intercondylar notch, anterior to the ACL graft. The lesion demonstrates typical morphology that can cause extension deficit by mechanical impingement. Panel B provides a corresponding histopathological view via light microscopy (H&E stain). The section, marked with an asterisk, shows dense, hypocellular fibrous connective tissue. The tissue exhibits a relatively uniform, wavy collagenous texture with scattered spindle-shaped fibroblasts, closely resembling the organized structure of tendinous or ligamentous tissue. This comparison facilitates the understanding of postoperative complications in orthopedic surgery, specifically the fibroproliferative response of ACL remnants or graft material that leads to symptomatic intra-articular masses.

This composite diagnostic image displays multiple MRI views of a human knee joint following anterior cruciate ligament (ACL) reconstruction. The imaging set includes Proton Density-Weighted Fat-Suppressed (PDW FS) sequences in sagittal (top left), coronal (top right), and axial (bottom left) planes, alongside a T1-weighted Turbo Spin Echo (TSE) sagittal sequence (bottom right). The images demonstrate the status of an ACL graft, which appears continuous. A key pathological finding is a focal, low-to-intermediate signal intensity mass located anterior to the ACL graft near the tibial insertion, characteristic of a 'cyclops lesion' (localized anterior arthrofibrosis). This lesion is most clearly demarcated on the sagittal and coronal views (indicated by a white arrow in the coronal plane). The MRI also shows surgical hardware artifacts in the femoral and tibial tunnels. The patellofemoral compartment and joint space are visible across planes to assess for secondary signs of graft dysfunction, such as impingement or altered knee mechanics.

This composite figure presents diagnostic imaging of a cyclops lesion, a common complication following anterior cruciate ligament (ACL) reconstruction. Image A is a sagittal CT arthrogram showing focal soft tissue thickening in the Hoffa’s fat pad region, with visible hardware from a prior ACL repair in the tibia and femur. Image B is a corresponding axial CT arthrogram slice highlighting a well-defined, rounded, 'ballooning' soft tissue mass (indicated by green arrows) located within the anterior intercondylar notch. Image C provides a comparison using a PD-weighted sagittal MRI, which demonstrates a developing cyclops lesion (green arrow) that appears as a low-to-intermediate signal intensity mass anterior to the ACL graft. This collection illustrates the characteristic morphology and anatomical location of localized anterior arthrofibrosis, which clinically correlates with a loss of terminal knee extension. The images highlight the utility of multi-planar CT and MRI in identifying these postoperative soft tissue impingement lesions.

A comparative diagnostic series of the knee joint post-anterior cruciate ligament (ACL) reconstruction. (a) Lateral radiograph demonstrating optimal tibial tunnel positioning. A reference line (Blumensaat’s line) is superimposed, showing the tunnel exit situated entirely posterior to the line of the intercondylar roof, preventing impingement. (b) Sagittal T1-weighted MRI and (c) Sagittal T2-weighted MRI of a different patient demonstrating suboptimal, anterior tibial tunnel placement. The MRI scans reveal the ACL graft is positioned anterior to the projected Blumensaat's line, causing mechanical impingement. Visually, this results in a characteristic 's-shaped' deformity or buckling of the graft, as indicated by the white arrow in (c). High signal intensity within the graft on T2-weighted imaging and thinning of the fibers at the point of impingement are evident, suggesting graft irritation or partial tearing. The images serve as an educational comparison between successful surgical tunnel placement and the radiological signs of impingement syndrome in ligament reconstruction.

This diagnostic image is a sagittal MRI of a human knee post-anterior cruciate ligament (ACL) reconstruction, demonstrating the methodology for measuring the graft inclination angle. The image features the distal femur, proximal tibia, and an ACL graft passing through a tibial bone tunnel. To calculate the inclination angle, two primary reference lines are superimposed: Line I is drawn tangential to the anterior border of the ACL graft, and Line II is drawn tangential to the anterior aspect of the intercondylar eminence, perpendicular to the long axis of the tibia. The intersection of these lines defines the sagittal obliquity of the graft. Additional white annotations indicate the tibial long axis and segmental markers along the tibia for orientation. This visualization is used in orthopedic radiology to assess the anatomic positioning of the reconstructed ligament, which is critical for evaluating surgical outcomes, joint stability, and the risk of graft impingement or failure. The clinical significance lies in ensuring the graft's orientation mimics the native ACL's biomechanical properties.

A composite of three sagittal T2-weighted MRI slices of a human knee joint, demonstrating the quantitative assessment of the anterior cruciate ligament (ACL) orientation and femoral morphology. (a) Illustrates the ACL-inclination angle, measured between a tangent line along the anterior aspect of the ACL and a line perpendicular to the longitudinal tibial axis. (b) Depicts the ACL-Blumensaat angle, defined as the angle formed between the Blumensaat line (the roof of the intercondylar notch) and the tangent to the anterior ACL fibers. (c) Displays the roof angle, which is the angle between the femoral longitudinal axis and the Blumensaat line, with an annotated value of 37.1 degrees. The images highlight key anatomical landmarks including the patella, distal femur, proximal tibia, and the fibrillar structure of the ACL. These measurements are clinically relevant in orthopedics for evaluating ACL graft placement, impingement risk, and native ligament biomechanics.

Diagnostic Image: Two T2-weighted MRI scans of the knee joint in sagittal (left) and coronal (right) planes, illustrating a partial rupture of an anterior cruciate ligament (ACL) graft. In the sagittal view, the anterior portion of the ACL graft exhibits a localized region of increased signal intensity (hyperintensity) and visible fiber discontinuity, indicated by a white arrow, suggesting a focal tear or fluid accumulation within the ligament. The coronal view demonstrates similar findings, with an arrow pointing to a high-signal area in the anterior-medial aspect of the graft, reflecting edema or intrasubstance disruption. These radiological features differentiate a partial rupture from a normal graft, which typically maintains low signal intensity across all planes. The imaging also captures the postoperative anatomy, including the surgical tunnels and surrounding soft tissues of the knee joint, emphasizing the importance of MRI in evaluating graft integrity and identifying late-stage complications such as partial or total failure.

This sagittal T2-weighted fluid-sensitive MRI of the human knee demonstrates multi-ligamentous injury. The image shows a complete rupture of the posterior cruciate ligament (PCL), characterized by clear discontinuity of the fibers and retraction of the proximal segment near its femoral origin. Significant hyperintense signal edema and hemorrhage are visible surrounding the expected PCL location. The anterior cruciate ligament (ACL) follows a continuous anatomical course but exhibits altered internal signal intensity and fiber irregularity suggestive of a partial tear. Additionally, there is evidence of extensive bone marrow edema (trabecular microfracture) within the posterior tibial plateau and a joint effusion in the suprapatellar bursa. This diagnostic image is representative of high-energy knee trauma, illustrating the radiological findings necessary for evaluating acute ligamentous instability and structural disruption in orthopedic and musculoskeletal radiology.

Multi-modal diagnostic imaging of a knee joint post-ACL reconstruction with a synthetic LARS graft, demonstrating significant osteolysis and a pseudo-myxoid mass. (A) Anteroposterior and lateral X-rays show radiopaque fixation screws with marked widening of the femoral and tibial tunnels and increased radiolucency in the intercondylar eminence, indicating peri-tunnel bone resorption. (B-E) Sagittal MRI views demonstrate a large, well-defined mass occupying the intercondylar notch. The lesion is predominantly hypointense on T1-weighted sequences (B, D) and displays heterogeneous hyperintensity on STIR sequences (C, E), consistent with a multicystic, fluid-filled pseudo-myxoid mass that lacks a healthy ACL graft signal. (F-G) Coronal and sagittal CT scans highlight the precise morphology of the grade 3 osteolytic cavities, revealing extensive loss of subchondral and cancellous bone surrounding the femoral (F) and tibial (G) tunnels. This imaging series illustrates a severe inflammatory and osteolytic complication following synthetic ligament implantation, characterized by tunnel enlargement and intra-articular cystic mass formation.

This diagnostic image set consists of six MRI panels (A–F) demonstrating the methodology for measuring femoral and tibial tunnel expansion following Anterior Cruciate Ligament (ACL) reconstruction. Panels A, C, and E show the femoral tunnel in sagittal, coronal, and axial planes, respectively. Panels B, D, and F show the tibial tunnel in sagittal, coronal, and axial planes, respectively. In each plane, the tunnels appear as well-defined, low-signal (dark) cylindrical voids within the cancellous bone of the distal femur and proximal tibia. Orange bidirectional arrows illustrate the quantitative measurement technique, specifically identifying the tunnel diameter perpendicular to the greatest diameter or long axis. This visualization is used to assess post-operative biological complications such as tunnel widening or 'windshield-wiper' effect, which are critical for evaluating graft stability and planning potential revision surgery. The imaging highlights the precise anatomical placement and morphology of the tunnels within the knee joint structures.

This composite diagnostic image illustrates anatomical measurement protocols for knee morphology assessment, likely for evaluating risk factors in ACL injuries. The image consists of four panels: (1) PITS (Posterior-Inferior Tibial Slope): A lateral radiograph of the proximal tibia and distal femur showing the angle between the tibial longitudinal axis and the medial tibial plateau slope. (2) NWI (Notch Width Index): A coronal MRI slice at the distal femur demonstrating the ratio of the intercondylar notch width to the total bicondylar width. (3) NA (Notch Angle): A coronal MRI slice showing the angle formed by the intercondylar notch aperture. (4) RA (Roof Inclination Angle): A midsagittal MRI slice depicting the obtuse angle between the Blumensaat line (intercondylar roof) and the longitudinal axis of the knee. These measurements are clinical indicators for femoral notch stenosis and tibial slope steepness, which are critical in orthopedic biomechanics and ligamentous injury analysis.

A series of seven sagittal MRI frames of a human knee joint (labeled a-g) demonstrating quantitative morphometric measurements used in orthopedic assessment, specifically for ACL and meniscus injury risk profiling. Panels a-d illustrate slope measurements relative to a vertical tibial reference line: (a) Lateral Meniscal Slope (LMS) and (c) Medial Meniscal Slope (MMS) measured along the superior meniscal borders; (b) Lateral Posterior Tibial Slope (LPTS) and (d) Medial Posterior Tibial Slope (MTPS) measured along the subchondral bone surface. Panel (e) depicts the measurement of medial posterior tibial depth. Panel (f) demonstrates the method for establishing the femoral longitudinal axis by connecting the midpoints of two circles tangent to the femoral shaft cortex. Panel (g) shows the measurement of the medial femoral condyle (MFC) diameter (D) using parallel lines tangent to the anterior-most and posterior-most aspects, and the medial tibial plateau (MTP) anterior-posterior length (L) based on the cartilaginous surface outline. These quantitative parameters are critical for evaluating anatomical predispositions to ramp lesions and ACL instability.